Mars Astrobiology: Recent Status and Progress - Planetary Exploration and Science: Recent Results and Advances - page 226

EXPOSE-R was equipped with three trays housing eight experiments and 3
radiation dosimeters. Each tray was loaded with a variety of biological organisms
including plant seeds and spores of bacteria, fungi, and ferns that were exposed to
the harsh space environment for about one and a half years. The ROSE (response of
organisms to space environment) group of experiments is under the coordination of
the German Aerospace Center (DLR) and has been composed of scientists from
different European countries, from USA, and from Japan. In its 8 experiments
of biological and chemical content, more than 1,200 individual samples were
exposed to solar ultraviolet (UV) radiations, vacuum, cosmic rays, or extreme
temperature variations. In their different experiments, the involved scientists are
studying the question of life's origin on Earth, and the results of their experiments
are contributing to different aspects of the evolution and distribution of life in the
universe.
EXPOSE-E Results
PROCESS Experiment
The search for organic molecules at the surface of Mars is a top priority of Mars
exploration space missions. Therefore, a key step in interpretation of future data
collected by these missions is to understand the preservation of organic matter in
the Martian environment. A 1.5-year exposure to Mars-like surface UV radiation
conditions in space resulted in complete degradation of the organic compounds
(glycine, serine, phthalic acid, phthalic acid in the presence of a mineral phase,
and mellitic acid). Their half-lives were between 50 and 150 h for Martian surface
conditions.
To understand the chemical behavior of organic molecules in the space envi-
ronment, amino acids and a dipeptide in pure form and embedded in meteorite
powder were exposed to space conditions for 18 months; the samples were returned
to Earth and analyzed in the laboratory for reactions caused by solar UV and cosmic
radiation. The results show that resistance to irradiation is a function of the chemical
nature of the exposed molecules and the wavelengths of the UV light. The most
altered compounds were the dipeptide, aspartic acid, and aminobutyric acid. The
most resistant were alanine, valine, glycine, and aminoisobutyric acid. The results
also demonstrate the protective effect of meteorite powder, which reemphasizes the
importance of exogenic contribution to the inventory of prebiotic organics on early
Earth.
ADAPT Experiment
Bacterial endospores of the highly UV-resistant Bacillus subtilis strain MW01 were
exposed to low-Earth orbit and simulated Martian surface conditions for 559 days.
It was clearly shown that solar extraterrestrial UV radiation ( 110 nm) as well
as the Martian UV spectrum ( 200 nm) was the most deleterious factor applied;
in some samples, only a few spore survivors were recovered from Bacillus subtilis
MW01 spores exposed in monolayers. However, if shielded from solar irradiation,