The Viking lander recorded images of frost or snow-covered plains on Utopia Planitia in the late 1970s, and the Phoenix lander, which touched down in 2008 near the northern polar region of Mars, detected water ice and snow particles falling from clouds 2-4 kilometers above the planet.
But the mechanisms for how the snow forms in the rather dry Martian atmosphere are not well understood. Analysis of data from the Phoenix LIDAR instrument back in 2008 indicated that snow fell very slowly. Ice particles might take hours to descend to the surface and might not reach the surface at all, instead of evaporating in the upper atmosphere.
In a surprise to the researchers, data from the orbiters showed the formation of water-based ice clouds and the presence of atmospheric activity near the equator, which was unexpected. So Spiga and his team built their simulations around observations from all of the Mars spacecraft.
The new model suggests the snow could be falling in microbursts — as fast as 1-2 km in just 5-10 minutes — due to faster atmospheric wind speeds than expected.
The team said they were able to show that the Martian snowstorms would explain deep night-time mixing layers detected from orbit and precipitation signatures detected below water-ice clouds by the Phoenix lander. Their simulations also show “convective snowstorms occur only during the Martian night and result from atmospheric instability due to radiative cooling of water-ice cloud particles.”
That conclusion is consistent with the Phoenix lander data, which detected snowfall only at night. The researchers said the radiative cooling in the nighttime atmosphere triggers strong convection plumes with strong descending air currents – both within and below the clouds — with fast snow precipitation resulting from these energetic descending currents.
Spiga said future Martian climate models will need to account for the radiative effect of water-ice clouds.
“We found that water-ice clouds on Mars can create very strong local winds, turbulence, and mixing,” Spiga said. “This is important because not only water but heat, dust, chemical species can be transported by those strong winds.”
He said knowledge of wind variability is key for designing future landing and flying systems for Mars.
The researchers also indicated that nighttime weather activity is more intense than had been expected, and Spiga confirmed on Twitter the currents would be comparable to moderate storm clouds on Earth.
“So for what we are used to on Mars (especially at night),” he said, “it is a very violent storm.”
Confirmation of the team’s results might take a while because of damage to the Rover Environmental Monitoring Station aboard the Curiosity rover.
“The other [current] spacecraft do not have this capability, unfortunately,” Spiga said, “and snowstorms could be occurring above Curiosity or other rovers undetected, since orbiting spacecraft were able to detect mixing layers resulting from the snowstorms in the regions where the rovers are operating.”
Future rovers and orbiting spacecraft will be equipped to measure wind and cloud on Mars, he added.
The Mars 2020 Rover will include a weather instrument called the Mars Environmental Dynamics Analyser, which will measure temperature, wind speed and direction, atmospheric pressure, relative humidity, and dust particles.
NASA has said that a top priority for future exploration of Mars is better understanding its current climate and weather. This will help scientists more accurately model its past climatic behavior and determine if conditions were ever favorable for life on the Red Planet.