SNOWSTORMS more violent than any on Earth may have hit Mars 鈥� and could occasionally strike again, despite its extremely dry climate.
No rain or snowstorms have ever been observed on Mars, which has been mostly cold and dry for about 3.5 billion years. But mineral evidence suggests short-lived lakes have formed intermittently on the planet, sometimes inside craters. Lakes may form when meteorite impacts heat ice in the crust or when underground reservoirs of water kept liquid by geothermal heat leak onto the surface.
of the University of California, Berkeley, and colleagues wondered how the planet鈥檚 weather might change in the presence of such lakes. So they plugged Mars鈥檚 present-day conditions 鈥� which may be much the same as they have been for the last 3 billion years or so 鈥� into weather-prediction software, and modelled what would happen if the planet had a 65-kilometre-wide lake near the equator.
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The results were dramatic. Heat from the lake, although minimal, stirred the thin Martian atmosphere vigorously. In the simulation, this caused a plume of warm, moist air to rise from the lake at a top speed of 194 kilometres per hour, similar to the updraft speed in thunderstorms on Earth.
As the rising water condensed to ice within the plume, it formed a storm cloud that stretched to 35 kilometres in altitude. Earth鈥檚 storm clouds are stopped about 20 kilometres up by a layer of warm air heated by ozone, which absorbs the sun鈥檚 ultraviolet rays. Mars has no ozone layer to heat its upper atmosphere, so clouds can rise higher there. The simulated storm cloud dropped about 10 centimetres of snow per hour, comparable to extreme snowstorms on Earth ().
鈥淚magine being in the most severe thunderstorm you鈥檝e been in, where it鈥檚 really dark and ominous-looking,鈥� says team member of the Southwest Research Institute in Boulder, Colorado. 鈥淭hen make it darker and more ominous, with snow coming down at an unbelievable blizzard-like rate.鈥�
Periodic changes in Mars鈥檚 tilt 鈥� thought to occur due to gravitational tugs by Jupiter 鈥� could later melt the snow. That may explain the presence of water-formed minerals downwind of suspected former lakes, including one in a canyon called Juventae Chasma, the team say.
The study shows Mars鈥檚 climate can vary dramatically depending on local conditions, says Anthony Colaprete of NASA鈥檚 Ames Research Center in Moffett Field, California.
