Dust towers may have helped dry out ancient Mars

The 2018 global dust storm on Mars that killed NASA’s Opportunity rover is providing scientists with new insights into both Martian weather and how the Red Planet may have lost its atmosphere over billions of years. Based on data from the space agency’s Mars Reconnaissance Orbiter (MRO), the key could lie in dust towers that storms push as high as 50 mi (80 km).

One of the most dramatic of Martian phenomena is the tendency to roughly once a decade be suddenly subject to gigantic dust storms that completely engulf the planet, blotting out the Sun. These storms were first seen by earthbound telescopes and confirmed when NASA’s Mariner 9 probe reached Mars only to find a fuzzy, reddish-brown ball. However, 2018 was a landmark because when the global storm broke out, there was a small fleet of spacecraft in orbit and instruments on the surface to record its life cycle. The MRO was particularly valuable because its Mars Climate Sounder and Mars Context Imager (MARCI) allowed scientists to peer deep into the structure of the storm.

According to NASA, one of the things that was discovered was that the global storms generate dust towers – concentrated columns of dust that are caused by sunlight warming dust particles that rise high into the atmosphere in great, massive, churning clouds. Though they can occur under normal conditions, the dust storms appear to produce them in large numbers. Each can be as wide as the state of Nevada when they reach heights of 50 mi (80 km), and when they decay they form a layer of dust at around 35 mi (56 km) above the surface that is wider than the continental United States.

These towers are of particular importance because they may be one way in which Mars lost its atmosphere in the ancient past. This is because the dust towers are surprisingly long-lasting as well as large. Some even lasted for up to 3 ½ weeks. If ancient Mars had similar towers, then the dust could have carried water vapor along with it to the edge of space, where solar radiation would cause the water molecules to break down into hydrogen and oxygen atoms and escape into space.

“Global dust storms are really unusual,” says Mars Climate Sounder scientist David Kass of JPL. “We really don’t have anything like this on the Earth, where the entire planet’s weather changes for several months.”