InSight touched down in November 2018 after surviving “seven minutes of terror” — the descent, during which mission control can do nothing but wait, from when the lander met the Martian atmosphere to when it touched down on the planet’s surface. The robot landed on a Martian plain, Elysium Planitia, in a dirt-filled crater nicknamed Homestead Hollow.
There the robot deployed most of its instruments and has been transmitting data back to Earth. InSight’s “mole,” its subterranean heat probe, has so far failed to penetrate the cementlike soil in the hollow. The probe will require a push from the robot’s arm.
In April 2019, InSight made the first-ever detection of seismic activity, known as a marsquake, on the planet. By the end of September 2019, InSight had detected 174 seismic events on Mars. Twenty-four of those rumbled up from the planet’s mantle and were relatively large marsquakes, between 3 to 4 on the moment magnitude scale (roughly similar to quakes of the same size on the Richter scale).
Data from InSight, NASA administrator Jim Bridenstine said in 2018, could supply human explorers with knowledge about Mars’s natural resources, as well as its dangers, such as asteroid impacts.
Quakes and volcanic action
“We’ve finally, for the first time, established that Mars is a seismically active planet,” Bruce Banerdt, a geophysicist at the Jet Propulsion Laboratory in California and the mission’s principal investigator, told reporters at a news conference Thursday. It shakes with more activity than the moon, but Mars is less seismically active than Earth.
“It’s probably close to the kinds of seismic activity you would expect to find away from the plate boundaries on the Earth,” Banerdt said. Quakes on Mars are caused by the planet’s long-term cooling. “When the planet cools, it contracts, and then the brittle outer layers then have to fracture,” he said.
On Earth, many quakes occur at comparatively shallow depths, of about 3 to 6 miles, said study author Philippe Lognonné, a seismologist at the University of Paris. Marsquakes, he said, begin at depths of 18 to 30 miles.
The majority of the quakes InSight sensed were so small they would pass by humans unnoticed. “If you are on the Earth, these quakes,” Lognonné said, “you will not be able to detect them.” If you were standing at the right place on Mars, you might feel the larger quakes, but they would not be dangerous.
Two of the largest quakes came from Cerberus Fossae, large fissures that split open the Martian surface in the last few million years. “That’s the area that is the most recent geologically and volcanically active,” said Suzanne Smrekar, a geophysicist at the Jet Propulsion Laboratory and InSight’s deputy principal investigator.
A record of old magnetic fields
Martian explorers won’t be able to use a compass to find their way. Mars no longer has a magnetic north or south, as Catherine Johnson, a geophysicist at Canada’s University of British Columbia and Arizona’s Planetary Science Institute, told The Washington Post. When Mars was young, its liquid metal interior generated a global magnetic field, like Earth’s. But the inner Martian dynamo stopped about 3.5 billion years ago, and its planetwide magnetic field went with it.
Yet observations from satellites suggested there may still be magnetism on Mars. And InSight backed that up with a remarkable observation — the lander is sitting in a patch of a magnetic field 10 times stronger than scientists expected.
At the landing site, Mars has a local “crustal field,” Johnson said. Deep and ancient rocks, buried 2.5 miles or more below InSight, retain traces of the long-ago magnetic environment. “They’re like little tape recorders,” said Johnson, a member of the InSight mission. Minerals in the 4-billion-year-old rocks aligned with the now-vanished global field. The ancient magnetism remains essentially frozen in the rock, she said.
Electric currents in the upper atmosphere, which vary from day to night, are also a source of small magnetic fields, InSight revealed.
When it comes to electromagnetism, the biggest question for future human exploration on Mars is “what happens at the surface” during space weather, Johnson said. The sun’s solar cycle is ramping up, she said, and InSight should be able to sense magnetic signatures from solar storms that zap into Mars.
Dust devils and shining nights
InSight sensed thousands of pressure changes that could be strong enough to pick up dust, possibly producing the small whirlwinds known as dust devils. Lognonné hesitated to say that each vortex was a dust devil — the robot is sensitive to pressure, he said, but lacks a monitor to confirm dust flying through the atmosphere.
NASA scientists already know the power of massive dust storms scour the Martian surface. A monster dust storm swamped the Opportunity rover in 2018, killing its power and ending its mission.
But it can be a peaceful planet, too. As night falls, Mars goes quiet. “The wind fluctuations die out quite suddenly and the planet remains very quiet into the early night hours,” write the authors of the new Nature Geoscience paper on seismic activity.
InSight’s cameras captured images of noctilucent, or “night-shining” clouds, just after sunset. These clouds shine at the outer edges of the atmosphere. They form when ice collects around the dusty streaks left by meteors. It’s a phenomenon that also happens on Earth, as astronaut Jessica Meir recently observed from the International Space Station.