From Newsgroup: sci.space.news


http://www.esa.int/esaSC/SEMT4TZ57NG_index_0.html

Mars Express sees deep fractures on Mars
European Space Agency 
6 May 2011

Newly released images from ESA's Mars Express show Nili Fossae, a system
of deep fractures around the giant Isidis impact basin. Some of these
incisions into the martian crust are up to 500 m deep and probably
formed at the same time as the basin.

Nili Fossae is a 'graben' system on Mars, northeast of the Syrtis Major
volcanic province, on the northwestern edge of the giant Isidis impact
basin. Graben refers to the lowered terrain between two parallel faults
or fractures in the rocks that collapses when tectonic forces pull the
area apart. The Nili Fossae system contains numerous graben
concentrically oriented around the edges of the basin.

It is thought that flooding of the basin with basaltic lava after the
impact that created it resulted in subsidence of the basin floor, adding
stress to the planet's crust, which was released by the formation of the
fractures.

A strongly eroded impact crater is visible to the bottom right of the
image. It measures about 12 km across and exhibits an ejecta blanket,
usually formed by material thrown out during the impact. Two landslides
have taken place to the west of the crater. Whether they were a direct
result of the impact or occurred later is unknown.

A smaller crater, measuring only 3.5 km across, can be seen to the left
of centre in the image and this one does not exhibit any ejecta blanket
material. It has either been eroded or may have been buried.

The surface material to the top left of the image is much darker than
the rest of the area. It is most likely formed of basaltic rock or
volcanic ash originating from the Syrtis Major region. Such lava
blankets form when large amounts of low-viscosity basaltic magma flow
across long distances before cooling and solidifying. On Earth, the same
phenomenon can be seen in the Deccan Traps in India.
 
Nili Fossae interests planetary scientists because observations taken
with telescopes on the Earth and published in 2009 have shown that there
is a significant enhancement in Mars' atmospheric methane over this
area, suggesting that methane may be being produced there. Its origin
remains mysterious, however, and could be geological or perhaps even
biological.

As a result, understanding the origin of methane on Mars is high on the
priority list and in 2016, ESA and NASA plan to launch the ExoMars Trace
Gas Orbiter to investigate further. Nili Fossae will be observed with
great interest.

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