EXOA8
Carbon chemistry is ubiquitous in the dense interstellar medium, with chemical modelling, laboratory experiments, and astrophysical observations suggesting that the complex macro-molecular building blocks of life could be synthesised in ices under these conditions. Such material can be incorporated into planetesimals during their accretion, and planetary bodies can today play host to complex chemistry. This is significant across many aspects of exploration in the outer solar system, particularly in the potentially habitable satellites of the giant planets. The subsurface liquid water oceans of the moons Enceladus (the only extraterrestrial ocean to have been sampled) and Europa are likely habitable, whilst Titan could be a natural prebiotic laboratory. Clearly, the characterisation of these fascinating geochemical environments is critical to understand habitability and search for extraterrestrial life. The New Horizons mission and JWST observations have characterised the compositions of primitive Trans-Neptunian Object (TNOs) in the farthest reaches of the solar system, enabling a direct comparison with the ices in protoplanetary disks that are the feedstock for carbonaceous molecules in extra-solar planetary systems.
This symposium will discuss our current understanding of chemistry and the emergence of life in the solar system and beyond, welcoming contributions related to icy ocean worlds, ring systems, comets, asteroids, surfaces, TNOs, protoplanetary disks, and the interstellar medium. Results derived from space mission data, detections of organic molecules via telescopic observations, laboratory experiments predicting or characterising chemical processes, and theoretical approaches including quantum chemistry and geochemical modelling are encouraged. We encourage submissions on biological, physicochemical, astrophysical, and paleontological studies of the living-matter origination problem, the conditions necessary and sufficient for living-matter origination and development, mechanisms of living-matter origination on the Earth and other celestial objects. Submissions on promising celestial objects for the living-matter occurrence, and other experimental, theoretical, and observational works related to the emergence and development of life in our Solar System and beyond are also welcomed.
Several chemical routes are proposed to understand the synthesis of biologically significant molecules on early earth. However, the research has just began to discover the feasibility of these reactions under prebiotic conditions and the physical factors influencing their efficiency in a planetary context. Hydrogen cyanide (HCN) has emerged one of the key molecules for the synthesis of major building blocks of life – lipids, sugars and nucleotides – through a series of chemical reactions, some mediated by ultraviolet light along with other scenarios. The amount of cyanide available in a natural environment can be predicted from the rate at which it is produced in an environment plus the rate it is introduced to the environment, versus the rates it is destroyed and leaves the environment. One of the most important mechanisms of HCN loss is hydrolysis. The rate of hydrolysis is known to depend on the physical and chemical conditions of the environment.
I will present the most comprehensive study thus far of the hydrolysis of HCN. I explore hydrolysis across a range of temperatures, pH and in the presence of salts like sulphite, sulphide and phosphate (for two example measurements. We determine the degradation rate for this range of conditions and predict the rate constants for acid-catalyzed hydrolysis and base- catalyzed hydrolysis of cyanide, along with uncertainties. These uncertainties are critical for comparing our results to similar studies, and applying our results to environmental conditions. We find that the hydrolysis rates are significantly influenced by pH and temperature with significant variations observed with salts. The activation energy for acid-catalyzed and base-catalyzed hydrolysis of HCN is found to be 75.7 ± 6.7 KJ/mol and 49.7±4.0 KJ/mol, respectively. This result is consistent within the errors to the literature but are systematically faster than the literature values and favours maximum lifetime around pH-7 rather than pH-4. We apply our results, in comparison to a variety of cyanide sources found in the literature to provide new predictions of cyanide availability in natural waters. Our results are critical for constraining the prebiotic environment where the prebiotic synthesis of amino acids, nucleotides and phospholipids could have occurred.
How to cite: Murali, S. S. and Rimmer, P.: Confronting the Water Problem: The Lifetime of Aqueous Cyanide and its Role in Origins of Life , Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1168, https://doi.org/10.5194/epsc2026-1168, 2026.
The Hadean (4.6-4.0 Ga) is one of the least understood eons in Earth’s history. Yet it was one of the most important, as it represents the formation of the planet and the establishment of the physical, chemical and geological conditions necessary for life. However, the only evidence from this period consists of zircons dated to 4.4 Ga, suggesting that there was an ocean of water on Earth at that time.
In this study, we examine the potential influence of the mantle redox state on the surface temperature and climate of Hadean Earth, both during and following the crystallisation of the global magma ocean after the Moon-forming impact, in order to determine the likelihood of an ocean of water existing.
The redox state of the magma ocean significantly impacts the properties and sizes of Earth's reservoirs, controlling its internal structure, atmospheric evolution and, more broadly, surface habitability. We investigate the impact of redox conditions but also carbon, nitrogen, sulphur and total hydrogen content on the speciation and cycling of volatiles, redox reactions, radiative transfer in the atmosphere, and surface temperatures on early Earth. We model the coupled evolution of the mantle and atmosphere during and after magma ocean crystallisation. By linking geochemical processes in the mantle consistently with atmospheric composition and climate, we explore a wide range of redox states and bulk volatile inventories.
Our findings reveal that atmospheric composition, mantle crystallisation timescales, and post-crystallisation surface temperatures are highly sensitive to the redox state. In all scenarios, the resulting atmospheres lead to persistently high surface temperatures. These findings imply a significant interplay between the geochemical evolution of the mantle and the emergence of habitable conditions on the earliest Hadean Earth.
To conclude, we find that forming oceans under typical volatile conditions through bottom-up crystallisation and mantle H2O outgassing alone is challenging. This differs from previous models in the literature and suggests that additional processes may have been necessary for liquid water oceans to have existed as early as 4.4 Ga.
How to cite: Decocq, E., Lichtenberg, T., and van Westrenen, W.: Redox sensitivity of the surface conditions and climate state of the Hadean Earth, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-666, https://doi.org/10.5194/epsc2026-666, 2026.
Organic matter (OM) has been found in numerous meteorites, and recently on comets and asteroids. The OM from primitive small bodies contains a soluble (SOM) and an insoluble part (IOM) locked in the mineral matrix. This OM is extracted using different protocols based on the separation of SOM with various solvents, followed by mineral digestion using acid treatments.[2-3] These treatments may transform the molecules found within each fraction. Therefore, assessing the effect of these extraction procedures is crucial.
Previous works used infrared spectroscopy (IR) to reveal the varying effects of several extraction protocols.[4-5] Authors reported differences in C-rich fragments of meteorites and asteroids for treated and untreated OM. Increase of C=O bond intensities and CH2/CH3 ratios, together with more pronounced aromatic C-H features, confirm alterations induced by treatment. However, due to the limitations of IR analysis and the absence of sufficient quantities of untreated material, a more detailed evaluation of possible alterations is still missing.
We suggest using synthetic analogues of primordial OM (in our case from the Nebulotron experiment, which mimics gas-phase reactions in the solar nebula) to study the effect of extraction protocols. Previous analyses of untreated Nebulotron organics confirmed their similarity to IOM extracted from chondrites,[6] while they still contain a minor soluble fraction. These synthetic samples provide abundant mineral-free material to assess the effect of extraction protocols, both in separating and transforming the soluble and insoluble fractions potentially found in primordial OM.
Current work is focused on solid fractions, using IR spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to assess potential alterations in Nebulotron OM resulting from common extraction protocols. We describe results for the starting material (Neb-OM, grey), the "harsh" protocol based on HCl/HF treatment after [3] (H, red) and the "mild" protocol based on CsF/dioxane biphasic extraction after [2] (M, blue).
The intensity ratios obtained from IR experiments confirmed structural modifications induced by each treatment (Figure 1A). We noticed a decrease in the C=C/CH ratio for both H and M compared to the starting material, even more significant for M (Figure 1B). Together with more pronounced aromatic C-H features for both treated samples compared to the starting Neb-OM (Figure 1A), it might indicate fragmentation of large condensed ring structures into smaller aromatic units.
Figure 1. A – Stack of IR spectra from two acquisitions of the same treated/untreated solid OM material, with interpretation of regions of interest; untreated Neb-OM – grey, H – red, M – blue. Relative intensity ratio of B – C=C stretching (1612 cm-¹) to aliphatic C-H bending (1444 cm-¹); C – CH₂ asymmetric stretching (2923 cm-¹) to CH₃ asymmetric stretching (2954 cm-¹). Error bars corresponding to 4 acquisitions.
The CH2/CH3 ratio (Figure 1C) increases for H, consistent with acid-promoted cleavage of terminal methyl groups and shortening of aliphatic chains, while M leaves this ratio unchanged, suggesting that dioxane-CsF affect less aliphatic chain length. These IR results are consistent with tendencies previously reported in [4-5]. No clear trend is observed yet for the C=O/C=C ratio.
FT-ICR MS measurements provide the m/z distribution of molecules. Venn diagram analysis (Figure 2A) shows 2332 peaks (48%) are common to all three samples. H generates more exclusive peaks (1049, 22%) than M (284, 6%), suggesting acid treatment produces a greater diversity of new molecular species. Additionally, 848 peaks (17%) are shared by H and M but absent in Neb-OM, while 229 Neb-OM-exclusive peaks (5%) are irreversibly lost after both treatments.
The average m/z distribution (Figure 2C) reveals that H is strongly enriched in low molecular weight compounds (m/z 100–250) compared to untreated Neb-OM, consistent with acid-promoted fragmentation of larger molecules into smaller species. M follows the Neb-OM distribution more closely, suggesting a milder effect on the sample. DBE (Double Bond Equivalents) represents the number of rings and double bonds in detected molecules. Both H and M treatments result in a significant shift of the DBE distribution of detected compared to untreated Neb-OM (Figure 2B).
Figure 2. A – Venn diagram of common and unique molecular peaks between H, M and Neb-OM (H and M represent the union of two replicates). B – Average DBE distributions of H, M and Neb-OM. Bars represent relative intensities summed at each DBE value and averaged across replicates; IOM is shown as a polynomial fit. C – Average m/z distributions of H, M and Neb-OM, showing only m/z values common to all three samples; lines are polynomial fits. Bars represent relative intensities summed within 5 Da bins and averaged across replicates.
The peak of the polynomial fit is at a maximum DBE of 15 for H, 19 for M, and 21 for Neb-OM, with a significant loss of peaks in the 20-40 DBE range for both protocols. H shows a larger difference, consistent with acid-promoted cleavage of organic structures, supported by the increased CH₂/CH₃ ratio and pronounced aromatic C–H features observed in IR spectroscopy. M has a milder effect and shows slightly lower depletion at DBE values below 15. Molecules above DBE 40, likely corresponding to highly condensed, graphite-like polycyclic aromatic structures, demonstrated only minor changes due to their chemical inertness.
These preliminary results, obtained from a single Neb-OM batch, demonstrate that commonly used extraction protocols induce measurable and chemically distinct alterations, detectable after just one treatment cycle. Future work will extend these findings using solid-state nuclear magnetic resonance (ssNMR), more detailed FT-ICR-MS analysis, and characterisation of the collected SOM fractions, alongside a second set of experiments on a different IOM batch to confirm reproducibility. This better understanding of protocol-induced alterations will provide a more reliable framework for the interpretation of IOM composition in extraterrestrial samples.
Literature References:
[1] Pizzarello et al., Acc. Chem. Res. 2006, 39, 4, 231–237.
[2] Cody et al., GCA, 2002, 66, 1851-1865.
[3] Remusat et al., Meteorit.Planet.Sci., 2008, 43, 1099-1111.
[4] Kebukawa et al., 2024, Meteorit Planet Sci, 59, 1845-1858.
[5] Kebukawa et al., 2019, Meteorit.Planet.Sci., 54-7, 1632–1641.
[6] Lévêque et al., 2024, ACS Earth Space Chem., 8, 1281-1295.
How to cite: Shvetsova, A., Fariñas, M., Bollengier, O., La, C., Paris, M., and Sotin, C.: Assessing the Chemical Impact of Insoluble Organic Matter Extraction Protocols and Its Implications for Extraterrestrial Organic Matter, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-352, https://doi.org/10.5194/epsc2026-352, 2026.
Abstract
The Galilean moons of Jupiter have been of great interest over the past years and are the targets of the JUICE and Europa Clipper missions. Europa is an ocean world that may potentially be suitable for hosting life, while Io is the most volcanically active world of the solar system. Despite their apparent differences, Europa and Io are expected to have accreted in a similar environment in the circumjovian disk [1]. Determining the interior structure, chemical composition and thermal evolution of Europa and Io is crucial to understanding the origin and the history of the Jovian system and assess the habitability of Europa’s subsurface ocean. In previous studies, the low bulk density of icy moons and dwarf planets was classically associated with low Fe/Si ratios [2], [3], [4]. More recent studies motivated by space mission observations suggested that carbonaceous organic matter (COM) may be present in significant amounts in most planetary objects of the outer solar system [5], [6]. Carbonaceous matter in the rocky interior could indeed decrease the mean bulk density and thus explain the values observed for Io and Europa. The presence of COM within these bodies may have considerable implications on their bulk composition, internal structure and their thermo-chemical evolution.
In this study, the interior structure and composition of Io and Europa are modeled through a joint analysis using a MCMC scheme constrained on the mass, radius and Moment-of-Inertia factor retrieved during the Galileo mission [7], [8]. Density profiles are calculated using state-of-the-art equations of state for a large range of Fe/Si and Mg/Si ratios. We show that Io and Europa can have Fe/Si and Mg/Si ratios comparable to the solar composition only if a low-density component here taken as graphite is considered. The graphite content in Io's and Europa's refractory interior is estimated between 3-8 wt% and 1-22 wt%, respectively, which can exceed up to a factor five the typical carbon content in carbonaceous chondrites. The amount of graphite within Europa is anti-correlated with the thickness of the hydrosphere and positively correlated with the radius of the inner metallic core. A hydrosphere thickness larger than ~125 km would suggest an undifferentiated rocky core with low carbon fractions while a thinner hydrosphere (<125 km) would be indicator of a differentiated interior into an inner metallic core and a rocky mantle containing more than 5 wt% of graphite. Thermal metamorphism of the accreted carbonaceous matter in Europa leads to its graphitization and release of water and volatiles, which may contribute to a significant, possibly dominant fraction of its hydrosphere. Thermal degradation of carbonaceous matter may thus be a major contributor to the water and volatile budget of Europa. Future gravimetric, altimetric and magnetic measurements by Europa Clipper will refine the Moment-of-Inertia factor and determine the hydrosphere thickness. Such information are crucial to determine carbon content and differentiation state of Europa and hence the thermo-chemical evolution of Europa and the habitability of its subsurface ocean. The SUDA dust analyzer on board Europa Clipper will also provide constraints on the composition of Europa's ice grains and volcanic dust ejected by Io, thus allowing testing of the potential contribution of carbon to their bulk composition.
References
[1] Estrada, P.R. et al. Formation of Jupiter and conditions for accretion of the Galilean satellites. In: Pappalardo, R.T., McKinnon, W.B., Khurana, K. (eds.) Europa, pp. 27–58. University of Arizona Press, Tucson, AZ (2009)
[2] Sohl et al. (2002). Implications from Galileo observations on the interior structure and chemistry of the Galilean satellites. Icarus, 157:104-119.
[3] Kuskov, O. L. and Kronrod, V. A. (2001). Core sizes and internal structure of Earth’s and Jupiter's satellites. Icarus, 151(2):204–227.
[4] Petricca, F. et al. (2025). Partial differentiation of Europa and implications for the origin of materials in the Jupiter system. Nature Astronomy, pages 1–11. doi: https://doi.org/10.1038/s41550-024-02469-4
[5] Néri, A. et al. (2020). A carbonaceous chondrite and cometary origin for icy moons of Jupiter and Saturn. Earth and Planetary Science Letters, 530:115920. doi: https://doi.org/10.1016/j.epsl.2019.115920
[6] Reynard, B. and Sotin, C. (2023). Carbon-rich icy moons and dwarf planets. Earth and Planetary Science Letters, 612:118172. doi: https://doi.org/10.1016/j.epsl.2023.118172
[7] Anderson, J. et al. (1998). Europa’s differentiated internal structure: Inferences from four Galileo encounters. Science, 281(5385):2019–2022.
[8] Casajus, L. et al. (2021). Updated europa gravity field and interior structure from a reanalysis of Galileo tracking data. Icarus, 358:114187. doi: https://doi.org/10.1016/j.icarus.2020.114187
Acknowledgments
This work was supported by the Agence Nationale de la Recherche (ANR, project OSSO-BUCO, ANR-23-CE49-0003 to BR) and by the European Union (ERC, PROMISES, project #101054470 to CS). Views and opinions expressed are, however, those of the authors only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. This research utilized the resources of the GLiCID Computing Facility (Ligerien Group for Intensive Distributed Computing, www.glicid.fr, Pays de la Loire, France). The work of M.B. was supported by the Czech Science Foundation (project No. 26-21877S). GT benefits from financial support from CNES for the preparation of the NASA Europa Clipper and ESA JUICE missions, for his participation to the Clipper/SUDA investigation, and the JUICE/3GM and MAJIS investigations.
How to cite: André, V., Tobie, G., Běhounková, M., Kervazo, M., Reynard, B., and Sotin, C.: Interior models imply the presence of carbon inside Io and Europa, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-112, https://doi.org/10.5194/epsc2026-112, 2026.
The icy moons Europa and Enceladus are key targets for life detection space exploration missions, due to the evidence for subsurface liquid water oceans beneath their icy crusts. Hydrothermal vents at the interface of the rocky cores and water oceans of icy moons are considered a promising region for habitability, owing to the potential for organisms to harness energy from surrounding temperature and redox gradients [1]. For life in these environments to be detected, chemical biosignatures must be delivered to surface plumes for direct measurement by mass spectrometric instruments, such as MASPEX and SUDA onboard the Europa Clipper space probe [2]. Due to the high temperature conditions surrounding hydrothermal vents, this transportation process will involve significant thermal degradation of any organic materials. It has been previously shown, through laboratory simulation, that organic biosignatures survive hydrothermal processing [3][4]. However, hydrothermal fluids at icy moons may be significantly alkaline and saline [5], and this has not been accounted for in laboratory simulations to date.
Here, we simulated hydrothermal processing of microbial biomass under alkaline and saline aqueous conditions. Roughly 10 mg biomass from multiple microbial strains, including those relevant to habitable icy moon environments, was individually loaded into glass tubes. 0.4 ml deionised water, or sodium hydroxide solution for the alkaline experiments, was added to the tubes. For saline experiments, 20 mg solid magnesium or sodium salts were added. The tubes were then flame-sealed under vacuum and heated at 150 °C and 250 °C for 3 days in a stainless-steel reactor vessel. The organic products were extracted, derivatised and then analysed using gas chromatography-mass spectrometry (GC-MS).
In comparison to control experiments performed in deionised water, saline conditions led to subtle changes in the organic products. Generally, condensation reactions that formed nitrogen heterocycles were favoured in the presence of dissolved salts, likely as a result of the reduction in water activity. Under alkaline conditions, more significant changes were observed, with the deamination of amino acids substantially promoted. This mechanism could hinder the detection of amino acids, which if unaccounted for, could lead to false-negative detections of proteinaceous organic molecules at icy moons. However, some detectable organic products from amino acid degradation persisted through hydrothermal processing, which could be targeted as a potential biosignature by future chemical analysis at icy moons.
References:
[1] Jebbar et al., 2020, Space Science Reviews; [2] Waite et al., 2024, Space Science Reviews; [3] Salter et al., 2022, ACS Earth and Space Chemistry; [4] Tan et al., 2023, Astrobiology; [5] Glein and Truong, 2025, Icarus
How to cite: Hirsch, S., Balakrishnan, A., and Sephton, M. A.: Organic biosignatures from alkaline hydrothermal environments at icy moons, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-116, https://doi.org/10.5194/epsc2026-116, 2026.
Introduction
High‑resolution spectroscopy (HRS) has become one of the most powerful tools for characterising planetary atmospheres, enabling the detection of molecules whose individual spectral lines are too weak to be identified directly [1, 2]. Within this framework, high‑resolution cross‑correlation spectroscopy (HRCCS) has emerged as a particularly effective technique for isolating faint atmospheric signatures by correlating observed spectra with modelled molecular templates [1, 2]. HRCCS has been widely used to detect atomic and molecular species in exoplanet atmospheres and is increasingly being applied to constrain metallicities and elemental ratios such as C/O [3–6].
A major challenge for HRCCS is its strong dependence on the availability and quality of high‑resolution opacity data. Traditional template construction relies on radiative transfer models using line-by-line molecular spectra, but many molecules of atmospheric and astrobiological interest lack complete or accurate line lists [7, 8]. This limitation restricts the chemical space accessible to HRCCS, particularly for larger molecules, for which obtaining line-by-line molecular spectra is significantly more challenging. In contrast, laboratory absorption cross‑sections are far easier to obtain and are available for a much wider range of molecules, even though they are measured at specific temperature and pressure conditions and, thus, are not as universally applicable as line lists [7, 8].
Targets in the solar system offer an ideal environment for addressing these challenges, since their atmospheric compositions are better constrained than those of exoplanets, and their spectra typically have higher signal‑to‑noise ratios [9, 10], allowing new HRCCS methodologies to be tested and validated under controlled conditions. Titan, the largest moon of Saturn, is particularly well suited for this purpose. Its atmosphere hosts a rich hydrocarbon chemistry and decades of observations from Cassini‑Huygens and ground‑based facilities have established Titan as one of the best‑characterised planetary atmospheres in the solar system [11, 12], making it an ideal testbed for developing and validating molecular detection techniques.
In this work, we apply HRCCS to CRIRES+ K‑band observations of Titan (1.99–2.48 µm) to evaluate the performance of molecular cross‑section‑based templates as an alternative to traditional line‑list‑based models. Our goal is to assess whether laboratory cross‑sections can be used to construct reliable HRCCS templates for molecules that currently lack high‑resolution line lists. We focus on hydrocarbons as a test case, given their importance for Titan’s photochemistry and their relevance for exoplanet atmospheres.
Results
Applying HRCCS to the CRIRES+ dataset, our analysis recovers methane (CH4), its isotopologue 13CH4, and acetylene (C2H2) in the near‑infrared spectrum of Titan. Yet, the most significant result of this work is the first HRCCS detection of ethane (C2H6), obtained at a peak significance of 5.17σ [Figure 1]. Ethane is a key product of methane photochemistry [12], but no high‑resolution line list currently exists for this molecule. As a result, traditional line‑list‑based HRCCS searches cannot target C2H6. The detection reported here is made possible exclusively using cross‑section‑based templates, demonstrating that laboratory absorption cross‑sections can serve as an alternative for HRCCS template construction when line lists are unavailable.
Figure 1. Cross-correlation results for ethane (C2H6). Left panel: CCFs obtained from 2000 Monte Carlo realisations. For each Monte Carlo realisation, the normalised spectrum was perturbed within its flux uncertainties and the CCF recomputed [14]. The black-solid line shows the median CCF, while the dashed line represents the autocorrelation of the template used to compute the cross-correlation. The shaded region marks the velocity interval used to estimate the noise statistics. Right panel: distribution of the central-peak SNR values. This constitutes the first detection of ethane using HRCCS.
To assess the fidelity of the detections, we performed cross‑correlations between hydrocarbon templates to test for potential spectral degeneracy [10]. In the 3.0–3.5 µm region dominated by fundamental C–H stretching modes, many hydrocarbons exhibit similar band shapes and line‑density patterns, making them difficult to distinguish [13, 10]. However, the CRIRES+ K‑band (1.99–2.48 µm) probes overtone and combination bands whose higher‑order vibrational transitions produce more molecule‑specific line patterns. Consistent with this expectation, the cross‑correlations of 13CH4, C2H2, and C2H6 against the CH4 template show no significant peaks at the rest‑frame velocity of Titan, confirming that the detections reported here are not artefacts of template degeneracy.
Conclusion
This work establishes Titan as a benchmark for developing and validating HRCCS detection strategies and demonstrates that cross‑section‑based templates can be used to detect multiple hydrocarbons in the atmosphere of Titan, including species for which no high‑resolution line lists exist. The successful detection of ethane provides a proof‑of‑concept for extending HRCCS to a wider range of molecules, particularly those relevant to photochemistry, atmospheric evolution, and prebiotic chemistry.
Furthermore, this approach is directly applicable to future observations with ground‑based high‑resolution spectrographs and to the highest‑resolution modes of JWST, offering new opportunities for detecting and characterising molecules in both solar system and exoplanet atmospheres.
Acknowledgments
This work was financially supported by LA/P/0056/2020 (IMS DOI https://doi.org/10.54499/LA/P/0056/2020) and CQE UID/00100/2025 (https://doi.org/10.54499/UID/00100/2025), UID/PRR/100/2025 (https://doi.org/10.54499/UID/PRR/00100/2025) and UID/PRR2/00100/2025 (https://doi.org/10.54499/UID/PRR2/00100/2025) funded by national funds through FCT/MECI (PIDDAC). The authors also acknowledge funding by the Portuguese Foundation for Science and Technology (FCT) through project UID/04434/2025, and project ORIGINS (2022.05284.PTDC). RS acknowledges funding through the FCT PhD fellowship 2024.02527.BD.
References
[1] Snellen, I. A. G. Annual Review of Astronomy and Astrophysics, 63, 83–125, 2025.
[2] Yurchenko, S. et al. Nature Reviews Physics, 7, 645–659, 2025.
[3] Snellen, I. A. G. et al. Nature, 465, 1049–51, 2010.
[4] Birkby, J. L. et al. The Astronomical Journal, 153(3), 138, 2017.
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[7] Tennyson, J. et al. Journal of Molecular Spectroscopy, 327, 73–94, 2016.
[8] Gordon, I. E. et al. Journal of Quantitative Spectroscopy and Radiative Transfer, 277, 107949, 2022.
[9] Branco, A. et al. Atmosphere, 15(12), 2024.
[10] Niraula, P. et al. The Astrophysical Journal Letters, 995(2), L66, 2025.
[11] MacKenzie, S. et al. The Planetary Science Journal, 2(3), 112, 2021.
[12] Nixon, C. ACS Earth and Space Chemistry, 8(3), 406–456, 2024.
[13] Sousa-Silva, C. et al. Physical Chemistry Chemical Physics, 21, 2019.
[14] Esparza-Borges, E. et al. Monthly Notices of the Royal Astronomical Society, 543(4), 3456–3473, 2025.
How to cite: Coelho, M., Rianço-Silva, R., Gonçalves, D., Machado, P., and Martins, Z.: Detection of Complex Hydrocarbons in Titan Using High-Resolution Cross-Correlation Spectroscopy, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-82, https://doi.org/10.5194/epsc2026-82, 2026.
The volatile carbon, oxygen, and nitrogen budget of forming planets is set by the inventory of ices and refractory organics carried on dust grains in protoplanetary disks. Connecting this disk-stage volatile reservoir to the compositions of comets, Kuiper Belt objects, icy moons, and exoplanet atmospheres requires direct constraints on where carbon-bearing species are frozen out, how they are mixed with other ices, and how their observable signatures depend on grain growth and vertical disk structure. Edge-on protoplanetary disks provide the required geometry for these measurements: the optically thick midplane obscures the central star, allowing solid-state absorption features to be detected against scattered infrared continuum emission from the inner disk.
We present new JWST NIRSpec IFU and MIRI MRS observations of the highly inclined protoplanetary disk ESO-Hα 569, covering the principal near- and mid-infrared diagnostics of disk ices and refractory organics. We focus on CO and CO₂ as tracers of the volatile carbon reservoir available for incorporation into icy planetesimals; H₂O anchors the total ice content, and PAH emission traces carbon-bearing material in irradiated disk surface layers.
Interpreting these spectra requires three-dimensional radiative transfer modelling, because ice-band depths in highly inclined disks depend not only on abundance, but also on the scattering surface, grain-size distribution, and vertical location of the ice-bearing material. To scale this analysis to the growing JWST sample of edge-on disks, we have developed a neural emulator that reproduces radiative-transfer spectra of highly inclined disks and accelerates inference by a factor of 10⁶.
For ESO-Hα 569, we recover the radial and vertical distributions of CO, CO₂, and H₂O ices, the grain population producing the absorption features, and the origin of the PAH emission. Comparison with HH 48 NE places these results in the context of the emerging JWST sample and links carbon-bearing solids in planet-forming disks to the volatile inventory inherited by comets, TNOs, and exoplanet atmospheres.
How to cite: Welzel, L. and McClure, M.: Carbon-bearing ices and PAHs in the edge-on protoplanetary disk ESO-Ha 569, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-452, https://doi.org/10.5194/epsc2026-452, 2026.
Organics are present throughout a wide range of Solar System objects, including dust particles, small bodies (comets, meteorites, asteroids), and planetary objects (planets, satellites, and trans-Neptunian objects (TNOs)). Significant quantities of primordial organic matter may have survived the accretion and differentiation of colder planetary bodies, as inferred from the moment of inertia of several icy moons1. These organic materials would affect the physical and chemical evolution of these worlds, and hold major astrobiological implications as potential precursors of molecules of known life2. Hydrous pyrolysis can be used to simulate parent-body processing (e.g., thermal metamorphism and aqueous alteration) and estimate its impact on organic chondritic material3. In this context, this study investigates the molecular evolution of bulk synthetic primordial organic matter under pyrolytic conditions, focusing on the influence of temperature, time, and water content on volatile release and molecular transformation.
To this end, synthetic analogues of primordial organic matter produced in the Nebulotron experiment4, through ionization of gas mixtures in a high-temperature plasma reactor, were used as the starting materials. The bulk composition of the organics has been estimated through elemental analysis at C100H34O20N8. The samples were loaded in Au/Pd capsules under dry and hydrous conditions (0, 20, and 50 wt.% H₂O) before precision welding under an Ar atmosphere. They were then pressurized at 400 MPa in an internally heated pressure vessel and held at 150, 250, or 350 °C for 2, 24, or 240 h. Each T-t batch involved six capsules (three water ratios, each with a duplicate). Following thermal treatment, volatile species were analyzed using two different detection strategies: either gas chromatography (GC-TCD) or a quadrupole mass spectrometer (QMS), both coupled to capsule-piercing devices. Evolved volatile species (H₂O, H₂, CO, CO₂, and CH₄) were monitored, with CO₂ consistently quantified (>LOQ) across experiments. The residual organic matter was subsequently characterized by positive-mode LDI-FTICR-MS.
The results show that volatile release is clearly controlled by temperature and water content. The amounts of H₂O and CO₂ increase with temperature and initial water content. CO₂ production increases notably between dry (0 wt.%) and low-water (20 wt.%) conditions, with only minor differences at higher water content (50 wt.%). Only limited differences between 2 and 24 h are observed, though a general increase in CO₂ production at is seen at 240 h. H₂ was only quantified by QMS under the most severe conditions (350 °C, 240 h, 20–50 wt.% H₂O), accompanied by a maximum in CH₄ production measured by GC, in agreement with previous works5,6.
FTICR-MS results reveal that temperature is the main driver of molecular evolution among the three experimental variables explored. This is supported by the systematic shift toward higher double bond equivalency (DBE) values with increasing temperature (Fig. 1), which reflects a progressive increase in the unsaturation of the residual organic matter. Time becomes a secondary control, relevant at 350 °C, where longer times enhance the enrichment in more unsaturated populations. Water content, for its part, promotes a strong transition between dry (0 wt.%) and hydrous (20 wt.%) conditions, followed by a smaller additional change at higher water content (50 wt.%), suggesting a threshold response of the organic matrix.
A complementary perspective on the results helps complete the evolutionary picture: the initial organic matter is dominated by functionalized CHN and CHNO families, and increasing temperature, time, and water content drive a progressive compositional shift toward CHN-dominated assemblages (Fig. 2, 3), consistent with deoxygenation, cleavage of functional groups, and condensation processes. A key point is that, even under hydrous conditions, thermal decomposition appears to dominate over oxidation. Under the most severe conditions, the organic residue evolves toward increasingly reduced compositions through progressive heteroatom loss, ultimately yielding a residue with an important contribution from C-only species, together with an overall reduction in molecular diversity. This trend is further captured in the H/C–O/C space, where increasing temperature concentrates molecules in more reduced and less oxygenated domains, while water modulates the redistribution of molecular populations.
Ultimately, we address (i) some consequences of exposing primordial organic matter to different pyrolytic conditions, a process that not only provides insight into its chemical evolution but has also been proposed as a potential pathway for nucleobase formation7, and (ii) an interpretation of the results without the influence of the multiple overlapping processes inherent to natural samples, such as contamination and chemical pretreatment (reported even in returned asteroid samples8), which can complicate the analysis of intrinsic chemical signatures.
References
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Fig. 1. Distribution of relative intensity as a function of DBE across all experimental conditions.
Fig. 2. Comparison of intensity-weighted chemical family distributions between the first (150 °C-24 h) and final (350 °C-240 h) experimental conditions.
Fig. 3. Sector representation of the molecular family distribution under selected experimental conditions for (a) dry (0 wt.% H₂O) and (b) hydrous (50 wt.% H₂O) systems. Colors indicate molecular families (e.g., CHN in green) and each point in the x–y compositional space represents a subfamily (e.g., CHN1). Size is proportional to the weighted relative abundance, calculated from the mean intensity between the two experimental batches.
How to cite: Fariñas, M., Bollengier, O., Lévêque, P., Shvetsova, A., Champallier, R., Hertzog, J., Le Menn, E., Queffelec, C., Toffolo, L., Tumiati, S., and Sotin, C.: Thermochemical evolution of chondritic organic matter analogs under (hydrous)pyrolytic conditions, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-358, https://doi.org/10.5194/epsc2026-358, 2026.
The icy ocean moons Enceladus and Europa offer potentially habitable environments below their icy crusts. Ice grains ejected from cryovolcanic plumes [1,2] and micrometeorite bombardment can be sampled by impact ionization mass spectrometers, as performed in the past by the Cosmic Dust Analyzer (CDA; [3]) onboard Cassini in the Saturnian system. Successor instruments to the CDA include the SUrface Dust Analyzer (SUDA; [4]) onboard NASA’s Europa Clipper mission and the HiFi instrument for a future Enceladus mission [5]. The strongly enhanced capabilities of SUDA and contemporary instruments, relative to CDA, allow the identification of molecular biosignatures. Among possible molecular biosignatures, amino acids are essential building blocks of proteins and play a crucial role in the formation of water-based life as we know it, thus their identification on extraterrestrial water worlds is key to the search for life beyond Earth.
Laboratory analogue experiments using laser-induced liquid beam ion desorption (LILBID [6]) have demonstrated that impact ionization mass spectrometers can detect amino acids [7] down to the ppm or ppb level, if they are entrapped in emitted ice grains, and can distinguish between abundance patterns of abiotic and biotic formation processes [8]. However, at any given molecular mass of an amino acid, several isomers (identical molecular formula but distinct arrangements of atoms in space) exist, which are indistinguishable by their molecular peaks in recorded mass spectra. Until now, it was unclear whether isomeric amino acids can be discriminated from each other, e.g., by fragmentation patterns in impact ionization mass spectra.
Here, using LILBID mass spectrometry, we conducted a cation mode analysis of eight isomeric amino acids with an identical molecular mass of 131.173 u and formula C6H13NO2 [9]. The recorded mass spectra were investigated for spectral features that enable differentiation of the different isomeric amino acids, with the aid of quantum chemistry calculations.
We show that the amino acid isomers (including diastereoisomers) can be uniquely identified due to their distinct mass spectral features and fragmentation patterns. Several observed fragments and their intensities can be explained through intramolecular hydrogen bonding and other structural effects originating from the parent molecules. Importantly, α-amino acids can be clearly differentiated from non-α-amino acids, because they have lower proton affinities than non-α-amino acids, which result in lower ionization efficiencies for α-amino acids. Additionally, we further complement the LILBID database [10], which already contains a large variety of analogue mass spectra of both organic and inorganic compounds, for upcoming missions to icy ocean moons.
The ability to discriminate amino acid isomers in a robust and reliable manner highlights a novel ability of impact ionization mass spectrometers that has significant implications for the search of biosignatures in the solar system, in particular for SUDA on Europa Clipper and other future instruments onboard missions exploring ocean worlds.
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How to cite: Napoleoni, M., Bönigk, J., Klenner, F., O’Sullivan, T. R., Hortal Sánchez, L., Khawaja, N., Bera, P. P., Malaska, M. J., Cable, M. L., and Postberg, F.: Identifying Amino Acids Isomers with Dust Analyzers in Ice Grains from Enceladus and Europa , Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-645, https://doi.org/10.5194/epsc2026-645, 2026.
Ice grains ejected by the ocean world Enceladus were measured in situ by multiple instruments onboard the Cassini spacecraft during its exploration of the Saturnian system. Analysis of material emitted within a plume at the moon's south pole revealed the presence of a global subsurface salty liquid water ocean containing organic compounds and evidence of hydrothermal activity [1-5]. Ice grains sampled by Cassini’s impact ionization mass spectrometer, the Cosmic Dust (CDA), have revealed a diverse suite of organic species, including high-mass organic compounds, intermediate mass species, and small aromatic moieties [6-8]. The coexistence of liquid water, organic material, and hydrothermal chemistry satisfies key criteria for habitability, making interpretation of Enceladus' ocean chemistry particularly important in the search for life in the solar system. This is highlighted by the recently announced ESA L4 mission to investigate the habitability of Enceladus and search for biosignatures.
To investigate the possible origin of organic compounds on Enceladus, it is necessary to understand their evolution under different physio-chemical conditions from the core to the plume. We performed laboratory experiments simulating Enceladean hydrothermal conditions to understand the chemical evolution of organics identified in past and future observations. Low-mass organic compounds with functional groups including aromatic rings and carbonyl groups have been identified in Enceladean ice grains [7]. Benzoic acid, consisting of phenol and carbonyl groups, thus serves as a model compound for which to test the effects of Enceladus-like hydrothermal conditions on small aromatic compounds. The ERC-CoG Analogue Icy Moon Simulations (AIMS) project’s hydrothermal laboratory simulates the processing of ocean material within the temperature range 80–150°C and the pressure range 80–130 bar, representing conditions suggested for the water–rock interface on Enceladus [9]. In this study, we prepared solutions of benzoic acid (0.008 M) in an analog “Enceladus Ocean” consisting of NaCl (10-6 M), and a sodium carbonate-bicarbonate buffer system (0.025 M) adjusted to pH 10. The solution was then processed in a hydrothermal reactor at a pressure of 80 bar and temperature of 80 °C for 16 days. Mass spectra produced in the laboratory by the laser-induced liquid beam ion desorption (LILBID) technique serve as an analog [10] for those obtained by CDA or future Enceladus dust analyzers like the High Ice Flux Instrument (HiFi) [11]. The LILBID spectra were evaluated and the contrast between hydrothermally processed and unprocessed benzoic acid is discussed.
The outcome of this work will improve our understanding of the hydrothermal chemistry of small aromatic compounds occurring in the core of Enceladus. These results can guide the interpretation of existing CDA data and future measurements obtained by Europa Clipper's SUrface Dust Analyzer (SUDA) [12], while supporting science planning for ESA'S L4 mission. Future work will extend these experiments to additional aromatic compounds to further constrain the evolution and detectability of hydrothermally processed organics in Enceladus-like environments.
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How to cite: Ladd, J., Hortal Sánchez, L., O’Sullivan, T. R., Dannenmann, M., Napoleoni, M., Postberg, F., and Khawaja, N.: Effects of Hydrothermal Conditions on a Model Simple Aromatic Compound using an Enceladus Ocean Laboratory Analogue , Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-366, https://doi.org/10.5194/epsc2026-366, 2026.
Introduction.
Titan’s atmosphere is a compelling laboratory in which to study organic photochemistry and haze formation in a reduced environment [1]. Starting with the photolysis of the primordial methane and nitrogen, the neutral and charged photochemistry produces a wide range of organic compounds, which eventually aggregate to produce Titan’s ubiquitous refractory haze [2, 3]. Although molecular abundance measurements are mostly limited to species with six or fewer carbon atoms [4], there is also compelling evidence of polycyclic aromatic hydrocarbons (PAHs) in Titan’s upper atmosphere [3, 5, 6]. However, the largest molecules currently included in models of Titan’s photochemistry are substituted benzene species [7]. In this work we give an overview the most promising neutral pathways for forming naphthalene (C10H8), the simplest PAH, and share preliminary results from including these species in an existing model of Titan photochemistry [8, 9].
Background.
Photochemical models. To decipher Titan’s complex atmospheric chemistry, several groups have assembled photochemical models with networks of hundreds or thousands of neutral and charged reactions, photolysis of major species, haze formation, and condensation [8, 7, 10]. While small molecules with few carbon atoms can be simulated with relatively simple chemical networks, the number of possible isomers for a given stoichiometric formula grows exponentially with the number of carbon atoms. Because of this, photochemistry models have mostly focused on simulating the lowest-energy isomers. Recently, there has been a renewed effort to improve the small-molecule photochemistry by accounting for isomers of three- and four-carbon species [9]. We build on this work to extend the chemical network to larger aromatic species.
PAH chemistry. The chemistry of PAHs is of great interest in fields ranging from combustion chemistry [e.g., 11, 12] to interstellar chemistry [e.g., 13], but most of the work on PAH formation and growth has focused on high-temperature conditions [e.g., 11]. Significant effort has been dedicated to determining empirical methods of estimating chemical bahavior of large PAHs in interstellar conditions [e.g., 14], but the chemistry driving the formation of small PAHs is less generalizable and remains an active area of research [e.g., 13]. Similar methods of simulating molecular growth have been used in models of Titan’s photochemistry, but they have been focused on particle formation rather than molecular growth [2]. Recent work in theoretical and experimental chemistry has revealed several potential pathways for forming naphthalene in low-temperature conditions relevant to Titan [e.g., 11, 12], though these reactions are highly dependent on the availability of specific isomers of the reactants. Given the recent advances in Titan isomer chemistry, it is now possible to explicitly simulate the gas-phase formation of naphthalene.
Preliminary findings.
Naphthalene formation. We have assembled a preliminary chemical network that produces the naphthalene skeleton via neutral gas-phase reactions (see figure). Many of these pathways involve multiple reactions, sometimes producing non-naphthalene C10H8 isomers as intermediate steps. Thus, we find it is critical to explicitly account for different isomers when modeling naphthalene formation.
Naphthalene sinks. We have identified no neutral chemical reactions that destroy the naphthalene skeleton, but addition reactions with small radicals like C2H and CN are expected to be rapid. Photolysis of naphthalene also appears ineffective at destroying the naphthalene structure (only ~1% at 193 nm) [15], though to our knowledge there are no experimental branching ratios available. Thus, the naphthalene skeleton can only be destroyed at high altitudes where far UV radiation is most intense.
More information required. Although we have assembled a simple network for naphthalene formation, a lack of published data means that many of the inputs to the photochemical model must be estimated. Theoretical or experimental rates are needed for many reactions, and there is little information available regarding rates and products of reactions of large species with abundant small radicals such as H, CH3, C2H, and CN, all of which react rapidly with less abundant species in Titan’s atmosphere. There is a need for UV absorption cross-sections and photolysis branching ratios for most of the species included in the figure. Finally, there is a need for more study into ion-molecule pathways to PAH formation, which may dominate in Titan’s ionosphere [7].
Outlook.
With an understanding of the chemistry producing the smallest PAHs, it will be possible to begin to bridge the gap between small molecules, which are modeled explicitly, and large PAHs that can be modeled empirically. Models that can simulate PAH formation will be useful to interpret the infrared PAH-related emission features [5, 6], measurements of ionospheric composition and haze [e.g., 3], and the coming measurements from Dragonfly of the haze composition at the surface.
Figure. A preliminary low-temperature chemical network for forming the naphthalene skeleton (purple boxes) from precursor species (green boxes) via neutral radical-molecule reactions. Some of these reactions are slow but included for completeness. Most of these reactions also produce many non-PAH products which are not included in this schematic.
References.
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How to cite: Hanson, L., Candian, A., Lavvas, P., and Vuitton, V.: Polycyclic Aromatic Hydrocarbons in Titan’s atmosphere, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-574, https://doi.org/10.5194/epsc2026-574, 2026.
Introduction
Macromolecular organic refractory materials are widespread in primitive bodies in the Solar System, including meteorites, comets, and trans-neptunian objects (TNOs) [1].
Information on the composition of TNOs mainly comes from observations in the visible (Vis) and near-infrared (NIR) that allow us to reveal the ices at the object surfaces. Data also show positive slopes that are attributed to reddish complex organics. James Webb Space Telescope observations revealed three main compositional classes of mid-sized TNOs, namely water-rich (or bowl), CO2-rich (double-dip), and organics-rich TNOs [2,3]. Both CO2-rich and organics-rich types are the most likely to contain macromolecular matter.
Constraining the properties of organics on the body surfaces is of primary importance to shed light on their origin and on alteration processes at work. On the one hand, various evidence suggests that TNOs inherited matter from the protoplanetary disk, where ices and organics formed in the earlier stages of the Solar System formation are exposed to heating and mixing. On the other hand, post-accretion processes, including the exposure to solar particles and galactic cosmic rays (GCRs) of TNO surfaces contributed to enriching their inventory of organics and macromolecular materials [4].
The faint signatures of macromolecular organics in the Vis-NIR hinder a detailed characterization of their properties. Experiments allow us to reproduce in the laboratory the formation of macromolecular organics possibly at the surface of TNOs, following the exposure of surficial ices to ion bombardment by solar particles and GCRs. We provide insights on the chemical composition and physical properties of the organics, as well as on the irradiation timescales necessary for their formation in the outer Solar System.
Methods
We perform laboratory experiments focused on the production and spectroscopic analysis of organic refractory residues (ORRs), samples left over after irradiation and warm-up to room temperature of simple C-bearing ices [5, 6, 7, 8].
ORRs are produced in an ultra-high vacuum chamber (P~10-9 mbar) by depositing volatile C-bearing species at low temperature (18 K) on substrates placed in thermal contact with a He-cryocooler. The deposited ices contain compounds revealed on TNO surfaces, including CO, CO2, CH3OH, CH4, also in presence of H2O and N-bearing compounds, such as N2 and NH3. Ices are then exposed to a 200 keV ion beam (H+ or He+) to simulate the effect induced by solar particles and GCRs. After ion bombardment, processed ices are gently warmed-up to room temperature, and ORRs are formed. Some ORRs are also exposed to further ion bombardment or thermal processing to high temperatures.
During the experiments, we acquire mid-IR spectra that allow us the characterization of the chemical changes induced by the ion bombardment and the subsequent heating. ORRs are further analyzed by Raman spectroscopy, which is sensitive to the presence of amorphous carbon.
Results
The IR spectra acquired during ion bombardment show that all infrared features attributed to the deposited species decay following an exponential trend with increasing the irradiation dose. At the same time, new absorption bands attributed to irradiation by-products appear. The irradiation by-products, the produced quantities, as well as their formation rate are strongly related to the initial mixture. With increasing temperature, we observe IR features typically associated with the growth of carbon-rich networks, compatible with the formation of macromolecular organic matter (Urso et al., in prep.). We also reveal the formation of OCN- and nitriles, whose IR features were recently revealed on organics-rich TNOs and are proposed as key compounds to clarify the origins of materials in these bodies [9].
The exposure to further ion bombardment and thermal processing of ORRs causes strong changes in the IR spectra of the samples. In particular, during warm-up we observe shifts and decrease in the intensity of all features. No IR feature is detected in the spectra acquired after warm-up to about 700 K. Interestingly, the Raman spectra acquired after ion bombardment or thermal processing of ORRs show the presence of the D and G bands of amorphous carbon [10]. The properties of the amorphous carbon detected in ORRs exhibit dependence on initial ice composition, irradiation and thermal history, in some cases showing a close match with carbonaceous extraterrestrial particles (Germanà et al., submitted MAPs, Urso et al., in prep).
Conclusion
Our data show that exposure of simple, pristine ices observed on the surface of TNOs to ionizing radiation can lead to the formation of macromolecular organic materials. The properties of organic matter primarily depend on the composition of ices and on the dose. Ion bombardment is thus of primary relevance in the formation of complex organic materials in the outer Solar System, where amorphous carbon could also be present.
References:
[1] Barucci, M. A. & Merlin, F. 2020, in The Trans-Neptunian Solar System, ed. D. Prialnik, M. A. Barucci, & L. Young, 109–126
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[8] Urso, R. G., Vuitton, V., Danger, G., et al. 2020, A&A, 644, A115
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How to cite: Germanà, M., Urso, R. G., Baratta, G., Fulvio, D., Scirè, C., and Palumbo, M. E.: Ion bombardment induces the formation of macromolecular organics on TNO ices, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-513, https://doi.org/10.5194/epsc2026-513, 2026.
The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will deliver multiband time-domain photometry for an unprecedented number of sources (Ivezić et al. 2019), motivating a shift from single-feature anomaly detection toward structured biosignature searches in observable space (Gallay, Davenport & Croft 2025; Kovačević, Mason & Ćiprijanović 2025; Li et al. 2022). Correlated, coherent perturbations across the six LSST passbands (320–1100 nm) can encode surface reflectance, haze, and biologically motivated spectral features. Building on the coherence framework of Kovačević, Mason et al. (2026) and aerial-biosphere scenarios in sub-Neptune atmospheres (Seager et al. 2021), we test whether a Vegetation Red Edge (VRE) signature produces a statistically detectable, directionally coherent displacement in the LSST multiband colour vector, separable from astrophysical noise without spectroscopy.
We simulated a 649-spectrum grid spanning pressure, H₂/He composition, CH₄, and haze in a GJ 1214b-like sub-Neptune template (PSG; Villanueva et al. 2022). A VRE sigmoid proxy was injected at λ₀ = 0.705 µm with f_VRE = 0.00, 0.10, 0.30 and widths w = 0.02, 0.05 µm, then convolved through Rubin/LSST throughput curves to produce synthetic AB magnitudes. Figure 1 shows the differential flux ΔFVRE for a representative model (0.1 bar, 95.5% H₂/He, methane-poor, haze-free): a sigmoid rise from zero shortward of the VRE edge projecting into correlated broadband colour shifts across the r and i passbands.
Figure 1 . Differential VRE flux signature through LSST filters. The black curve shows ΔFVRE for a representative PSG model (0.1 bar, 95.5% H₂/He, methane-poor, haze-free). The shaded green region marks the VRE edge (0.68–0.75 µm), straddling the r and i filters. The perturbation projects into correlated colour shifts across multiple LSST bands — a broadband coherent displacement, not an isolated narrow feature.
After penalising haze and methane nuisance directions using a generalised Rayleigh quotient, the learned VRE coherence score is SVRE = Δ(r−i) + 0.661 Δ(i−z), with propagated noise floor σVRE = 0.024 mag. The weights W₁ = 1.0 and W₂ = 0.661 maximise VRE sensitivity while penalising the CH₄ and haze response directions. Figure 2 shows the differential colour heatmaps conditioned on VRE fraction (fVRE) for all 649 spectra. At fvre = 0.00 the entire population collapses to the origin. At fVRE = 0.10 the cloud shifts coherently to Δ ≈ 0.004 mag, and at fVRE = 0.30 it migrates further to Δ ≈ 0.010 mag. The population migrates as a compact directional cloud rather than diffusing, confirming that the VRE perturbation produces a reproducible colour displacement consistent across all atmospheric nuisance parameter combinations.
Figure 2. Differential colour space conditioned on VRE fraction. Density histograms for all 649 PSG spectra at fVRE = 0.00 (left), 0.10 (centre), and 0.30 (right). The population migrates coherently as a compact directed cloud with increasing VRE coverage.
Figure 3 shows the SNRVRE distribution (left) and nuisance analysis (right) for fVRE = 0.00, 0.10, and 0.30, yielding SNR ≈ 0.00, 0.25, and 0.63 respectively — all sub-threshold (SNR < 1) at single-epoch LSST precision. The empirical coherence threshold τ = 0.3 marks where the VRE projection begins separating systematically from baseline and nuisance directions in differential colour space. The right panel's three flat horizontal bands confirm that the penalised score successfully projects out the methane nuisance direction across four decades of CH₄ abundance. The signal is thus sub-threshold but non-zero, coherent, and growing monotonically with fVRE — the ideal regime for considerening survey-scale stacking (Figure 4).
Figure 3. VRE coherence score distribution and CH₄ nuisance analysis. Left: stacked histogram of SNRVRE by VRE fraction. Three peaks at SNR ≈ 0.00, 0.25, 0.63 confirm the signal is sub-threshold at single epoch. Dashed line: τ = 0.3 . Right: log₁₀(CH₄) versus SNRVRE density. Flat horizontal bands across four CH₄ orders of magnitudes confirm the penalised score projects out the methane nuisance direction.
Figure 4 presents the stacking feasibility forecast. Following Pont et al. (2006), stacked significance follows S(N, f_sys) = √N · D₀ / √(1 + N · f²_sys), where N is independent LSST targets or epochs, D₀ the median single-object VRE coherence score, and f_sys the fractional systematic floor. For f_sys = 0, significance grows as √N, reaching 3σ at N ≈ 53 and 5σ at N ≈ 148. Systematics saturate the ceiling at S_max = D₀/f_sys: moderate f_sys = 0.10 caps significance near 3σ, while f_sys = 0.20 prevents 3σ detection entirely. Achieving 5σ requires f_sys < D₀/5, imposing a sub-millimagnitude calibration requirement on r−i and i−z bands. Since the VRE signal is sub-threshold but coherent and nuisance-free, population-scale stacking over N = 53–148 targets is the natural path to a significant biosignature detection.
Figure 4. Stacking feasibility forecast for LSST. Stacked significance versus N independent objects or epochs for f_sys = 0.00, 0.05, 0.10, 0.20. Ideal case reaches 3σ at N ≈ 53 and 5σ at N ≈ 148. f_sys = 0.10 saturates near 3σ; f_sys = 0.20 capped below 2σ. Shaded: small-stack (N = 5–40) and survey-stack (N = 40–200) regimes.
Outlook
We demonstrate that VRE-like biosignature perturbations produce statistically coherent displacements in Rubin/LSST broadband colour space, separable from CH₄ and haze nuisance directions through penalised coherence scoring. The signal is sub-threshold at single-epoch precision but accumulates to statistical significance through survey-scale stacking. Future work will extend the framework to realistic LSST cadences, a wider range of host star types, extinction corrections, and machine learning classifiers trained on the full Δ-colour manifold.
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How to cite: Kovacevic, A., Mason, N., and Moore, M.: Prototype Coherence-Based Biosignature Searches with Vera C Rubin Observatory Legacy Survey of Space and Time, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-763, https://doi.org/10.5194/epsc2026-763, 2026.
