SB6

How to cite: Hunziker, S. and Sterken, V. and the Interstellar Probe ISD Team: Interstellar dust as a unique and interdisciplinary science case for the Interstellar Probe, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1002, https://doi.org/10.5194/epsc2022-1002, 2022.

Interstellar dust has been and will be measured by many spacecraft, both directly (e.g. by Cassini, Ulysses, DESTINY⁺, IMAP) and indirectly (e.g. by Voyager, Wind). The flux of interstellar dust at these spacecraft can be enhanced, in particular for small dust grains (<0.3µm), due to the so-called focusing phase of the solar cycle (for dust), in the early 2030s.

Through their surface charges, these small particles are coupled to the solar-cycle-dependent magnetic fields inside and to interstellar fields outside of the heliosphere. By comparing the measurements to simulations of interstellar dust, inferences about the outer regions of the heliosphere and its boundary can be made. The quality of these inferences highly depends on the availability of detailed measurements of interstellar dust, highlighting the necessity of a space-based dust detector operating during the upcoming focusing phase, such as the proposed DOLPHIN mission.

In this talk we give an overview of measurements and simulations of the measurements of various missions so far, and their link to interstellar dust simulations. 

How to cite: Baalmann, L. R., Hunziker, S., Strub, P., Malaspina, D., Schroffenegger, U., Krüger, H., Hervig, M., Jaynes, A. N., Kurth, W., Wilson III, L. B., and Sterken, V. J.: Investigating the outer regions of the heliosphere with measurements and simulations of interstellar dust, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-785, https://doi.org/10.5194/epsc2022-785, 2022.

The Trans-Neptunian Object (50000) Quaoar, classified as a cubewano, is a dwarf planet candidate with a diameter of 1110 km [Br13], semi-major axis of 43.7 au and orbital eccentricity of 0.04. Its satellite Weywot orbits at 13,300 km from the primary object, and from its flux [Fr10], its diameter is about 90 km, assuming the same albedo as Quaoar. Several campaigns were conducted under the umbrella of the Lucky Star project (https://lesia.obspm.fr/lucky-star/) to observe stellar occultations by Quaoar and Weywot. Besides measuring Quaoar's and Weywot's size and shapes, those campaigns aimed at searching for material around Quaoar.

Here, we will present the results of our search for rings around Quaoar based on the following observations: 

Dates                      Places of observations
2 September 2018   Namibia
5 June 2019            Canary Islands
11 June 2020          Australia, CHEOPS satellite
27 August 2021       Australia

These campaigns were undertaken in a context where rings are already known to exists around other small bodies of the solar system: the Centaur object Chariklo [Br14] and the dwarf planet Haumea [Or17]. These two ring systems, in spite of large differences in sizes and heliocentric distances, both orbit close to the 1/3 Spin-Orbit Resonance (SOR) with the central body [Or17,Le17], meaning that the latter completes three rotations while a ring particle completes one orbital revolution. Because of their non-axisymmetric shapes, and contrarily to giant planets, Chariklo and Haumea induce strong SORs [Si19]. Theoretical calculations [Si21] and numerical simulations of collisional disks [Sa21] show that the 1/3 SOR is indeed a possible cause of confinement of a narrow ring.

If ring exists at the Quaoar 1/3 SOR, it should be close to an orbital radius of 4,200 km. This represents 7.5 Quaoar's radii, well outside the Roche limit of the central body. So, if a dense ring were to be confined near this resonance, it is expected to accrete into a satellite, and thus disappear over a short time scale. We will discuss models that could maintain a colliding disk near the Quaoar 1/3 SOR in spite of this obstacle.

Acknowledgments. The work leading to these results has received funding from the European Research Council under the European Community's H2020 2014-2021 ERC Grant Agreement no. 669416 "Lucky Star"

[Br13] Braga-Ribas et al., ApJ 773, 26 (2013)
[Fr10] Fraser and Brown, ApJ, 714, 1547 (2010)
[Le17] Leiva et al., Astron. J. 154, 159 (2017)
[Or17] Ortiz et al., Nature 550, 219 (2017)
[Sa21] Salo, H. et al., European Planetary Science Congress, EPSC2021-338 (2021)
[Si19] Sicardy, B. et al., Nature Astronomy 3, 146 (2019)
[Si21] Sicardy, B. et al., European Planetary Science Congress, EPSC2021-91 (2021)

How to cite: Sicardy, B., Morgado, B., Braga-Ribas, F., Ortiz, J. L., Desmars, J., Pereira, C., Viera-Martins, R., Salo, H., de Santana, T., Sfair, R., Assafin, M., Benedetti-Rossi, G., Camargo, J., Fernandez-Valenzuela, E., Gomes-Júnior, A., Kretlow, M., Rommel, F., Santos-Sanz, P., Souami, D., and Vachier, F. and the Quaoar team: Search for rings around the large Trans-Neptunian Object (50000) Quaoar, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-82, https://doi.org/10.5194/epsc2022-82, 2022.

Rare presolar grains originating by condensation in circumstellar atmospheres are known from meteorites [1]. These escaped processing in the solar nebula and are identified via their extremely diverse isotopic composition [1,2]. However, it is uncertain if such grains are representative for dust from the interstellar medium (ISM) [3–5], particular as [5] postulated a high fraction of interstellar grain population that formed directly in the ISM.

In 1992 the Ulysses spacecraft discovered a dust flow from the Local Interstellar Cloud (LIC) [6]. During the Cassini mission at Saturn, the Cosmic Dust Analyser (CDA) could identify and analyse the chemical composition of 36 individual interstellar dust (ISD) particles [7]. These grains were distinguished from Saturn bound dust by their direction and high velocity. Their mean mass is consistent with the typical size [3-5] derived from astronomical observations. As major result, each individual ISD grain contains the major rock forming elements (Mg, Si, Fe, Ca) in roughly cosmic abundances, indicating compositional homogeneity at spatial scales as small as 100 nm. In contrast, CDA did neither detect carbon-rich grains such as graphite or SiC, nor pure metal grains (upper limit of 8% at the 2 sigma confidence level) [7].

This homogeneity cannot be reconciled with isotopically and compositionally diverse populations of circumstellar dust inherited from AGB stars and supernovae found in meteorites. These grain populations consist mainly of silicates with a more diverse composition (e.g., olivine, pyroxene), however, also minor contributions (few %) of Al-oxides (e.g., corundum, hibonite), as well as carbonaceous grains (mainly silicon carbide) which contribute 20-50%, of the grains in the most primitive meteorites [2]. In contrast to circumstellar grains found in meteorites, the LIC-ISD grains detected by Cassini have a much lower variation of Mg/Si or Mg/Fe ratios [7], and appear to be a grain population homogenized by destruction, recondensation and equilibration processes in the ISM. This can be reconciled with astronomical observations of the diffuse ISM demonstrating that condensable elements of atomic mass >23 are depleted in the gas phase and hence bound in solids. Considering that the mean lifetime of ISD grains against destruction by supernova shocks is much shorter (c. 0.5 Ga) than the average residence time of ISM matter of 2.5 Ga [5], an origin of a high fraction of ISD by grain destruction followed by recondensation was suggested by [5,7]. While grain destruction most likely occurs in the hot interstellar medium, i.e., low-density cavities formed by supernova shock fronts, condensation likely occurs in the cold interstellar medium, i.e., cold molecular clouds which are also formation regions of stars and planets.

The upcoming DESTINY+ mission [8] will be equipped with an improved impact ionization mass spectrometer, the DESTINY+ Dust Analyser (DDA). During the mission, hundreds of ISD particles are expected to be measured [9]), yielding high quality mass spectra with a resolution of c. 100-200 when compared to c. 20-50 of Cassini CDA [10]. This will allow much better resolution of mass peaks at 23-28 amu (Na, Mg, Al, Si) and 39-41 (K, Ca), particularly yielding improved constraints on abundances of Al and Si. This will allow, e.g., to distinguish between Mg silicates like pyroxene and olivine or Al-rich feldspar type silicates. Also, more precise values for Na and K can be expected, particularly as some of the Cassini CDA data were compromised by alkali contamination of the Rhodium target [7]. Furthermore, the higher number of ISD particle detections will allow to better quantify the ISD fraction of non-silicate particles (oxides, SiC, graphite, metal, see [1]). This will also provide constraints on dynamic forces acting on the ISD particle flux, particularly the question if high beta particles are preferentially deflected from the inner solar system by solar radiation forces. Finally, DDA measurements will also contribute to solve the problem of apparently low or “missing” organic components in CDA detected particles, which may be caused by volatilization of refractory organic material in ISD mantles upon entering the heliosphere [11].

Hence, interstellar dust detections by the DESTINY+ Dust Analyser will likely improve our understanding of the chemical nature of interstellar dust, its processing and lifetime in various phases of the interstellar medium, possible processing and volatile loss upon traversing our solar system to 1 AU, flux modulations upon interaction with solar electromagnetic forces, and last but not least, a tight age constraint on the LIC dust.  

References:

[1] E. Zinner (2014) In Meteorites and Cosmochemical Processes (ed. Davis A. M.). Elsevier, Amsterdam, pp. 181–213

[2] J. Leitner, C. Vollmer, P. Hoppe, J. Zipfel (2012) Astrophysical Journal 745, 38

[3] P. C. Frisch et al. (1999) Astrophysical Journal 525, 492

[4] H. Kimura, I. Mann, E. K. Jessberger (2003) Astrophysical Journal 583, 314

[5] S. Zhukovska, H.-P. Gail, M. Trieloff (2008) Astronomy & Astrophysics 479, 453

[6] E. Grün et al. (1993) Nature 362, 428-430

[7] N. Altobelli, F. Postberg, K. Fiege, M. Trieloff et al. (2016) Science 352, 312

[8] H. Arai, M. Kobayashi, et al. (2018) Lun. Planet. Sci. Conf. 49, abstr. #2570

[9] Krüger H., Strub P., et al. (2019) Planetary & Space Science 172, 22-42.

[10] Srama R. et al. (2004) Space Science Reviews 114, 465-518.  

[11] H. Kimura, F. Postberg, N. Altobelli, M. Trieloff (2020) Astronomy & Astrophysics 643, A50

How to cite: Trieloff, M., Kimura, H., Postberg, F., Krüger, H., Strub, P., Leitner, J., Sterken, V., Hunziker, S., Hillier, J., Hirai, T., Yabuta, H., Ito, M., Khawaja, N., Schwarz, W. H., Ludwig, T., Schmitt, J., Sasaki, S., Arai, T., Kobayashi, M., and Srama, R.: Comparing meteoritic stardust with contemporary interstellar dust measured by Cassini and DESTINY+  -  constraining models of dust processing in the interstellar medium, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-961, https://doi.org/10.5194/epsc2022-961, 2022.

The X-Ray Observatory eROSITA on board the Spectrum Roentgen Gamma (SRG) satellite has been operational in a halo orbit around the Sun-Earth Lagrange point L2 since summer 2019. Between December 2019 and January 2022 the eROSITA instruments registered at least seven non-nominal events which are likely related to micrometeoroid impacts, leading to permanent local defects in the X-ray CCD sensor. Each of the micrometeoroid events showed different features and effects in the CCD. In order to test the hypothesis that the defects in the CCDs are indeed related to micrometeoroid impacts, we performed numerical simulations with two interplanetary dust models, taking into account the exact times of the events, orbital position including velocity vector, and the telescope pointing and eROSITA instrument field-of-view. 

In order to identify time intervals when the SRG space telescope traversed cometary meteoroid trails, we used the IMEX dust streams in space model (Soja et al. 2015, Astron Astrophys, 583, A18). The model generates trails for 420 comets available in the JPL Small Body Database (SBDB) as of 1 August 2013, and simulates the dynamics of individual dust particles released from these comets in the size range of 100 micrometers to 1 centimeter, taking into account all relevant forces (solar and planetary gravity, solar radiation pressure, and Poynting-Robertson drag). 

Our simulations reveal at least two candidate cometary trail crossings of SRG in the L2 point with predicted micrometeoroid fluxes sufficiently large that individual particle impacts have to be expected. However, a comparison of the particle impact directions predicted by the model with the telescope pointing during the impact events are in disagreement for all events, implying that none of the registered events is likely connected with dust impacts from a dedicated cometary micrometeoroid trail. However, based on these simulations, it became clear that caution is needed during time periods of cometary trail crossings when high particle fluxes are expected. Here, telescope pointings should avoid looking into the radiant direction of a meteoroid trail.

In a second analysis step, we tested the hypothesis that the events registered by eROSITA may be related to sporadic impacts of particles from the zodiacal dust cloud. To this end, we used the Interplanetary Meteoroid Environment Model 2 (IMEM2; Soja et al. 2019, Astron Astrophys, 628, A109). The model integrates the orbits of cometary and asteroidal particle distributions in the size range 1 micrometer to 1.25 millimeters over 1 Myr, including solar gravity and radiation forces, as well as particle disruptions due to mutual particle collisions. It provides the distribution of dust particles from different cometary and asteroidal sources in the inner solar system. Our results show that many of the registered events occurred when eROSITA was pointing towards directions of increased sporadic interplanetary dust flux as predicted by the model. Several of the events occurred when the telescope was pointing in the direction close to toroidal zones of the sporadic interplanetary dust flux. The modelled dust fluxes predict that approximately two to five micrometeoroid impacts of approximately 1 micrometer sized particles are expected within eROSITA’s operational timeframe of 2.5 years, in rough agreement with the number of events registered by eROSITA. 

Acknowledgements: The IMEM2 model and the IMEX Dust Streams in Space model were developed under ESA funding (contracts 4000114513/15/NL/HK and 4000106316/12/NL/AF ‐ IMEX). 

How to cite: Strub, P., Müller, T., Moragas-Klostermeyer, G., Freyberg, M. J., and Krüger, H.: Micrometeoroid Impacts on to the SRG/eROSITA X-Ray Telescope, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-563, https://doi.org/10.5194/epsc2022-563, 2022.