Importance de la réactivité thermique au sein d'analogues de glaces interstellaires pour la formation de molécules complexes

Dust grains in the interstellar medium (ISM) play an important role in dense molecular clouds chemistry in providing a surface (catalyst) upon which atoms and molecules can freeze out, forming icy mantles. Dense molecular clouds are characterized by low temperature (10-50 K) and represent the birth sites of stars. After a gravitational breakdown, a part of the dense molecular cloud collapses toward the formation of star and subsequently a protoplanetary disk from which planets, asteroids and comets will appear. During this evolution, interstellar organic material inside ices undergoes different range of chemical alterations (thermal cycling process, ultraviolet photons, cosmic rays irradiation) hence increasing the molecular complexity before their incorporation inside precometary ices. In laboratory, in order to better understand the evolution of molecules in interstellar ices, we developed a new approach by making "specifics" interstellar ices analogues submitted to one energetic process at time. Consequently we showed the importance of thermal reactivity (neglected effect for long time) for the formation of complexes organics molecules (HMT, trimers, aminoalcools) which are more refractory compounds than water. Our works have many implications in astrophysics since we gave crucial informations on the chemical processes that are happening in solid phase chemistry of the ISM, and on the formation of news molecules which could be incorporated in parent's body of meteorites/comets. We also show some Exobiological implications particularly for the formations of amino acids in the ISM.Dans le milieu interstellaire (MIS) les grains de poussière jouent un rôle très important pour la chimie au sein des nuages moléculaires offrant une surface froide sur laquelle les atomes et molécules de la phase gazeuse vont s'accréter, formant un manteau de glace. Les nuages moléculaires sont caractérisés par des basses températures (10-50 K) et sont le lieu de formation des étoiles. Après effondrement gravitationnel du nuage suite à une trop forte densité en son sein, celui-ci devient le lieu de formation d'une nouvelle étoile. L'enveloppe autour de l'étoile évolue en disque dans lequel pourra se former des planètes, astéroïdes, comètes et autres objets d'un système planétaire. Durant cette formation stellaire, les glaces interstellaires (et les molécules qu'elles contiennent) sont alors soumises à plusieurs processus énergétiques (cycle de réchauffement, irradiations par des photons UV ou des particules chargées) qui vont affecter leurs compositions chimiques et finalement augmenter la complexité moléculaire avant leur incorporation dans les différentes objets du futur système planétaire. En laboratoire, afin de mieux comprendre l'évolution des molécules, composantes des glaces, nous avons développé une nouvelle approche qui consiste à réaliser des analogues "spécifiques" auxquels un seul processus énergétique à la fois est appliqué. Nous avons alors montré l'importance de l'effet thermique longtemps négligé pour la formation de molécules organiques complexes, montrant plusieurs implications astrophysiques et exobiologiques. Nos études permettent une meilleure compréhension des processus chimiques qui ont lieu dans la phase solide du MIS

Identification of Ammonium Salts on Comet 67P/C-G Surface from Infrared VIRTIS/Rosetta Data Based on Laboratory Experiments. Implications and Perspectives

The nucleus of comet 67P/Churyumov-Gerasimenko exhibits a broad spectral reflectance feature around 3.2 $\mu$m, which is omnipresent in all spectra of the surface, and whose attribution has remained elusive since its discovery. Based on laboratory experiments, we have shown that most of this absorption feature is due to ammonium (NH4+) salts mixed with the dark surface material. The depth of the band is compatible with semi-volatile ammonium salts being a major reservoir of nitrogen in the comet, which could dominate over refractory organic matter and volatile species. These salts may thus represent the long-sought reservoir of nitrogen in comets, possibly bringing their nitrogen-to-carbon ratio in agreement with the solar value. Moreover, the reflectance spectra of several asteroids are compatible with the presence of NH4+ salts at their surfaces. The presence of such salts, and other NH4+-bearing compounds on asteroids, comets, and possibly in proto-stellar environments, suggests that NH4+ may be a tracer of the incorporation and transformation of nitrogen in ices, minerals and organics, at different phases of the formation of the Solar System

Importance of thermal reactivity in interstellar ice analogue for the formation of complex organics molecules

Dans le milieu interstellaire (MIS) les grains de poussière jouent un rôle très important pour la chimie au sein des nuages moléculaires offrant une surface froide sur laquelle les atomes et molécules de la phase gazeuse vont s'accréter, formant un manteau de glace. Les nuages moléculaires sont caractérisés par des basses températures (10-50 K) et sont le lieu de formation des étoiles. Après effondrement gravitationnel du nuage suite à une trop forte densité en son sein, celui-ci devient le lieu de formation d'une nouvelle étoile. L'enveloppe autour de l'étoile évolue en disque dans lequel pourra se former des planètes, astéroïdes, comètes et autres objets d'un système planétaire. Durant cette formation stellaire, les glaces interstellaires (et les molécules qu'elles contiennent) sont alors soumises à plusieurs processus énergétiques (cycle de réchauffement, irradiations par des photons UV ou des particules chargées) qui vont affecter leurs compositions chimiques et finalement augmenter la complexité moléculaire avant leur incorporation dans les différentes objets du futur système planétaire. En laboratoire, afin de mieux comprendre l'évolution des molécules, composantes des glaces, nous avons développé une nouvelle approche qui consiste à réaliser des analogues "spécifiques" auxquels un seul processus énergétique à la fois est appliqué. Nous avons alors montré l'importance de l'effet thermique longtemps négligé pour la formation de molécules organiques complexes, montrant plusieurs implications astrophysiques et exobiologiques. Nos études permettent une meilleure compréhension des processus chimiques qui ont lieu dans la phase solide du MIS.Dust grains in the interstellar medium (ISM) play an important role in dense molecular clouds chemistry in providing a surface (catalyst) upon which atoms and molecules can freeze out, forming icy mantles. Dense molecular clouds are characterized by low temperature (10-50 K) and represent the birth sites of stars. After a gravitational breakdown, a part of the dense molecular cloud collapses toward the formation of star and subsequently a protoplanetary disk from which planets, asteroids and comets will appear. During this evolution, interstellar organic material inside ices undergoes different range of chemical alterations (thermal cycling process, ultraviolet photons, cosmic rays irradiation) hence increasing the molecular complexity before their incorporation inside precometary ices. In laboratory, in order to better understand the evolution of molecules in interstellar ices, we developed a new approach by making "specifics" interstellar ices analogues submitted to one energetic process at time. Consequently we showed the importance of thermal reactivity (neglected effect for long time) for the formation of complexes organics molecules (HMT, trimers, aminoalcools) which are more refractory compounds than water. Our works have many implications in astrophysics since we gave crucial informations on the chemical processes that are happening in solid phase chemistry of the ISM, and on the formation of news molecules which could be incorporated in parent's body of meteorites/comets. We also show some Exobiological implications particularly for the formations of amino acids in the ISM

Exobiologie

La vie existe sur Terre, nul n’en doute, même si on ne sait pas vraiment la définir autrement que par opposition à la mort. Il faut donc admettre qu’elle est apparue, sur Terre ou ailleurs dans l’Univers, dans des conditions que l’on suppose et qu’il faut préciser, soumises aux lois physico-chimiques universelles.Le terme « exobiologie » est né en 1960 pour désigner alors étymologiquement la recherche et l’étude de la vie extraterrestre. Depuis, sa définition a évolué, réunissant désormais tout ce qui a trait à la question de l’origine et à l’évolution de la vie sur Terre et ailleurs dans l’Univers. Tant que l’apparition de la vie sur Terre n’a pas été comprise et tant que l’on ne peut pas déterminer s’il s’agit d’un hasard ou d’un phénomène reproductible sous certaines conditions et dans un environnement précis, il est impossible de se prononcer sur une possible vie ailleurs dans l’Univers, bien que celle-ci soit activement recherchée, jusqu’ici sans succès. Les recherches sur les mécanismes à l’origine de la vie vont donc se dérouler sur Terre, avec la quête de formes fossiles primitives et la chimie des molécules du vivant, et dans l’espace, avec la recherche de manifestations du vivant, molécules et formes. L’exobiologie tente ainsi de répondre à cette fameuse question existentielle : sommes-nous seuls dans l’Univers 

Formation of complex organic molecules in astrophysical ice analogs: A mechanistic approach

WOS:000348457603494International audienceno abstrac

Formation of complex organic molecules in astrophysical ice analogs: A mechanistic approach

WOS:000348457603494International audienceno abstrac

Formation of Hexamethylenetetramine – Comment

International audienc

The mechanism of hexamethylenetetramine (HMT) formation in the solid state at low temperature

WOS:000307648700033International audienceThere is convincing evidence that the formation of complex organic molecules occurred in a variety of environments. One possible scenario highlights the universe as a giant reactor for the synthesis of organic complex molecules, which is confirmed by numerous identifications of interstellar molecules. Among them, precursors of biomolecules are of particular significance due to their exobiological implications, and some current targets concern their search in the interstellar medium as well as understanding the mechanisms of their formation. Hexamethylenetetramine (HMT, C6H12N4) is one of these complex organic molecules and is of prime interest since its acid hydrolysis seems to form amino acids. In the present work, the mechanism for HMT formation at low temperature and pressure (i.e. resembling interstellar conditions) has been determined by combining experimental techniques and DFT calculations. Fourier transform infra-red spectroscopy and mass spectrometry techniques have been used to follow experimentally the formation of HMT as well as its precursors from thermal reaction of NH3:H2CO:HCOOH and CH2NH:HCOOH ice mixtures, from 20 K to 330 K. DFT calculations have been used to compute the mechanistic steps through which HMT can be formed starting from the experimental reactants observed in solid phase. The fruitful interplay between theory and experiment has allowed establishing that the mechanism in the solid state at low temperature is different from the one proposed in liquid phase, in which a new intermediate (1,3,5-triazinane, C3H9N3) has been identified. In the meantime, aminomethanol has been unambiguously confirmed as the first intermediate whereas the hypothesis of methylenimine as the second is further strengthened

CARBON DIOXIDE INFLUENCE ON THE THERMAL FORMATION OF COMPLEXORGANIC MOLECULES IN INTERSTELLAR ICE ANALOGS

International audienceInterstellar ices are submitted to energetic processes (thermal, UV, and cosmic-ray radiations) producing complexorganic molecules. Laboratory experiments aim to reproduce the evolution of interstellar ices to better understandthe chemical changes leading to the reaction, formation, and desorption of molecules. In this context, the thermalevolution of an interstellar ice analogue composed of water, carbon dioxide, ammonia, and formaldehyde isinvestigated. The ice evolution during the warming has been monitored by IR spectroscopy. The formation ofhexamethylenetetramine (HMT) and polymethylenimine (PMI) are observed in the organic refractory residue leftafter ice sublimation. A better understanding of this result is realized with the study of another ice mixturecontaining methylenimine (a precursor of HMT) with carbon dioxide and ammonia. It appears that carbamic acid, areaction product of carbon dioxide and ammonia, plays the role of catalyst, allowing the reactions toward HMTand PMI formation. This is the first time that such complex organic molecules (HMT, PMI) are produced from thewarming (without VUV photolysis or irradiation with energetic particles) of abundant molecules observed ininterstellar ices (H2O, NH3, CO2, H2CO). This result strengthens the importance of thermal reactions in the ices’evolution. HMT and PMI, likely components of interstellar ices, should be searched for in the pristine objects ofour solar system, such as comets and carbonaceous chondrites

Overview of the organic matter present in Asuka 12236: a primitive meteorite?

International audienceMeteorites, which are the remnants of our protoplanetary disk, provide a rich source of chemical information to investigate the origin of organic matter that have fallen on Earth and may have thus contributed to the emergence of life. Among meteorites, carbonaceous chondrites that contain organic matter are among the most primitive materials in the Solar System. Asuka 12236, found in Antarctica in 2012, has been classified as a member of the CM group. According to the first mineralogical analyses (Kimura et al., 2020, Nittler et al., 2021), Asuka 12236 is among the most primitive member of this group showing very few signs of aqueous alteration in its mineralogy.Here, we have performed an overview of the soluble organic matter (SOM) present in this primitive meteorite, and compared it with other carbonaceous chondrites of the same family group. Two types of analysis were carried out on the SOM: a non-targeted analysis and then a targeted one on the basic so-called building blocks of life such as nucleobases and amino acids