In a first, NASA Mars lander feels shockwaves from meteor impacts

In a first, NASA Mars lander feels shockwaves from meteor impacts

Though nearing its end, the plucky InSight lander is still doing groundbreaking science–including the first observations of their kind on the red planet.

Published September 19, 2022

8 min read

On the red planet next door, a plucky spacecraft is busy recording the fits and spasms of the world beneath its feet–even as it approaches the end of its life.

NASA’s InSight lander, which arrived on Mars in 2018, wasn’t designed to look outward–it was designed to feel the planet tremble, to measure its quakes and rumbles, and to help scientists map the Martian interior. The lander has also detected the jitters from a planet being pummeled with space rocks. InSight’s InSight lander arrived on Mars in . It was not designed to look outward, but to feel the planet tremble and measure its quakes and rumbles and to map the Martian interior

“These observations are very exciting,” says Elizabeth Silber of Canada’s Western University, who studies similar phenomena but was not involved in the InSight observations. “It is awesome that we have arrived at a technological point at which we’re advanced enough to be able to detect and link seismic signatures to impact events on another planet.”

On Earth, scientists have made such a link only once. And on the moon, where more than a hundred impacts shook Apollo-era seismometers, none could be linked to any resulting craters. Scientists can now use Mars’ cosmic pummeling to create better maps of its interior.

“The great advantage of these impacts is we know the location of the source,” says Raphael Garcia of the Aeronautics and Space Institute at the University of Toulouse in France, the lead author of a paper reporting the impacts, published today in the journal Nature Geoscience. “All the unknowns that remain are only the internal structure.”

But with its solar panels covered in dust, InSight’s time is running out and mission leaders suspect it might not make it through the end of the year.

“Our optimistic but plausible projections are taking us into January, but the more likely situation is that between now and then, we will get a spike in atmospheric dust and we may not be able to operate through that,” says the Jet Propulsion Laboratory’s Bruce Banerdt, InSight’s principal investigator.

Trembling planet

InSight touched down on Mars in the blandest spot its team members could identify–a flat, sandy plain called Elysium Planitia near the planet’s equator.

“I’m very, very happy that it looks like we have an incredibly safe and boring-looking landing plain. That’s exactly what we were going for–it’s what the landing site selection people promised me,” JPL’s Tom Hoffman, the InSight project manager, said in 2018, after it landed. “They promised me sandy without rocks. But there’s one rock, so I might have to talk with them about that.”

Unlike the spacecraft that focus on dramatic Martian terrains–the planet’s massive volcanoes, dramatic rift valleys and polar ice caps–InSight’s job was to look beneath the surface. It didn’t need distractions and had plenty of sunlight to power its instruments. InSight quickly deployed its solar panels and a sensitive seismometer to monitor the planet’s shaking. The planet shakes and seismic waves travel through its interior. Those waves carry information about the materials and boundaries they’ve moved through, so scientists can collect them and use those records to make a map of the Martian crust, mantle, and curiously large core.

Over nearly four Earth-years, InSight has measured more than 1,300 tremors. For much of the mission, the Marsquakes have been small; but over the past year, a handful of large quakes have jolted the planet, with the strongest–nearly a magnitude 5, something scientists had been hoping forrolling through in May. Mission leaders now say that the spacecraft has lived a happy life despite its declining power. With the exception of one hiccup, a heat probe that couldn’t burrow into the Martian soil as expected, the mission has met its objectives.

“We’ve been able to illuminate the interior structure of Mars for the first time, instead of having a fuzzy picture that is informed by analogy to the Earth, or the moon,” Banerdt says. “Mars is now a well-understood planet. It’s not like we know everything about what’s going on inside, but we know what the basic building blocks of Mars are.”

Measuring impact

In addition to deciphering the planet’s innards, scientists also wanted to measure the impact rate at Mars, or how frequently the planet gets smacked by incoming space rocks. It seemed that this might not be possible for a while. The team did not detect any impacts in the first two years of the mission.

But in a twist, it turns out that among those 1,300-plus tremors are a handful produced by crater-forming meteors. Three of these impacts occurred over six months in 2021–on February 18, August 31, and September 5. One had actually occurred earlier, in May 2020, producing a 36-foot-wide cluster of craters spotted from overhead by the Mars Reconnaissance Orbiter, which has surveilled the planet since 2006. However, scientists hadn’t found that fingerprint in the data until recently.

Garcia and his colleagues identified the impacts based on telltale acoustic waves produced as meteors explode in the atmosphere as they streak toward a planet’s surface. These sonic signals can travel hundreds of miles through the Martian atmosphere’s bottom layer. Scientists can use the combined information from the acoustic and impact-generated seismic waves to determine the meteor’s trajectory, and crash site.

When the three impacts occurred in 2021, Garcia says the resulting acoustic waves were so strong the team almost didn’t believe they were real. They were real, and when the Mars Reconnaissance Orbiter took images of potential crash sites, it discovered new craters. Later, when scientists went back through the data, they uncovered the acoustic signature of the event from 2020.

“That was iron-clad proof that these seismic records were caused by those cratering events,” Banerdt says.

The fresh craters are between 13 and 25 feet across, the work of objects so small they would likely burn up in Earth’s thicker, more protective atmosphere. Scientists can study the energetics of collisions by linking a seismic signal to a resulting planet crater. The calculated rate of impacts is consistent with predictions. However, scientists aren’t certain why the three collisions in the last three years seem to be clustered at the same time and why there haven’t been any impacts in the first two years.

“We don’t really know why that is,” Banerdt says. “It’s definitely kind of mysterious.”

Shutting down

Now, after nearly four years on the Martian surface, InSight’s mission is ending. The fate of InSight’s spacecraft is now in the hands the Martian winds. These winds carry the planet’s vermillion dust high above the surface, sometimes whipping it into dust-devils and planet-spanning hurricanes. The spacecraft’s solar panels have already been covered in dust, which has blocked the sunlight from reaching its instruments and the lander. As the spacecraft’s power declined, mission leaders calculated that InSight’s seismometer could collect data through the end the summer. However, this was dependent on Martian weather.

“This is a very dynamic season on Mars–it’s dust storm season,” Banerdt told National Geographic at the time. “Even if we don’t get a dust storm right here at InSight, there are dust storms kicking up all over the planet that inject stuff into the atmosphere that can affect the amount of solar energy we’re getting.”

“That said,” he continued, “we’ve gotten really good at finding change in the couch cushions.”

Since May, Mars has been kinder to the lander than expected.

“The dust has been holding very steady, maybe even dropping a little bit, and our power has actually been rising, just a little bit, over the last month or so,” Banerdt says. “But all of our historical data suggests the dustiness in the atmosphere will increase pretty significantly in the next month or so.”

If the team is lucky, InSight could continue taking the planet’s pulse through the end of the year–or perhaps a bit longer. If they’re really fortunate, a dust devil could spin through InSight’s perch on Elysium Planitia to clear the solar panels and allow the spacecraft once again to soak up the sun.

But that remains to be seen. Mars is a fickle planet, full of promise and danger. It is a world that has seduced scientists with hints at life, while confusing efforts to detect it. It is a world with terrains that look almost like Earth but are deadly to life as we know.

Beneath those bewitching blue sunsets, not even robots can live forever.

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