The weather
on Mars was much balmier in the recent past than scientists have previously
thought, according to a new interpretation of the formation of certain
landforms on the surface.
The finding
could have implications for the possibility of finding signs of life on
Mars.
Matthew
Balme, of The Open University in the United Kingdom, studied detailed images of
equatorial landforms taken by the HiRISE (High Resolution Imaging Science
Experiment) instrument onboard NASA's Mars Reconnaissance
Orbiter (MRO), currently circling the red planet.
Ample
evidence has been found to show that liquid water once covered parts of the
Martian surface in the early history of the planet several billion years ago,
but whether water flowed more recently has been less certain. Several studies
in recent years have started to point to possible evidence of more recent water
flow though.
For
example, a system of
gullies suggests the most recent period of water flow was only 1.25 million
years ago. Another recent study found that rivers might have
flowed on the Martian surface within the last billion years.
Balme's
analysis indicates that the landforms he examined formed by the melting of
ice-rich soils during "freeze-thaw" cycles that continued until as
recently as 2 million years ago. The pictures show polygonally patterned
surfaces, branched channels, blocky debris and mound/cone structures. These
features are similar to landforms on Earth in areas where permafrost is melting.
Permafrost
is ground that remains frozen for years or even millennia, such as in the Arctic, but which can melt if the climate changes.
"The
features of this terrain [on Mars] were previously interpreted to be the result
of volcanic processes. The amazingly detailed images from HiRISE show that the
features are instead caused by the expansion and contraction of ice, and by
thawing of ice-rich ground," Balme said. "This all suggests a very
different climate to what we see today."
All of the
landforms observed are in an outflow channel, thought to have been active as
recently as 2 million to 8 million years ago. Since the landforms exist within,
and cut across, the pre-existing features of the channel, this suggests that
they too were created within this timeframe.
"These
observations demonstrate not only that there was ice near the Martian equator
in the last few million years, but also that the ice melted to form liquid
water and then refroze. And this probably happened for many cycles," Balme
said.
Balme's
study, funded by a UK Science and Technology Facilities Council grant, will be
detailed in an upcoming issue of the journal Earth and Planetary Science
Letters.
Signs of
more recent water activity could aide the search for past or present life on
Mars as such life, or signs of it, would be more likely to have survived than
any that might have existed earlier in the planet's history.
"Given
that liquid water seems to be essential for life, these kinds of environments
could be a great place to look for evidence of past life on Mars," Balme
said.
advertisement
