Comets, asteroids, and other small bodies are thought to be remnants of the original planetesimal population of the Solar System. As such, their physical, chemical, and isotopic properties hold crucial details on how and where they formed and how they evolved. Yet, placing precise constraints on the formation region of these bodies has been challenging. Data from spacecraft missions has a particularly high potential of addressing the question of the origin of the visited bodies. ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko returned data from the comet for two years on its journey around the Sun. This extensive data set has revolutionised our view of comets and still holds unsolved problems. Here we present the elemental composition of 67P [Fig. 1]. We constrain the refractory-to-ice ratio to 0.5 < χ < 1.7, and present the bulk elemental abundances for 67P of H, C, N, O, Na, Mg, Al, S, K, Ar, Ca, Cr, Mn, Fe, Kr, and Xe [Marschall, Morbidelli, and Marrocchi 2025]. We find the noble gas xenon in near-solar elemental abundance in comet 67P. This is notable because the cometary xenon has a non-solar isotopic composition [Marty et al. 2017]. The fact that comets have xenon in solar elemental abundance but not in solar isotopic composition does not fit into the current scheme for the formation and evolution of the proto-solar disk [Nanne et al. 2019]. That cometary xenon is depleted in r-process isotopes, which is usually associated with non-carbonatious material, is puzzling. By modifying the Nanne scheme, we will present a new model that can reconcile these constraints from comet 67P. 

Figure 1: The elemental abundane of comet 67P using Rosetta/ROSINA and Rosetta/COSIMA data for a  refractory-to-ice ratio to χ = 1.1 . The figure is adapted from Marschall, Morbidelli, and Marrocchi 2025.

How to cite: Marschall, R., Morbidelli, A., Marrocchi, Y., and Kleine, T.: A modified formation scenario of the proto-solar disk constrained by comets, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1696, https://doi.org/10.5194/epsc-dps2025-1696, 2025.

In recently published work we found that because Rosetta coma composition observations of 67P/Churyumov-Gerasimenko (67P/C-G) are local coma measurements, they are highly sensitive to being influenced by ice sublimating from dust near the spacecraft. This means that the local dust cycle on the comet should be considered when driving values meant to reflect the nucleus abundances and isotope ratios. Previous analysis of the Rosetta mass spectrometer (ROSINA DFMS) data took a least squares approach to fitting that stepped through each unknown parameter one parameter at a time. However, each DFMS spectrum has at least six and as many as fifteen free parameters. By fitting one parameter at a time, the uncertainty in the fit of each parameter propagates through the fit creating much greater uncertainties than represented by any difference between the fit and the data. We have developed a new technique for evaluating the Rosetta observations that fits all unknown parameters of a single spectrum. Through this approach we derive more accurate estimates of the true uncertainty in the fit and are able to reliably fit a much larger number of spectra. When we applied this method to derive D/H we found that the previously reported anomalously high D/H was a result of enrichment in D/H on dust grains and was not inherent to the comet. By evaluating measurements in the context of the well-established dust cycle we determined that the nucleus D/H is closer to terrestrial values. These values are more reasonable allowing 67P/C-G to agree with other Jupiter Family Comets (JFCs) as well as the abundances of CO and N₂ measured by DFMS. In this presentation we provide an update to the abundances of hypervolatiles and other isotope ratios base on our new method for fitting the observations and on our understanding of the comet dust cycle.

How to cite: Mandt, K., Luspay-Kuti, A., and Lustig-Yaeger, J.: Variability of hypervolatile abundances and isotope ratios in the coma of 67P/Churyumov-Gerasimenko, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-894, https://doi.org/10.5194/epsc-dps2025-894, 2025.

Cometary dust is a key tracer of early Solar System material, preserving primitive components that offer insight into comet formation and evolution. ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provided an unprecedented opportunity to study the dust and gas environment of a comet's inner coma in situ, over a two-year period surrounding its perihelion in August 2015. Due to the spacecraft’s low relative velocity with respect to the nucleus, dust particles could be collected with minimal alteration (Longobardo et al., 2022).

Dedicated dust instruments aboard Rosetta, including GIADA (Grain Impact Analyzer and Dust Accumulator) and COSIMA (Cometary Secondary Ion Mass Analyzer), characterized dust grain velocities, sizes, and densities (Agarwal et al., 2017), while MIDAS (Micro-Imaging Dust Analysis System), the first Atomic Force Microscope flown in space, revealed detailed micro- and nanoscale structures (Bentley et al., 2016; Mannel et al., 2019). In addition, the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) suite – though primarily a gas analyzer – also contributed to dust studies. Its COPS (Comet Pressure Sensor) detected transient dust events (Pestoni et al., 2023) and the DFMS (Double Focusing Mass Spectrometer) enabled chemical analysis of volatiles released during phases with a lot of dust in the coma (Hänni et al., 2022).

We report on the detection of H₃O⁺ (hydronium ion) at m/z = 19 in DFMS’s neutral mode and its correlation with gas species associated with dust events, pointing to a link between H₃O⁺ formation and salt-bearing dust grains. Salts, particularly ammonium salts, have also been proposed as key contributors to the nitrogen depletion observed in cometary comae (Altwegg et al., 2020, 2022; Poch et al., 2020). Additionally, we present a comparative analysis of the D/H ratio in H₂O in the ambient gas coma versus that observed during dust events, when water was released from grains. These results are further compared to D/H ratios from the literature for the gas and dust phase, for instance in the refractory organics measured by the COSIMA instrument (Paquette et al., 2021).

We discuss the implications of the presence of H₃O⁺ released from dust grains, its potential formation pathways, and isotopic ratios for understanding salt chemistry and the coupling between volatile and solid phases in cometary comae.

References:
Agarwal, J. et al., 2017, MNRAS, https://doi.org/10.1093/mnras/stx2386
Altwegg, K. et al., 2020, Nat Astron., https://doi.org/10.1038/s41550-019-0991-9
Altwegg, K. et al., 2022, MNRAS, https://doi.org/10.1093/mnras/stac2440
Bentley, M. et al., 2016, Nature, https://doi.org/10.1038/nature19091
Hänni, N. et al., 2022, Nat. Commun., https://doi.org/10.1038/s41467-022-31346-9
Longobardo, A. et al., 2022, MNRAS, https://doi.org/10.1093/mnras/stac2544
Mannel, T. et al., 2019, A&A, https://doi.org/10.1051/0004-6361/201834851
Paquette, J. A. et al., 2021, MNRAS, https://doi.org/10.1093/mnras/stab1028
Pestoni, B. et al., 2023, A&A, https://doi.org/10.1051/0004-6361/202245279
Poch, O. et al., 2020, Science, https://doi.org/10.1126/science.aaw7462

How to cite: Müller, D., Altwegg, K., Berthelier, J.-J., Bonny, R., Combi, M., De Keyser, J., Doriot, A., Fuselier, S., Hänni, N., Rubin, M., and Wampfler, S.: H3O+ and D/H ratios in dust-related outgassing at 67P: Evidence for salt-rich grains?, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1257, https://doi.org/10.5194/epsc-dps2025-1257, 2025.

The primary goal of this work is to investigate the properties of the inner coma of comets and establish connections between the processes occurring within it and specific locations on the surface and subsurface of the comet. The analysis of gas and dust in the inner coma and their connection with the surface of comets is crucial to understand the context of cometary activity and represents an important reference for the ESA and JAXA missions as Comet Interceptor and for small bodies showing ‘’cometary activity’’. Additionally,  future Vera C. Rubin Observatory observations, the James Webb Space Telescope (JWST), and the Extremely Large Telescope (ELT) will increase the need for understand comet activity as they rapidly discover and characterize new objects. Those efforts rely on the capability to model and forecast the activity of comets, which in turn relies on connecting observed activity to surface properties and regions.

The work is developed in two parts:

1-  Our first focus is the analysis of the dust and gas coma of comet 67P using data acquired by the ESA Rosetta mission during the period between July and November 2015, when activity was near its peak postperihelion.

2-  The second focus is the development of a Lagrangian code based on the Smoothed Particle Hydrodynamics (SPH) method to investigate transient phenomena, such as volatile and refractory emissions from the surface (M. Teodori et al. 2024, 2025).

The Visible InfraRed the Thermal Imaging Spectrometer (VIRTIS) and the ALICE ultraviolet spectrograph, observed and detected a series of outbursts and jets (Rinaldi et al. 2018, Noonan et al. 2021). H2O, CO2, and O2 were all indirectly observed by ALICE within outbursts via emission fingerprints of dissociative electron impact from the daughter products H, C, and O, identified in the spectra as the first two members of the H I Lyman series, OI multiplets at 1152, 1304, and 1356 Å, and weak multiplets of C I at 1561 and 1657 Å . VIRTIS detected and characterized the dust properties of the jets and outburst in terms of radial profile, light curve, color, and dust mass loss in the VIS and IR wavelength range. The outburst observations show that mixed gas and dust outbursts can have different spectral signatures representative of their initiating mechanisms, with outburst showing indicators of a cliff collapse origin or showing fresh volatiles being exposed via a deepening fracture. Preliminary analysis shows the cometary activity observed after some outburst events has a moderate CO2/H2O ratio, while others show only a large increase in reflected light due to dust. When connected to specific surface regions and provided with the proper spectral signal, this analysis opens up the possibility of remote spectral classification of cometary activities with future work.

The second focus of this work is to consider the physical processes driving the comet activity. We aim at simulating gas and dust emission from a surface fracture, by introducing an advanced numerical model that adopts the Smoothed Particle Hydrodynamics (SPH) approach. The code accounts for multiple components and incorporates several physical mechanisms. Among them, phase transitions (mainly sublimation and deposition), viscous dynamical interaction between gas and solid components (dust and eventually icy grains), solar radiation, and volatile-surface dynamical and thermal interactions. Preliminary results will be presented during this session.

How to cite: Rinaldi, G., Noonan, J., Teodori, M., Maggioni, L., Jindal, A., Formisano, M., and Magni, G.: The analysis of dust and gas emission at 67P/Churyumov-Gerasimenko sheds light on cometary activity, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1556, https://doi.org/10.5194/epsc-dps2025-1556, 2025.

Abstract

Rosetta measurements at comet 67P revealed ion speeds of 5–10 km/s, far exceeding the observed speed of the neutral gas of 0.5–1 km/s. Models assuming an ion speed similar to the neutral gas also give good agreement with measurements of ion densities. This discrepancy points to a missing mechanism in our understanding of ion-neutral coupling. One possible explanation would be a presence of counter-streaming ions. Two ion populations, moving anti-cometward and cometward, respectively, would result in a low bulk speed but high individual velocities. Such counter-streaming populations may also drive wave generation, particularly ion acoustic waves, which have been detected within the diamagnetic cavity and could arise from ion-ion instabilities.

Using high- and normal-resolution data from Rosetta’s RPC-ICA instrument recorded near the diamagnetic cavity, we identify and statistically characterize counter-streaming ion populations. We find the counter-streaming ions are often observed in this region. Our results further reveal a dependence on cometocentric distance which can be seen in Figure 1. At smaller distances, (1) the ratio between the mean energy of the anti-cometward and cometward ions is higher, (2) the ratio of the observed number of counts of anti-cometward and cometward ion is lower, and (3) the angle between the streaming directions of the two populations is larger. In addition, we find that some parameters, for example the angle between the streaming populations, is different inside and outside of the diamagnetic cavity. These findings provide statistical insights into counter-streaming ions, demonstrating how local plasma conditions shape ion dynamics in the cometary environment

Figure 1. Statistical analysis of counter-streaming ion populations. (a–c) Stacked histograms showing the distributions of (a) the ratio of the mean energy, (b) the ratio between the observed counts, and (c) angular separation between ion flow directions. Yellow and blue bars represent populations outside and inside the diamagnetic cavity, respectively. Red and blue dashed lines denote the mean values for each parameter outside and inside the cavity, respectively. (d–f) Same as (a–c), but omitting the mean value lines (red/blue dashed lines), and adding a right y-axis showing cometocentric distance (±SD) as a magenta solid line with dots marking bin means and vertical error bars representing standard deviations.

How to cite: Yun, X., Stenberg Wieser, G., Nilsson, H., Bergman, S., Fu, S., and Ni, B.: Characteristics of Counter-Streaming Ions at Comet 67P, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1944, https://doi.org/10.5194/epsc-dps2025-1944, 2025.

The Rosetta spacecraft orbited comet 67P/Churyumov-Gerasimenko (C-G) from 2014-2016, where it characterized the comet's behavior in detail.  Although the in situ mission is over, remote observations monitoring the comet's behavior should be continued, to reveal how the comet evolves over the course of subsequent apparitions.

The Transiting Exoplanet Survey Satellite (TESS) was designed to observe extrasolar planets by continuously staring at a wide-field (24° x 96°) sector of the sky for 27 days.  Comets occasionally pass through the TESS field of view, where high-cadence images are recorded for as long as the comet remains in the field.  We can use these images to study the long-term spatial and temporal behavior of the comet. TESS' excellent photometric qualities track the secular and rotational lightcurves of the comet to reveal how its activity changes with time.  The continuous, extended duration of the observations is also ideal for monitoring for outbursts and other spontaneous transient events.  The thousands of images obtained by TESS can also be registered on the nucleus and coadded to produce deep images that reveal faint morphological features.  This capability has made TESS an excellent tool for discovering and characterizing cometary dust trails and for characterizing comae in weak and distant comets.

Due to fortuitous circumstances, comet C-G was ideally placed for TESS observations during its 2021 apparition.  C-G passed through six consecutive sectors, where it was imaged almost continuously every 10 minutes for 159 days (21 Aug 2021 through 27 Jan 2022).  These observations bracketed perihelion (r=1.2 AU), with r ranging from 1.5 AU inbound to 1.6 AU outbound, and provide a record of the object's long-term behavior during this time period.  Preliminary analyses of the observations show activity levels that peaked about three weeks post-perihelion, with several small outbursts detected at random times.  C-G displays a moderate dust tail as well as a bright dust trail that extends several tens of degrees from the nucleus (see figure).

How to cite: Farnham, T. L., Hood, M., Sunshine, J. M., and Kelley, M. S. P.: TESS Observations of Comet 67P/Churyumov-Gerasimenko, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-867, https://doi.org/10.5194/epsc-dps2025-867, 2025.

Comets are among the most primitive and unaltered small bodies in the solar system, offering critical insights into the early conditions of solar system formation. Originating from distant reservoirs such as the Oort Cloud, Scattered Disk, and Kuiper Belt, these icy relics preserve material from the primordial solar nebula. As they aproach the Sun, sublimation of volatile ices and dust creates expansive comae and tails, the structures of which reveal details about the physical properties and activity of their nuclei. Here, we present the results of narrowband imaging and morphological analysis of the coma of comet C/2006 P1 (McNaught), focusing on constraining its rotation period.

Comet C/2006 P1 was observed using the 3.6-meter New Technology Telescope (NTT) at La Silla Observatory, Chile, with the ESO Multi-Mode Instrument (EMMI). Observations were conducted between January 27 and February 4, 2007, with an additional observing run from February 25 to 28, 2007, approximately 15 to 48 days post-perihelion. The imaging programme employed both broadband filters (B, V, R) and six comet-specific narrowband filters (CN, C₃, C₂, NH₂, and blue/red continuum) to isolate various gas and dust components within the coma.

We used multiple image processing techniques to enhance the cometary coma structures. These included azimuthal mean and median profile subtraction and division, azimuthal renormalization, and division by a 1/ρ profile. These techniques revealed diversed morphological features such as spiral arcs, linear jets, and fan-shaped structures, particularly prominent in the CN-filter images. We used periodic repetition and evolution of these features over time to constrain the comet’s rotation period.

To constrain the rotation period of C/2006 P1, we used two techniques independently: (1) Root Mean Square (RMS) analysis of time-series morphological variability and (2) tracking of angular displacement of distinct coma features. Both methods rely on the assumption of a stable, principal-axis rotational state and persistent active regions on the nucleus.

In the RMS approach, we normalized and divided sequential images by each other to highlight temporal changes in morphology. We plotted RMS of resultant division as a function of the time difference between observations as shown in figure 1. Here, the minima correspond to epochs where the coma morphology matches earlier states, implying integer multiples of the rotation period have elapsed. This technique was applied to the January 31–February 4 and February 25–28 epochs separately, as they provided good but different temporal coverage with different number and types of structures. We obtained a rotation period estimate of 11.3 ± 0.5 hours from the RMS minima.

In our second approach, angular displacement technique, we measured the position angles of distinct structures (e.g., linear jets and fans) at multiple epochs. The angular displacement ∆θ between features observed at times t₁ and t₂ was computed and used to obtain angular velocity ω = ∆θ/∆t. The rotation period P was subsequently calculated using P = 360^◦/ω. This method gave us a rotation period of 5.65 ± 0.9 hours, approximately half the value obtained from the RMS. Such a discrepancy may reflect challenges in distinguishing between full and half-rotation periods, especially in cases where the coma displays symmetric morphological features. The factor-of-two difference likely arises from the RMS method capturing repeated morphology at intervals corresponding to twice the rotation period. This might be because of insufficient temporal coverage, as our observations were limited to only about 30-minute windows at the beginning or end of the night, making it impossible to reliably detect periods under 8-10 hours using RMS approach.

Both methods showed strengths and limitations. The RMS approach offers statistical robustness and is relatively insensitive to subjective feature identification but can be affected by transient non-periodic events or variable seeing conditions. The angular displacement method provides a direct geometric interpretation but is more sensitive to feature misidentification and measurement uncertainties. By employing both techniques, we achieved a more comprehensive constraint on the rotational state of C/2006 P1.

Despite its exceptional brightness, the rotation period of comet C/2006 P1 (McNaught) had never been directly determined. A 21-hour estimate proposed by Kulyk et al. (2010), based on tail simulations, lacked confirmation from morphological observations. The results presented in this study represent the first observationally grounded constraints on the comet’s rotation period derived from narrowband imaging of its coma. The inferred rotation periods of C/2006 P1 suggest a relatively rapid nucleus spin rate, consistent with its pronounced and dynamic coma morphology. Moreover, the results offer insights into the spatial distribution of activity on the nucleus, possibly indicating two dominant sources or a highly anisotropic activity pattern.

Figure 1: A plot of the RMS resulting from division of normalized CN images with each other as a function of the time difference (in days) between the images, covering observation between 29 Jan to 04 Feb (Left) and 26-28 Feb, 2007 (Right). The minima in the RMS repeats itself at an integer number times the rotation period. It suggests a rotation period estimate of C/2006 P1 to be 11.3 ± 0.5 hours, a factor of two difference from the jet angular tracking method which gave an estimate of 5.65 ± 0.9 hours.

How to cite: Okoth, V., Opitom, C., and Snodgrass, C.: Rotation Period of Comet C/2006 P1 (McNaught) Through Coma Morphology, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-941, https://doi.org/10.5194/epsc-dps2025-941, 2025.

Comets are primitive planetesimals we can study to infer knowledge about the initial stages of formation of our Solar System. Dust is the largest mass component among cometary materials. Emitted dust particles are anysotropic scatterers of the incident solar light and their nature can be investigated with remote sensing studies. Among such studies, the measurement of the coma phase function curve has an important role for several aspects. Once inverted with theoretical and laboratory studies, the intimate nature (i.e. size, size distribution, composition, and shape) of the emitted dust particles can be investigated. The phase function knowledge is needed when adjusting cometary dust production rates for effects depending on the observational geometry when correlation of data obtained throughout large time intervals is performed. Finally, the coma phase function is useful for space instruments planning since it provides inputs for optimal exposure times, mainly in case observations are spanning a large range of phase angles during close approaches. This will be particularly valuable in the framework of the future ESA Comet Interceptor mission which is going to pass close to a Dynamically New Comet, carrying instruments such the EnVisS (Entire Visible Sky) camera which will image the coma with a large phase angle coverage in a short amount of time.

In order to provide an useful tool to address the aforementioned scientific topics, we used literature data to build a new composite phase function for cometary dust comae. We fitted Henyey-Greenstein (HG) functions to the literature data of 11 comets covering different dynamical classes and we connected them in a continuous way as all data values were coming from a single comet with average scattering properties. We then fitted our result with a compound HG curve and compared it with previous comprehensive models. Our approach contains recent literature data which were not included in previous models. These recent data are providing a good temporal coverage of the cometary coma scattering behavior at small and large phase angles. The most notable difference between our and previous models is found in the description of the forward scattering surge, where our model depicts a scattered intensity one order of magnitude larger than previous ones. This finding is extremely important since it shows that the choice of the phase function model may have severe consequences when scientific interpretation and planning of the observational strategy regarding forward scattering data are taken into account.

Acknowledgements: Contribution of I. Bertini and L. Inno was supported by the ASI-INAF agreement n. 2023-14-HH.0.

How to cite: Bertini, I., Vincent, J.-B., Marschall, R., La Forgia, F., Mura, A., Inno, L., Ivanovski, S., Küppers, M., Tubiana, C., and Zakharov, V.: A Composite Phase Function for Cometary Dust Comae, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1414, https://doi.org/10.5194/epsc-dps2025-1414, 2025.

Introduction. Comets play a crucial role in understanding the formation and evolution of the Solar System, as they preserve the most pristine material from its early stages. Composed of rock, dust, organic material, and ices, comets release gases and dust when heated by the Sun, forming an atmosphere (coma) and characteristic tails. To advance our understanding of comets, it is essential to determine  their composition and the physical processes at play and one method is the analysis of the optical spectra of their gazeous coma. At optical wavelengths, these spectra are characterized by emission lines mainly produced from fluorescence-resonance of cometary radicals, ions, and atoms which are the subproducts of the photionization and other processes acting on the larger parent molecules sublimating from the nucleus ices. Identifying correctly these lines among the forest of thousands of lines of the molecular bands at high resolution, is a first and essential step, especially as many remain unidentified despite advances in telescope technology, instrumentation, and laboratory line lists. This has motivated our team to build an atlas of cometary lines, which is a list of validated lines from high resolution and high signal to noise spectra obtained in the last two decades by the Liège team with the 8-m ESO Very Large Telescope (VLT) and covering the whole near-UV and optical range from 3040 A to 10400 A.

High resolution optical spectra. The most comprehensive catalog of cometary optical spectral lines until recently was that of comet 122P/de Vico, compiled by Cochran and Cochran at the McDonald Observatory and published in 2002 [1]. The observation of the bright long period comets C/2002 T7 (LINEAR) in 2004 and more recently in 2018 comet C/2016 R2 (PANSTAARS) with the high-resolution UVES spectrometer (R~100,000) coupled with the large telescope area of the VLT led to some of the best cometary optical spectra ever obtained. These spectra were reduced using the ESO UVES pipeline [2], cosmic rays were removed and SNR improved by combining several spectra taken the same night, and they were wavelength calibrated and shifted in the Earth frame, by considering the geocentric velocities. After a very careful dust continuum subtraction by small wavelength regions using the solar spectrum of Kurucz [3], as well as the removal of the telluric absorptions in the redest part of the spectrum,  we studied the cometary emission lines by developing an automatic line detection tool [4], and by identifying them using high-resolution molecular line lists found in the Exomol database [5], derived from recent fluorescence models [6, 7], or more generally found in the literature [1,4,8,9]. The sky emission line atlas observed by VLT/UVES in 2001 [10] was used to confirm the cometary nature of detected emission lines. Emission lines of CO+ and N2+ ions were analyzed thanks to the unique spectrum of comet C/2016 R2 (PanSTARRS), because those species are much brighter in this comet compared to most of other comets [6, 7, 11].

The Cometary line Atlas.   We present here a new atlas containing about 22,000 detected emission lines. Among those, approximately 75% were successfully identified as radicals (OH, NH, S2, CN, CH, C3, C2, NH2), ions (OH+, CH+, H2O+, CO+, N2+, CO2+) or atoms ([OI], [CI], [NI], NaI, FeI, NiI). The online tool allows you to check those emission lines, or the species your are interesed in, for a given wavelength range, by displaying them to the high quality spectrum of comet C/2002 T7 (LINEAR), or any comet spectrum normalised and wavelength calibrated to the laboratory rest frame into the system in ascii format (wavelength; flux). With the input of the velocity of the comet with respect to the Earth (the Doppler shift) you can also check the position of the sky lines in the spectrum. Figure 1 represents a small region of the atlas, where C2, NH2, and unidentified lines are indicated and shows the line list and transitions information that can be retreived as a table for the displayed spectrum.

Perspectives. A key aspect of the project involves conducting up-to-date laboratory measurements and developing models to obtain new modelled line positions for comparison with the observed spectra in order to solve the puzzle of the still thousands of lines not identified yet and improve the atlas.

Link to the online atlas. The Liège cometary line atlas can be reached on the following webpage. Comments to improve the tool are welcome.
https://www2.cometa.uliege.be/Cometary_Lineatlas

References

[1] Cochran, A. L., & Cochran, W. D. (2002). "A high spectral resolution atlas of comet 122P/de Vico". Icarus, 157(2), 297-308.

[2] Ballester, P., Modigliani, A., Boitquin, O., et al. (2000). "The UVES Data Reduction Pipeline" The Messenger, 101, 31

[3] Kurucz, R. L. (2005). "New atlases for solar flux, irradiance, central intensity, and limb intensity" Mem. S.A.It Suppl., vol. 8, 189. 

[4] Hardy, P. (2022) “Atlas of cometary lines obtained from a high-resolution spectrum of comet C/2002 T7 (LINEAR),” Master’s thesis, University of Liège.

[5] Tennyson, J., “The 2024 release of the ExoMol database: Molecular line lists for exoplanet and other hot atmospheres”, Journal of Quantitative Spectroscopy and Radiative Transfer, vol. 326, 2024. 

[6] Rousselot, P., Jehin, E., Hutsemékers, D., Opitom, C., Manfroid, J., & Hardy, P. (2024). "12CO+ and 13CO+ fluorescence models for measuring the 12C/13C isotopic ratio in comets." Astronomy & Astrophysics, 683, A50.

[7] Rousselot, P., Anderson, S. E., Alijah, A., et al. (2022). N+2 fluorescence spectrum of comet C/2016 R2 (PanSTARRS) Astronomy & Astrophysics, 661, A131.

[8] Hardy, P., Jehin, E., Rousselot, P., Hutsemekers, D., & Manfroid, J. (2023, August). "Atlas of Cometary Lines Obtained from High-Resolution Optical Spectra of Comets C/2002 T7 (LINEAR) and C/2016 R2 (PanSTARRS)". In Asteroids, Comets, Meteors Conference.

[9] Blond-Hanten, E. (2024) "Investigation of unidentified lines in optical cometary spectra", Master’s thesis, University of Liège.

[10] Hanuschik R. W. (2003) " A flux-calibrated, high-resolution atlas of optical sky emission from UVES". Astronomy & Astrophysics 407, 1157-1164

[11] Opitom, C., Hutsemékers, D., Jehin, E., et al. (2019). Astronomy & Astrophysics 624, A64

How to cite: Jehin, E., Hardy, P., Blond Hanten, E., Hutsemékers, D., Manfroid, J., and Sohy, S.: An online high resolution atlas of near-UV and optical cometary emission lines, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1777, https://doi.org/10.5194/epsc-dps2025-1777, 2025.

Despite over a century of cometary observations, we are still struggling to understand the activity of comets. Questions such as ‘what drives the activity of comets at different distances from the Sun?’ or ‘Does the activity of all comets evolve in a similar way?’ remain  unanswered. This is in part due to the difficulty to observe the drivers of cometary activity: H₂O, CO, and CO₂ can only be detected simultaneously using space observatories. JWST has proven an incredible resource to answer these questions [1,2], but only a limited number of comets have been observed so far.

The last decade has seen the advent of large field of view Integral Field Spectrographs (IFUs) for observations at optical wavelengths. These instruments, such as MUSE on the 8-m Very Large Telescope [3], present an interesting opportunity to characterize the distant activity of comets, due to the combination of spatial and spectral information they provide. Large scale IFUs on ground-based telescopes can be particularly useful to probe cometary activity drivers that are typically difficult to measure from the ground, including H₂O, CO, CO₂- and potentially O₂ - through the study of some of their dissociation products such as oxygen [4,5]. IFUs are generally very sensitive to faint extended emission and are thus ideal tools for the observations of active small bodies in the solar system.

We have observed a number of comets over a wide range of distances from the Sun with the MUSE instrument of the VLT over the last 7 years. We use these data to measure the ratio between the green (557 nm) and the two red line (630 and 637 nm) forbidden oxygen lines at optical wavelength, usually referred to as G/R ratio. We focus on observations of 29P//Schwassmann–Wachmann 1, the most distant comet observed with MUSE, for which we were able to detect forbidden oxygen lines. Comparing the very high measured G/R ratio, consistent with an activity driven by CO, to that measured for other comets at smaller heliocentric distances, and to direct observations of the activity drivers with JWST or ground-based radio observatories, we demonstrate that MUSE constitutes a powerful tool to study the activity evolution of comets that were previously thought too distant or too faint for ground-based optical spectroscopy.

References: [1] Snodgrass C. et al., 2025, MNRAS in press (arXiv 2503.14071) [2] Faggi S.  et al., 2024, Nature Astronomy, Volume 8, Issue 10, pp. 1237-1245 [3] Bacon R., et al., 2010, Proceedings of the SPIE, Volume 7735, id. 773508 [4] Kwon Y., Opitom C., Lippi M.,   Astronomy & Astrophysics, Volume 674, id.A206, 11 pp. [5] Opitom C., et al., 2020, Astronomy & Astrophysics, Volume 644, id.A143, 7 pp.

How to cite: Opitom, C. and McLeod, M.: Using ground-based IFUs to constrain cometary activity drivers, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-824, https://doi.org/10.5194/epsc-dps2025-824, 2025.

Comets are icy small bodies assumed to be mostly unaltered since their formation, making them key tracers of the early stages of the Solar System. Efforts have been deployed to establish classifications of comets in the hope of connecting the current populations to different formation and evolution histories. On the one hand, from a dynamical standpoint, it has been found that comets exist in two main reservoirs before being deflected towards the inner Solar System: the Oort Cloud and the Kuiper Belt. On the other hand, by quantifying the composition of the gas produced by comets, it has also been shown that some comets could be considered as carbon-depleted, displaying low C₂/CN abundance ratios (e.g. [1],[2],[3]). This talk will present two surveys tackling current challenges in our understanding of dynamical and composition-based classifications of comets:

Probing the composition of comets via optical spectroscopy

While carbon-depletion is believed to be a primordial feature of depleted comets, there is no direct link between the dynamical origin of a comet and its carbon content, which is puzzling. Some studies (e.g. [4],[5]) have reported a decrease of the measured C₂/CN ratio with the heliocentric distance of comets at the time of observation, suggesting that our understanding of C₂ production in comae might be incomplete and that C₂ based taxonomies could be biased. Since previous composition studies have typically covered short heliocentric distances (<2au) and different authors have used different sets of modelling parameters (in particular photodissociation scalelengths) to derive these abundance ratios, it is difficult to compare their findings and assess these effects.

I will present a survey of comet volatiles using optical long-slit spectroscopy, aiming to investigate trends and biases in observed compositions. Spectra were acquired for 35 comets using the Isaac Newton Telescope’s Intermediate Dispersion Spectrograph. Having produced a semi-automated pipeline to reduce and analyse this large volume of data, I calculated production rates and upper limits for the main volatile species visible in the near-UV/optical range: OH, NH, C₂, CN, C₃, CH.

From these production rates, derived from a Haser outgassing model and commonly used photodissociation scalelengths, I find C₂/CN ratios consistent with a decreasing trend between 1 and 3.5au (Fig 1a). This effect compromises the validity of a universal depletion-threshold, as most comets observed beyond 2au fall into the depletion range. For a few comets such as 12P or C/2017 K2, I determined and modelled the spatial distributions of volatiles as seen along the slit. This analysis shows that a Haser model using literature scalelengths often does not reproduce the measured C₂ profiles (e.g. Fig 1b), rendering C₂ production rate measurements inaccurate.

A targeted search for Main Belt Comets

The recent discovery of comets hidden in the Main Asteroid Belt [6][7] blurs the traditional distinction between asteroids and comets. However, too few Main Belt Comets (MBCs) are currently known to understand the characteristics and origin of this third comet reservoir.

I will present an imaging survey looking for active asteroids in the hope of identifying more MBCs. Using the Isaac Newton Telescope’s Wide Field Camera, r-band observations of more than 500 asteroids were conducted. These were selected based on their closeness to perihelion and on a hypothesis from [8] that MBCs would more likely be found among objects with a longitude of perihelion close to that of Jupiter. After applying wedge photometry and point-spread function analysis methods adapted from [9] to detect activity features, I made one tentative tail detection on images of asteroid 2001 NL19 (279870) (Fig 2). From images acquired with the Liverpool Telescope at the asteroid’s following perihelion, I did not detect recurring activity.

Fig 1a: Measured C₂ to CN ratios vs. heliocentric distance over on our entire sample of comets. Different marker types represent different dynamical types of comets. JFC: Jupiter Family Comet; HTC: Halley-Type Comet; ETC: Encke-Type Comet; LPC: Long-Period Comet; HypC: Hyperbolic Comet. Dark and light blue markers indicate 3-σ measurements and marginal detections respectively. A yellow dashed line indicates the depletion threshold corresponding to the survey of [1].

Fig 1b: Molecular density profiles of CN (top) and C₂ (bottom) observed in C/2017 K2 along the slit of the spectrograph. Solid lines represent Haser model profiles with literature photodissociation scalelengths, modelling the expected distribution of a daughter species produced by the dissociation of a parent species coming from the nucleus. Dotted lines represent Haser model profiles with parent scalelengths adjusted to match the observed profiles, ultimately resulting in higher C₂ to CN ratios.

Fig 2: INT-WFC r-band image of asteroid 2001 NL19 (279870) observed on 2019 November 07. The circular plot in the top-right figure shows the relative brightness of different wedges around the object, showing a bright anomaly towards the West which was flagged as statistically significant compared to bright wedges found around reference stars on the same image. A faint tail like feature is visible in the West direction, consistent with the anti-solar and anti-velocity directions, and inconsistent with the trailing direction of a potential background star.

References:

[1] A’Hearn M. F., Millis R. C., Schleicher D. O., Osip D. J., Birch P. V., 1995, Icarus, 118, 223

[2] Fink U., 2009, Icarus, 201, 311

[3] Cochran A. L., Barker E. S., Gray C. L., 2012, Icarus, 218, 144

[4] Langland-Shula L. E., Smith G. H., 2011, Icarus, 213, 280

[5] Newburn R. L., Spinrad H., 1989, AJ, 97, 552

[6] Hsieh H. H., Jewitt D. C., Fernández Y. R., 2004, AJ, 127, 2997

[7] Kelley, M.S.P., Hsieh, H.H., Bodewits, D., Saki M., Villanueva G. L., Milam S. N., Hammel H. B., 2023, Nature, 619, 720–723

[8] Kim Y., JeongAhn Y., Hsieh H. H., 2018, AJ, 155, 142

[9] Sonnett S., Kleyna J., Jedicke R., Masiero J., 2011, Icarus, 215, 534

How to cite: Ferellec, L.: Searching for new insights into dynamical and composition-based comet taxonomies, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1691, https://doi.org/10.5194/epsc-dps2025-1691, 2025.

Introduction  Water ice, the most abundant solid in protoplanetary disks, plays a critical role in planet formation by enhancing grain growth and  planetesimal formation. In the Solar System, it likely contributed to the cores of giant planets and the volatiles of the terrestrial planets. The physical structure of water ice, amorphous versus crystalline, is sensitive to the temperature and pressure at the time of formation, as well as to the subsequent thermal evolution. Comets, as some of the best-preserved icy relics of the protoplanetary disk, offer a unique window into the physical properties of primordial materials. Recent discoveries of distant, active Oort cloud comets, beyond the water-ice sublimation line, present rare opportunities to study intrinsically bright, minimally evolved nuclei under conditions of reduced coma activity relative to comets observed at smaller heliocentric distances. Targeted observations of kilometer-sized, non-outbursting distant comets are an important piece of the puzzle for probing the properties of water ice released from the surface and/or interior of minimally processed nuclei, shedding light on the characteristics of ices in the Oort Cloud reservoir.
Observations  We conducted near-infrared (IR) spectroscopic observations of three typical-sized, quiescent distant comets—C/2019 O3, C/2019 E3, and C/2019 F2, using the Near-Infrared Spectrograph (NIRSpec) Integral Field Unit (IFU) on board the James Webb Space Telescope (JWST). All targets have perihelia beyond 8.8 au, where the local blackbody temperature is ~93 K. At such low temperatures, if amorphous water ice is present in the nucleus, it may never undergo large-scale crystallization. Our primary goal was to detect and characterize diagnostic features of crystalline water ice, particularly the 1.65-μm absorption band and the 3.1-μm Fresnel reflection peak. We also searched for supervolatiles species (CO, CO₂) and organics, including methanol, HCN, and aromatic and aliphatic hydrocarbons.
Results and Discussion JWST spectra reveal diagnostic water ice absorption features in all three comets, along with fluorescence emissions from CO and CO₂. Despite similar heliocentric distances, the comets display striking diversity in both volatile production rates and the characteristics of the water ice features, including variations in band depth and spectral shape. While comets C/2019 O3 and C/2019 E3 exhibit a typical 1/ρ coma profile consistent with steady-state outflow, comet C/2019 F2 shows a markedly different morphology, suggesting a non-standard ejection mechanism or evolutionary history. We explore possible explanations for this unusual coma structure and discuss its implications for understanding the drivers of activity in distant comets.  These findings enhance our knowledge of the physical state of water ice and contribute to a broader understanding of volatile evolution in outer solar system bodies.

How to cite: Yang, B., Protopapa, S., and Kelley, M. S. P.: Characterizing the Properties of Water Ice in Distant Oort Cloud Comets with JWST, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-721, https://doi.org/10.5194/epsc-dps2025-721, 2025.

1. Introduction

Centaurs are small bodies on unstable orbits between Jupiter and Neptune that dynamically evolve from the trans-Neptunian scattered disk into Jupiter family comets (JFCs). Their intermittent cometary activity, driven by sublimation of volatiles at 5–10 au, offers unique windows into the primordial volatile inventory of the outer Solar System. Before JWST, direct measurements of CO₂, and CO in Centaur comae were sparse: CO was detected in a few centaurs, CO₂ remained directly undetected.In this presentation we will discuss the comparisons and correlations of centaurs with trans Neptunian objects, and Oort cloud comets.

2. Observations and Data

2.1 Centaurs

JWST program GO 2416 observed five active centaurs: 29P/SW1, C/2008 CL94 (Lemmon), C/2014 OG392 (PanSTARRS), C/2019 LD2 (ATLAS), and 39P/Oterma; in IFU prism mode with dedicated background visits. Each spectrum spans 0.6–5.3 µm at R ∼ 100, enabling detection of emission lines and absorptions of volatiles and ices.

2.2 Trans-Neptunian Objects

Recent JWST observations of TNOs have classified their near-IR reflectance spectra into three classes—Bowl, DoubleDip, and Cliff-type—based on absorption features around 3 µm and spectral slopes (Licandro et al., 2024). These classes correlate with water ice, organics, and silicates, tracing different formation environments in the outer disk.

2.3 Oort Cloud Comets

JWST observations of OCCs have employed NIRSpec and MIRI IFUs to study these comets at a variety of heliocentric distances. Recent sutdies reveal hyperactive water production (>90% active fraction), multiple volatiles (H₂O, ¹²CO, ¹³CO, CO₂, CH₃OH, CH₄, CN, H₂CO, C₂H₆, HCN, NH₂, OH prompt emission), and a dust composition dominated by amorphous carbon, Mg–Fe silicates, and Mg-rich crystalline olivine (Woodward et al., 2025).

3. Results

Several centaurs exhibit clear detections of CO (4.7 µm), CO2 (4.26 µm), and H₂O (2.7 µm) emission lines. 29P/SW1 shows heterogeneous outgassing regions traced by mapped CO jets, indicating localized active areas (Faggi et al., 2024). JWST provided the first detection of CO₂ in 39P/Oterma beyond 5 au, demonstrating sensitivity orders of magnitude beyond previous limits (Harrington Pinto et al., 2023).

4. Discussion and Conclusions

Centaurs occupy an evolutionary niche; they bear surface signatures of TNOs yet they show early stages of volatile loss into JFCs. The matching volatile ratios (CO/H₂O, CO₂/H₂O) across centaur and Oort Cloud comet populations support a continuum of primordial compositions modified by heliocentric distance and thermal history. JWST NIRSpec IFU has, for the first time, provided a direct and sensitive inventory of volatiles in active centaurs, revealing two distinct compositional groups that align with TNO spectral classes and connect to Oort Cloud comet properties. These findings strongly suggest centaurs as transitional bodies bridging outer-solar-system reservoir compositions and the dynamic, compositional diversity of inner solar system comets. Future JWST monitoring over multiple apparitions and expanded target samples will further elucidate the thermal and chemical evolution of small bodies tracing planetary system origins.

References:

Faggi, S., Villanueva, G. L., McKay, A., Harrington Pinto, O., Kelley, M. S. P., Bockelee-Morvan, D., Womack, M., ´ Schambeau, C. A., Feaga, L., DiSanti, M. A., Bauer, J. M., Biver, N., Wierzchos, K., and Fernandez, Y. R. (2024). Heterogeneous outgassing regions identified on active centaur 29P/Schwassmann–Wachmann 1. Nature Astronomy, 8(10):1237–1245.

Harrington Pinto, O., Kelley, M. S. P., Villanueva, G. L., Womack, M., Faggi, S., McKay, A., DiSanti, M. A., Schambeau, C., Fernandez, Y., Bauer, J., Feaga, L., and Wierzchos, K. (2023). First Detection of CO2 Emission in a Centaur: JWST NIRSpec Observations of 39P/Oterma. , 4(11):208.

Licandro, J., Pinilla-Alonso, N., Holler, B., Wong, I., de Pra, M., Melita, M., Souza Feliciano, A. C., Brunetto, R., Guilbert-Lepoutre, A., Henault, E., Lorenzi, V., Stansberry, ´ J., Schambeau, C., Harvison, B., Pendleton, Y., Cruikshank, D., Mueller, T., Emery, J., McClure, L., and Peixinho, N. (2024). Deciphering TNOs thermal evolution through Centaur surface studies using JWST. In European Planetary Science Congress, pages EPSC2024–984.

Woodward, C. E., Bockelee-Morvan, D., Harker, D. E., Kelley, M. S. P., Roth, N. X., Wooden, D. H., and Milam, S. N. (2025). A JWST Study of the Remarkable Oort Cloud Comet C/2017 K2 (PanSTARRS). arXiv e-prints, page arXiv:2504.19849.

How to cite: Harrington Pinto, O. and Bodewits, D.: Volatile Voyagers: How Centaurs Chart the Transition from TNOs to Inner-System Comets, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1155, https://doi.org/10.5194/epsc-dps2025-1155, 2025.

Comets are some of the oldest objects in our solar system and are often seen as remnants from its formation. The nuclei of comets are thought to have formed inward in the solar system, in the giant planets’ region, where ice can easily form. Later, the giant planets changed the paths of smaller bodies and pushed many into areas where comets are now found (Ceccarelli et al. 2022). The Kuiper Belt contains the precursors of short-period comets, which have low-inclination orbits, while the Oort Cloud is a distant region with long-period comets that are considered to be among the least altered objects since the formation of the solar system. The outside of a comet’s nucleus is exposed to cosmic and interstellar radiation, which creates a protective layer of tough material. This layer helps to keep the ices inside safe (Prialnik & Bar-nun 1988).

The upcoming Comet Interceptor (CI) mission by ESA (Jones & et. al 2024) represents the initial attempt to strategically meet an Oort Cloud comet as it travels toward the inner Solar System. The mission aims to intercept a Dynamically New Comet (DNC) or an interstellar object (Meech et al. 2017; de León et al. 2019) before its perihelion passage, offering a unique chance to collect data on its composition, activity, and the surrounding dust and gas. Given the brief timeframe between a comet’s detection and its approach to perihelion, the CI mission is set to launch without a specific target. Instead, it will depend on identifying a suitable target post-launch. This strategy requires a solid understanding of the expected behaviour and activity of DNCs. Understanding these comets’ evolution is vital to optimize the mission’s scientific results.
Spectroscopic analysis plays a crucial role in defining the composition of cometary ices, providing insights about a wide range of molecules detectable across various wavelengths. In the visible range, cometary spectra are dominated by molecular bands of daughter species such as OH, CN, C2, C3, CH,
and NH2, which result from the photolysis of parent molecules. These daughter species can either sublimate directly from the nucleus or be ejected into the coma, with their distribution acting as a key indicator of the comet’s internal composition. In the infrared range, spectra display rovibrational transitions of primary parent molecules, such as H2O, CO2, CH4, HCN, NH3, and NH2 (Bockelée-Morvan & Biver 2017). Additionally, atomic lines from alkali metals like Na and K are observed in the coma, providing essential data for studying the solar system’s original elemental abundances (Fulle et al. 2013). 

Observing comets from a high inbound distance from perihelion is crucial to understand their behaviour as they approach the Sun for the first time. One of the main objectives of current research, in anticipation of the Comet Interceptor mission, is to identify the primary drivers of cometary activity.
The purpose is to determine how and when the transition from one activity driver to another occurs. For instance, several comets with well-documented high-distance activity, such as C/2017 K2 (active at rh = 23.7 AU) (Jewitt et al. 2017), C/2010 U3 Boattini (active at 25.8 AU) (Hui et al. 2019), and
C/2014 UN271 Bernardinelli-Bernstein (active at 23.8 AU) (Farnham et al. 2021), are believed to have their activity driven by volatile species other than water ice. These comets are thought to be primarily influenced by sublimation of supervolatiles like CO or CO2 (A’Hearn et al. 2011). 
In preparation for the Comet Interceptor mission, a detailed series of spectroscopic observations of Oort Cloud comets has been carried out using the Telescopio Nazionale Galileo with the DOLORes and NICS instruments, covering a total wavelength range of 3800 - 25000 Å. This initiative involved six programs (AOT 37-41-42-43-44-45), through which 31 comets were observed, of which 11 are long-period comets and 20 are Hyperbolic. Notably, four of the hyperbolic comets meet the criteria for classification as DNC. These programs encompass heliocentric distances ranging from 1.4 to 9.2 AU, offering an extensive overview of the general behaviour of long-period and hyperbolic comets along various segments of their inbound trajectories.

Preliminary results indicate that there are few signs of activity in terms of gas emissions. At great distances from the Sun, the primary indicator of a comet’s activity is its dust environment. In addition to spectral data, imaging frames of the targets have been collected to monitor the shape and development of the coma alongside gas emission observations. In these data, beyond 5 AU, the coma appears condensed, and the continuum shape in the spectrum is very narrow. As we get closer, the thickness of the continuum increases, the diameter of the coma begins to expand, and only below 3 AU, certain
spectroscopic features start to emerge, such as CN blue band and C2 Swan bands.

This work presents the preliminary results from the analysis of this large campaign of observations with TNG. Also, one of the newest discoveries of ideal Comet Interceptor virtual targets is covered by this presentation.
C/2024 E1 (Wierzchos) is one of the most recently discovered long-period comet currently in its inbound arc and very little is still known about this target. Discovered in March 2024, C/2024 E1 was located 8 AU from the Sun and is expected to pass perihelion on January, 20, 2026 within Earth’s orbit. For this
target, at the time of this writing, two spectra with MODS at LBT and three spectra from AFOSC at INAF Copernico telescope in the visual range have been collected. The results of these spectra will be compared with JWST observation of the comet (PI: C. Snodgrass, Snodgrass et al. (2025), preprint). 

How to cite: Mura, A., Lazzarin, M., La Forgia, F., Cremonese, G., Bizzocchi, L., Farina, A., Ochner, P., Cambianica, P., and Munaretto, G.: Spectroscopy of Dynamically New and Long Period Comets from TelescopioNazionale Galileo, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-972, https://doi.org/10.5194/epsc-dps2025-972, 2025.

We present our recent efforts to measure the dust-to-gas ratio in several comets, motivated by the need to improve our understanding of this critical parameter, which provides key constraints for dust-to-ice interior models and dust-gas interaction processes. We will focus on the results obtained for the Jupiter Family Comet (JFC) 7P/Pons-Winnecke (hereafter 7P) during its 2021 apparition (Mariblanca-Escalona et al. 2025). Additionally, we are conducting similar observations of the dynamically new comet (DNC) C/2024 E1 (Wierzchos). We will share preliminary results based on the data collected so far.

• BACKGROUND:

Comets belong to different dynamical classes that reflect their origins and evolutionary histories. JFCs, such as 7P, have undergone multiple perihelion passages, leading to thermal processing and alteration of their surface layers. In contrast, DNCs are considered among the most pristine objects in the Solar System, offering valuable insights into its formation and early evolution. However, determining how unaltered these comets truly are remains challenging, largely because critical magnitudes such as the dust-to-ice ratio cannot be measured directly. Even for the well-studied 67P/Churyumov-Gerasimenko, accurately determining the dust-to-ice ratio has proven elusive (e.g., Choukroun et al. 2020). From ground-based observations, the dust-to-gas ratio measured in the coma provides the most accessible proxy for this critical parameter. 

However, accurately determining the dust-to-gas ratio requires thorough characterization of both the dust and gas components of the coma. Moreover, due to the variability of cometary activity, continuous monitoring is essential to capture the coma’s changing properties over time, and therefore, to properly capture the evolution of the dust-to-gas ratio. Driven by the need to better understand the evolution of the dust-to-gas ratio in comets, we have initiated an observational program to characterize the gas and dust environments of multiple comets. Our program is also developed in support of the Comet Interceptor mission. By focusing on DNCs and backup candidates like 7P (initially proposed as a mission target in Schwamb et al. 2020), our work bridges fundamental cometary science with practical mission needs, supporting the planning of the instrument onboard and data interpretation of the Comet Interceptor mission. 

• OBSERVATIONS: 

After estimating the dust-to-gas ratio for 7P at 1.25 AU using broadband imaging and long-slit visible spectroscopy, we began a similar observational program for the DNC C/2024 E1 (Wierzchos) at Calar Alto Observatory (Spain) in March 2025. So far, we have obtained data at heliocentric distances around 4 AU, with guaranteed observing time until 3.4 AU and additional time requested down to 2.2 AU. Our observations are designed to capture data at intervals of roughly 0.1 AU, allowing us to tightly constrain the temporal evolution of the dust-to-gas ratio throughout the comet’s trajectory.

• METHODS:

Dust: We analyse the dust environment using a forward Monte Carlo dust tail code (Moreno, F.,  2022), which uses images to derive the dust production rate, size distribution, and ejection velocities of the dust particles. Reliable modeling requires images at several heliocentric distances, therefore, comprehensive and continuous monitoring is essential.

Gas: We derive column density profiles of the observed radicals (CN, C₂, C₃, and NH₂) and fit the column density profiles using the classical Haser and Festou models to estimate production rates of the observed radicals. If these standard models fail to fit the data reliably using classical scale lengths, we plan to to better explore additional processes, such as grain fragmentation and distributed sources, to better understand the coma’s physical and chemical complexity.

We calculate the dust-to-gas ratio by estimating the water production rate using the empirical relation log⁡(Q_OH/Q_CN) = 2.5 (A'Hearn et al. 1995) and combining this with the dust loss rate derived from our Monte Carlo dust tail model.

• RESULTS (7P): 

We observed 7P during its 2021 apparition from Calar Alto Observatory (Spain), using broadband imaging (1.71–1.25 AU pre-perihelion) and long-slit spectroscopy near 1.25 AU pre-perihelion, supplemented by ZTF r-Sloan images before and after perihelion. 

Dust analysis: Our Monte Carlo model generally matched the observed isophotes covering both pre- and post-perihelion observations. We found a peak dust production rate of 83 kg s⁻¹ occurring 15 days after perihelion (see Fig. 1). The derived parameters, including a power-law size distribution index of −3.7 and ejection velocities ranging from 3 m s⁻¹ for the largest particles (0.1 m) to 23 m s⁻¹ for the smallest (5 µm), are consistent with typical cometary dust characteristics.

Figure 1. Derived dust mass loss rate as a function of time to perihelion for 7P.

Gas: We fitted the column density profiles with a classical Haser mode, analyzing sunward and anti-sunward directions separately. We adopted parent and daughter scale lengths from A’Hearn et al. (1995), scaling them as rₕ². Tab. 1 shows the production rates obtained along with the logarithmic ratios of the production rates of C₃ and C₂ relative to CN. Using the C₃/CN and C₂/CN ratios, we found that  7P cannot be classified as carbon-depleted, though it is somehow C₃-depleted. 

Table 1: Gas production rates of 7P for different species (in units of 10²³ s⁻¹), and the logarithmic ratios of the production rates of C₃ and C₂ relative to CN:  C₃ /CN and C₂ /CN.

We estimated a dust-to-gas mass ratio of ∼2 at 1.25 AU, indicating a dust-rich composition. Our work significantly broadens the previously limited understanding of the activity and characteristics of 7P.

References

• A'Hearn M. F., et al., 1995, Icarus, 118, 223
• Choukroun M., et al., 2020, Space Sci. Rev , 216, 44
• Mariblanca-Escalona I., et al. 2025, MNRAS, 538, 1329
• Moreno F., 2022, Universe, 8, 366
• Schwamb M. E., et al., 2020, RNAAS, 4, 21

How to cite: Mariblanca-Escalona, I., Lara López, L. M., Moreno Danvila, F., Gutiérrez Buenestado, P. J., and Evangelista Santana, M.: Dust and gas characterization of 7P/Pons-Winnecke and C/2024 E1 (Wierzchos) in support of the Comet Interceptor mission, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-830, https://doi.org/10.5194/epsc-dps2025-830, 2025.

C/2017 K2 (PanSTARRS), hereafter K2, is a dynamically new comet, discovered by the Pan-STARRS survey [1] in May 2017, when it was at a heliocentric distance of rh=16.1 au [2]. Further investigations enabled to find a prediscovery images of comet K2 exhibiting activity at a very large distance of 23.8 au in May 2013 ([3]). K2 is the second most distant active comet ever discovered, with CO detected in significant abundance at 6.72 au by Yang et al. (2021) [4], potentially accounting for its activity at such a large heliocentric distance.

I will present a detailed study of the comet activity and composition while crossing the water sublimation line using various instruments, including broad and narrow band photometry with TRAPPIST and optical and NIR high-resolution spectroscopy with UVES and CRIRES+ at the 8-m ESO-VLT.

We used both TRAPPIST-North (TN) and –South (TS) [5], to monitor comet K2 for almost eight years. Our observations started with the TN on October 25, 2017, using broad-band filters. At that time, the comet was 15.18 au from the Sun and had a visual magnitude of 19.7 (Figure1). We continued observing the comet with both broadband and HB comet narrowband filters using the TS telescope from September 9, 2021, when it became visible and brighter from the southern hemisphere (rh=5.4 au), until April 20, 2025, after perihelion at 8.46 au. We collected a total of 2204 BB and 174 NB images. The light curve is shown in Figure 1. The brightest magnitude of the comet, with a 5 arcsecond aperture, was 11.18 in the R filter on January 30, 2023. The colors are surprisingly constant throughout the whole range of heliocentric distances, except near the perihelion (< 2.0 au), where the gas contamination of the broadband filters B and V by CN and C₂, respectively, is visible. We first detected CN and C₂ radicals at the end of March 2022, followed by the majority of other radicals that appeared in the coma about a month later, except for NH, which was observed in mid-August 2022. CN remained detectable in our data until mid-October 2023 at 3.88 au, while C₂ and C₃ were no longer observed after early October at 3.83 au. OH was detected until September 20 at 3.69 au, while NH was detected until the end of March 2023 at 2.20. The production rates of these daughter species have been derived from a Haser model [6] using the main emission bands and compared to expected parent species detected with CRIRES+ simultaneously.

The Afρ parameter, a proxy for the dust production [7], reached a peak value of approximately 15,000 cm on January 29, 2023, at 1.87 au, placing comet K2 among the most active long-period comets. The Afρ values exhibit significant trends, including a peculiar behavior observed between −260 and −170 days before perihelion (corresponding to heliocentric distances of 3.60 to 2.74 au), where a notable drop is followed by a rapid increase. Based on the production rates, we calculated their ratios relative to CN and OH, as well as the dust-to-gas ratios. Comet K2 falls into the typical compositional group, which is defined by a characteristic abundance of C₂ and C₃ relative to CN and OH.

 To thoroughly investigate the composition of K2 in the optical range and its evolution while getting closer to perihelion, and compare it to other long-period comets. We conducted a program with the high-resolution Ultraviolet Visual Echelle Spectrograph (UVES) at the VLT, at three different epochs before and after the water sublimation line (≈3.5 au). CO₂⁺ ions are detected, but CO+ are never detected, showing that K2 is not a CO⁺ rich comet like C/2016 R2 [8], observed at the same distance and whose optical spectrum was dominated by CO⁺ bands. The high resolution and sensitivity of UVES enabled the detection of all three forbidden oxygen [OI] emission lines at each epoch. This also allowed for the calculation of the green-to-red (G/R) intensity ratio.

Observations were conducted with CRIRES+ over three nights, simultaneously with UVES. The settings were chosen to capture major primary volatiles (e.g., H₂O, CO, C₂H₆, CH₄, HCN, NH₃) and monitor their evolution as the comet approached the Sun. Despite K2’s significant activity at large heliocentric distances, our infrared observations show a contrasting picture: a very weak dust continuum and faint emission lines from several parent species. Notably, the infrared signatures of species commonly seen in the optical, such as H₂O, C₂H₂, and HCN, were barely detectable even when the comet appeared bright. This suggests the comet remained too far from the Sun (Rh > 2 au) for efficient sublimation of water and other less volatile species. Instead, hypervolatiles like CO and CO₂ were likely the main drivers of the strong activity observed at these distances. Due to the weak flux, deriving accurate production rates was challenging, however, the data still allowed comparison between parent species in the infrared and daughter species in the optical.

This combined observational approach underscores the value of integrating high-resolution spectroscopic data of both optical and IR with photometric measurements to achieve a comprehensive understanding of cometary activity and composition.

Figure 1: TRAPPIST light curve of comet C/2017 K2 measured within a radius aperture of 5-arcseconds.

References:
[1] Kaiser, N. & Pan-STARRS Team. 2002, in American Astronomical Society Meeting Abstracts, Vol. 201
[2] Wainscoat, R. J., Wells, L., Micheli, M., & Sato, H. 2017, Central Bureau Electronic Telegrams, 4393, 1
[3] Jewitt, D., Hui, M.-T., Mutchler, M., et al. 2017, ApJ, 847, L19
[4] Yang, B., Jewitt, D., Zhao, Y., et al. 2021, ApJ, 914, L17
[5] E. Jehin et al. 2011, The Messenger, 145, 2-6
[6] Haser, L. 1957, Bulletin de l’Academie Royale de Belgique, Vol. 43
[7] A’Hearn, M. F., Schleicher, D. G., Millis, R. L., Feldman, P. D., & Thompson, D. T. 1984, The Astronomical Journal, 89, 579
[8] Opitom, C., Hutsemékers, D., Jehin, E., et al. 2019, A&A, 624, A64

How to cite: Hmiddouch, S., Jehin, E., Lippi, M., Vander Donckt, M., Jabiri, A., Moulane, Y., Manfroid, J., Hutsemekers, D., and Benkhaldoun, Z.: Long-Term Activity and Compositional Evolution of Comet C/2017 K2(PanSTARRS) from Photometric and High-Resolution Spectroscopic Observations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1785, https://doi.org/10.5194/epsc-dps2025-1785, 2025.

Comet C/2022 E3 (ZTF) is a long-period comet discovered on March 2, 2022 by the Zwicky Transient Facility. Initially a faint object, it brightened significantly as it approached the inner Solar System, becoming visible to the naked eye in early 2023 under dark skies. The comet passed perihelion at 1.11 au on January 12, 2023, and made its closest approach to Earth on February 1, 2023, at a distance of about 0.28 au. C/2022 E3 was notable for its green coma, caused by strong diatomic carbon (C₂) emission, providing a valuable opportunity for photometric and spectroscopic studies of its activity and composition.

In this work, we present a comprehensive study of comet C/2022 E3 based on a multi-epoch observational campaign combining imaging (broad band BVRI filters and narrow-band HB filters; OH, CN, C₂, C₃, NH for gas species and BC, GC, RC for the dust continuum [1]) from the TRAPPIST-North and -South telescopes [2], with low- and high-resolution optical spectroscopy from the Himalayan Chandra Telescope in India. The comet was monitored over a span of approximately 373 days encompassing its perihelion passage, from 2022 May 12 (r_h = 3.52 au, inbound) to 2023 May 20 (r_h = 2.22 au, outbound). This extensive dataset allowed us to trace the evolution of dust activity (using the proxy Af(0)ρ [3]) and production rates and rate ratios of key gas species and investigate the physical and compositional properties of the comet's coma. The optical spectrum revealed emissions from the regular neutral molecular species CN, C₂, C₃, NH₂, and forbidden oxygen line as shown in Figure 1.

The combined dataset was utilised to extract the production rates and activity trends of the dust and gas species. The complete activity trend reveals a structured evolution of volatile release, with asymmetric behaviour around perihelion for a few species and evidence for changing molecular dominance as a function of heliocentric distance. Over the period of observation, C/2022 E3 demonstrates a behaviour consistent with a typical carbon-chain comet. While the production rates of the gas species peaked around perihelion; Q(OH) = (3.72+/-0.35)x10²⁸ molec/s, Q(NH) = (2.63+/-0.21)x10²⁶ molec/s, Q(CN) = (8.13+/-0.32)x10²⁵ molec/s, Q(C₂) = (1.07+/-0.02)x10²⁶ molec/s, Q(C₃) = (2.09+/-0.08)x10²⁵ molec/s, and the Afrho measured in the narrow band filters peaked 25 days prior to perihelion; Afρ(BC) = (3802+/-114) cm, Afρ(RC) = (5370+/-53) cm; the apparent magnitude peaked at about 22 days after perihelion which is not usually observed. This difference in peak for the apparent magnitude was a direct effect of the close approach of the comet with Earth, about 22 days after perihelion, as shown in Figure 2.

The extensive photometric data was used to analyse the dust color in both broad and narrow band images across the heliocentric range to look for any variation. The series of CN imaging data obtained from the TRAPPIST telescopes allowed us to estimate the comet’s nucleus rotation period through the analysis of periodic structures in the coma morphology. Medium-resolution spectroscopy (R~30,000) was employed to investigate the forbidden atomic oxygen lines [OI] at 5577 Å (green) and 6300/6364 Å (red doublet). The moderate spectral resolution allowed us to disentangle cometary and telluric components, enabling the computation of the green-to-red (G/R) intensity ratio. We analysed the variation of the G/R ratio as a function of both nucleocentric distance and heliocentric distance, providing insight into the relative contributions of H₂O, CO₂, and CO as the parent species of atomic oxygen [4,5,6].

This combined observational study highlights the importance of linking low- and high-resolution spectroscopic datasets with imaging for a holistic understanding of cometary activity and composition.

Acknowledgements

A.K acknowledges support from the Wallonia-Brussels International (WBI) grant. This work is a result of the bilateral Belgo-Indian projects on Precision Astronomical Spectroscopy for Stellar and Solar system bodies, BIPASS, funded by the Belgian Federal Science Policy Office (BELSPO, Government of Belgium; BL/33/IN22_BIPASS) and the International Division, Department of Science and Technology, (DST, Government of India; DST/INT/BELG/P-01/2021(G)). 

References

[1] Farnham, T., The HB Narrowband Comet Filters: Standard Stars and Calibrations. Icarus 147, 180–204 (2000); [2] Jehin, E. et al., TRAPPIST: TRAnsiting Planets and PlanetesImals Small Telescope. The Messenger 145, (2011); [3] A'Hearn et al., Comet Bowell 1980b, The Astronomical Journal 89-4, 579-591 (1984);[4] Festou M., Feldman P. D., 1981, A&A, 103, 154; [5] Bhardwaj A., Raghuram S., 2012, ApJ, 748, 13; [6] Raghuram S., Bhardwaj A., 2014, A&A, 566, A134

How to cite: Krishnakumar, A., Vander Donckt, M., Moulane, Y., Hmiddouch, S., Jehin, E., Ahuja, G., Ganesh, S., Sahu, D., Abdelhadi, J., and Benkhaldoun, Z.: Investigating the Molecular Activity and Composition of Comet C/2022 E3 via Photometry and Optical Spectroscopy, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1066, https://doi.org/10.5194/epsc-dps2025-1066, 2025.

Comets afford a window into the chemistry and physics of planet formation. Through remote sensing of coma gases, the composition of nucleus ices can be inferred and placed into the context of the protoplanetary disk midplane and solar system formation. As all-sky survey capabilities continually improve, comets are being discovered at ever larger heliocentric distances (r_H), enabling investigations of their outgassing behavior far outside the r_H = 2-3 au window where H₂O, the dominant ice in most comets, first begins vigorously subliming. On the other hand, some of these comets will never cross the H₂O sublimation zone. Understanding what clues to solar system formation are preserved in the nuclei of these distantly active comets requires relating compositional measurements at much larger r_H to the majority of remote sensing work, which takes place when comets are at or inside 1 au from the Sun.

Here we report analysis of ALMA observations of distantly active comet C/2017 K2 (PanSTARRS) in three epochs when the comet was at r_H = 4 au, 3.5 au, and 3 au. We observed emission from HCN, CO, CH₃OH, H₂CO, CS, HNC, and thermal emission from the nucleus and dust coma at millimeter wavelengths. We will discuss the evolution of the spatial distributions, outgassing kinematics, and molecular abundances in the coma as the comet approached the H₂O sublimation zone and compare our results to measurements taken when H₂O sublimation had activated [1,2] thereby placing them into context with the larger comet population.

This work makes use of ALMA data ADS/JAO.ALMA #2021.1.00862.S.

References:

[1] Woodward et al. 2025, “A JWST Study of the Remarkable Oort Cloud Comet C/2017 K2 (PanSTARRS)”, PSJ, In Press, doi: https://doi.org/10.3847/PSJ/add1d5

[2] Ejeta et al. 2025, “Infrared Compositional Measurements of Comet C/2017 K2 (Pan-STARRS) at Heliocentric Distances Beyond 2.3 au”, AJ, 169, 102

How to cite: Roth, N., Milam, S., Cordiner, M., Woodward, C., Biver, N., Bockelee-Morvan, D., Boissier, J., Remijan, A., and Charnley, S.: ALMA Imaging of Comet C/2017 K2 (PanSTARRS) En Route to the H2O Sublimation Zone, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-917, https://doi.org/10.5194/epsc-dps2025-917, 2025.

Comets are among the most primitive bodies in the Solar System, preserving primordial materials from the early formation of the Solar System. Among various species observed in cometary comae, sodium is relatively lesser understood due to the high environmental temperature required for its sublimation, which restricts the observable samples to near-Sun comets. Here we present an analysis of five comets using a combination of narrowband imaging and high-resolution spectroscopy.

Coronagraph Imaging

In early July 2020, comet C/2020 F3 (NEOWISE) approached the Sun for the first time in nearly 4,500 years. Comet NEOWISE was observed by the Planetary Science Institute’s Io Input/Output Facility (IoIO; Morgenthaler et al., 2019) 35-cm coronagraph from July 7-16. Narrowband filters were used to isolate the dust and sodium gas emissions in the comae, and this apparition at only 0.33 AU from the Sun allowed some of the best quality images of a cometary sodium tail taken to date, as seen in Figure 1.  For inner solar system comets, sodium is often the brightest emission line available to ground-based telescopes thanks to its efficient resonant scattering of sunlight near the maximum of the solar irradiance spectrum. Strong radiation pressure from resonant scattering shapes sodium gas into a vast anti-sunward tail.

Figure 1: Narrowband filtered images of continuum dust reflectance and sodium D line emission in C/2020 F3 (NEOWISE). At 86° phase angle, the sodium tail here appears nearly orthogonal to the line of sight.

Structure in cometary sodium emissions is shaped by the collisional entrainment in the bulk outflow from the nucleus, additional dusty sources, the temperature of the atoms, absorption of intervening sunlight in the dense coma regions, and radiation pressure. At a certain radius from the nucleus, Na atoms collisionally decouple from the bulk outflow velocity with a thermal distribution. While it is challenging to uniquely parameterize the collisional radius, outflow velocity, and gas temperature, additional insight can be gained from emission line profiles at ample spectral resolutions of R >100,000 thanks to Doppler broadening.

Resolved Linewidth Measurements

During the IoIO imaging campaign, C/2020 F3 (NEOWISE) was also observed with the Lowell Discovery Telescope’s Extreme Precision Spectrometer (EXPRES; Jurgenson et al., 2016), at a resolving power of R = 150,000. At a phase angle of 108° and heliocentric distance of 0.46 AU, forward modeling of the line profiles that accounts for hyperfine structure retrieves effective temperatures ranging 1750 to 1950 K. The RMS velocity of this Doppler broadening is equivalent to 1.13 to 1.19 km/s, which suggests that collisional coupling to the bulk water outflow velocity is the dominant component in the emission line shape.

Figure 2: Outflow velocity at five comets with varying heliocentric distances as derived from resolved Na D emissions. Comets near 90° phase angle roughly follow the r^-0.5 relationship outlined by Budzien et al. (1994). C/2023 A3 was measured at both ~0.4 and 0.85 AU and shows variation consistent with this trend. Comets with phase angle >20° from quadrature are shown as outlines.

The water outflow velocity in comets is well known to vary with heliocentric distance. The often-cited relationship of v_H2O = 0.85r^-0.5 applied by Budzien et al. (1994) is a compromise between hydrodynamical models, which suggest 0.7r^-0.5 (Gombosi et al., 1986), and radio observations of OH and HCN at 1P/Halley, which suggest 1.1r^-0.5 (Combi, 1989). By comparing Na linewidths in a survey of comets at varying heliocentric distance, we find that the thermal velocity derived from Na linewidths produces a similar relationship. Figure 2 shows linewidth-derived outflow velocity for five comets at a range of heliocentric distances. All spectra were obtained with EXPRES, with the exception of the C/2023 A3 data point at 0.85 AU, which was obtained using the Large Binocular Telescope’s Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI; Strassmeier et al., 2015). Na D2 speeds appear systematically higher, implying that the line core may exceed unity optical depth. Comets 96P, 2P, and C/2023 A3 were observed at phase angles >20° from quadrature, which caused distortion of the line shape due to projection effects along the tail, resulting in outflow speeds higher than the overall trend.

Monte-Carlo Modeling

Figure 3: Preliminary results of Monte-Carlo modeling sodium gas in the coma of C/2020 F3 (NEOWISE), assuming here a collisional radius of 10,000 km, bulk outflow speed of 1.5 km/s and gas temperature of 150 K.

Phase angle distortion of the emission line profiles can be accounted for with Monte-Carlo modeling, and with nearly concurrent imaging and spectroscopy in the case of C/2020 F3 (NEOWISE), this approach has good potential to uniquely quantify the parameters that control sodium dynamics in its coma. We adapt the Monte-Carlo model of C/2012 S1 (ISON) by Schmidt et al. (2015), and this presentation will describe attempts to self-consistently simulate both spatial structure in the tail and Doppler broadening near the optocenter, using C/2020 F3 (NEOWISE) as a case study. A preliminary model run is shown in Figure 3, though it does not yet include emission from within the collisional radius and emission from dusty sources, which will broaden the tail. Work thus far suggests that spectrally resolved sodium emissions could offer a proxy for the water outflow velocity, enabling a new method at optical wavelengths.

How to cite: Lierle, P., Schmidt, C., Morgenthaler, J., Ye, Q., Zhang, Q., Cremonese, G., Munaretto, G., Cambianica, P., and Ilyin, I.: Sodium in Cometary Comae at Various Distances from the Sun, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1065, https://doi.org/10.5194/epsc-dps2025-1065, 2025.

Introduction: Comets are among the most pristine remnants of the early Solar System [1], preserving volatile ices, refractory dust, and organic compounds that offer insights into the protoplanetary disk [2, 3, 4]. When approaching the Sun, sublimation processes release gas and dust, making comets key targets to study chemical and physical evolution. Molecular emissions in cometary comae reveal volatile inventories and photochemical processes. Comet C/2023 A3 (Tsuchinshan-ATLAS) is an Oort Cloud comet discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) on January, 2023. This dynamically new comet reached its perihelion on September 27, 2024, at a distance of 0.39 au from the Sun. As the comet approached the inner Solar System, its activity increased significantly, with a substantial production of dust [5]. In this study, we analyze pre- and post-perihelion optical spectra of comet C/2023 A3, obtained with DOLORES at the Telescopio Nazionale Galileo (TNG) on May 1, 2024, and with the PEPSI spectrograph on the Large Binocular Telescope (LBT) on October 27, 2024. We derive the CN production rate and upper limits for other volatiles. Additionally, we present a post-perihelion high-resolution catalog of emission lines, and compare the emission features and elemental abundances of C/2023 A3 with those observed in other comets.

Methods: Due to the strong dust contamination and low gas emission observed pre-perihelion, only the CN emission band could be detected (see Fig. 1), while upper limits were derived for other molecular species (C₂, C₃, NH₂, see Fig. 2). Post-perihelion, thanks to high-resolution spectroscopy, we built a detailed catalog of emission lines for comet C/2023 A3.

Fig. 1. 𝑇𝑜𝑝 𝑝𝑎𝑛𝑒𝑙. Gaussian fit to the CN emission band centered at 3881.68 Å in the comet’s spectrum. The black line represents the observed spectrum, the red line is the fitted Gaussian profile, the blue dashed line indicates the central wavelength, and the shaded area corresponds to the total flux under the curve. 𝐵𝑜𝑡𝑡𝑜𝑚 𝑝𝑎𝑛𝑒𝑙. Zoomed-in view of the CN emission band and its Gaussian fit. The detailed view highlights the agreement between the fitted Gaussian profile (red line) and the observed data (black line), with the shaded area representing the integrated flux. The central wavelength is marked by the blue dashed line [10]. The CN production rate was determined by fitting a Gaussian profile to the CN (B–X) emission band at 3883 Å and applying a Haser model [8] to account for the spatial distribution in the coma. Fluxes were converted into production rates using standard fluorescence efficiencies and expansion velocities scaled to the heliocentric distance. For undetected species, upper limits were calculated based on the noise level around the expected emission wavelengths, assuming a 3σ threshold, and converted into 

production rates using the same formalism adopted for CN. The strong dust continuum was modeled and subtracted by fitting a low-order polynomial to emission-free regions and using a scaled solar analog spectrum. Following [9], the post-perihelion catalog includes both molecular bands (e.g., CN, C₂, NH₂) and atomic lines (e.g., Na I, K I), enabling a comprehensive analysis of the comet's volatile and atomic inventory. Emission line fluxes were measured by fitting Gaussian profiles after local subtraction of residual solar and telluric features, and were used to derive relative abundances and to compare C/2023 A3 with other comets.

Fig. 2. Top panel: Observed spectrum of comet C/2023 A3 in the spectral region of the C₂ bandhead at 5168.64 Å. The black line represents the observed spectrum, while the blue dashed line marks the expected central wavelength of the molecular feature. The shaded red region indicates the area where the emission would be expected, but no significant detection is observed. Middle panel: Same as the top panel but for the C₃ bandhead at 4003.65 Å. Bottom panel: Same as the previous panels but for the NH₂ bandhead at 5537.27 Å.

Results: Pre-perihelion observations revealed the presence of CN emission in comet C/2023 A3, with a derived production rate of (3.89 ± 0.21) × 10²⁵ molec/s. Due to the strong dust contamination, no other molecular emissions were detected, and we derived upper limits for C₂, C₃, and NH₂: Q(C₂) < 1.30 × 10²⁵ molec/s, Q(C₃) < 3.12 × 10²⁴ molec/s, and Q(NH₂) < 2.79 × 10²⁵ molec/s. The Afρ parameter, an indicator of dust production, was measured at 4329 ± 56 cm, confirming the comet's high dust activity. The production rate ratios log(Q(C₂)/Q(CN)) < −0.48 and log(Q(C₃)/Q(CN)) < −1.10 classify C/2023 A3 as a carbon-depleted comet [10]. Post-perihelion, high-resolution observations with PEPSI at the LBT allowed the construction of a detailed catalog of emission lines. We identified several molecular and atomic species, including CN, C₃, C₂, CH, CO⁺, Na, O I, NH₂, and K.

Conclusions: Comet C/2023 A3 (Tsuchinshan-ATLAS) exhibits characteristics typical of dynamically new, carbon-depleted comets. Pre-perihelion observation confirmed significant dust activity and indicates that C/2023 A3 is a carbon-depleted comet, consistent with previous classifications of dynamically new comets. Post-perihelion high-resolution spectroscopy enabled the detection of multiple molecular and atomic species, enriching our understanding of the comet's chemical inventory.
These results contribute to the broader characterization of volatile and elemental abundances in Oort Cloud comets, providing important constraints for models of Solar System formation and evolution.

Acknowledgements: This research used the facilities of the Italian Center for Astronomical Archive (IA2) operated by INAF at the Astronomical Observatory of Trieste.

References: [1] Morbidelli, A., et al., 2015. A&A 583, A43 [2] Russo, N.D., et al., 2016. Icarus 278, 301–332. [3] Mumma, M.J., et al., 2011. Annu. Rev. Astron. Astrophys. 49, 471–524. [4] Lippi, M., et al., 2024. APJ. Lett. 970, L5. [5] Mugrauer, M., 2024. Astron. Telegram 16911, 1. [6] Tody, D., 1986. Proc. SPIE 627, 733–748. [7] Horne, K., 1986. Publ. Astron. Soc. Pac. 98, 609. [8] Haser, L., 1957. Bull. Acad. R. Belg. 43, 740–750. [9] Cambianica, P., et al., 2021. A&A. 656, A160. [10] Cambianica, P., et al., 2025, PSS, Volume 261, 106102.

How to cite: Cambianica, P., Munaretto, G., Cremonese, G., Mura, A., La Forgia, F., Bizzocchi, L., Lazzarin, M., Puzzarini, C., Melosso, M., Lorenzi, V., and Boschin, W.: Pre- and post-perihelion observations of the carbon-depleted comet C/2023 A3 (Tsuchinshan-Atlas) , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-74, https://doi.org/10.5194/epsc-dps2025-74, 2025.

Cometary outbursts are sudden increases in brightness caused by various mechanisms, including cliff collapse, pressure pockets, or impacts etc. The most plausible explanation for recurring and large-scale outbursts may be the crystallization of amorphous water ice. 12P/Pons-Brooks, a Halley-type comet with recurring outbursts, presents a valuable case study for understanding the nature of cometary activity. This work aims to analyze the near-infrared (NIR) and optical spectra of 12P during two major outbursts in October and November 2023, characterize its dust and gas properties, and explore the underlying triggering mechanisms.

We obtained three NIR spectra during two outbursts in October and November 2023, using the 3-m Infrared Telescope Facility (IRTF) and the Palomar 200-inch Telescope (P200), respectively. As shown in Figure 1, all three NIR spectra exhibited absorption bands at 1.5 and 2.0 μm, consistent with the diagnostic absorption features of water ice, superimposed on a red dust-scattering continuum. Through a single-scattering dust model, we found that the November 2 spectrum can be well explained by micrometer-sized crystalline ice at 140-170 K, along with sub-micrometer-sized amorphous carbon. Analysis of the NIR spectra reveals no significant weakening in the depth of the water ice absorption bands from October to November, despite stronger sublimation being expected at smaller heliocentric distances. Possible explanations include: a slight shift in size distribution towards larger grains; continuous replenishment of icy grains from the nucleus; or the presence of exceptionally pure ice.

An optical spectrum was obtained with the Lijiang 2.40-m Telescope during the November outburst.  As shown in Figure 2, emission bands of CN, C₂, C₃ and NH₂ were detected. The C₃/CN and C₂/CN ratios suggest that 12P was “typical” in C₃ abundance but near the limit of C₂-depletion at the time of observation. In terms of the Afρ value, 12P is a dusty comet when compared to Halley-type and Jupiter-family comets at similar heliocentric distances.

Combining NIR and optical observations, we found that the specific kinetic energy of the November outburst was about 8 × 10³ J kg^-¹, suggesting a triggering mechanism similar to 332P/Ikeya--Murakami and 17P/Holmes, likely the crystallization of amorphous water ice, though other mechanisms remain possible due to limited evidence. In addition, a refractory-to-ice ratio of >1.7 is derived from the total mass loss of dust and gas.

This study provides new insights into the physical properties of water ice grains in outbursting comets. The findings reinforce the hypothesis that crystallization of amorphous water ice is a dominant mechanism driving such events. The results have broader implications for understanding cometary evolution and outburst dynamics, particularly for Halley-type comets.

Figure 1: NIR spectra of 12P taken with SpeX and TSpec. The date and instrument are labeled below the respective spectrum. The red-system band of CN and the two water ice absorption bands are labeled. Spectral regions heavily contaminated by telluric absorption are masked in gray. The “emission” feature near 1.3 μm in the Nov. 3 spectrum is due to imperfect telluric correction. The Nov. 2 spectrum is well reproduced by a dust model (red line), with the best-fit parameters labeled at the bottom: δ-the mass ratio of amorphous carbon to water ice in the coma, α-power-law index of the grain size distribution, a_p-the peak grain size.

Figure 2: (a) Optical spectrum of 12P taken on Nov. 2. Also shown are the spectrum of a G2V star (grey line) and the reproduced dust continuum (red dashed lines). (b) Emission component in the spectrum of 12P. Emission bands of CN, C₃, C₂, and NH₂ are labeled.

How to cite: Zhao, R., Yang, B., Kelley, M. S. P., Protopapa, S., Li, A., and Liu, J.: Optical and Near-Infrared Spectroscopy of Outbursting Comet 12P/Pons-Brooks, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1309, https://doi.org/10.5194/epsc-dps2025-1309, 2025.

We present the results obtained from VLT/CRIRES⁺ observations of the Halley-type comet 12P/Pons-Brooks, during its exceptional apparition in 2024. 

Comets are considered among the least processed bodies of the solar system. Stored in a frozen environment from their formation to the present day, they are expected to retain most of the chemical and mineralogical properties associated with their formation site. Thus, chemical differences among comets coming from different reservoirs (e.g., Jupiter Family vs Oort Cloud comets) can provide important insights into the chemical and physical conditions prevalent in our protoplanetary disc about 4.6 billion years ago, and test a possible radial gradient in the chemistry of forming icy planetesimals, along with the dynamical models that predict their dissemination [1,2,3].

Infrared (IR, 2 - 5 μm) spectroscopic studies of comets provide key information on the relative abundances of many primary (parent) molecules thought to be released directly from the nucleus (e.g., H₂O, CH₃OH, CH₄, C₂H₆, CO, NH₃, H₂CO, …), allowing for chemical characterisation. The most recent IR statistics show chemical variability within the comet population but no distinct chemical groups [4,5]. Nonetheless, several dynamical classes of comets remain underrepresented in terms of compositional studies, with Halley-type comets (HTCs) being the least investigated. HTCs are linked to the Oort cloud, but have dynamically evolved into shorter (decades long) orbital periods. 

In 2024, 12P/Pons-Brooks (hereafter 12P) reached perihelion on April 20, at 0.78 au, becoming one of the brightest comets in the last decades, and giving the opportunity to easily measure its chemical composition from ground-based observatories. 

We will show 12P spectra obtained in July 2024 using the cross-dispersed spectrograph CRIRES⁺ at ESO/VLT, and report retrieved rotational temperatures, production rates and relative abundances for H₂O, CO, CH₃OH, CH₄, C₂H₆, NH₃, H₂CO, HCN, C₂H₂. In addition, we will explore for significant upper limits for species characterised by fainter spectral emission lines such as HDO, HCl and C₂H₄. 

Results for 12P will be put in the overall picture of comet composition, taking into account results from CRIRES⁺ observations of comets in the last four years (e.g., C/2021 A1 (Leonard) [6], C/2023 H2 (Lemmon) [7], and C/2017 K2 (PANSTARRS) [8]), and more generally considering the existing databases [4,5], to determine whether there are statistically significant differences in composition among the various dynamical types (Halley-type vs Jupiter Family vs long-period and dynamically new Oort Cloud comets).

Following [9], we will finally compare abundance ratios measured in 12P and other comets to those found in planet-forming disks surrounding young solar analogues (10⁴ — 10⁶ years old, see for example [10,11]), with the final aim of understanding the degree of chemical reprocessing in the disk (inherited vs reset scenario) and/or the possibility of material evolution in comets after their formation. 

References: [1] Mumma, M. J., & Charnley, S. B., 2011, ARA&A, 49, 471; [2] Eistrup, C., et al., 2019, A&A, 629, A84; [3] Morbidelli, A., & Rickman, H., 2015, A&A, 583, A43; [4] Dello Russo, N., et al., 2016, Icarus, 278, 301; [5]  Lippi, M., et al., 2021, AJ, 162, 74; [6] Lippi et al., 2023, A&A, 676, A105; [7] Lippi et al., 2024, A&A, 689, A77; [8] S. Hmiddouch et al., in preparation; [9] Lippi, M., et al., 2024, ApJ, 970, L5; [10]​​ Podio L., et al., 2020, A&A, 644, A119; [11] Yang et al., 2021, APJ, 910, 1.

How to cite: Lippi, M., Faggi, S., Cordiner, M., Bonev, B., Opitom, C., and Villanueva, G.: CRIRES+ investigations of the volatile composition of Halley-type comet 12P/Pons-Brooks during its exceptional passage in 2024, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-540, https://doi.org/10.5194/epsc-dps2025-540, 2025.

Comets are remnants from the early solar system and retain volatiles from the time and place of their formation in the outer protoplanetary disk. Gravitational interactions with the young giant planets scattered many of them into one of two main dynamical reservoirs where they have been preserved since their formation: the Kuiper Belt and the Oort Cloud. Subsequent perturbations have modified some cometary orbits towards the inner solar system where they can be observed. Comets from the Kuiper Belt may be perturbed into short period (<20 year) orbits that are primarily affected by Jupiter’s gravity. These are known as Jupiter Family comets (JFCs). Oort cloud comets (OCCs) can be perturbed, primarily by galactic tides, into very long period (>200 year) orbits.  The long residences of cometary nuclei in the cold, outer solar system has allowed them to preserve the volatiles they formed with, giving them the potential to provide a window on the chemical and physical processes that occurred during planet formation.

A subset of OCCs have dynamically evolved into shorter (decades long) orbital periods. These Halley-type comets (HTCs) are the least well studied class because there are relatively few of them compared to other OCCs. In addition, their relatively longer orbital periods, compared to JFCs, results in a very small number of bright apparitions since the advent of sensitive high-resolution spectrographs. For these reasons, only two HTCs (1P/Halley and 8P/Tuttle) have had their parent volatile compositions well characterized to date, which is insufficient to make a meaningful compositional comparison with the other dynamical families. However, HTCs are of particular interest because they have the potential to help resolve long-standing questions in comet science.

This work focuses on HTC 12P/Pons-Brooks (hereafter 12P), which was discovered in 1812 and observed again in 1883-84 and 1953-54. Its 2024 apparition was particularly favorable for infrared daytime observations. We performed high-resolution (λ/Δλ~50,000), near-infrared spectroscopic measurements with iSHELL at the NASA Infrared Telescope Facility (IRTF) on eight dates between 2024 February 15 (pre-perihelion, R_h = 1.4 au) and 2024 May 1 (post-perihelion, R_h = 0.80 au). With these observations we address four key questions in comet science:

• Does comet volatile composition depend on the comet’s dynamical history? In particular, is the observed composition of comets with shorter periods affected by thermal processing during multiple close approaches to the Sun? Volatile compositions have been measured in both JFCs and OCCs and vary within each dynamical class. Of particular interest are hypervolatiles, which have been suggested to be depleted in JFCs relative to OCCs. One possible explanation is that multiple (and frequent) close perihelion passages cause preferential loss of more hypervolatile ices from the nuclei of JFCs. Another is that JFCs and OCCs may have formed in different (or not entirely overlapping) regions of the protoplanetary disk. One way to distinguish between these two scenarios is to study HTCs, which come from the Oort cloud, but have dynamically evolved to much shorter orbital periods than other OCCs.
• Does small heliocentric distance affect the composition measured in the coma of a comet? Past observations have suggested a systematic enrichment of H₂CO, NH₃, and C₂H₂ for comets observed within approximately 0.8-1 au from the Sun, thought to be caused by more complex (less volatile) species that disintegrate at small heliocentric distances once a thermal threshold is reached. 12P was observable between 1.4-0.78 au, enabling investigation of the heliocentric dependences of these key volatiles. 
• How is the composition of volatiles subliming from the comet’s surface connected to that of the interior? 12P underwent repeated outbursts during its two most recent apparitions and was observed to outburst repeatedly in 2024. Such outbursts have been observed in other comets (such as 67P/Churyumov-Gerasimenko) and are often attributed to the collapse of surface features, such as cliff walls, exposing fresh material to sublimation. Hence 12P offered the possibility to sample more pristine subsurface material that had not been subject to surface heating and processing.
• How do seasons affect observed compositions? Depending on nucleus size, shape, orientation, and rotational properties, different areas of the surface may be exposed to solar irradiation and sublimate as a comet orbits the Sun. The Rosetta mission demonstrated that the high obliquity (52⁰) of 67P led to variations in coma composition owing to both diurnal and seasonal effects. 12P was observed before, near, and after perihelion in search of coma compositional variations owing to seasonal changes on its large (33 km) nucleus, if such occur on this comet.

We report production rates (molecules s^-1), rotational temperatures, and relative abundances among measured volatiles (C₂H₆, CH₃OH, H₂CO, HCN, C₂H₂, NH₃, CO, OCS, and H₂O) in 12P. We will compare the composition of 12P to the few other HTCs observed to date (see also the DiSanti et al. and Saki et al. presentations at this meeting), as well as to comets of other dynamical types, and discuss implications for addressing the four science questions above. 

This work was supported by the NSF AARG program (awards 2009910 and 2009398) and NASA SSO (80NSSC22K1401). We also thank the IRTF staff for helping to make these challenging daytime observations successful.

How to cite: Gibb, E., Saki, M., DiSanti, M., Bonev, B., Roth, N., Faggi, S., Dello Russo, N., Vervack, R., Villanueva, G., Kawakita, H., and Khan, Y.: Comet 12P/Pons-Brooks: The Importance of Halley-Type Comets to Understanding the Early Solar System, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-801, https://doi.org/10.5194/epsc-dps2025-801, 2025.

Comets contain the best-preserved known remnant material of solar system formation. Their volatile compositions provide clues to extant conditions in the protosolar disk at the time and place of their formation [[i],[ii]]. Subsequent gravitational interactions with the young giant planets scattered comet nuclei into the Kuiper belt and Oort cloud reservoirs, representing the primary dynamical source regions for ecliptic comets and nearly isotropic comets, respectively. Ecliptic comets have low orbital inclinations and typically become observable as Jupiter-family comets (JFCs) at smaller heliocentric distances (R_h). Nearly isotropic comets have random inclinations and manifest as longer period or non-returning comets, a dynamical class often termed Oort cloud comets (OCCs). Through gravitational interaction with the giant planets, a subset of OCCs transition to Halley-type comets (HTCs), having semi-major axes < 40 au [[iii]].

Spectroscopic studies at IR and millimeter / submillimeter wavelengths permit quantifying constituent ices housed in cometary nuclei (referred to as “native” ices). When sublimed through solar heating, these ices release parent volatiles (molecules) into the coma. Measuring abundances for 8 – 10 distinct parent volatiles (at times more) has become common in the IR (from l ~ 2.8 – 5.0 µm). The number of comets so characterized to date is ~ 50, and these comprise a continually evolving parent volatile compositional taxonomy [[iv]]. Characterizing the parent volatile compositions of HTCs provides an important bridge between JFCs, which experience frequent solar heating due to their short orbital periods, and dynamically new or very long-period comets that have experienced relatively little heating. However, to date only two HTCs have been characterized in detail, 1P/Halley and 8P/Tuttle, with only 8P having been available for study using high-resolution IR spectroscopy. Therefore, more HTCs are needed to draw meaningful comparisons to the overall population of comets.

Fortuitously, 2024 provided relatively rare opportunities to measure the compositions of two HTCs, 12P/Pons-Brooks and 13P/Olbers. For results from our observational campaign on 12P, see the Gibb et al. presentation (this meeting). Here, we report production rates and abundance ratios for six parent volatiles in 13P from daytime observations using iSHELL [[v]] at the NASA-IRTF on UT 2024 August 16. H₂O and CO were measured together in one iSHELL setting, and CH₄, C₂H₆, CH₃OH, and H₂CO were measured together in a second setting.  Our study is coordinated with a dedicated 13P iSHELL run in early August that characterized the parent volatile composition in greater detail (see Saki et al. presentation, this meeting), yet lacked sufficient geocentric Doppler shift (Δ_dot) to test CO or CH₄. By mid-August, Δ_dot had increased sufficiently to test these two critical “hypervolatile” species.

Our measurements revealed significantly enriched abundances (relative to H₂O) of CO and CH₄ (the two most volatile ices/parent molecules measured in the IR), compared with their mean abundances among OCCs, whereas C₂H₆ and CH₃OH were close to their mean values [4]. Possible interpretations regarding the processing history of the ices incorporated into the nucleus of 13P will be discussed.

We acknowledge support through NASA SSO Program awards 22-SSO22_0013 (MD, SF, NXR) and 80NSSC22K1401 (NDR, BPB, RJV), and through NSF award AST-2009398 (NDR, BPB). We also thank the IRTF staff for their help in making these challenging daytime observations successful.

How to cite: DiSanti, M., Gibb, E. L., Saki, M., Bonev, B. P., Dello Russo, N., Vervack, Jr., R. J., Khan, Y., Faggi, S., Roth, N. X., Kawakita, H., and Villanueva, G. L.:  Enriched CO and CH4 abundances in Halley-Type Comet 13P/Olbers through high-resolution near-IR spectroscopy, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1102, https://doi.org/10.5194/epsc-dps2025-1102, 2025.