Mars is beginning to reveal its innermost secrets, thanks to NASA’s InSight lander. The newest findings, about subsurface marsquakes, unusual magnetic signals and dust devils in the atmosphere, have been published in six new papers.
The papers were published in Nature Geoscience on February 24, 2020. Two of the papers, ‘Initial results from the InSight mission on Mars‘ and ‘Geology of the InSight landing site on Mars,’ are currently open access for the public, while the others are behind a paywall.
InSight landed on Mars on November 26, 2018 in Elysium Planitia, a large region of ancient lava flows, in a shallow crater called Homestead Hollow.
InSight’s primary mission is to study the interior of Mars in detail, something no other mission has done before. The lander’s seismometer detects marsquakes, the magnetometer detects leftover magnetic signals from Mars’ once-powerful magnetic field, the heat-flow probe measures temperatures underground and atmospheric sensors measure wind and look for dust devils.
First the marsquakes. Scientists had predicted that Mars would still have some seismic activity, but InSight, with its instrument called the Seismic Experiment for Interior Structure (SEIS), found that quakes occur more often than expected. They are, however, also milder. As of the end of September 2019, InSight had detected 174 marsquakes, and as of now, more than 450. So far the largest quake InSight has detected is about 4.0. Interestingly, it was months before InSight detected its first quake after it first landed. But by the end of 2019, it was “hearing” two quakes per day. This suggests that InSight landed during a relatively quiet period.
Even though Mars doesn’t have tectonic plates like Earth, it does have volcanic regions that can also cause some shaking. At least two of the quakes so far have been linked to a region far away from the lander called Cerberus Fossae. From orbiting spacecraft, scientists have seen boulders in the area that have rolled down hillsides. There are also lava flows less than ten million years old that have filled ancient channels first carved by water. Some of those channels are fractured, which scientists think was caused by quakes less than two million years ago.
“It’s just about the youngest tectonic feature on the planet,” said planetary geologist Matt Golombek of JPL. “The fact that we’re seeing evidence of shaking in this region isn’t a surprise, but it’s very cool.”
Closer to the surface, InSight has detected magnetic signals in rocks between 200 feet (61 meters) and several miles below ground. The signals at Homestead Hollow are 10 times stronger than had been anticipated.
“This magnetism must be coming from ancient rocks underground,” said Catherine Johnson, a planetary scientist at the University of British Columbia and the Planetary Science Institute. “We’re combining these data with what we know from seismology and geology to understand the magnetized layers below InSight. How strong or deep would they have to be for us to detect this field?”
InSight also found that those signals vary over time. They vary by day and night and also “pulse” around midnight. Scientists don’t know the explanation for this yet, but one possibility is the solar wind from the Sun interacting with the atmosphere.
InSight is also looking much deeper into Mars, right to its core. A powerful X-band radio called the Rotation and Interior Structure Experiment (RISE) is used to study the planet’s “wobble” as it rotates on its axis. Data is still preliminary, and a full martian year (two Earth years) of data will be needed to determine whether Mars’ core is liquid or solid.
InSight also probes the martian atmosphere. Other landers and rovers have done this as well, but InSight can do it nearly continuously with its weather sensors. Thousands of dust devils have been detected already.
“This site has more whirlwinds than any other place we’ve landed on Mars while carrying weather sensors,” said Aymeric Spiga, an atmospheric scientist at Sorbonne University in Paris.
InSight’s cameras, however, have not photographed any dust devils yet. But they could; dust devils were imaged by both the now dead Opportunity and Spirit rovers, as well as the Curiosity rover, which is still busy exploring Gale crater. Dust devils are also useful for seismic studies, since they “pull on the surface like a giant vacuum cleaner.”
“Whirlwinds are perfect for subsurface seismic exploration,” said Philippe Lognonné of Institut de Physique du Globe de Paris (IPGP), principal investigator of SEIS.
Last September, it was also reported that InSight found evidence for an electrically conducive layer below the surface, as might be expected with water or water-rich soil. It may be an aquifer or water/ice layer, which stretches around the planet. More study is needed however to determine exactly what this layer is.
Meanwhile, the mission team is still trying to fix the problem with the lander’s heat probe, called the mole. It was announced a few days ago that InSight’s robotic arm will now be used to try to push the mole deeper into the ground while it burrows down:
The new findings from InSight show that Mars is not as dead geologically as had been previously thought. Even though it doesn’t have active plate tectonics and its volcanoes are no longer erupting, it still rumbles underground and what’s left of its magnetic field still pulses, at least a bit. Mars is still alive.
InSight was launched on May 5, 2018, on a United Launch Alliance Atlas V “401” rocket from Vandenberg AFB, California.
More information about InSight is available on the mission website.