EXPOSE

[3] The results will contribute to our understanding of photobiological processes in simulated radiation climates of planets (e.g. early Earth, early and present Mars, and the role of the ozone layer in protecting the biosphere from harmful UV-B radiation), as well as studies of the probabilities and limitations for life to be distributed beyond its planet of origin.

[4] EXPOSE data support long-term in situ studies of microbes in artificial meteorites, as well as of microbial communities from special ecological niches.

Their collective objective is to better understand the nature and evolution of organic matter present in extraterrestrial environments and their potential implications in astrobiology.

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.

[1] The biology experiments used the full extraterrestrial spectrum of solar UV radiation and suitable cut-off 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 different experiments consisted in exposing solid molecules, gas mixtures or biological samples to the solar ultraviolet (UV) radiation, cosmic rays, vacuum and temperature fluctuations of outer space as the ISS repeatedly passed between areas of direct sunlight and the cold darkness of Earth's shadow.

[3][7] 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.

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.

[10] To understand the chemical behavior of organic molecules in the space environment, 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 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.

[12] 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.

Also, the first-generation cells and spores derived from space-exposed samples exhibited elevated ultraviolet-C resistance when compared with their ground control counterparts.

[21] According to the researchers, the studies provide experimental information on the possibility of eukaryotic life transfer from one planet to another by means of rocks and of survival in Mars environment.

[20] Cryptoendolithic microbial communities and epilithic lichens have been considered as appropriate candidates for the scenario of lithopanspermia, which proposes a natural interplanetary exchange of organisms by means of rocks that have been impact ejected from their planet of origin.

Of the 2100 exposed wild-type Arabidopsis thaliana and Nicotiana tabacum (tobacco) seeds, 23% produced viable plants after being returned to Earth.

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 are under the coordination of the German Aerospace Center (DLR) and has been composed of scientists from different European countries, from United States and from Japan.

[1] In its 8 experiments of biological and chemical content, more than 1200 individual samples were exposed to solar ultraviolet (UV) radiations, vacuum, cosmic rays or extreme temperature variations.

[30] As the brown film should have impacted the quantity and quality of solar light that reached the test samples, affecting the core of the scientific goals, an investigation was started to identify the properties and the root cause of the colour change.