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With the experiments on board of the EXPOSE facilities, various aspects of astro-
biology were investigated that could not be sufficiently approached by the use of
laboratory facilities on ground. The chemical set of experiments is designed to reach
a better understanding of the role of interstellar, cometary, and planetary chemistry
in the origin of life. Comets and meteorites are interpreted as exogenous sources of
prebiotic molecules on the early Earth. All data achieved from the astrobiological
experiments on both EXPOSE missions will add to the understanding of the origin
and evolution of life on Earth and on the possibility of its distribution in space or
origin elsewhere, as planet Mars.
The biology experiments used the full extraterrestrial spectrum of solar UV
radiation and suitable cutoff filters to study both the role of the ozone layer in
protecting our biosphere and the likelihood of resistant terrestrial microorganisms
(extremophiles) to survive in outer space. The latter studies will provide experi-
mental data to the lithopanspermia hypothesis, and they will provide basic data
to planetary protection issues. To get better insight into the habitability of Mars,
one set of samples was exposed to simulated Martian conditions (UV radiation
climate, pressure, atmosphere), with and without a protective cover of simulated
Martian soil. The biological test samples selected are hardy representatives of
various branches of life.
General Mission Description
There were two EXPOSE facilities, EXPOSE-E and EXPOSE-R. The EXPOSE-
E was launched on February 7, 2008, on board the Space Shuttle Atlantis and
was mounted on the ISS European module Columbus to the European Technology
Exposure Facility (EuTEF). EXPOSE-R was launched to the ISS on November
26, 2008, from Baikonur in Kazakhstan on board of a Progress capsule and was
mounted on the ISS Russian module Zvezda. EXPOSE-E provided accommodation
in three exposure trays for a variety of astrobiological test samples that were exposed
to selected space conditions: either to space vacuum, to solar electromagnetic
radiation at >110 nm and cosmic radiation (trays 1 and 3), or to simulated Martian
surface conditions (tray 2) (Baqué et al.
2013
). The different experiments consisted
of exposing solid molecules, gas mixtures, or biological samples to solar ultraviolet
(UV) radiation, cosmic rays, vacuum, and temperature fluctuations of the outer
space as the ISS repeatedly passed between areas of direct sunlight and the cold
darkness of Earth's shadow.
At the end of the exposition period, EXPOSE-E was brought back to the ground
in September 2009 as part of the Space Shuttle Discovery mission STS-128.
EXPOSE-R was brought back in 2011 by a Soyuz spacecraft. From the landing
site in Kazakhstan, the trays were returned via Moscow and distributed to scientists
for further analysis in their laboratory.
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