Scientists with the Phoenix Mars mission yesterday declared for certain
that there is ice on the Red Planet, putting them an essential step
closer to answering the question that has driven three decades of Mars
exploration and centuries of Earth-bound speculation: Could there have
been life there?
Pictures beamed 170 million miles to Earth from the Phoenix lander atop Mars's northern polar plain erased any doubt about the presence of ice, they said.
But the evidence came in a roundabout way. Last Sunday, several
dice-size solids were observed at the bottom of a trench that had been
dug by Phoenix's robotic arm. On Thursday, they were gone.
The only reasonable explanation, the scientists said, is that the
objects were pieces of ice that evaporated into the dry Martian
atmosphere through a process called sublimation. And the presence of
ice means that Mars might once have had liquid water, which is
essential for life -- at least as it is known on Earth.
It is too soon to know whether the entire astrophysical community
will accept the disappearing objects reported yesterday as proof, but
the Phoenix researchers said they do not need any more convincing.
The rocket thrusters that slowed Phoenix to a soft landing revealed
a white, hard substance in the ground beneath it -- and tantalizingly
out of reach -- when the lander touched down on May 25. Similar white
material was visible when the robotic arm began to dig below the top
few inches of Martian soil.
One possibility was that it was salt of some sort. But ice was always the more likely explanation.
"Salt does not behave like that," said Mark Lemmon, a scientist at
Texas A&M University who is in charge of Phoenix's stereo
surface imager. "We found what we were looking for. This tells us we
have water ice within reach of the arm."
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