A vanished
glacier with a mysterious calling card suggests Mars went through many ice ages
in its very recent past.
A fresh
look at images from the Mars Reconnaissance Orbiter indicates thick glaciers
may have existed in the past 100 million years in the planet's equatorial
region, but vanished after planetary
wobbles changed the climate in certain areas.
"We've
gone from seeing Mars as a dead planet for three-plus billion years to one that
has been alive in recent times," said Jay Dickson, a geologist at Brown University and lead author of the study. "[The finding] has
changed our perspective from a planet that has been dry and dead to one that is
icy and active."
Strange
flow
Dickson and
other researchers looked at a dead-ended box canyon that slopes down into a
larger valley, and discovered glacial deposits of rocks marking a glacier's
advance heading upslope into the canyon – something which seems physically
impossible.
Here's how
it happened, according to the team's calculations: An ice pack at least .62
miles (1 kilometer) thick filled the larger valley to a height exceeding that
of the box canyon walls. Glacial ice flowed in the larger valley upstream of
the box canyon. So when the glacier reached the box canyon, the ice actually
pushed uphill into it.
When the
glacier ice retreated, it left behind the mystery of the box canyon and a
freshly-paved surface that suggests a recent event.
"We
don't see many craters on the glacial deposits," Dickson told SPACE.com.
"That's a yardstick we can use for measuring geological age."
Craters on
Mars, caused by meteor impacts, remain for hundreds of millions of years, and
their prevalence in an area can, like a wrinkled face, indicate an old surface.
Newer surfaces lack the multitudes of scars.
Multiple
episodes
The finding
further suggests that Mars has endured repeated periods of glacial activity
instead of just one single event, Dickson said, whose new work on this topic is
detailed in the May issue of the journal Geology.
The past
presence of glaciers could also spark further debate about whether water
flowed recently on Mars, given that pressure from the weight of glaciers
can melt ice. However, no direct evidence of recent flowing water has been
found.
"We
don't yet see evidence for melt water at this location, but the fact that there
was so much ice here expands our understanding of how active Mars climate has
been," said Dickson.
advertisement
