[meteorite-list] Mars Water Story Spawns Kudos and Controversy (Phoenix)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 26 Mar 2009 10:28:28 -0700 (PDT)
Message-ID: <200903261728.KAA00266_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n0903/24marswater/

Mars water story spawns kudos and controversy
BY CRAIG COVAULT
SPACEFLIGHT NOW
March 24, 2009

HOUSTON -- Phoenix science team findings that their spacecraft
discovered liquid water on the surface of Mars sailed through their
first scientific peer review unchallenged at the 40th Lunar and
Planetary Science Conference in Houston this week.

But some of the world's top planetary explorers said on background that
the Phoenix team arguments are being oversold on the potential for the
nature of the water found to significantly boost the chances for current
microbe habitability on Mars. This is because the water builds up as
thin films on the soil. They also note, however, that microbes can
thrive in such conditions.

Peter Smith, principal investigator for the mission at the University of
Arizona, said that peer review for the landmark findings are only just
beginning. "We have a long way to go" for full acceptance of the
discovery, he told Spaceflight Now.

Nilton Renno of the University of Michigan, who lead the water analysis,
told a standing-room-only hall filled with 500 people that the Phoenix
"evidence for liquid water is overwhelming."

NASA's Mars exploration motto should be updated to "follow the 'liquid'
water," he told the audience.

The report on liquid water was signed by 22 science team members but is
not supported by some key team members, like Bill Boynton, who headed
work with the spacecraft's TEGA Thermal and Evolved Gas Analyzer. He
does not believe the evidence is complete.

Smith, who heads the mission and also signed the water finding document,
is also the author of another paper that says Phoenix did not see any
liquid water.

Reminded that his stance in these two papers places him "with a foot in
each bucket, one filled with water and the other not," he noted "that's
a good observation."

Renno and his colleagues showed imagery of spheroids apparently splashed
onto one landing strut as evidence of the presence of liquid water. They
then cited point after point on temperature, pressure, chemistry, and
the affect of perchlorate salts as supporting evidence.

Another team member's analysis said the same data, combined with
seasonal variations and sun angles, indicate that liquid water can exist
between the ice and soil layers at the north polar landing site for 100
days out of each Martian year.

The movement and merger of the spheroids is what initially caught
Reeno's attention, but he has also conducted substantial ground-based
testing, including how the light wavelengths reflected from the
spheroids change under different sunlight conditions. Those changes seen
on Mars match what was found in the lab on Earth.

The existence of perchlorate salts that lower the freezing point for
water at the site is the key to the water, along with a presence of
calcium carbonate, which is unlike anything seen on Mars before.

Thermodynamic calculations offer additional evidence that salty liquid
water can exist where Phoenix landed and elsewhere on Mars. The
calculations also predict a droplet growth rate that is consistent with
what was observed. And they show that it is impossible for ice to
sublimate from the cold ground just under the strut of the lander's leg
and be deposited on a warmer strut, a hypothesis that has been suggested.

The lander's wet chemistry lab found evidence of perchlorates, which
likely include magnesium and calcium perchlorate hydrates. These
compounds have freezing temperatures of about -90 and -105 Fahrenheit,
respectively. The temperature at the landing site ranged from
approximately -5 to -140 Fahrenheit, with a median temperature around
-75 Fahrenheit. Temperatures at the landing site were mostly warmer than
this during the first months of the mission. Scientific literature was
also cited, predicting that brines would be found on Mars much like they
have been found in Antarctica, where they support exotic life forms.

The amount of carbonates is what really is telling us we had to have
liquid water, says Susanne Young of the science team. Apparent carbonate
seams are visible in meteorites that have come Mars and been recovered
on Earth. Sawdust from a carbonate layer in the Allen Hills meteorite
that in 1996 revealed potential evidence for life is being compared with
the Phoenix carbonate measurements directly on Mars.

All of this evidence has given the Mars Phoenix lander's north polar
site a higher rating for potential habitability for current and past
Martian life that is far greater than that found by either the Spirit
and Opportunity rovers, Mars Pathfinder, or the twin Viking landers of
the 1970s, says Carol Stoker, who headed habitability assessments for
the Phoenix mission.

The specific message the Phoenix data convey is "to search for life,
future missions should land at the same location Phoenix did," she said.

The entry, descent and landing planners for any future mission like that
would relish the knowledge that the landing area is a vast smooth arctic
plain with only a few large rocks and craters.
Received on Thu 26 Mar 2009 01:28:28 PM PDT