A meteor crashed into Mars on Christmas Eve 2021, and shook the planet so much that NASA's InSight lander recorded the rumblings.
Scientists didn't know where the quake came from until NASA's Mars Reconnaissance Orbiter, a spacecraft circling the red planet, captured images of the new impact crater.
NASA revealed the discovery on Thursday.
"It was immediately clear that this is the biggest new crater we've ever seen," Ingrid Daubar, InSight impact science lead, said in a press briefing.
"It's about 500 feet wide or about two city blocks across. And even though meteorites are hitting the planet all the time, this crater is more than 10 times larger than the typical new craters we see forming on Mars."
Around the new crater there was a telling shine: boulder-sized blocks of water ice, kicked up from beneath the surface in the explosion.
It's the closest to the Martian equator that NASA has ever found water. Until now, scientists had only seen water ice clustered near the poles.
The discovery is promising for NASA's plan to one day send astronauts to Mars.
To avoid excessively hostile weather, NASA would prefer to land astronauts close to the equator.
But wherever those explorers go, they'll need to mine water, both for basic human needs and to break it down into hydrogen and oxygen to provide rocket fuel for the journey home.
Meteor-impact Mars quakes can help solve a centuries-old mystery
Among the more than 1,300 quakes InSight has detected, scientists identified one other tremor that came from a meteor impact. The two meteors generated surface-level seismic waves – the first ever detected on another planet.
Before these meteor impacts, all the quakes InSight detected came from deep underground, producing what seismologists call "body waves," rather than surface waves.
"This is really exciting," Doyeon Kim, a geophysicist at ETH Zurich, who analyzed data from those quakes, told Insider, adding, "This was one of the mission goals, to detect and identify surface waves."
For almost as long as astronomers have studied Mars, they've wondered why its northern and southern hemispheres look so different. The North is flat lowlands, while the South is full of mountains.
According to Kim, there are two leading theories for this juxtaposition. One is that the North and South are made of two different types of rock. The other is that the planet's crust is simply thicker in the South.
Whatever the answer is, it would be another piece in the complex puzzle of how Mars formed, which is a model for how other rocky planets around other stars may have formed.
The surface waves from the meteor impacts gave scientists a peek at the nearby Martian crust. It's a small sample of the crust, so it can't solve the North-South mystery on its own, but it fits into the second theory: that the crust is thicker in the South and thinner in the North.
"This just provides a single or a tiny piece of evidence to start to uncover the mystery," Kim said.
InSight is dying
The Insight lander is wrapping up its mission due to waning power levels, and will likely run out of energy in the next six weeks, NASA said.
"For the last four years, the lander has been collecting a lot of dust on its solar panels," Bruce Barnerdt, the principal investigator for the Insight mission, said at a press briefing Thursday.
"We've been sort of cutting back on the operations of the spacecraft as that's happened in order to squeeze out as much science data as we can."
A recent dust storm could've been the final nail in the coffin, but it skirted past InSight's location.
Still, it filled the Martian atmosphere with dust particles, reducing the amount of sunlight that gets to the ground.
This story was written by Morgan McFall-Johnsen, Marianne Guenot, & Paola Rosa-Aquino.
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