Geoscience Reference
In-Depth Information
Shergotty
The Shergotty meteorite, a 4 kg Martian meteorite, fell on Earth on Shergotty,
India, on August 25, 1865, and was retrieved by witnesses almost immediately. This
meteorite is relatively young, calculated to have been formed on Mars only 165 Ma
ago from volcanic origin. It is composed mostly of pyroxene and thought to have
undergone pre-terrestrial aqueous alteration for several centuries. Certain features in
its interior suggest remnants of a biofilm and its associated microbial communities.
Work is in progress on searching for magnetite within alteration phases.
Yamato 000593
Yamato 000593 is the second largest meteorite from Mars found on Earth. Studies
suggest the Martian meteorite was formed about 1.3 billion years ago from a lava
flow on Mars. An impact occurred on Mars about 12 Ma ago and ejected the
meteorite from the Martian surface into space. The meteorite landed on Earth in
Antarctica about 50,000 years ago. The mass of the meteorite is 13.7 kg (30 lb) and
has been found to contain evidence of past water movement. At a microscopic level,
spheres are found in the meteorite that are rich in carbon compared to surrounding
areas that lack such spheres. The carbon-rich spheres may have been formed by
biotic activity according to NASA scientists.
8.5.1.4
Geysers on Mars
The seasonal frosting and defrosting of the southern ice cap results in the formation
of spiderlike radial channels carved on 1-m-thick ice by sunlight. Then, sublimed
CO
2
- and probably water - increases pressure in their interior producing geyser-like
eruptions of cold fluids often mixed with dark basaltic sand or mud. This process is
rapid, observed happening in the space of a few days, weeks, or months, a growth
rate rather unusual in geology - especially for Mars.
A team of Hungarian scientists proposes that the geysers' most visible features,
dark dune spots and spider channels, may be colonies of photosynthetic Martian
microorganisms, which over winter are beneath the ice cap, and as the sunlight
returns to the pole during early spring, light penetrates the ice; the microorganisms
photosynthesize and heat their immediate surroundings. A pocket of liquid water,
which would normally evaporate instantly in the thin Martian atmosphere, is trapped
around them by the overlying ice. As this ice layer thins, the microorganisms show
through gray.
When the layer has completely melted, the microorganisms rapidly desiccate and
turn black, surrounded by a gray aureole. The Hungarian scientists believe that even
a complex sublimation process is insufficient to explain the formation and evolution
of the dark dune spots in space and time.
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