The first and only spacecraft to study quakes on Mars is about to die. A recent Martian storm blanketed the solar panels of NASA’s InSight lander with dust, blocking much of the sunlight it needs to charge its batteries. Mission controllers are now running its seismometer intermittently to conserve energy. In weeks, the spacecraft will probably stop responding to commands from Earth and slide into oblivion.
But InSight isn’t going out without a bang. On 27 October, scientists reported that last year, the mission detected seismic waves created by the biggest meteorite impacts ever seen on Mars. Both meteorites hit the planet with the energy of a small nuclear bomb. By tracing how the massive seismicity rippled through Mars, scientists were able to study properties of the red planet’s crust thousands of kilometres from InSight, and resolve a mystery about whether the spacecraft happens to sit in a geologically unusual spot.
The findings add to InSight’s rich legacy of discovery. Since arriving on Mars in November 2018, it has gathered information on more than 1,300 ‘marsquakes’. This has allowed researchers to calculate, among other things, the long-sought size of Mars’s core and the thickness of its crust. Just last month, researchers used data from five marsquakes to determine that Mars’s mantle is richer in iron than is Earth’s. All of this information on Mars’s internal layers will help scientists to understand how the planet formed and evolved over billions of years.
“Before the mission, I always showed all these cartoons of cut-in-half planets,” says Mark Panning, InSight’s project scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, California. “Now the cartoon has moved from question marks and fuzzy boundaries to a real picture of what the Mars interior is. That was what we promised, and we did it.”
Seismic revelations
It wasn’t always clear that scientists would succeed. In 2012, NASA decided to build and launch the US$994-million InSight, a controversial choice because the agency had several other Mars missions already in its queue. Then, problems in building its super-sensitive seismometer forced a $150-million, two-year launch delay. Once InSight finally arrived at Mars, a German-built instrument nicknamed the Mole, which was meant to measure heat flow in the soil, failed when it couldn’t bury itself in the ground. The mission didn’t even detect its first marsquake until five months after landing—and when it finally did, researchers struggled to interpret what they were seeing.
“At the beginning, we were not really sure how much we could get from the data,” says Brigitte Knapmeyer-Erdrun, a planetary scientist at the University of Cologne in Germany.
But things picked up for InSight during its second Martian year. The spacecraft sits near the Martian equator, in a region known as Elysium Planitia. Many of the quakes it detects come from a geologically active region known as Cerberus Fossae, about 1,500 kilometres away, where underground injections of magma are thought to cause tremors. In August and September 2021, the spacecraft detected marsquakes on the other side of the planet for the first time.
And on 4 May this year, InSight detected a magnitude 4.7 quake—the biggest by far (most of InSight’s detections are in the magnitude 2–3 range). On Earth, such a quake could be felt by humans if they were near the epicentre.
“This is a beautiful gift given by Mars,” says Philippe Lognonné, a geophysicist at the Paris Institute of Earth Physics who leads the seismometer team.
Researchers haven’t yet published what they have learnt from the ‘big one’. But it was so large that it sent seismic energy through the surface layers of the Martian crust, creating what’s known as a surface wave—which can reveal more information about a planet’s interior than can other types of seismic wave. “I don’t want to tip our hand too much,” says Bruce Banerdt, a geophysicist at JPL and InSight’s principal investigator. “But it’s really giving information all across the spectrum, from the shallow crust all the way down to the deepest mantle and core.”
Deep impacts
Meanwhile, scientists have analysed surface waves generated during the two record-setting meteorite impacts last year, on 18 September and 24 December. InSight picked them up from thousands of kilometres away.
They rippled through the Martian crust to the north of InSight, which sits near a key geological boundary where the terrain is smoother and lower in elevation than the heavily cratered southern highlands. The way the surface waves travelled through the crust to the north suggests that it is denser than the crust beneath Insight, which landed in a region where the rocks are particularly porous.
InSight was able to tell where the quakes originated thanks to NASA’s Mars Reconnaissance Orbiter (MRO). Scientists who were looking through images from the orbiter spotted craters on the surface left by each of the impacts, and were able to pinpoint the dates on which they formed. Both of the craters are more than 130 metres across, making them the largest fresh craters observed in the 16 years that the MRO has been studying the planet. “This is a very unique data set of this size of impact,” says Liliya Posiolova, orbital-science operations lead for the MRO at Malin Space Science Systems in San Diego, California. When the first images arrived, she says, “it was like nothing we had ever seen before, and we almost did a double-take”.
Saying goodbye
Just because InSight is almost finished doesn’t mean discovery will stop. A ‘marsquake service’ based at the Swiss Federal Institute of Technology (ETH) in Zurich has been archiving the mission’s data. Researchers will probably use that information to make fresh findings for years to come, as they have with decades-old Apollo data collected during quakes on the Moon. “I’m quite sure we’re going to do the same with Mars,” says Anna Horleston, a seismologist at the University of Bristol, UK.
Researchers have already benefited from re-evaluating InSight data. Initially, they could determine only the magnitude of marsquakes, but usually not their location. Scientists led by Géraldine Zenhäusern, a geophysicist at ETH, figured out how to use the polarity of seismic waves from a marsquake to calculate its location. Separately, new techniques such as machine learning are already starting to unearth more marsquakes in InSight’s data.
Once InSight dies, Mars will be without a seismometer for a while; one was planned for the European Space Agency’s ExoMars lander, but that mission involved a collaboration with Russia and is on hold in the wake of Russia’s invasion of Ukraine.
There is a tiny chance that a dust devil might blow off the dust covering InSight’s solar panels and prolong the mission’s life. But researchers are preparing themselves to say goodbye. “There is definitely a sense of, oh my goodness, this is about to end,” Horleston says.
This article is reproduced with permission and was first published on October 27 2022.
