Winter is coming – to Mars. In fact,
according to a new Nature Geoscience study,
it appears that it snows every night on the Red Planet, but not in the way you
might expect. Rather than having widespread snow cover, the rusty red soil sees
explosions of snow known as “ice microbursts” – something that only occurs in
the shadows. Think less White Christmas idyllic expansive snow
clouds, and more along the lines of snow ambushes.
Even weirder still, the
clouds have to be pretty low – about 1 to 2 kilometers (0.61 to 1.24 miles)
above the surface – or else the snow particles will be annihilated before
they reach the rusty soil. This is because the air pressure increases rapidly
as you head downwards, which in turns boosts the local temperature and causes
the snow to reach evaporation-ready temperatures.
Until this point, it was
thought that “snow precipitation occurs only by the slow sedimentation of
individual particles,” the authors explain in their study. However, their
research indicates that this isn’t the case, and that this sudden snow
explosion mechanism must have affected “Mars’ water cycle, past and present”.
Thanks to its incredibly
thin atmosphere, the thermal insulation on Mars is pretty low. At night, on the
surface, the mercury on Mars can plunge to temperatures as low as -73°C
(-100°F) on the equator and -125°C (-195°F) at the poles.
When exposed to sunlight,
however, water at the equator is given just enough energy to evaporate and form
low-pressure clouds – something that NASA’s Curiosity rover keeps an eye on from
time to time.
A team of researchers, led
by Aymeric Spiga – a
planetary scientist at the National Center for Scientific Research in Paris
(CNRS) – wanted to know if snowstorms could be produced by these clouds.
As aforementioned, at night,
the temperature of Mars drops considerably. CNRS’s atmospheric models reveal
that these clouds of water ice suddenly experience a rapid crystallization
event. At the same time, thanks to this rapid and localized redistribution of
heat, the air currents around them become unstable – and both conspire to cause
those water ice crystals to dramatically fall out.
Some reach the surface, but
if it’s left to heat up for too long as it falls, it sublimates into a gas.
These ephemeral streaks of snowfall that fail to reach their destination are
known as “virgas”. The atmospheric conditions on Mars are simply too unstable
and mercurial to allow regular snow to fall. Unlike Earth, the Red Planet is
a world of extremes –
and right now, only robots, not humans, get to experience it for real.
Sadly though, most of the
robots on Mars are unable to see these storms in person.
“Snowstorms
could be occurring above Curiosity or other rovers – undetected!” Spiga said,
adding that, indirectly, “snow precipitation has been spotted solely by the
Mars Phoenix lander at night, using LIDAR laser sounding.”
You may be wondering about
the ice caps on Mars too. They contain more ice than Earth’s Greenland Ice
Sheet, but they’re not just made of water ice, but frozen carbon dioxide. Could
you get sudden nighttime snowstorms of carbon dioxide too, instead of only
water?
“You
might. The convection in CO2 snowstorms would be triggered by
the energy released when CO2 vapor condenses into CO2 ice
particles; kind of like thunderstorms on Earth with the condensation of water.”
Spira said.
Mars isn’t the only
extraterrestrial world that experiences snow, by the way. Jupiter’s volcanic
moon Io experiences a global sulfuric snowstorm when
it moves into the gas giant’s shadow.