[meteorite-list] Water Flows on Mars, Before Our Very Eyes

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 6 Dec 2006 12:23:13 -0800 (PST)
Message-ID: <200612062023.MAA05014_at_zagami.jpl.nasa.gov>

http://space.newscientist.com/article/dn10740

Water flows on Mars, before our very eyes
David Shiga
New Scientist
06 December 2006

Liquid water has flowed on the surface of Mars within the past five
years, suggest images by the now lost Mars Global Surveyor (MGS). The
results appear to boost the chances that Mars could harbour life.

In 1999, MGS spotted gullies carved on the sides of Martian slopes.
Thousands of gullies have been imaged since then, most recently by the
Mars Reconnaissance Orbiter (MRO) (see Stunning snaps from the best
camera ever sent to Mars
<http://space.newscientist.com/article/dn10714-stunning-snaps-from-best-camera-ever-sent-to-mars.html>).

Many scientists believe the gullies were carved by liquid water,
although others have argued they are due to avalanches of carbon dioxide
gas or rivers of dust.

The gullies appear to have formed sometime in the past several hundred
thousand years, since impact craters have not accumulated on top of
them. But exactly how long ago material flowed through them has not been
clear.

Now, new flows have appeared in two of the gullies monitored by MGS,
showing that they have been active within the past several years. The
research was led by Michael Malin of Malin Space Science Systems in San
Diego, California, US. That company operates the Mars Orbiter Camera on
MGS, which acquired the images.

Ice shell

One gully on a crater wall that was imaged in 2001 was found to have
filled with light-coloured material when it was re-imaged in 2005. A
similar new light-coloured deposit appears in a 2004 image of crater
gullies previously imaged in 1999.

The researchers suggest the deposits were made by liquid water flowing
out from beneath the surface. The researchers estimate that each flow
would have involved 5 to 10 swimming pools' worth of water.

It would have been similar to a flash flood in the desert, says team
member Ken Edgett of Malin Space Science Systems. "If you were there and
this thing was coming down the slope, you'd probably want to get out of
the way," he says.

Any liquid water exposed to Mars's atmosphere would quickly freeze, but
Malin's team says even if the exterior of the flow rapidly freezes,
water could continue flowing much farther inside this ice shell,
developing into a thick mixture of ice and sediment that would
eventually freeze completely.

Active today

In Mars's thin atmosphere, ice left on the surface would quickly
sublimate, changing from a solid to a gas, and disappear. But water
vapour diffusing out from deeper in the mixture of ice and sediment
could repeatedly coat the surface with frost, maintaining its light
colour long enough for MGS to spot it, the researchers say.

Alternatively, salt deposited from salty water or sediment placed there
by water flow may be responsible for the light colour.

MGS team member Phil Christensen of Arizona State University in Tempe,
US, who was not involved in this study, says he is convinced that the
gullies were formed by the action of liquid water.

"It says something is actively going on today in at least some of these
gullies and one intriguing possibility is that water was released," he
told New Scientist.

"I think they make a pretty good case that these aren't simply dust
avalanches or some wind-related process," he says. He adds that the
sublimating carbon dioxide scenario is even less likely, because
temperatures in the regions where the gullies are found - between 30?
and 60? from the equator - are too high for the gas to get frozen in the
first place.

Just dust?

Allan Treiman of the Lunar and Planetary Institute in Houston, Texas,
US, agrees that something flowed recently to make the observed changes.

But he is not convinced that water was involved. "There is no direct
evidence of water in the images - only that something flowed downhill.
My money is on sand and dust, because there's lots and lots of sand and
dust on Mars."

Streaks on slopes have been observed before and interpreted as the
result of dust avalanches. But these appear to be a separate phenomenon
from the new light-coloured gully deposits, the researchers say.

Newly formed dust streaks have been observed, but are always dark. The
dust streaks are also usually observed in areas where the surface
clearly has a thick coating that could be dust, unlike the two craters
in question. And dust streaks have never been observed on the same
slopes where gullies carve into the surface.

The formation of new gullies has been observed before also, but these
were on the sides of sand dunes, and were more clearly related to
avalanching sand (see Landslips, impacts and eroding ice revealed on
Mars
<http://space.newscientist.com/article/dn8029-landslips-impacts-and-eroding-ice-revealed-on-mars.html>).

Melting snow

If the deposits are the result of liquid water flow, the source of the
water is not clear. Malin's team suggests it comes from underground
aquifers, perhaps kept liquid at low temperatures with the help of high
salt concentrations.

Christensen says it could result from the removal of dust from a
hypothetical layer of snow, which would then melt when exposed to sunlight.

The SHARAD radar on MRO is potentially capable of detecting any
underground pockets of water that the flows might have come from, Malin
says. "We're hopeful that as SHARAD flies of over these locations it may
be able to detect these subsurface aquifers," he says.

The new evidence that liquid water may flow on Mars today boosts the
chances that life could be present, Christensen says. "I believe that we
have found places on Mars where you could take terrestrial life forms
that live on snow or in aquifers and put them there and they would
survive," he says.

Malin's team also reports in the same study the formation on Mars of 20
new craters between 2 and 150 metres across since 1999, confirming the
previously estimated rate of crater formation and reinforcing the view
that crater-free areas of Mars must truly be young or recently modified.

The discovery may be one of the last from MGS, which went silent shortly
before its 10th launch anniversary in early November, and has not been
heard from since (see Europe joins hunt for missing Mars probe
<http://space.newscientist.com/article/dn10669-europe-joins-hunt-for-missing-mars-probe.html>).

Journal reference: Science (vol 314, p 1573)
Received on Wed 06 Dec 2006 03:23:13 PM PST