Mars Express Reveals
The Red Planet's Volcanic Past
(14 March 2008) 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 is an image of Daedalia Planum, located 1000 km south of Arsia Mons, a southern volcano of the Tharsis Montes. The image was taken on 19 July 2005, from a distance of 302 km from the surface. The image is centred at 235.4° east and 26.2° south. The scene spans a width of 100 km and the ground resolution is 25 m/pixel. (courtesy: ESA/ DLR/ FU Berlin (G. Neukum))
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 has 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.
This graph illustrates volcanic episodes in martian history, as inferred by G. Neukum et al. using pictures from the High Resolution Stereo Camera on board Mars Express. The image shows the five major volcanic episodes in the history of the Red Planet. The X-axis represents time, beginning from 4.5 thousand million years into the past, until the present. Scientific names for the epochs of martian history are given corresponding to the dates on the X-axis. The Y-axis shows the number of craters per square km that are larger than 1 km in diameter. The scale is logarithmic, which means that when a point that corresponds to lower than 1 on the Y-axis, a crater larger than 1 km in diameter is found over several tens of kilometres and so on. 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. (courtesy: Neukum and HRSC Team, 2008, chronology: Neukum & Hartmann, 2001)
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.
This article is based on results being
presented today at the Lunar and Planetary Science Conference at League City,
Texas, USA.
(source: ESA)
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