NASA's Mars InSight Lander Detects Large Meteorite Impact

Remember the InSight lander on Mars since November of 2018?  It isn't in the news much, but an item came out in the last several days telling the story of the probe detecting a quake which was traced to a meteorite impact.  That was followed by determining its exact location on Mars.  Actual detection of the impact site was by another satellite, the Mars Reconnaissance Orbiter - the MRO.  

NASA’s InSight lander recorded a magnitude 4 marsquake last Dec. 24, but scientists learned only later the cause of that quake: a meteoroid strike estimated to be one of the biggest seen on Mars since NASA began exploring the cosmos. What’s more, the meteoroid excavated boulder-size chunks of ice buried closer to the Martian equator than ever found before – a discovery with implications for NASA’s future plans to send astronauts to the Red Planet.

Scientists determined the quake resulted from a meteoroid impact when they looked at before-and-after images from NASA’s Mars Reconnaissance Orbiter (MRO) and spotted a new, yawning crater. Offering a rare opportunity to see how a large impact shook the ground on Mars, the event and its effects are detailed in two papers published Thursday, Oct. 27, in the journal Science.

Those two paragraphs are from the NASA/JPL website for the program linked in the first paragraph.  What the JPL site doesn't discuss is how they knew approximately where to look on MRO's photos to see if there was evidence of impacts.  For that, the coverage is on Ars Technica.  

Here on earth, we have seismographs all around the globe.  It's fair to say we have them everywhere.  This allows the users to triangulate the location of a quake by the time differences of arrival at various locations.  On, Mars, though there's only the InSight lander, so how can they figure out how far away the quake was?  Seismologists have named different types of seismic waves and determined different speeds for them, giving them different times of arrival.  That gives an expected distance from the lander to search for new impact craters.

The cameras on the Mars Reconnaissance Orbiter (MRO) have been observing Mars for 16 years. Before 2021, they had not observed any impacts that formed a crater over 130 meters across. In 2021, it spotted two. One of them was not especially useful. MRO imaging didn't capture exactly when the impact occurred, and it was far enough from the site of the InSight lander that direct seismic waves ran into the planet's core, which meant that only indirect seismic energy reached the instruments on InSight.
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Knowing that these two impacts generated events allowed for a direct comparison between the estimates and the impact location. And it turns out the estimates are quite good. One event was estimated at 3,530 ± 360 km away, and it turned out to be 3,460 km from the lander, a difference of just 70 km. The second was at 7,591 ± 1,240 km away, and that estimate was off by only 130 km. In both cases, the actual error was far smaller than the estimated error.

The MRO before (left panel) and after photos that isolated the bigger impact.  Not much doubt about the change there: 

NASA, Mars MRO photo.  NASA/JPL-Caltech/MSSS all get credit.

Color photos of the fresh crater taken later show white specs that are described as water ice boulders - and the closest to the equator water ice has ever been found. 

All in all, an excellent geek story.  To be extremely geeky, NASA released a 57 second video of the sounds that InSight recorded.  That's posted on CNN, of all places.  You can actually hear the sounds of a meteorite impact on another planet.  Considering I've never heard a meteorite impact here on Earth, that's saying something.  Lots more geeky details at Ars Technica, NASA's mission website, and CNN.

Unfortunately, InSight's solar panels have been covered in dust by Martian storms according to Bruce Banerdt, the InSight principal investigator.  The probe isn't expected to survive much longer. Still, the mission has survived twice as long as its intended mission. 

“For the last four years we’ve gone well beyond the intended lifetime of the mission, which was two years,” Banerdt said. ” And even now as we’re winding down, we’re still getting these amazing new results.”