- Mars appears to have been volcanically active more recently
than previously supposed, according to growing evidence from Europe's Mars
Express orbiter.
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- New estimates suggest volcanoes could have been active
between one million years ago and 20 million years ago, but more work is
needed to refine the dates
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- Previous spacecraft data suggested that volcanism on
Mars ceased some time around 600-500 million years ago.
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- Some researchers even speculate Mars could be volcanically
active today.
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- Mars Express project scientist Agustin Chicarro said
some volcanoes were "extremely young" based on current data.
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- "For volcanic phenomena, we may be talking about
a few million years, meaning in the order of one to 20 million years. But
this depends very much on the data we have and in a few months we may have
much better data," he told BBC News Online.
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- Crater counting
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- The ages were estimated by counting the number of impact
craters associated with volcanoes in images from the High-Resolution Stereo
Camera (HRSC) aboard Mars Express.
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- This is a method widely used by planetary scientists
to estimate the ages of planetary surfaces. However, these estimates are
relative, Dr Chicarro cautioned, and involve a certain amount of guesswork.
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- More cratered surfaces are deemed older, while smoother
surfaces are considered younger. This assumes a constant cratering rate
since the heavy bombardment that terrestrial planets underwent about four
billion years ago.
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- But there are complications on Mars, according to Dr
John Murray of the Open University, a co-investigator on the HRSC.
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- "You can get dust storms and ice near the poles,
so you find that the smaller craters are gone and the larger ones are still
there," he said.
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- Those volcanoes with the most recent activity appear
to be the massive Olympus Mons and three other giant volcanoes in Mars'
Tharsis region: Arsia Mons, Pavonis Mons and Ascraeus Mons (collectively
known as the Tharsis Montes).
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- Dr Chicarro is open-minded on the question of present-day
volcanism on Mars.
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- "It would have to be quite coincidental that just
in our terrestrial space age, volcanism on another planet would cease,"
he observed.
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- "If [volcanism] does exist, it doesn't mean we have
to have major volcanic flows. If, let's say, the last big volcanic explosion
happened a few million years ago, it could happen again - or not.
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- "There may also be much smaller domes elsewhere
that are still active. But at the moment, things like hydrothermal activity
are perhaps a bit more likely."
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- Hydrothermal, or hot water, systems similar to terrestrial
hot springs may once have existed on Mars.
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- The existence of hydrothermal activity on the Red Planet
today might make the existence of Martian life that little bit more plausible,
Dr Chicarro suggested.
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- On our own planet, hydrothermal systems are havens for
thermophilic (heat-loving) microbes and may have given life a foothold
on the early Earth.
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- Nick Hoffman of the University of Melbourne, Australia,
has suggested that ice towers might form next to steaming hydrothermal
vents on Mars. Microbial life forms live on chemical energy in similar
ice towers in Antarctica.
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- Previous estimates of the last volcanic activity on Mars
were largely based on data from Nasa's Viking missions in the 1970s.
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- © BBC MMIV http://news.bbc.co.uk/2/hi/science/nature/3535498.stm
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