NASA/JPL
The sand on Mars may be floating on air. Warm temperatures in Martian summer combined with a thin atmosphere and deposits of ice may cause sand to levitate and carve out deep gullies.
Mars can get quite balmy in the summer, reaching temperatures up to 20°C. That’s warm enough to melt some of the ice deposits speckled across the planet. But because Mars has just one hundredth the atmospheric pressure of Earth, that liquid water doesn’t last long on the surface before it boils away.
Jan Raack at the Open University in the UK and his colleagues found that the resulting pockets of water vapor can loft sediment into the air and move it across the ground.
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“We saw in our experiments that wet sand pellets were somewhat ‘floating’ over the sediment,” Raack says. He says that this was caused by evaporating water, which created a cushion beneath the sand particles, turning them into tiny hovercrafts.
The researchers found this phenomenon by creating Mars-like conditions in a laboratory. They mimicked the gullies of Mars because previous work has suggested that the landslides that appear there may be caused by water flowing down Martian hillsides.
Hovering along
They subjected a sample of Mars-like soil to the relatively low pressures and temperatures that characterise the Martian atmosphere. When they added liquid water, it evaporated nearly immediately.
The pockets of water vapour caused a levitation effect, where the sand bubbled up as if hovering on air. The effect lasted just a few seconds on Earth, but calculations taking into account weaker Martian gravity show that it could persist for up to a minute, depending on the amount of water. As the sand hovers along, it could cut the deep gullies we see on the planet’s surface.
If dust really does levitate on Mars, it will only occur in a few isolated areas, Bruce Jakosky at the University of Colorado at Boulder says.
“The key thing I wonder is whether there are very many environments that could have enough water to see these effects,” Jakosky says. While gullies and the briny flows called recurring slope lineae appear wet, there is a chance they may actually be dry landslides.
Unfortunately, it will be hard for us to look for floating dust on the Red Planet. The orbiters currently circling Mars don’t have high enough resolution to make out such a fine surface detail, and rovers aren’t allowed near any location that might have water for fear of contamination.
So for now, this levitation trick may only be visible in a lab.
Read more: Electrified sand could explain Titan’s odd backward-facing dunes
Journal reference: Nature Communications, DOI: 10.1038/s41467-017-01213-z
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