A series of huge cracks etched
across crater basins on Mars were caused by lakes that have since evaporated, a
new study concludes.
The cracks were initially
thought to have been merely a byproduct of thermal contractions in the Martian
permafrost. But a closer examination revealed the cracks were too big for that
explanation. Cracks caused by thermal contraction have a maximum diameter of
roughly 213 feet (65 meters), according to analytical models.
"They resembled the desiccation
cracks that we see on Earth in dried up lakes, said M. Ramy El Maarry of the
Max Planck Institute for Solar System Research. "These are the same type of
patterns you see when mud dries out in your back yard, but the stresses that
build up when liquids evaporate can cause deep cracks and polygons on the scale
I was seeing in the craters."
The average diameter of the
cracks in the survey was between 230 and 460 feet (70 to 140 meters).
"When a meteorite impacts with
the Martian surface, the heat can melt ice trapped beneath the Martian crust
and create what we call a hydrothermal system. Liquid water can fill the crater
to form
a lake, covered in a thick layer of ice. Even under current climatic
conditions, this may take many thousands of years to disappear, finally
resulting in the desiccation patterns," explained El Maarry.
It had been estimated that Mars
was covered in significant
amounts of water between 4.6 and 3.8 billion years ago. Rain and
river water would have collected inside impact crater basins and formed lakes
that may have existed for several thousand years before drying out.
However, these latest findings
suggest that in the northern hemisphere, some of the crater floor cracks could
have been formed much more recently.
Cracks on the crater floor were
identified using images taken by the MOC camera on Mars Global Surveyor and the
HiRISE and Context cameras on Mars Reconnaissance Orbiter. The findings were
presented today at the European Planetary Science Congress.
Correction: Due to an error in press materials provided by the European Planetary Science Congress Press Office, we incorrectly reported the lake-bed cracks to have an average diameter of 70-140 kilometers. The figure has been corrected to 70-140 meters.
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