Glaciers Reveal
Martian Climate Has Been Recently Active
(23 April 2008) Brown University
researchers have found compelling evidence of thick, recurring glaciers on
Mars, a discovery that suggests that the Red Planet's climate was much more
dynamic than previously believed - and could change
again.
Results are published on the cover of Geology
magazine.
The prevailing thinking is that Mars is a planet whose active
climate has been confined to the distant past. About 3.5 billion years ago, the
Red Planet had extensive flowing water and then fell quiet - deadly quiet. It
didn't seem the climate had changed much since.
Now, in a research
article that graces the May cover of Geology, scientists at Brown University
think Mars' climate has been much more dynamic than previously believed. After
examining stunning high-resolution images taken last year by the Mars
Reconnaissance Orbiter, the researchers have documented for the first time that
ice packs at least 1 kilometre (0.6 miles) thick and perhaps 2.5 kilometres
(1.6 miles) thick existed along Mars' mid-latitude belt as recently as 100
million years ago. In addition, the team believes other images tell them that
glaciers flowed in localised areas in the last 10 to 100 million years - akin
to the day before yesterday in Mars' geological timeline.
This evidence
of recent activity means the Martian climate may change again and could bolster
speculation about whether the Red Planet can, or did, support
life.
"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
research analyst in the Department of Geological Sciences at Brown and lead
author of the Geology paper. "[The finding] has changed our perspective from a
planet that has been dry and dead to one that is icy and active."
In
fact, Dickson and his co-authors, James Head, a planetary geologist and the
Louis and Elizabeth Scherck Distinguished Professor at Brown, and David
Marchant, an associate professor in the Department of Earth Sciences at Boston
University, believe the images show that Mars has gone through multiple Ice
Ages - episodes in its recent past in which the planet's mid-latitudes were
covered by glaciers that disappeared with changes in the Red Planet's
obliquity, which changes the climate by altering the amount of sunlight falling
on different areas.
Dickson and the other researchers focused on an area
called Protonilus Mensae-Coloe Fossae. The region is located in Mars's
mid-latitude and is marked by splotches of mesas, massifs and steep-walled
valleys that separate the lowlands in the north from the highlands in the
south.
The team looked in particular at a box canyon set in a low-lying
plain. Images show the canyon has moraines - deposits of rocks that mark the
limits of a glacier's advance or the path of its retreat. The rock deposit
lines appear to show a glacier that flowed up the box canyon, which "physically
cannot happen," Dickson said.
Instead, the team deduced the ice in the
surrounding plain grew higher than the canyon's walls and then flowed downward
onto the top of the canyon, which had become the lowest point on the ice-laden
terrain. The team calculated the ice pack must have been one kilometre thick by
past measurements of height between the plain and the lip of the canyon. Based
on the ice flow patterns, the ice pack could have reached 2.5 kilometres at
peak thickness during a period known as the late Amazonian, the authors said.
The finding could have implications for the life-on-Mars argument by
strengthening the case for liquid water. Ice can melt two ways: by temperature
or by pressure. As currently understood, the Martian climate is dominated by
sublimation, the process by which solid substances are transformed directly to
vapour. But ice packs can exert such strong pressure at the base to produce
liquid water, which makes the thickness of past glaciers on its surface so
intriguing.
Dickson also looked at a lobe across the valley from the box
canyon site. There, he saw a clear, semi-circular moraine that had spilled from
an ancient tributary on to the surrounding plain. The lobe is superimposed on a
past ice deposit and appears to be evidence of more recent glaciation. Although
geologists can't date either event, the landscape appears to show at least two
periods in which glaciation occurred, bolstering their theory that the Martian
climate has undergone past Ice Ages.
(source: Brown University)
