Periodic Reporting for period 4 - SOLARYS (Composition of solar system small bodies)
Okres sprawozdawczy: 2022-10-01 do 2023-09-30
The solar system is made of 1 star, 8 planets, several hundredth of satellites, but also of millions of so-called small bodies (asteroids and comets). These small solar system objects are thought to be primitive, because being small they should have escaped the profound thermal processing experienced by planets. They are also the building blocks of planets and giant planetary cores: understanding how they were formed and what they are made of provides information on how our planetary system was formed. The overall objectives of this project is to provide constrains on the composition of solar system small bodies, through laboratory measurements. We are using a multi-scale approach to understand their composition, based on analysis of extra-terrestrial samples (meteorites, IDPs, sample return missions).
We obtained the following conclusions
-the darkness of comets and related asteroids is related to the presence of fine-grained opaques (Fe metal, sulfide). These opaques are the key to understand the peculiar spectra of comets in the mid-infrared.
-the red slope reflectance spectra of cometary nuclei may be related to the small grains they are made of (<1 µm) ,combined with porosity.
-primitive extra-terrestrials samples contain grains (µm sized) of complex organic matter, that were produced abiotically in the solar protoplanetary disk or before the begining of the solar system.
-primitive asteroids and comets contain ammonium salt. These salts are an important carrier of nitrogen, a key element for life, and that may have been delivered in the form of salts to terrestrial planets.
-L-type asteroids, which were suspected to be very anomalous and formed under very refractory conditions (high-temperature) are in fact related to the relatively abundant CO-CV meteorites.
-the simplification of the optical spectra of small bodies after 3.8 a.u. is likely to e a grain size effect.
We obtained the following conclusions
-the darkness of comets and related asteroids is related to the presence of fine-grained opaques (Fe metal, sulfide). These opaques are the key to understand the peculiar spectra of comets in the mid-infrared.
-the red slope reflectance spectra of cometary nuclei may be related to the small grains they are made of (<1 µm) ,combined with porosity.
-primitive extra-terrestrials samples contain grains (µm sized) of complex organic matter, that were produced abiotically in the solar protoplanetary disk or before the begining of the solar system.
-primitive asteroids and comets contain ammonium salt. These salts are an important carrier of nitrogen, a key element for life, and that may have been delivered in the form of salts to terrestrial planets.
-L-type asteroids, which were suspected to be very anomalous and formed under very refractory conditions (high-temperature) are in fact related to the relatively abundant CO-CV meteorites.
-the simplification of the optical spectra of small bodies after 3.8 a.u. is likely to e a grain size effect.
In the first work package, we had a look at fragments of small bodies that were delivered to Earth, by setting up and developing a new analytical technique in Grenoble (Nano-infrared spectroscopy). We developped analytical protocols as well sample preparation protocols, in order to build and validate our approach (published in paper led by Solarys Postdoc Phan 2021,2022,2023). We could show that the technique can be used to study mixtures of silicates and organics, and applied this method to the most primitive samples we have from the Early solar system (Phan et al., 2024).
We also developed protocol to produce porous surfaces made of silicate and sub-µm particles of silicates, sulfides and organic materials. We have also set-up a methodology that enables to incorporate these small grains inside water-ice sphere, and produce hyper-porous samples by sublimation of the ice. This work led to several important results. First we showed that there is a small grains degeneracy for weakly absorbing material. In other words, when small grains are present (<1 µm), as expected in comets and primitive small bodies, the diagnostic signature of minerals decrease significantly (Sultana et al; 2020). We also show that the presence of elevated porosity maximize these effects. Last we added small opaque particles to the mixture and could reproduce all known optical properties of cometary matter and primitive asteroids (Sultana et al., 2023).
Our laboratory characterization have been used to compare and confront to available observations of the small bodies population. This is where the most striking results have been obtained. First we have used the sample preparation protocol designed to understand the presence of a peculiar absorption of comet 67P around 3-µm. We have shown that it is due to the presence of ammonium salts, with strong implications for the budget of nitrogen (Poch et al., 2020). Second, we have assessed how much water is present in the main-asteroid belt, based on reflectance spectra obtained on primitive extra-terrestrial samples. From this work we shown that main-belt asteroids appear dehydrated when compared to their asteroidal counterpart, and that the mass of water in the main-belt is of the order of the mass of Enceladus (Beck et al., Icarus 2021). Last, we have started to shade light on the links between primitives meteorites families and dark asteroids types. We have shown that many carbonaceous chondrites are not related to C-type asteroids, and proposed associations of asteroids spectral types to primitive meteorites groups (Eschrig et al., Icarus 2022, Prestgard et al., 2021,2023). Finally, we investigated how asteroid environmental conditions can impact reflectance spectra, with implication for the connection between meteorites and asteroids (Potin et al, 2019, 2020,2021).
Most of the results were shared through publication in peer review journals, conference participation, and last, through open access datasets.
We also developed protocol to produce porous surfaces made of silicate and sub-µm particles of silicates, sulfides and organic materials. We have also set-up a methodology that enables to incorporate these small grains inside water-ice sphere, and produce hyper-porous samples by sublimation of the ice. This work led to several important results. First we showed that there is a small grains degeneracy for weakly absorbing material. In other words, when small grains are present (<1 µm), as expected in comets and primitive small bodies, the diagnostic signature of minerals decrease significantly (Sultana et al; 2020). We also show that the presence of elevated porosity maximize these effects. Last we added small opaque particles to the mixture and could reproduce all known optical properties of cometary matter and primitive asteroids (Sultana et al., 2023).
Our laboratory characterization have been used to compare and confront to available observations of the small bodies population. This is where the most striking results have been obtained. First we have used the sample preparation protocol designed to understand the presence of a peculiar absorption of comet 67P around 3-µm. We have shown that it is due to the presence of ammonium salts, with strong implications for the budget of nitrogen (Poch et al., 2020). Second, we have assessed how much water is present in the main-asteroid belt, based on reflectance spectra obtained on primitive extra-terrestrial samples. From this work we shown that main-belt asteroids appear dehydrated when compared to their asteroidal counterpart, and that the mass of water in the main-belt is of the order of the mass of Enceladus (Beck et al., Icarus 2021). Last, we have started to shade light on the links between primitives meteorites families and dark asteroids types. We have shown that many carbonaceous chondrites are not related to C-type asteroids, and proposed associations of asteroids spectral types to primitive meteorites groups (Eschrig et al., Icarus 2022, Prestgard et al., 2021,2023). Finally, we investigated how asteroid environmental conditions can impact reflectance spectra, with implication for the connection between meteorites and asteroids (Potin et al, 2019, 2020,2021).
Most of the results were shared through publication in peer review journals, conference participation, and last, through open access datasets.
We made several progresses beyond state of the art on the following topics:
The demonstration of the capability of AFM-IR to provide spectroscopic information at the 100 nm scale for natural samples made of silicate-organic mixtures is a significant breakthrough. We showed that the method can be used for natural (and then complex) sample, and that it can probe the mineralogy of silicate, carbonate or sulphate phases. This opens new perspectives for the use of this technique which was so far mostly dedicated to synthetic organics material (i.e. polymer science).
The discovery of ammonium salt on comet 67P is a significant breakthrough. In comets, nitrogen was thought to be hosted in ices (mainly HCN) or organics compounds. We identified a new reservoir of nitrogen with several cosmochemical and astrophysical implications, opening a lot of different research path to be followed.
The results obtained on radiative transfer of hyperfine and hyperporous samples is clearly beyond the state of the art and demonstrate that this type of material cannot be treated with available theories for particulate sample. We revealed first order effects that need to be taken into account when trying to undserstand the optical spectra of primitive small bodies. The methods we developed to produce these analogues can be of use for other scientific domains.
The demonstration of the capability of AFM-IR to provide spectroscopic information at the 100 nm scale for natural samples made of silicate-organic mixtures is a significant breakthrough. We showed that the method can be used for natural (and then complex) sample, and that it can probe the mineralogy of silicate, carbonate or sulphate phases. This opens new perspectives for the use of this technique which was so far mostly dedicated to synthetic organics material (i.e. polymer science).
The discovery of ammonium salt on comet 67P is a significant breakthrough. In comets, nitrogen was thought to be hosted in ices (mainly HCN) or organics compounds. We identified a new reservoir of nitrogen with several cosmochemical and astrophysical implications, opening a lot of different research path to be followed.
The results obtained on radiative transfer of hyperfine and hyperporous samples is clearly beyond the state of the art and demonstrate that this type of material cannot be treated with available theories for particulate sample. We revealed first order effects that need to be taken into account when trying to undserstand the optical spectra of primitive small bodies. The methods we developed to produce these analogues can be of use for other scientific domains.