Geoscience Reference
In-Depth Information
Cryptoendolithic microbial communities and epilithic lichens have been consid-
ered 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. A 1.5-year exposure experiment in space
was performed with a variety of rock-colonizing eukaryotic organisms.
Selected organisms are known to cope with the environmental extremes of their
natural habitats. It was found that some - but not all - of those most robust microbial
communities from extremely hostile regions on Earth are also partially resistant
to the even more hostile environment of outer space, including high vacuum,
temperature fluctuation, the full spectrum of extraterrestrial solar electromagnetic
radiation, and cosmic ionizing radiation. Although the reported experimental period
of 1.5 years in space is not comparable with the time span of thousands or millions of
years believed to be required for lithopanspermia, the data provide the first evidence
of the differential hardiness of cryptoendolithic communities in space.
SEEDS Experiment
The plausibility that life was imported to Earth from elsewhere was tested by
subjecting plant seeds to 1.5 years of exposure to solar UV, solar and galactic cosmic
radiation, temperature fluctuations, and space vacuum outside the International
Space Station. Of the 2100 exposed wild-type
Arabidopsis thaliana
and
Nicotiana
tabacum
(tobacco) seeds, 23 % produced viable plants after being returned to
Earth. Germination was delayed in seeds shielded from solar light, yet full survival
was attained, which indicates that longer space travel would be possible for seeds
embedded in an opaque matrix. The team concluded that a naked, seed-like entity
could have survived exposure to solar UV radiation during a hypothetical transfer
from Mars to Earth, and even if seeds do not survive, components (e.g., their DNA)
might survive transfer over cosmic distances.
The radiation dose during the mission was 1823.98 MJ m
2
for PAR,
269.03 MJ m
2
for UVA, 45.73 MJ m
2
for UVB, or 18.28 MJ m
2
for UVC.
Registered sunshine duration during the mission was about 152 days (about 27 %
of mission time). The surface of EXPOSE was most likely turned away from the
Sun for considerably longer time. The highest daily averaged absorbed dose rate of
426 Gy per day came from the “South Atlantic Anomaly” (SAA) region of the
inner radiation belt; galactic cosmic rays (GCR) delivered a daily absorbed dose rate
of 91.1 Gy per day, and the outer radiation belt (ORB) source delivered 8.6 Gy
per day.
EXPOSE-R Results
TROPI Experiment
TROPI, or “Analysis of a Novel Sensory Mechanism in Root Phototropism,” is an
experiment on the International Space Station (ISS) to investigate the growth and
development of plant seedlings under various gravity and lighting combinations. It
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