Mars Express reveals the Red Planet's volcanic past (Forwarded)

ESA News
http://www.esa.int

14 March 2008

Mars Express reveals the Red Planet's volcanic past

A new analysis of impact cratering data from Mars reveals that the planet
has undergone a series of global volcanic upheavals. These violent
episodes spewed lava and water onto the surface, sculpting the landscape
that ESA's Mars Express looks down on today.

Using images from the High Resolution Stereo Camera (HRSC) on Mars
Express, Gerhard Neukum, Freie Universität Berlin, Germany, and colleagues
are discovering the history of the Red Planet's geological activity. "We
can now determine the ages of large regions and resurfacing events on the
planet," says Neukum. Resurfacing occurs when volcanic eruptions spread
lava across the planet's surface.

This work has suggested that the sculpting of the Martian surface has not
proceeded in a steady fashion, as it does on Earth. Rather, the team have
discovered that Mars has been wracked by violent volcanic activity five
times in the past, after the early supposedly warmer and wetter phase,
more than 3.8 thousand million years ago. In between these episodes, the
planet has been relatively calm.

The five volcanic episodes stretch throughout Martian history, occurring
around 3.5 thousand million years ago, 1.5 thousand million years ago,
400-800 million years ago, 200 million years ago and 100 million years
ago. Neukum estimates that the dates of the earlier episodes are correct
to within 100-200 million years and that the later dates are correct to
within 20-30 million years.

The ages have been estimated by counting the number of small craters that
appear on the landscape. The idea is simple: the older the surface, the
more craters it will have accumulated as meteorites of all sizes have
struck over the ages.

There has been a debate recently about the validity of this method. Some
researchers believe that the small craters are not produced by incoming
meteorites but by chunks of Martian rock blasted over the surface after a
single large impact. However American researchers, analysing seven years'
worth of images from the Mars Orbiter Camera (MOC) on NASA's Mars Global
Surveyor, have found new craters appearing on the surface during that
time.

"The present day cratering rate can be calculated from their
observations," says Neukum. It fits very closely with the cratering rate
he established from the Mars Express data with Bill Hartmann, Planetary
Science Institute, Tucson, Arizona, giving him confidence in the
estimates.

During these volcanic episodes, eruptions of lava flowed across Mars. The
internal heat generated by the volcanic activity also caused water to
erupt from the interior, causing wide-scale flash flooding.

As for why Mars behaves like this, geophysical computer-based models
suggest that the planet has been trying to establish a system of plate
tectonics, as there is on Earth where the crust is broken into slowly
moving plates. On Mars, the volcanic episodes represent the planet almost
achieving, but not actually attaining, plate tectonics -- and these
volcanic episodes might not be over.

"The interior of the planet is not cold yet, so this could happen again,"
says Neukum.

Far from revealing a geologically dead world, Mars Express is exposing a
place of subtle activity that could still erupt into something more
spectacular.

Notes for editors:

This article is based on results being presented today at the Lunar and
Planetary Science Conference at League City, Texas, USA.

For more information:

Gerhard Neukum, HRSC Principal Investigator
FU Berlin, Germany
Email: Gneukum @ zedat.fu-berlin.de

Agustin Chicarro, ESA Mars Express Project Scientist
Email: Agustin.Chicarro @ esa.int

[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaCP/SEMCPLM5NDF_index_1.html ]