Like many seismologists, Bruce Banerdt checks his email every morning for the latest quake report. Unlike others, however, he fervently hopes that the “big one” has finally hit. That’s because the information in his daily briefing comes from an entirely different planet, where “marsquakes” pose no threat to human lives or infrastructure. If a big one does come along, traveling straight through the planet and shaking NASA’s InSight Lander on the surface, it will bring nothing but good news to the researchers seeking a window into Mars’s insides.
The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) probe landed on Mars in November of 2018, and its suite of instruments, which includes an exquisitely sensitive seismometer as well as magnetic field and weather sensors, has been monitoring the Red Planet’s various rumbles and hums for more than a year. On Monday, the InSight team shared what they’ve learned from the probe’s first ten months of activity with five articles published in Nature Geoscience. The initial results support some expectations while raising new mysteries, and represent a step toward the ultimate goal of understanding why our neighbor looks so different from Earth.
“InSight’s understanding of how these two planets formed and evolved differently will help us understand the formation and evolution of our own planet, and ultimately even planets in other solar systems,” says Ingrid Daubar, a planetary scientist at Brown University and InSight team member.
The mission highlight has been confirming that Mars, like the Earth and the moon, shakes.
“We finally, for the first time, have established that Mars is a seismically active planet,” said Banerdt, the InSight Principal Investigator, in a press briefing on February 21.
NASA first sought marsquakes with the Viking landers in the 1970s, but their seismometers remained on the decks of the probes where they measured only wind. InSight placed its instrument directly on the ground with a robotic arm, where it can pick up tremors finer than the width of a single hydrogen atom, according to Daubar. As of September 30, it had registered 174 seismic events, more than 20 of which reached magnitude 3 to 4—perhaps just strong enough for an astronaut to notice, depending on the quake’s depth, but not strong enough to damage any infrastructure.
Earthquakes originate mostly from friction as the tectonic plates that make up our planet’s crust catch and slip on one another as they float over molten rock below. The Martian surface, however, sits more or less still. Most of its quakes come from that surface’s slow contraction over time. Deep down the planet still harbors heat from its formation, and it shrinks as it cools, forcing the crust to crack and shrink with it.
The modest quakes InSight has recorded so far appear to have traveled through the crust, and their numbers more or less match what seismologists predicted based on the behavior of the Earth and moon. Bigger rumbles travel farther though, so the team hopes to infer the location and makeup of Mars’s mantle if they can record some stronger vibrations in the mission’s second year. The current dearth of large quakes is slightly surprising relative to their frequency on Earth and the moon, according to Banerdt, but that could change any day (the catalog of quakes has since reached 450 and counting).
But even the shallow shaking hints at new discoveries. The team tracked two large tremors back to Cerberus Fossae, a region showing visible signs of new faults and lava flows in the last 10 million years (which counts as recent in geologic terms). Simple models predict that this area should have settled down by now, but the quakes suggest that it could still be active today, perhaps even hiding molten magma underground.
More surprises have arisen from InSight’s instrument for measuring magnetism. Earth’s magnetic field springs from its churning metal core, but Mars’s center congealed billions of years ago. Nevertheless, the lander measured an unwavering magnetic field at the surface ten times stronger than what orbiting spacecraft had measured from 100 miles in the sky.
The team interprets this field as evidence of an invisible layer of magnetized rocks buried perhaps a few miles beneath the lander. Back when Mars had a molten core, its field would have lined up the metals in the rocks, and they stayed that way even after the planet froze—a sign that the crust hasn’t experienced any dramatic heatwaves that could have disrupted the magnetization. By further studying the field and even surface rocks in the future, researchers hope to also determine exactly when the core solidified.
More mysterious are magnetic blips and spikes lasting just seconds to minutes long. Researchers say these measurements point to new phenomena high in the atmosphere, perhaps complex interplay between Mars and the solar wind’s electric and magnetic fields.
Missing dust devils
But what might be InSight’s most puzzling mystery is unfolding where the atmosphere meets the surface. The lander doubles as a weather station, measuring wind, temperature, and pressure in nearly real time (you can check out what the weather was doing this week, with a 12 to 24 hour time delay, here). It appears to have touched down in one of the windiest places yet explored, detecting whirling vortices approaching 60 miles per hour—although in the thin Martian air that would feel like a light breeze.
But dust devils—when a windy vortex visibly spins dust into the air—are nowhere to be seen. “The weird thing is,” says Don Banfield, a planetary scientist at Cornell and InSight team member, “we’ve looked several hundred times in the midafternoon timeframe and we have not yet imaged a single one.”
There’s plenty of dust though. InSight’s solar panels are slowly getting blocked by falling grains and satellite imagery confirms that the vortices leave visible tracks across the land surrounding the probe. But the two are barely interacting, and no one knows why. “We really don’t get it. It’s not like one of these things I’m throwing out like, ‘this is fascinating for science,’” Banfield says. “No, we really don’t understand this.”
That’s a problem for a desert planet, where dust shapes the climate much like water shapes that of Earth. What’s more, dust management will be a big part of the lives of any future explorers. Moon dust gave the Apollo astronauts endless trouble during their brief jaunt off world, from hay fever to jammed suit joints, and Mars dust will be no different. NASA will have to understand how the red sand gets into the air and where it goes quite well before it designs airlocks and spacesuits that have to operate for months to years in the gritty environment.
So far InSight may have raised more questions than it’s answered, but when you’re landing novel instruments on an alien planet, what else would you expect? “We’re still trying to get our arms around what Mars is telling us,” Banerdt said during the briefing. “We’re really in the same situation geophysicists were for the Earth in the early 1900s, seeing these wiggles and using the best analysis tools we have. But it’s still a very mysterious situation.”