[FPSPACE] First liquid water spotted on Mars? Phoenix lander may have photographed this

[Peter Pesavento]

>From New Scientist (UK)
two photos included at original webpage

 

http://www.newscientist.com/article/dn16620-first-liquid-water-may-have-been
-spotted-on-mars.html?page=1

 


First liquid water may have been spotted on Mars 


*	01:16 18 February 2009 by
<http://www.newscientist.com/search?rbauthors=David+Shiga> David Shiga 

NASA's Phoenix lander may have captured the first images of liquid water on
Mars - droplets that apparently splashed onto the spacecraft's leg during
landing, according to some members of the Phoenix team.

The controversial observation could be explained by the mission's previous
discovery of perchlorate salts in the soil, since the salts can keep water
liquid at sub-zero temperatures. Researchers say this antifreeze effect
makes it possible for liquid water to be widespread just below the surface
of Mars, but point out that even if it is there, it may be too salty to
support life as we know it.

A few days after Phoenix landed
<http://www.newscientist.com/article/dn13979-phoenix-lander-safely-touches-d
own-on-mars.html>  on 25 May 2008, it sent back an image showing mysterious
splotches of material attached to one of its legs. Strangely, the splotches
grew in size over the next few weeks, and Phoenix scientists have been
debating the origin of the objects ever since.

One intriguing possibility is that they were droplets of salty water that
grew by absorbing water vapour from the atmosphere. Arguments for this idea
are laid out in a study by Phoenix team member Nilton
<http://aoss.engin.umich.edu/people/nrenno>  Renno of the University of
Michigan in Ann Arbor, and co-authored by 21 other researchers, including
the mission's chief scientist, Peter Smith of the University of Arizona in
Tucson. The study <http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1440.pdf>
(pdf) will be presented in March at the Lunar and Planetary
<http://www.lpi.usra.edu/meetings/lpsc2009/>  Science Conference in Houston,
Texas.


Widespread water


Gaping canyons and river-like channels attest to the fact that large amounts
of liquid water once flowed on Mars. The surface now appears dry, though the
changing
<http://www.newscientist.com/article/dn10740-water-flows-on-mars-before-our-
very-eyes.html>  appearance of some crater gullies over a period of several
years has hinted at the existence of subsurface aquifers that occasionally
release bursts of water.

Certainly, at Phoenix's landing site in the Martian arctic, it is too cold
for pure water to exist in liquid form - the temperature never rose above
-20° C during the five-month-long mission.

But salty water can stay liquid at much lower temperatures. And perchlorate
<http://www.newscientist.com/article/dn14474-phoenix-soil-results-released-a
fter-days-of-speculation.html>  salts, which were detected for the first
time on Mars by Phoenix, would have an especially dramatic 'antifreeze'
effect. An extremely salty mixture of water and perchlorates could stay
liquid all the way down to -70° C.

If perchlorates are widespread on Mars at high concentrations, then pockets
of liquid water might also be widespread below the planet's surface.
"According to my calculations, you can have liquid saline solutions just
below the surface almost anywhere on Mars," Renno told New Scientist.

And Phoenix may have already snapped images of water kept liquid thanks to
perchlorate salts.


Melted ice


The clumps may have come from ice melted by the lander's thrusters.
Phoenix's thrusters cleared away the topsoil at the landing site, exposing
an ice
<http://www.newscientist.com/article/dn14044-phoenix-digs-up-possible-ice-on
-mars.html>  layer below.

Laboratory experiments the team carried out on Earth suggest the thrusters
would have melted the top millimetre or so of this layer and then could have
splashed the melted water onto the lander's leg. If enough perchlorate was
mixed into the droplets, they could have stayed liquid during the daytime,
though they may have frozen each night.

Alternatively, Renno says the clumps may have come from a thin layer of
perchlorate-rich water that was already liquid.

Why does the team think the clumps might be liquid water in the first place?
The argument rests on the fact that salt is hygroscopic, meaning it attracts
water <http://en.wikipedia.org/wiki/Hygroscopic> . So droplets of salty
fluid on Mars would tend to absorb water vapour from the atmosphere,
explaining why the clumps grew over time. Indeed, at the temperatures and
humidity observed at the Phoenix site, the expected growth rate of salty
droplets matches the observations, the team says.

Most provocatively, a series of images (pictured here
<http://www.newscientist.com/data/images/ns/cms/dn16620/dn16620-2_800.jpg> )
appears to show one candidate droplet growing after absorbing the liquid
from its neighbour - a behaviour the team ascribes to liquid water.


'Convincing story'


Mark Bullock of the Southwest Research Institute in Boulder, Colorado, who
has experimented with salty water under Martian conditions but was not
involved in Renno's study, is impressed with the results. "I think it makes
a pretty convincing story for the existence of exotic brines on the Phoenix
lander leg," he told New Scientist.

But Phoenix team member Michael Hecht of NASA's Jet Propulsion Laboratory in
Pasadena, California, disagrees. He says the clumps were probably patches of
ice that formed and grew from water vapour freezing onto the leg.

Renno counters that ice would be more likely to sublimate than grow on the
leg, which would have been warmed by heat leaking from the spacecraft's
body. Indeed, the layer of ice exposed beneath Phoenix was observed to
vaporise over time.

But Hecht argues that the leg may have been colder than its surroundings.
Though there were no temperature sensors on the leg, he says the surface of
the ice patch was warmed by direct sunlight, whereas the lander leg was in
shadow. Water vapour that sublimated from the ice below Phoenix might have
recondensed as ice on its cold leg, he argues.


Too salty for life?


Phoenix, which ran
<http://www.newscientist.com/article/dn16010-nasa-bids-farewell-to-phoenix-l
ander.html>  out of solar power five months after landing, is not expected
to wake up again, so there is no way to further investigate the bumps on its
leg. But Renno hopes to bolster the case for salty droplets with future
experiments on perchlorate-rich water under Mars-like conditions. He says
those tests should be completed in a few months.

Regardless of their outcome, the discovery of perchlorates in the Martian
soil suggests that pockets of liquid water may dot the planet. Could life
eke out an existence in such pockets? "It's possible," Renno says, pointing
out that there are microorganisms on Earth that can survive
<http://www.newscientist.com/article/dn14208-the-most-extreme-lifeforms-in-t
he-universe.html>  extreme conditions, including very salty water.

But it may
<http://www.newscientist.com/article/dn14016-was-mars-too-salty-for-life.htm
l>  be difficult. One way to describe salt concentrations is with a number
called the water activity, which is 1 for pure water, and smaller for
saltier solutions. The most salt-tolerant organism known on Earth is a
fungus that can survive down to a water activity of 0.61.

However, to lower water's freezing point all the way down to -70 °C with
perchlorates, the necesssary concentration of perchlorate salts would give a
water activity of just 0.5. "If you tried to put any kind of life-form you
can imagine on Earth in a brine solution of that sort, the water would be
sucked out of the cells," mission leader Peter Smith told New Scientist.

 

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