Martian aurora, high-altitude dust clouds surprise scientists

Martian auroras! Mystery dust clouds! Just a few months into its mission, NASA’s newest Mars orbiter is finding an assortment of oddities in the Martian atmosphere, researchers report March 18 at the Lunar and Planetary Science Conference in The Woodlands, Texas.

Shortly after arriving at Mars in September, the Mars Atmosphere and Volatile Evolution mission, or MAVEN, discovered a wispy layer of dust suspended several hundred kilometers above the Martian surface. And then for five days in December, the spacecraft detected an ultraviolet glow blanketing the northern half of the Red Planet. The light show, similar to the northern lights on Earth, coincided with a fierce solar storm, when the sun flooded the solar system with charged particles.

“Nobody expected to see auroras in the northern hemisphere,” says Nick Schneider, a planetary scientist at the University of Colorado Boulder. “This changes our view of how the sun interacts with Mars.”

The European Space Agency’s Mars Express orbiter detected auroras in the Martian southern hemisphere in 2005, but they were concentrated over isolated magnetic spots on the surface. On Earth, auroras typically occur only at high latitudes. Earth’s magnetic field funnels and accelerates solar electrons and protons toward the poles where they slam into oxygen and nitrogen in the atmosphere, producing an ethereal glow.

Mars doesn’t have a global magnetic field to steer particles, so researchers didn’t expect to see anything like the northern lights. But some solar particles pack such a punch that they burrow into the atmosphere without any help from a magnetic field, Schneider says. Earth’s protective magnetic bubble deflects those high-energy particles away from the planet. Mars has no such defense.

“MAVEN is good at studying what happens to Mars when the sun throws stuff at it,” Schneider says. The probe is slated to spend one year measuring the rate at which molecules leave the atmosphere to better understand what the ancient Martian climate might have been like (SN: 1/10/15, p. 10).

Because the ultraviolet light from the Martian aurora is about as bright as that from Earth’s, Schneider suspects the same holds true for visible light. “I’m willing to bet that future astronauts will be able to see this aurora,” he says.

While the auroras were a surprise, researchers think that they understand the cause. The hovering dust clouds, however, have them stumped.

“This was completely unexpected,” says Bruce Jakosky, another University of Colorado planetary scientist.

MAVEN detected the dust as soon as it switched on its instruments. The dust preferentially hangs out where day turns to night, with a slight preference for the dayside of the planet. The bulk of the dust collects between 150 and 300 kilometers above the surface but flies as high as 1,000 kilometers.

Jakosky, who is principal investigator for MAVEN, has no idea where the dust comes from. Perhaps it’s lofted up from the surface or knocked off of Mars’ Lilliputianmoons, Phobos and Deimos. Or it could be interplanetary detritus swept up as the planet orbits the sun.

“It’s a real puzzle,” Jakosky says. There’s a lot of dust to be passing through either from the ground or from space. But if it’s not in transit, “I don’t know what would hold it there,” he says. Jakosky hopes the MAVEN team will get a better picture of where the dust lives and how it moves as the mission continues.

“It’s clear that the upper atmosphere of Mars is way more dynamic than anybody could have anticipated,” says Joel Hurowitz, a planetary scientist at Stony Brook University in New York who is not involved with the mission. Hurowitz is excited for MAVEN to reveal not just how the Martian atmosphere has changed (SN Online: 4/13/14) but how those changes tie into the historical record locked away in sedimentary rocks on the planet’s surface.

With so much going on in the atmosphere and the amount of information coming in, it will be a while before scientists can disentangle what’s going on in the skies over Mars, says Hurowitz. “We all have to sit back, be patient and give them some time to figure out what all the data’s telling them.”