May 23, 2008

Arctic Plains of Mars Await Robot’s Sunday Landing

When NASA's
Phoenix Mars Lander sets down in the Martian arctic on Sunday, it will open a
new, icy frontier for scientists back on Earth.

Phoenix, a
stationary lander set to make a planned
May 25 descent
to the Martian surface, is going to where no probe has gone
before - the northern plains of Vastitas Borealis on Mars.

"Ten years
ago, you wouldn't have chosen this spot at all because it looks just like every
other part of Mars," said Phoenix principal investigator Peter Smith of the
University of Arizona. "A lot of the features aren't even named up there."

But it's
the promise of what
lies beneath
the frozen surface features, signs of untouched Martian water
ice first spotted by orbiters in 2002, which spurred NASA engineers and
researchers to launch the $420 million Phoenix last August.

its robotic arm like a backhoe, Phoenix is designed to dig down in to the
Martian soil to collect water ice samples. It will feed them into small onboard
ovens and beakers to determine if its landing site may have once been habitable
for microbial life.

"We believe
that the ice is somewhere between 4 and 6 centimeters (1.5 to 2.3 inches) below
the surface," Phoenix deputy principal investigator Deborah Bass of NASA's Jet
Propulsion Laboratory (JPL) told "It's not going to be ice
skating rink-pure, white, shiny ice. It's going to be permafrost - dust, dirt
and ice all mixed together."

Only one
NASA spacecraft - the ill-fated Mars Polar Lander - has ever targeted a polar
region of Mars for study, but that spacecraft crashed just before landing near
the planet's south pole in December 1999. NASA's past successful Mars landers,
the two Viking probes of the 1970s and '80s, and the hardy Spirit and
Opportunity rovers that still explore the Martian surface today, set down near
the planet's equatorial regions.

The history
of Earth's own climate change and the building blocks of life are preserved in
the ices near the Arctic Sea, Smith said during a Thursday mission briefing at
the Pasadena, Calif.-based JPL.

wondering if this is true on Mars," he added.

second choice

Phoenix's targeted
landing zone
lies within an ellipse about 50 miles (80 km) long and 12.4
miles (20 km) wide, with the bull's eye sitting in a broad, shallow valley some
800 feet (250 meters) deep.

It's rather
chilly, with the average temperature expected to range between minus 110 to 28
degrees Fahrenheit (minus 73 to minus 33 Celsius) during Phoenix's primary
six-month mission. The probe is landing during the late Martian spring at its
target site to take advantage of long, sunlit days for its solar arrays.

But the
landing site, known as Region D, was not the Phoenix mission team's first
choice. It was selected only after high-resolution images from NASA's Mars
Reconnaissance Orbiter spotted fields of large boulders that could topple Phoenix during landing in 2006.

had to be safe, there had to be ice," Smith told of the landing
site selection
. "We wanted some sort of surface features that showed there
was ice so we weren't just going by other measurements, and those are the
polygons that we see, which are the same as you see in the Arctic and Antarctic
[on Earth]."

are crack features created by changes in subsurface ice, he added. Phoenix's
Region D has those features in spades.

"What we
see is a mottled terrain, caused by ice expanding and contracting underneath
the soil, and it shapes the surface," Smith said Thursday.

Of key
interest is whether the Martian soil will contain leftover salts from
evaporated liquid water, which Mars researchers have long held as a basic
ingredient for life, in the relatively recent past, Smith said.  The
Spirit and Opportunity rovers have found solid evidence that liquid water once
soaked regions of the Martian equator in the ancient past, he added.

evidence of recent liquid water near the Martian north pole, he added, would be
a boon for researchers studying the planet's water history, as well as for future
missions designed specifically to seek out signs of life.

"We are
going in blind into the northern plains," Smith said. "So we are just looking for
evidence that it was habitable."

NASA's will broadcast the Phoenix Mars Lander's red planet arrival live on NASA
TV, with the next mission briefing set for 3:00 p.m. EDT (1900 GMT) on
Saturday, May 24. Click
for's Phoenix mission coverage and a link
Senior Writer Andrea Thompson contributed to this story from Pasadena,