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Jupiter Trojan Asteroid Regolith Simulant

Presentation #520.01 in the session Trojan Asteroids (iPosters).

Published onOct 20, 2022
Jupiter Trojan Asteroid Regolith Simulant

We are developing a Jupiter Trojan asteroid regolith simulant to mimic their expected minerology and spectral properties. NASA’s Lucy mission is on its way to provide us with new knowledge, and one day the JAXA OCEANOS mission will ultimately return Trojan samples. Meanwhile a number of spectral mixture models have been tried to identify the composition, that would have spectral properties similar to Trojans, as reviewed in [1].

Compositional endmembers were identified after a literature search and discussions [1]. These endmembers included: olivine, iron sulfides (FeS) and coals. Endmember proportions were calculated based on solar and CI chondrite elemental abundances [2].

Relatively immature coal was chosen as an analog for organics in the Trojans. These coals have similar chemical and structural composition to insoluble organic matter (IOM) in meteorites [3]. Similar reasoning was used by [4] in the development of a cometary analog. Coals are easily accessible and cheap, which is an important point for a simulant production.

Endmembers were crushed and mixed with mortar and pestle. Dunite (92 % forsterite and 8 % fayalite) was used as olivine endmember. Olivine was crushed and sieved from 5 mm grains down to <100 μm. A powder made of FeS (55 vol.% troilite, 45 vol.% pyrrhotite) was readily available in two particle sizes <100 μm and <1 μm (hyperfine). Most coal samples were available in particle sizes <250 μm, but most immature coal PSOC1532 was available in various sizes, also hyperfine. Mixtures were prepared and spectra taken in IPAG, Grenoble, France.

Vis-NIR and MIR reflectance spectra and microscope images were taken of all endmembers and mixtures. FeS has no significant spectral features in NIR and MIR, its reflectance seems to depend on particle size. Olivine spectral features at wavelengths < 9 μm disappear in the mixtures with iron sulfide and coals, with coal features dominating spectra at these wavelengths.

Trojan spectra are red sloped and without prominent absorption features in Vis-NIR range. MIR emission spectra are not featureless, Trojans have a strong absorption plateau near 10 μm. It was previously shown that hyperfine and highly porous olivine might be responsible for this feature [5]. We do not observe this feature in MIR reflectance spectra, but the MIR spectral range is dominated by our olivine endmember, so we would expect to see the feature if olivine was hyperfine.

1. Šļumba, K. et al. (2022). LPSC2022 Abstr. 2014

2. Lodders, K. (2020). Oxford Research Encyclopedia of Planetary Science

3. Quirico, E. et al. (2016). Icarus

4. Rousseau, B. et al. (2018). Icarus

5. Emery, J.P. et al. (2006). Icarus

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