"Mars is not a dead planet -it undergoes climate
changes that are even more pronounced than on Earth."
James Head, planetary geologist, Brown University
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, recent studies by scientists at Brown University show that Mars' climate has been much
more dynamic than previously believed.
After examining stunning
high-resolution images taken last year by the Reconnaissance
Orbiter, researchers have documented for the first time that ice
packs at least 1 kilometer (0.6 miles) thick and perhaps 2.5 kilometers
(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 localized areas in the last 10 to 100
million years - a blink of the eye in Mars's 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 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. "[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,
and David Marchant, a associate professor at Boston University, believe the images show that 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.
NASA's Global Surveyor and Odyssey missions have provided
evidence of a relatively recent ice age on Mars. In contrast to Earth's
ice ages, a Martian ice age expands when the poles warm, and water
vapor is transported toward lower latitudes. Martian ice ages wane when
the poles cool and lock water into polar icecaps.
The catalysts of ice ages on appear to be much more extreme than
the comparable drivers of climate change on Earth. Variations in the
planet's orbit and tilt produce remarkable changes in the distribution
of water ice from Polar Regions down to latitudes equivalent to Houston
or Egypt. Researchers, using NASA spacecraft data and analogies to
Earth's Antarctic Dry Valleys, reported their findings in the journal
Nature.
"Of all the solar system planets, has the climate
most like that of Earth. Both are sensitive to small changes in orbital
parameters," said Head. "Now we're seeing that Mars, like
Earth, is in a period between ice ages," he said. 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.
Head and his team examined global patterns of landscape shapes and
near-surface water ice Nasa's orbiters mapped. They concluded a covering
of water ice mixed with dust mantled the surface of to latitudes
as low as 30 degrees, and is degrading and retreating. By observing the
small number of impact craters in those features and by backtracking
the known patterns of changes in Mars' orbit and tilt, they estimated
the most recent ice age occurred just 400 thousand to 2.1 million years
ago.
Marchant, a glacial geologist who spent 17 field seasons in the
Mars-like Antarctic Dry Valleys, said, "These extreme changes on Mars
provide perspective for interpreting what we see on Earth. Landforms on
that appear to be related to climate changes help us calibrate and
understand similar landforms on Earth. Furthermore, the range of
microenvironments in the Antarctic Dry Valleys helps us read the Mars
record."
According to the researchers, during a Martian ice age,
polar warming drives water vapor from polar ice into the atmosphere.
The water comes back to ground at lower latitudes as deposits of frost
or snow mixed generously with dust. This ice-rich mantle, a few meters
thick, smooths the contours of the land. It locally develops a bumpy
texture at human scales, resembling the surface of a basketball, and
also seen in some Antarctic icy terrains. When ice at the top of the
mantling layer sublimes back into the atmosphere, it leaves behind
dust, which forms an insulating layer over remaining ice. On Earth, by
contrast, ice ages are periods of polar cooling. The buildup of ice
sheets draws water from liquid-water oceans, which lacks.
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 kilometer 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
kilometers at peak thickness during a period known as the late
Amazonian, the authors said.
The finding could have implications for the life-on-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 vapor. 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.
Posted by Casey Kazan.
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Phoenix Lander and the 'Canals' of Mars
Sources:
http://news.brown.edu/pressreleases/2008/04/martian-glaciers
http://www.nasa.gov/home/hqnews/2003/dec/HQ_03415_ice_age.html
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