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Mars
Express reveals the Red Planet’s volcanic past
Friday, March 14, 2008
Credits:
Neukum and HRSC Team, 2008, chronology: Neukum & Hartmann,
2001
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,
analyzing 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.
Source:
ESA
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