If you’ve seen the movie The Martian or, better yet, read the book, you’ll know that our hero Mark Watney has to contend with hazardous dust storms on Mars. And a remarkable study has suggested we can predict when the next planet-encompassing storm will occur, and it might just be weeks away.
At the start of The Martian, Watney is left stranded on Mars by a violent storm. This type of storm isn’t realistic, as the air pressure is so low on Mars that a storm there is equivalent to someone breathing on you.
But what is more realistic is that, in the book and not the movie, a huge dust storm gradually descends on Watney later on, limiting the amount of solar power available to him. It’s so gradual that it’s almost undetectable, but we know these sort of storms occur. The Mars rovers Spirit and Opportunity had to contend with such an event in 2007, reducing their daily operations to almost zero.
And in a study published in the journal Icarus, James Shirley, a planetary scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, says we can predict when the next will occur.
It takes Mars 1.9 Earth years to orbit the Sun, and when the southern region experiences its summer while closer to the Sun, localized dust storms often occur. On rare occasions, these storms grow massively, and encompass the entire planet in dust. This was the scene for the Mariner 9 probe when it arrived in orbit around Mars in 1971, finding the entire planet wrapped in dust.
So far, it’s been unclear why a storm goes global. But Shirley says he has found a correlation with the orbit of Mars around the Solar System, specifically the Solar System’s center of mass, its barycenter.
The center of mass is not, as you might think, at the center of the Sun, but actually moves around the Sun depending on the positions of the planets. The orbits of the planets are not entirely circular, which means that their angular momentum, or speed, changes as they orbit.
For Mars, Shirley says this can explain the global dust storms. When the momentum is higher, there is an increased surface wind speed, which can spread the dust across the planet more. The momentum goes through cycles of 2.2 years, which is longer than the Martian year, but the global dust storms seemed to occur when the momentum was increasing during the start of the dust storm season. No global dust storms were found when the momentum was decreasing during this time.
The last five observed global storms were in 1977, 1982, 1994, 2001, and 2007, and almost all seemed to correlate with this idea. And that means we can predict the next one, because Mars is now showing similar signs to when it experienced previous global storms.
“Mars will reach the midpoint of its current dust storm season on October 29 of this year,” said Shirley in a statement. “Based on the historical pattern we found, we believe it is very likely that a global dust storm will begin within a few weeks or months of this date.”
He notes in his paper that correlation does not necessarily equal causation. There may be other factors at play, and this relationship between the angular momentum and global dust storms may be a coincidence. But if his prediction holds true, and there is a global storm before the end of the year, then the theory could be correct. There are a number of spacecraft in orbit that will be able to observe Mars during this time and see if it occurs.
And that has important implications for future missions to Mars. With NASA planning to send humans there in the 2030s, and Elon Musk’s SpaceX aiming for even sooner, understanding Martian storms will be key. They can dramatically reduce the amount of solar power available, just as Watney experienced, so we’ll need to prepare the astronauts for these events.
Knowing when they will occur could prove invaluable, and ensure the survival of the first Martian explorers.