Contact LISA : H. Cottin

PI: H. Cottin

 

PHILEO : PHotochemistry In Low Earth Orbit

EXPERIENCES IN EARTH ORBIT

Among the hypotheses investigated to explain the origin of biological building blocks on Earth, seeding of the primitive Earth by organic molecules from outer space more than four billion years ago by comets, meteorites and micrometeorites, is of growing interest. These objects contain organic molecules, such as amino acids. Associated to the water in liquid phase, they might have led to the emergence of life. Therefore, knowing under what conditions the organic molecules could be imported into the primitive atmosphere is therefore a matter of first importance.

Solar ultraviolet (UV) radiation is a major source of energy for the initiation of chemical evolution in the Solar System. As a consequence, studies of the photolysis of molecules related to various astrophysical environments are common in many laboratories; compounds of interest may be in the gas or solid phase, including condensed volatile compounds at low temperatures. Nevertheless, it is not possible to simulate globally the entire range of wavelengths corresponding to the most energetic parts of the solar UV spectrum below 200 nm. The lack of a source of adequate fidelity notwithstanding, such studies are necessary to understand chemical evolution in astrophysical environments, particularly those with astrobiological relevance: environments rich in organic molecules (comets, asteroids, meteorites, Titan, localized regions of the interstellar medium), or those hypothesized to be rich in organics (Mars, Phobos, etc.).

Three experiments in Earth orbit are coordinated by LISA: UVolution, PROCESS and AMINO.

 

UVOLUTION, PROCESS and AMINO

These three experiments of astrochemistry are supported by the CNES since they were selected by ESA. The PI (Principal Investigator) of these three experiments is Hervé COTTIN.

These three projects are particularly about the study of molecules of cometary interest (in preparation to the interpretation of the results of the ROSETTA mission), the Titan’s chemistry (Cassini Huygens mission), or even the organic chemistry in the Martian environment (future missions in situ).

The molecules of prebiotic interest exposed include :

- Polyoxymethylene (POM) : this compound could be the cause of distributed sources of formaldehyde (H2CO) detected in the comets Halley and Hale-Bopp. In the primitive terrestrial oceans, the POM may have been a source of concentrated formaldehyde, the latter being involved in the formation of sugars.

- Polymers of HCN and poly (carbonsuboxide)(poly C₃0₂)

These polymers can be synthesized after transformation by photons and protons of ice containing cyanide (HCN) hydrogen or carbon monoxide (CO). They may be the parent molecules of distributed sources of CN and CO when they are heated or photolyzed. In addition, the hydrolysis of poly (HCN) can lead to the formation of amino acids.

- Hexamethylenetetramine (HMT)

It composes up to 60% of the refractory residue obtained from photolysis of a mixture of cometary ice analogue. Its hydrolysis can also lead to amino acids.

- Tholins : these are laboratory analogues of organic aerosols of Titan. Their exposure will help us understand the evolution and the degradation of these chemical structures and thus understand the transformation of these aerosols during sedimentation in Titan‘s atmosphere. These samples will also help us to better understand the cycle of nitrogen on Titan.

- Gaseous mixtures N₂ /CH₄ and Ar/ CH₄ : such mixtures are intended to study the photochemistry of methane in Titan‘s atmosphere, and even for sufficiently long exposure times, the formation of Tholins.

- No complex organic compound has been identified so far on Mars. Environmental conditions of the planet may be the reason for the partial or total degradation of any organic material, and as such, UV radiation has been proposed as a "stressful" factor. Thanks to the exposition experiments in Earth orbit, we can study the evolution of organic compounds submitted to UV radiation similar to the one reaching the surface of Mars. The exposed organic compounds are basically carboxylic acids.

- Carbonates are also part of the samples exposed in orbit, because their detection on Mars could provide more information about the history of liquid water on the surface of this planet, the evolution of its atmosphere and its climate. In addition some carbonate could also be produced by rudimentary biological activity (bio-minerals).

 

INSTRUMENTATION

EXPERIMENT	SUPPORT	LAUNCH/RETURN	DURATION OF EXPOSURE	INTEREST FOR
UVolution	BIOPAN 6 ( capsule FOTON M3)	14/09/07 ? 26/09/07	11,8 days	Comets, Titan, Mars
PROCESS	? EXPOSE-E installed on : International Space Station Columbus module	February 2008-August 2009 Space shuttle Atlantis flight STS 122	18 month	Comets, Titan, Mars, meteorites
AMINO	?EXPOSE-R installed on : Internationale space station Russian module Zvezda	March 2009- March 2011 Progress 31 P	24 month	Comets, Titan, meteorites

 

Figure 1. The automatic Russian capsule Foton, and the International Space Station

Figure 2. To the left - BIOPAN before the flight, lid open. To the right, BIOPAN after return to Earth (closed lid - diameter 35 cm, height 19 cm). The experiment is protected by a heat shield to avoid overheating of the experiments during reentry into the atmosphere.

Figure 3. Left: EXPOSES-R during its installation (photo credit: ESA); right: schema support for cells (77 x 77 x 26 mm)