The planet
Mars conjures images of red rocks and arid, dusty plains, but as NASA's Phoenix
Mars Lander showed last year, it snows on Mars.
The
stationary robot observed ice
crystals falling to the martian surface near the end of its 5-month mission
in the arctic Vastitas Borealis plains last year. Today, scientists detail this
finding and others in a set of four papers in the journal Science. The
research could help shed light on the past and present action of water on the
martian surface and characterize the potential habitability of the red planet.
Phoenix landed on the red planet on May 25,
2008, with a mission to dig up and analyze samples of Martian dirt, confirm the
existence of a subsurface layer of water ice and observe the weather at its far
northern locale.
Cirrus
clouds...
Spacecraft
orbiting Mars had previously detected clouds high up in the Martian atmosphere
and low-level "ice fog," "but they've never seen precipitation,"
said James Whiteway of York University in Canada, the lead scientist for Phoenix's meteorological instruments.
From its
vantage point on the Martian surface, Phoenix used its LIDAR (light detection
and ranging) instrument, supplied by the Canadian Space Agency, to emit laser
pulses upward into the atmosphere and detected
clouds and precipitation above its landing site.
The clouds
were low-level, wispy clouds made up of ice crystals, similar to the cirrus
clouds that form over the Earth's polar regions in the winter. Whiteway also
likened them to the thin clouds jet planes fly through high in the Earth's
atmosphere.
"The
thin, wispy clouds up there have a similar water content," he told SPACE.com.
The clouds
didn't begin forming until around sol (Martian day) 80 or 90 of the mission,
when air temperatures were cool enough for water vapor in the atmosphere to
condense out, Whiteway explained.
As the
mission wore on, the clouds became thicker, lower to the ground and persisted
for longer.
...and
snow
The snow
didn't come until close to the end of the mission. It too is similar to the
snow that falls to the ground at Earth's
poles, sometimes called "diamond dust." Whiteway describes it as
"ice crystals sparkling in the air."
The snow
wasn't enough to build a snowmartian with, however, amounting to only a couple
micrometers (there are 1,000 micrometers in a millimeter) a day if it was
melted on the surface, Whiteway said.
The
observations show that "precipitation is a component of the hydrologic
cycle" on Mars, which was not suspected before the Phoenix mission,
Whiteway said.
How the
finding might impact our understanding of the global Mars water cycle — both
now and in the distant past, when the planet is suspected to have been warmer
and wetter — is not yet known.
The new
information can be used to modify Martian climate models, which currently don't
feature these newly discovered clouds and precipitation, "and then we'll
see what the implications are," Whiteway said.
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