From COSMOS US Correspondent
Richard A Lovett
Last year on Christmas Eve, Santa gave planetary scientists a rare gift. A once-in-a-lifetime asteroid smacked into Mars, just in time to be observed, not only from space, but also on the ground.
The Mars asteroid impact was first observed by NASA’s InSight lander, whose seismometer recorded it as a magnitude 4 temblor—one of the larger marsquakes in its 4-year mission to measure the Red Planet’s seismic activity.
InSight’s scientists quickly determined the epicenter of the temblor, but it wasn’t until six weeks later that a different team, working with cameras on NASA’s Mars Reconnaissance Orbiter (MRO) got wind of it took a look at their own data.
What they found startled them. Not only was there a new crater, right at InSight’s projected epicenter, but it was big enough to show up on low-resolution images used to produce daily weather maps of the entire planet: clearly visible on Christmas Day (thank you Santa), and not the day before.
When yet another team zoomed in on it, they found a 150-meter-wide crater with debris scattered tens of kilometers away, suggestive of an impact by an asteroid 5-12 meters in diameter. Such an asteroid would have burned up harmlessly in Earth’s atmosphere, but in the thin Martian air it would have hit with the impact of an atom-bomb burst.
MRO has been in orbit for 16 years, and scientists using it have found numerous newly created craters on Mars. But nothing like this. “It’s huge,” Liliya Posiolova, of Malin Space Science Systems, San Diego, California, said at a 27 October press briefing.
It was also the first time the moment of impact could be constrained that precisely. “Typically, we can do a few years, maybe occasionally down to one year,” Posiolova said.
All of that is exciting enough, but there’s also important science to be learned. Just to start with, says Bruce Banerdt, InSight’s principal investigator, being able to spot the exact location of the impact is invaluable for validating and calibrating his own team’s techniques for locating the source of seismic events. “It turns out they are pretty good,” he told Cosmos.
And it’s not just seismologists who are reaping the benefits. “There is a whole line of research this opens up into the dynamical process of crater formation during impact,” Banerdt said. “We have already been able to start differentiating the energy dispersed into the atmosphere versus that going into heat, fracturing, shaking, ejecta, etc.”
There is also an important practical implication. One of the things the orbiting cameras saw were blocks of ice blown onto the surface from the impact. These had to have come from belowground, and at only 35° from the equator (roughly the equivalent of Sydney) this is the closest to the Martian equator at which ice has ever been observed.
“This is the warmest spot on Mars we’ve ever seen ice,” says Ingrid Daubar, of Brown University, Providence, Rhode Island. “Scientists are going to use this to constrain past climate changes on Mars, when and how this ice was deposited, buried, and preserved.”
Not to mention that similar subsurface ice might be available to future astronauts. “This is really exciting,” says Lori Glaze, director of NASA’s Planetary Science Division. “We know that there’s water ice near the poles on Mars, but in planning for future human exploration, we want to land as near the equator as possible. Having access to ice at these lower latitudes can be really useful.”
Meanwhile, InSight is probably on its last legs. Dust has been collecting on its solar panels, and a giant dust storm has further reduced the amount of solar energy reaching them. Unless a miracle happens soon to blow the dust away, the end is probably near.
“That’s a sad thing to contemplate,” Banerdt says, “but we’ve gone well beyond the intended lifespan. “What we believe is that in somewhere between four and eight weeks we expect the lander to not have enough power to operate.”