December 4, 2014

Objectives of PROCESS, AMINO and PSS experiments

Comets are among the richest bodies in organic matter of the Solar System. Even if more than twenty volatile compounds can be observed in cometary atmospheres, there is to this day no direct indication about their nucleus molecular composition. Laboratory simulation experiments lead to think that much more complexe molecules might be synthetized in cometary ices from light molecules already observed. Among these molecules: the polyoxymethylene (POM : -(CH2-O-)n- ), the hexamethylenetetramine (HMT : C6N4H12) or the HCN polymers). In presence of liquid water, these molecules can have major exobiological implications once imported on Earth during impacts or by micrometeorits sedimentation of cometary origin in the atmosphere (sugar synthesis from formaldehyde emited by POM, and amino acids by HCN polymers hydrolysis). We search to determine if these molecules can survive in space on cometary grains after ejection from the nucleus, before an eventual import on Earth (exposition of the pure molecule, or in mineral or organic matrix in open cells), and if the degradation of these molecules (and their matrix in the case of an organic matrix) can be at the origin of the observed distributed sources in comets (H2CO, CN, CO...).

For Titan chemistry, we expose tholins (laboratory analogues of organic aerosols of Titan atmosphere) synthetized in laboratory under differents conditions to determine the evolution of their structures and optical properties, always with the possibility to collect degradation volatile residues. We also try to study the methane photochchemistry by exposing mixtures of N2/CH4 and Ar/CH4 in sealed cells.

For the Martian chemistry, we try to evaluate in which extent organic molecules could be detected at the surface of the planet by future exploration missions (amino acids, hopanes, hopanoids and benzoic acid).

For meteorites, our studies deal with amino acids stability and chemical reactivity. The compounds to be irradiated have been selected for their prebiotic interest and for the diversity of their functional groups. To dismiss all contamination possibility, proteic amino acid D enantiomers have been chosen for these studies. It is more particularly glycine (Gly), alanine (Ala), isobutyric amino acid (Aib), aminobutyric acid (Abu), serine (Ser), valine (Val), aspartic acid (Asp), dileucine (Leu2).

In AMINO experiment framework, one part of the samples is dedicated to the study of the hypothesis of the "RNA World" according to which RNA could have had a primordial role at the origins of life due to its informational and catalytic properties. It is thus important to study the small RNAs stability in environmental conditions similar to the primal terrestrial environment, where they were subjected to powerful solar radiation. In this framework, the goal is to expose a small ribozymic RNA (ADHR1) and to monitor its auto-cut catalytic activity after exposition. A study is performed on RNA alone or traped in salt (NaCl) to mimic the RNA conservation in salt deposits such as the ones found nowadyas on Mars.

In general, the objectives of these experiments is to measure the photolysis kinetics of the exposed products, and thus to evaluate their photochemical lifetime when they are exposed to the solar radiation.

The organic matter, base of the prebiotic chemistry, could have had a partially extraterrestrial origin. Indeed, the primitive Earth knew, over 4 billion years ago, an intense phase of bombing by comets, meteorites and micrometeorites. These objects contian organic molecules, amino acids for example, which could, when associated with liquid water, conduct to the apparition of life.

The objective is thus to understand what are the chemical mechanisms  at the origine of the evolution of the organic matter in the interstellar medium, the comets and the asteroids, for example which molecules can be present, or be rapidly destroyed or transformed.

The Photochemistry on the Space Station experiment (PSS) is a project very similar to PROCESS and AMINO experiments that were performed also with CNES support and with Hervé COTTIN from LISA as PI (Principal Investigator), this experiment aims at studying the behaviour of a large range of organic molecules (Carbone, hydrogen and eventually nitrogen and Oxygen compounds) when submitted to space conditions.

But one of the novelty of the new campaign, in addition to the analysis of photolysis of exposed molecules, is to study the resistance of different kinds of biochips faced with space constraints, such as the cosmic radiations and the extreme variations of temperature. These Biochips have a detection principle based on the recognition of a target molecule by affinity receptors (antibodies and aptameres) fixed on a solid surface. They could be used as sensors during planetary missions to help researching biomolecules of extraterrestrial life, past or present, in the Solar system. PSS is their space christening. If the biochips resist and keep the detection and identification capabilities when they will return, new in-situ analysis instruments based on this technology will appear in the next years.

More information about this last experiment (in French)