Mars: meteorite impacts provide InSight into planet’s interior
Acoustic and seismic waves from meteorite impacts are detected by NASA’s Mars InSight lander
Scientists have for the first time been able to find impact sites of incoming Martian meteorites using their sound and seismic waves, which might lead to greater understanding of the makeup of the planet they are headed for.
NASA’s InSight Mars Lander has been studying the red planet’s interior, from its surface, since November 26, 2018. Short for ‘Interior Exploration using Seismic Investigations, Geodesy and Heat Transport’, InSight has been using sensitive instruments to detect seismic waves, heat flow and accurate measurements of the shape and size of the planet – or, as NASA describes it, “the planet’s pulse, circulation and reflexes.”
Now, with the help of the Mars Reconnaissance Orbiter (MRO), which has been circling around Mars for the past 16 and a half years, researchers have been able to use data on waves travelling through the air and interior of the planet to estimate and confirm the location of an impact site of four incoming meteorites.
When energy travels through solids and gasses (such as the interior of planets or through air), it does so in the form of waves. When the energy waves encounter a new material – a new composition, pressure or temperature – some energy bounces off the interface, while some energy travels through into the new material, but with a different speed and at a different angle. This results in waves from an impact arriving at a detector at different times and from different directions.
A collaboration of researchers from Curtin University in Australia and the Université de Toulouse in France have analysed InSight lander seismometer data from 4 meteorite impacts and used the different arrival times of the wave fronts from each impact to estimate the location of the impact. They then compared this estimate with images from the MRO and were able to confirm crater impact sites – a first for planetary seismology.
Using this technique, suggest the researchers, will enable planetary scientists to understand more about how impacts shape the surface of planets and deliver gasses to the planet over time. Knowing the size of the craters and the energy of the waves created, also provides information on the relationship between size of the colliding body and the overall impact on the surface in addition to providing valuable insight into the composition and properties of the interior of Mars.
Comparing these results with previous seismic data from the Moon suggests this technique could be applied to other planets to help scientists understand more about their interiors and characteristics.
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.
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. But the lander has also picked up the jitters of a planet being pummeled by space rocks: InSight has detected the signatures of at least four meteors colliding with Mars, and scientists have spotted the resulting craters in images taken from orbit.
“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. At Mars, scientists can now use the planet’s cosmic pummeling to make even 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.
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 with no 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. And that meant it needed no distractions, plus plenty of sunlight to power its instruments. Soon after landing, InSight unfurled its solar panels and deployed an exquisitely sensitive seismometer that would monitor the trembling planet. As Mars shakes, seismic waves bounce around and travel through the planet’s 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 for—rolling through in May. Now, as the spacecraft’s power dwindles, mission leaders say the spacecraft lived a good life. 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 solidly 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.”
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. For a while, it seemed like that might not happen—the team detected no impacts during the mission’s first two years.
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. But scientists hadn’t identified that fingerprint in the data until more 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. On Mars, and at night, these sonic signals can travel for hundreds of miles through the bottom layer of chilled Martian atmosphere. By combining information from the acoustic waves and the impact-generated seismic waves, scientists can determine the meteor’s trajectory and eventual 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. But they were real—and when the Mars Reconnaissance Orbiter snapped images of the potential crash sites, it found fresh 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. By definitively linking a seismic signal with a resulting crater on another world, scientists can study the energetics of the collisions. And the calculated rate of impacts is in line with predictions, although the team isn’t sure why the latter three collisions appear to be clustered in time, and why there aren’t any obvious impacts during the mission’s first two years.
“We don’t really know why that is,” Banerdt says. “It’s definitely kind of mysterious.”
Now, after nearly four years on the Martian surface, InSight’s mission is ending. The spacecraft’s fate is in the hands of the Martian winds, which carry the planet’s vermillion sand aloft, sometimes whipping it into dust devils and planet-spanning storms. A thick layer of dust has already settled on the spacecraft’s solar panels, blocking the sunlight that powers the lander and its instruments. In May, as the spacecraft’s power dwindled, mission leaders estimated that InSight’s seismometer might take data through the end of the summer—but that depended on the 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. And if they’re really lucky, a dust devil will spin through the lander’s perch in Elysium Planitia, clear off the solar panels, and allow the spacecraft to once again soak up the sunlight.
But that remains to be seen. Mars is, after all, a fickle world—a planet of promise and peril. It’s a world that had seduced scientists with hints of life while confounding efforts to detect it, a world with terrains that are tantalizingly Earth-like yet lethal to life as we know it.
Beneath those bewitching blue sunsets, not even robots can live forever.
NASA’s InSight Waits Out Dust Storm
InSight’s team is taking steps to help the solar-powered lander continue operating for as long as possible.
NASA’s InSight mission, which is expected to end in the near future, saw a recent drop in power generated by its solar panels as a continent-size dust storm swirls over Mars’ southern hemisphere. First observed on Sept. 21, 2022, by NASA’s Mars Reconnaissance Orbiter (MRO), the storm is roughly 2,175 miles (3,500 kilometers) from InSight and initially had little impact on the lander.
The mission carefully monitors the lander’s power level, which has been steadily declining as dust accumulates on its solar arrays. By Monday, Oct. 3, the storm had grown large enough and was lofting so much dust that the thickness of the dusty haze in the Martian atmosphere had increased by nearly 40% around InSight. With less sunlight reaching the lander’s panels, its energy fell from 425 watt-hours per Martian day, or sol, to just 275 watt-hours per sol.
InSight’s seismometer has been operating for about 24 hours every other Martian day. But the drop in solar power does not leave enough energy to completely charge the batteries every sol. At the current rate of discharge, the lander would be able to operate only for several weeks. So to conserve energy, the mission will turn off InSight’s seismometer for the next two weeks.
“We were at about the bottom rung of our ladder when it comes to power. Now we’re on the ground floor,” said InSight’s project manager, Chuck Scott of NASA’s Jet Propulsion Laboratory in Southern California. “If we can ride this out, we can keep operating into winter – but I’d worry about the next storm that comes along.”
The team had estimated that InSight’s mission would end sometime between late October of this year and January 2023, based on predictions of how much the dust on its solar panels will reduce its power generation. The lander has long-since surpassed its primary mission and is now close to the end of its extended mission, conducting “bonus science” by measuring marsquakes, which reveal details about the deep interior of the Red Planet.
Studying Martian Storms
There are signs that this large, regional storm has peaked and entered its decay phase: MRO’s Mars Climate Sounder instrument, which measures the heating caused by dust absorbing sunlight, sees the storm’s growth slowing down. And the dust-raising clouds observed in pictures from the orbiter’s Mars Color Imager camera, which creates daily global maps of the Red Planet and was the first instrument to spot the storm, are not expanding as rapidly as before.
This regional storm isn’t a surprise: It’s the third storm of its kind that’s been seen this year. In fact, Mars dust storms occur at all times of the Martian year, although more of them – and bigger ones – occur during northern fall and winter, which is coming to an end.
Mars dust storms aren’t as violent or dramatic as Hollywood portrays them. While winds can blow up to 60 miles per hour (97 kilometers per hour), the Martian air is thin enough that it has just a fraction of the strength of storms on Earth. Mostly, the storms are messy: They toss billowing dust high into the atmosphere, which slowly drops back down, sometimes taking weeks.
‘My power’s really low’: Nasa’s Insight Mars lander prepares to sign off from the Red Planet
Robot says it might be sending its last message from Mars as dust chokes out its power supply
Nasa’s InSight lander has delivered what could be its final message from Mars, where it has been on a history-making mission to reveal the secrets of the Red Planet’s interior.
In November the space agency warned the lander’s time may becoming to an end as dust continued to thicken and choke out the InSight’s power.
“The spacecraft’s power generation continues to decline as windblown dust on its solar panels thickens,” Nasa wrote in an update on 2 November. “The end is expected to come in the next few weeks.”
A message shared on the Nasa InSight Twitter account on Monday read: “My power’s really low, so this may be the last image I can send. Don’t worry about me though: my time here has been both productive and serene. If I can keep talking to my mission team, I will – but I’ll be signing off here soon. Thanks for staying with me.”
The robotic geologist, armed with a hammer and quake monitor, first touched down on the barren expanse of Elysium Planitia in November 2018.
It has since undertaken geologic excavations, making the first measurements of marsquakes using a hi-tech seismometer placed directly on the Martian surface.
The solar-powered lander issued an update last month, reminiscing on its time in space.
“I’ve been lucky enough to live on two planets. Four years ago, I arrived safely at the second one, to the delight of my family back on the first. Thanks to my team for sending me on this journey of discovery. Hope I’ve done you proud,” it said.
Since its deployment, Insight has measured over 1,300 seismic events, and more than 50 of them had clear enough signals for the team to derive information about their location on Mars, according to published mission results.
The lander data has also yielded details about Mars’ interior layers, its liquid core, the surprisingly variable remnants beneath the surface of its mostly extinct magnetic field, weather and quake activity.
Ahead of its 2018 launch, Nasa chief scientist Jim Green said the mission was of “fundamental importance to understand the origin of our solar system and how it became the way it is today.”
Nasa will not declare the mission over until InSight misses two check-ins with the spacecraft orbiting Mars that relays its information back to Earth.
Back in 2018, the veteran Mars rover Opportunity declared the end of its 15-year mission by transmitting an incomplete image from Perseverance Valley.
An intense dust storm darkened the skies around the solar-powered rover, blotting out the Sun and leaving behind a dark image with white speckles from the camera noise. The transmission stopped before the full image was able to be sent.