Our scientific goals align with the context of observational tools and exploration missions within the solar system. In the laboratory, we are forging paths for analyzing and predicting processes occurring in astrophysical environments.
Studying the physico-chemistry of interstellar and interplanetary environments, through observation instruments (JWST, NOEMA, ALMA) and space experiments targeting primitive objects, will enable us to address the evolution of protoplanetary disks before planet formation, the history of interstellar dust, the chemical composition of comets and asteroids, and the relationship between these bodies. We are advancing convergent approaches involving astrophysicists, chemists, nuclear physicists, and cosmochemists, employing various analytical methods to study extraterrestrial solids comprehensively. The analysis of diverse extraterrestrial samples and the study of laboratory analogs coupled with "in-situ" observations (Rosetta mission) will help constrain the filial relationships between interstellar, cometary, and interplanetary matter.
The strategic choice is to develop: (i) spectroscopic and physico-chemical analyses through local experiments, and to leverage (ii) very large equipment and (iii) collaborations to expand our analytical capabilities into other specialized domains.
1. Energetic processes, reflectance, and connection with extraterrestrial matter
In parallel with studies on UV photolysis, we are developing:
- An activity on low-energy ion irradiation (in Orsay) and high-energy ion irradiation (at GANIL, Caen) to understand the microphysical and thermal evolution processes (20 – 300 K). These studies aim to elucidate the interplay between these processes and the generation and transformation of extraterrestrial organic matter.
- The irradiation of ices, meteorites, and carbon-rich micrometeorites, followed by their analysis through VIS-NIR reflectance (INGMAR project) (Lantz et al. 2018) and FIR-MIR reflectance (Brunetto et al. 2018 and 2020), aims to study spatial weathering (Surface alteration of small bodies in the solar system due to solar wind and cosmic radiation).
We study the evolution of spectra in micrometeorites before and after irradiation to establish direct connections between micrometeorite families and small celestial bodies. This analysis runs concurrently with the investigation into the destruction of molecules on the surfaces of parent bodies and the formation of an organic-enriched mantle. Irradiating N2:CH4 mixtures will enable the exploration of a pathway for the formation of organics observed in ultra-carbonaceous micrometeorites from the CSNSM collection (Dartois et al. 2013). These activities will strengthen collaboration between IAS and CSNSM in Orsay, providing essential support for interpreting data from space missions targeting primitive objects (Rosetta, New Horizons, OSIRIS-REx, Hayabusa 2). Application to observations will be done in collaboration with the Paris-Meudon Observatory. In the longer term, establishing an "astro" irradiation line will provide support for the JUICE mission (ESA).
2. Influence of cosmic rays on the structure of ices
The alteration of the physical state of solids is extremely significant in many astrophysical processes (e.g., interstellar chemistry leading to the formation of H2). The physical state of ice (amorphous, crystalline, metastable) results from interactions with ions and photons. We conduct ion irradiation experiments on water ice deposits, aiming to directly simulate cosmic irradiation. We utilize multiple high-energy ion beams provided by GANIL (Grand Accélérateur National d’Ions Lourds, Caen) to determine the cross-section over a broad range of energy loss.
3. Silicate-gas interaction surfaces
The coexistence of gases and silicate solid matter in the MIS naturally leads us to consider a common role played by these two components in planet formation. Thus, we have implemented the PRONEXT experiment. Its objective is to understand the gas/silicate grain interaction in the primitive nebula, assessing the potential role of silicates in contributing volatiles to the surface of the primitive Earth. Our approach involves comparing possible scenarios for volatile formation (irradiation versus adsorption on silicate surfaces) and studying their in-situ formation kinetics. An initial validation experiment for our setup involved studying the evolution of a silicate film in an atmosphere rich in water vapor at room temperature. Preliminary results indicate that silicates have a hydroxylation rate of approximately 7% (Djouadi et al., 2013). We deduce that the formation of OH hydroxyls in silicates is approximately three times more efficient through water adsorption at room temperature than through proton irradiation at low energies (Djouadi et al., 2011).
4. Continuum of production of analogs to carbonaceous matter in the MIS
The ice mantles covering interstellar dust grains are found in dense molecular clouds. These astrophysical environments are exposed to cosmic rays and UV photons, leading to a physico-chemical evolution of matter that can be simulated in the laboratory. Studying the progression of these ices toward more complex refractory organic materials, which will be incorporated into the protosolar nebula, is among the objectives of our research. Furthermore, the analysis of organic matter in cosmic materials reveals unexpected diversity, prompting us to explore a broader range of carbonaceous materials and production conditions. We will continue the work initiated on the production of analogs and their analysis.
4. a. Expansion of the range of films and residues produced
The a-C:Hs (hydrogenated amorphous carbons) produced by plasma in our team constitute one of the best spectroscopic analogs to the dust observed in absorption in the diffuse medium. In the future, we aim to produce amorphous carbons in a controlled manner using the same experimental setups, into which we will introduce heteroatoms to understand their influence on the intimate structure of the material. We will continue and expand our collaboration with ISMO on the production and analysis of soot by vacuum combustion using a flat flame (Nanograins/ISMO experiment). These soots serve as analogs to interstellar dust, closely resembling the most aromatic phase, ensuring continuity in the types of grain structures studied.
Exploring the diversity of material structures subjected to astrophysical environments includes the production of ice residues through irradiation with simulated cosmic rays in accelerators. In previous experiments conducted at GANIL in collaboration with G. Muñoz-Caro, we initiated a study on the complementarity of cosmic ion irradiation with UV photolysis of interstellar ices. We will continue in this direction and compare the effects of heavy ion irradiation (0.3-1 MeV/u) with those of low-energy ions (keV) and UV photons on the structure and chemical composition of ices. The results will also be connected to remote observations, using telescopes or satellites, of interstellar clouds.
4. b. Comprehensive characterization of these various materials
Analysis using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) at IPNO and support for COSIMA
A better understanding of the organic composition of cometary matter is one of the most anticipated outcomes of the Rosetta mission. Cometary organics, much like carbonaceous chondrites, consist of soluble and insoluble molecules and macromolecules. The insoluble macromolecular component of carbonaceous chondrites has been extensively studied. Its chemical structure resembles certain hydrogenated amorphous carbons (a-C:H) that we produce in the laboratory through experimental simulations of hydrocarbon-rich ices. These components, along with nitrogen-rich amorphous carbons, are of great astrophysical interest, as a-C:H with very few heteroatoms (O and N) are observed in the ISM, and, more recently, a nitrogen-rich phase has been measured in micrometeorites collected in Antarctica. With COSIMA, it will be interesting to focus on the macromolecular component of cometary carbonaceous matter to provide an overview of its chemical structure and composition. Measurements conducted by COSIMA can be analyzed in conjunction with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) measurements we perform on analogs and meteorites, to constrain possible links between ISM and protosolar nebula organics.
Analysis of the soluble macromolecular component
So far, studies aimed at characterizing soluble organic matter have focused on the search for relatively small organic molecules (e.g., amino acids). The ex-situ analysis techniques used primarily rely on gas chromatography coupled with mass spectrometry (GC-MS) and sample preparation methods that do not hesitate to alter and/or destroy them (extraction by acid hydrolysis). While having prebiotic significance, the results of these efforts provide only an unclear understanding of the actual chemical mechanisms occurring during the UV or ion irradiation of interstellar ice analogs and their heating. To access this chemistry, it is necessary to analyze and characterize what it produces—macromolecules, parent components that, when hydrolyzed, are altered and fragmented, releasing, among other things, amino acids. The challenge is significant and represents a certain experimental hurdle as it requires the establishment of a new and relatively unexplored experimental protocol. However, the collaboration initiated with LETIAM, along with the initial tests and experiments conducted, is promising and confirms our adopted approach. Our goal is to continue this analytical physico-chemical work to progressively characterize the soluble macromolecular components of various organic mixtures of astrophysical interest with increasing precision.
5. Spectroscopy of analogs in the UV-VUV (Ultraviolet to Vacuum Ultraviolet) range
The carbonaceous materials produced in our team exhibiting spectra that align remarkably well with observations in the infrared spectrum, need to be quantified across the entire spectral range. The far-UV (190 - 250 nm) and vacuum UV (100 - 190 nm) spectral range has been less explored but is of great importance for carbonaceous materials. It covers electronic transitions associated with sp3 and sp2 carbon bonds and represents the second astrophysical spectroscopic signature observed when compared to these analogs. VUV-UV measurements provide optical constants used in radiation transfer models, serving the astrophysical community. Such measurements determine the interaction cross-section with energetic photons leading to surface photochemistry, an essential comparison to assess the relative importance of low-energy ionizing versus low-energy photon processes for all these materials. The characterization of interstellar and cometary dust analogs produced by our team and collaborators will also contribute to establishing the optical constants of extraterrestrial materials irradiated at low energy.
6. 3D Physico-Chemical Structuring of Primitive Matter
Primitive bodies result from a complex assembly exhibiting high heterogeneity at both the micrometric and nanometric scales. Through the development of 3D characterization techniques, we can non-destructively analyze the interiors of highly valuable samples. We are interested in both physical properties (porosity, mineral assembly, fracturing) and chemical aspects (localization and correlation of different mineral/organic phases). These 3D studies enable us to better constrain the pre- and post-accretional processes experienced by their parent bodies (Dionnet et al., 2020 and 2023).