Most of Mars’ Dust Comes From One Place

Erosion of the Medusae Fossae Formation has, over billions of years, likely covered the entire planet in 10 feet of volcanic dust

Medusae Fossae Formation
An eroded area of the Medusae Fossae Formation. NASA/JPL/University of Arizona

In late May, a massive dust storm covering a quarter of the planet kicked up on Mars, forcing NASA’s Opportunity rover into hibernation mode and obscuring our orbiters' views.

That was just the beginning. Over the next month, the storm grew and turned into a planetary event—possibly the strongest Martian dust storm ever, planetary scientist Tanya Harrison told Gizmodo's Ryan F. Mandelbaum. It is estimated that it will take several months for the dust to settle (literally). So why is there a planet-engulfing amount of dust on the Red Planet? A new study in the journal Nature Communications suggests that most of it comes from one interesting feature on the surface of the planet.

Just like oxygen and water vapor have huge impacts on the atmosphere of Earth, dust is a major driver of the climate on Mars. It rises high into the atmosphere, reflecting sunlight and keeping the surface cooler than it would otherwise be but making the atmosphere warmer, a mismatch that leads to dust storms. But, according to a press release, researchers have long scratched their heads about where all the dust comes from. On Earth, wind, running water and glaciers have produced most of our dust by eroding rocks. Meteor impacts and volcanic eruptions have produced some as well. However, none of those explain all the dust on the Red Planet. “How does Mars make so much dust, because none of these processes are active on Mars?” asked lead author Lujendra Ojha, of Johns Hopkins University.

To find out, Ojha and her team looked at the composition of Martian dust analyzed by various landers, rovers and the Mars Odyssey orbiter's gamma-ray spectrometer over the years. They found that the dust is quite uniform across the planet, with a distinct ratio of sulfur to chlorine, suggesting the dust may have come from a single source. They then searched the surface of the planet, eventually matching the unique chemical signature of the dust to the Medusae Fossae Formation, a roughly 620-mile-long gash near the equator believed to be volcanic in origin. According to NASA, the formation is easily erodible, and the dust and volcanic ash produced is blown off the formation into the Martian atmosphere.

“Mars wouldn't be nearly this dusty if it wasn’t for this one enormous deposit that is gradually eroding over time and polluting the planet, essentially,” study co-author Kevin Lewis, a planetary geophysicist at Johns Hopkins, says in the release.

Just how much dust is this one formation producing? A study published in May, also by Ojha and Lewis, in the Journal of Geophysical Research: Planets found that the Medusae Fossae Formation is the largest deposit of volcanic dust in our Solar System. When it first formed about 3 billion years ago, it was half the size of the continental United States. Since then, much of the ash has been swept away and the formation is now about 20 percent the size of the U.S. That's enough to form a layer of dust 6.5 to 40 feet thick on the surface of the entire planet. Meghan Bartels at reports that the finding fits with the 10-foot-deep layer of dust scientists have observed on Mars.

As more dust is stripped off Medusae Fossae Formation and enters Mars' atmosphere, it could make planetary dust storms more frequent or more intense. Currently we don’t know what sets off these occasional global events, but figuring it out, and learning how to protect our probes and eventually humans (hi, Matt Damon) from the dust will become increasingly important as plans for a manned mission to Mars progress. In the meantime, we do have a pretty cool image of one of the smaller local dust storms in the Martian Arctic that combined to create Mars’ mega-haboob.

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