In a big breakthrough, the Phoenix Mars Lander has detected
snow falling from Martian clouds. "Nothing like this view has ever been
seen on Mars," says Jim Whiteway of York
University, Toronto,
lead scientist for the Canadian-supplied Meteorological Station on Phoenix. "We'll be
looking for signs that the snow may even reach the ground."
A laser instrument designed to gather knowledge of how the
atmosphere and surface interact on Mars has detected snow from clouds about 2.5
miles above the spacecraft's landing site. The snow vaporizes before reaching
the ground.
"We are still collecting data and have lots of analysis
ahead, but we are making good progress on the big questions we set out for
ourselves," says Phoenix Principle Investigator Peter Smith of the
University of Arizona, Tucson.
The Phoenix
landed
on May 25 and has already confirmed a hard subsurface layer at its
far-northern site contains water-ice. Determining whether that ice ever thaws
would help answer whether the environment there could ever have supported life
of some form.
Scientific investigators also think they have discovered
calcium carbonate, the main composition of chalk, and particles that could be
clay. That's important because most carbonates and clays on Earth form only in
the presence of liquid water. Spacecraft soil experiments also have provided
evidence of past interaction between minerals and liquid water, processes that
occur on Earth.
The evidence for calcium carbonate in soil samples from
trenches dug by the Phoenix robotic arm comes from two laboratory instruments
called the Thermal and Evolved Gas Analyzer, or TEGA and the wet chemistry
laboratory of the Microscopy, Electrochemistry and Conductivity Analyzer, or
MECA. "We have found carbonate," says William Boynton of the University of Arizona, lead scientist for the TEGA.
"This points toward episodes of interaction with water in the past."
The TEGA evidence for calcium carbonate came from a
high-temperature release of carbon dioxide from soil samples. The temperature
of the release matches a temperature known to decompose calcium carbonate and
release carbon dioxide gas, which was identified by the instrument's mass
spectrometer.
The MECA evidence came from a buffering effect
characteristic of calcium carbonate assessed in wet chemistry analysis of the
soil. The measured concentration of calcium was exactly what would be expected
for a solution buffered by calcium carbonate.
Both TEGA and the microscopy part of MECA have turned up
hints of a clay-like substance. "We are seeing smooth-surfaced, platy
particles with the atomic-force microscope, not inconsistent with the
appearance of clay particles," says Michael Hecht, MECA lead scientist at
NASA's Jet Propulsion Laboratory in Pasadena,
CA.
The Phoenix
mission, originally planned for three months on Mars, is now in its fifth
month. However, it faces a decline in solar energy that is expected to curtail
and then end the lander's activities before the end of the year. Before power
ceases, the Phoenix
team will attempt to activate a microphone on the lander to possibly capture
sounds on Mars.
"For nearly three months after landing, the sun never went below
the horizon at our landing site," says Barry Goldstein, JPL Phoenix
project manager. "Now it is gone for more than four hours each night, and
the output from our solar panels is dropping each week. Before the end of
October, there won't be enough energy to keep using the robotic arm."
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