LEILA FADEL, HOST:
For nearly four years, a NASA spacecraft has been studying Mars. The InSight lander is sitting near the red planet's equator. Now it's running out of power and could die as soon as next month. This isn't a surprise to mission managers, though. They'd expected Martian dust would build up on the probe's solar panels. Now it has, and panels can no longer generate the electricity needed for normal operations. NPR's Joe Palca has this report on what InSight has accomplished since it landed in 2018.
JOE PALCA, BYLINE: InSight's main scientific goal was to record marsquakes, the Martian equivalent of earthquakes, using an instrument called a seismometer. Northwestern University planetary scientist Suzan van der Lee says it took a leap of faith to base the success of the mission on recording marsquakes because...
SUZAN VAN DER LEE: Before the InSight mission, we had no idea that there were even going to be marsquakes.
PALCA: InSight principal investigator Bruce Banerdt was sure there would be - at least pretty sure.
BRUCE BANERDT: For the first two months, we did not see a single marsquake. And I was starting to get a little bit nervous at that point. You know, I was checking my email day after day - nothing yet, nothing yet.
PALCA: So it was a great relief to Banerdt and the rest of the team when, in March 2019, four months after landing, InSight did record a quake - and many more since.
BANERDT: By now we've been on Mars for about 3 1/2 years. We have over 1,300 quakes in our calendars.
PALCA: Unlike Earth, Mars doesn't have tectonic plates grinding together to cause rumbles. Suzan van der Lee says now that scientists know for sure Mars has quakes...
VAN DER LEE: We can start figuring out what kind of marsquakes these are, what kind of mechanisms are behind them.
PALCA: In addition to figuring out what's causing them, scientists can use the quakes to probe the interior of the planet. The seismic waves generated by the quakes have different patterns depending on what kind of material they're traveling through. Brown University's Ingrid Daubar says the seismometer can also measure the vibrations caused when meteorites crash into the planet.
INGRID DAUBAR: We thought that we would detect maybe a few to tens of meteorite impacts on Mars just from their seismic signals.
PALCA: But for the first two years, nothing. Finally, three impact craters were detected during InSight's third year on Mars. Cameras aboard a satellite orbiting Mars confirmed new craters appeared where the seismic signals said the impacts should be. As it reaches the end of its mission, InSight principal investigator Bruce Banerdt says it's fair to call InSight a success.
BANERDT: We've definitely accomplished all the things we set out to do with the one exception that our heat flow experiment was a disappointment.
PALCA: The heat flow experiment was supposed to use a special probe to measure heat flowing from the planet's interior. But to do that, the probe had to bury itself 15 feet below the surface, and no matter what commands they sent, the probe wouldn't stay buried. Banerdt says they're not sure why. Mars had one other surprise for the InSight team. When they listened closely, they could hear a faint hum coming from Mars - yes, I said hum.
BANERDT: And it seems to be there all the time, you know, day and night. And we really have been, you know, scratching our heads and trying to figure this out.
PALCA: You don't think maybe it's just a giant in the core of Mars snoring or something like that?
BANERDT: (Laughter) Maybe. Or a giant swarm of underground bees buzzing.
PALCA: Probably not. But we'll certainly let you know if that turns out to be the answer.
Joe Palca, NPR News.
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