For its next trick, NASA's Phoenix
Mars Lander will dig a trench in the Martian surface three times deeper than
any it has dug so far, as it completes its original three month-mission and
embarks upon its extended mission.
Today marked the last day of the
90-sol (1 sol is one Martian day) primary mission since the spacecraft landed
on Mars on May 25. Phoenix
will continue its
mission through the end of September, as NASA announced in July.
"As we near what we originally
expected to be the full length of the mission, we are all thrilled with how
well the mission is going," said Phoenix
project manager Barry Goldstein of NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Phoenix's main task for Sol 90 is to scoop
up a sample of dirt from the bottom of a trench called Stone
Soup, which is about 7 inches (18 centimeters) deep. This may not seem all that
deep, but it is the furthest
into the Martian surface that Phoenix
has penetrated so far. On a later day, Phoenix's
robotic arm will sprinkle some of the dirt from the sample into the third of
four cells in the lander's wet chemistry lab.
"In the first two cells we
analyzed samples from the surface and the ice interface, and the results look
similar. Our objective for Cell 3 is to use it as an exploratory cell to look
at something that might be different," said JPL's Michael Hecht, lead
scientist for Phoenix's
Microscopy, Electrochemistry and Conductivity Analyzer (MECA), which houses the
wet chemistry lab. "The appeal of Stone Soup is that this deep area may
collect and concentrate different kinds of materials."
MECA's wet chemistry lab dissolves samples
in water brought from Earth and looks for soluble minerals that might be in the
Martian dirt.
Stone Soup lies in a trough between
two of the polygonal hummocks (or mounds) that characterize the plains of the
Martian arctic where Phoenix
landed. While Phoenix
hit the subsurface layer of rock-hard water ice just 2 inches (5 centimeters)
beneath the ground in the center of one of the hummocks, it has yet to hit the
icy layer in the trough.
"The trough between polygons is
sort of a trap where things can accumulate," Hecht said. "Over a long
timescale, there may even be circulation of material sinking at the margins and
rising at the center."
The Stone Soup sample was one of two
sites scientists were considered for the wet chemistry lab's third sample.
"We had a shootout between
Stone Soup and white stuff in a trench called Upper Cupboard," Hecht said.
"If we had been able to confirm that the white material was a salt-rich
deposit, we would have analyzed that, but we were unable to confirm that with
various methods."
Salt would be an indicator of
whether or not liquid water had been present in the past, something that
Phoenix is looking for signs of to characterize Mars' potential past
habitability. Salt would concentrate in places that may have been wet. The
Stone Soup sample will also offer scientists a chance to analyze salt
distribution.
Phoenix is also analyzing a sample taken
from another trench at a depth
between the surface and the hard icy layer in its Thermal and Evolved-Gas
Analyzer, which heats up samples and analyzes the vapors they give off to
determine their composition.
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