Humans have never landed anything on a comet's surface. That may change tomorrow.
The European Space Agency's Rosetta mission is poised to send out a small probe to land on a comet known as 67P/Churyumov-Gerasimenko. Rosetta spent 10 years chasing the comet before arriving in August.
Catching up with 67P in time to watch it swing around the sun is an achievement, but Karl Battams, a researcher at the Naval Research Laboratory, says scientists want to do more. "I think it's kind of part of human nature to go up to something and touch it," he says.
And that's where Rosetta's refrigerator-sized lander comes in. Known as Philae, it will attempt to float down to the comet's surface and make contact. "It's our remote hands," Battams says.
Strictly speaking, scientists have made contact with a comet before. In 2005, a NASA probe called Deep Impact slammed into a comet's surface. But the spacecraft was destroyed in the process.
This time, the lander will attempt to gently touch down at about walking speed. That won't be easy. "There are some very steep cliffs, there are huge boulders," Battams says. "It's truly an alien landscape"
The landscape of 67P came as a surprise to those who built the probe. "We expected some more-or-less-roundish potato shape," says Stephan Ulamec, from Germany's aeronautics and space agency, DLR, and the lander's project manager. That view held right up until midsummer, when the comet started coming into focus. Instead of a potato, researchers saw a bizarre, two-lobed structure peppered with cliffs, boulders and craters.
"The more we saw the terrain and how rough the terrain is, we saw, of course, this is an extremely difficult target to land on," Ulamec says.
They're not even sure what the ground is like. It might be hard, or it might be soft and sandy.
And that's why this lander comes with harpoons.
"We've chosen these harpoons for anchoring because they would work in hard material just like in soft material," Ulamec says.
Moments after its feet touch down, the harpoons will fire, along with some thrusters to keep the lander grounded. Then screws in the feet will try to get a grip.
It's a good plan, but only if the lander comes down on a flat spot. Philae is designed to hold its ground on an impressive 30-degree grade, but it could hit a cliff or a boulder, says Hermann Böhnhardt of the Max Planck School for Solar System Science. The spacecraft is nearly 30 light-minutes from Earth, so controllers can't steer. They simply must let it fall. "We need quite a bit of luck [to have] a successful landing in the end," he says.
If it is successful, Battams says, the lander will provide a wealth of scientific knowledge. "It sounds basic, but they're going to stick a thermometer on the surface of the comet and say, 'Hey, how hot is the surface of a comet?' " he says. The lander will also drill into 67P, check it for seismic activity, and work with the Rosetta spacecraft to create an image of the interior. Plus, it should deliver some amazing photos.
The descent will take seven hours. Battams says the wait will be excruciating: "There's going to be a lot of sweaty palms, and tapping of fingers on desks, like, 'Well, did it, did it, did it?' "
STEVE INSKEEP, HOST:
Now let's talk about space research. Tomorrow, for the first time ever, humans - that's us - may succeed in landing something on the surface of a comet. A spacecraft chasing a comet is set to send out a landing probe, if it works. NPR's Geoff Brumfiel reports.
GEOFF BRUMFIEL, BYLINE: The European Space Agency's Rosetta mission took 10 years to catch this comment, which is orbiting the sun. Since August, the spacecraft has been circling just a few miles from the surface. But Karl Battams, who studies comets at the U.S. Naval Research Laboratory, says that's not good enough.
KARL BATTAMS: I think it's kind of part of human nature to want to go up to something and touch it.
BRUMFIEL: And so tomorrow, the spacecraft will release a refrigerator-sized probe to make contact.
BATTAMS: It's our remote hands.
BRUMFIEL: Researchers are expecting to learn all sorts of things from the lander.
BATTAMS: It sounds basic, but they're going to stick basically a thermometer on the surface of the comet and say, hey, how hot is the surface of the comet? We don't really know how - what sort of temperature the material is at.
BRUMFIEL: The lander will also drill into the comment. It will check for seismic activity, image its interior, but only if the probe can stick the landing.
BATTAMS: We've never done this before.
BRUMFIEL: The problem isn't hitting the comet. This thing is as big as a mountain, but the service is lumpy.
BATTAMS: It is what look like craters or big depressions, and these huge cliffs, boulders. There's what look like sand dunes. And there's no wind on a comet so you can't get sand dunes, but something has made the appearance of sand dunes. It's truly an alien landscape.
BRUMFIEL: And it's not the landscape scientists had in mind when they designed this mission 20 years ago.
STEPHAN ULAMEC: We expected some more-or-less roundish potato shape.
BRUMFIEL: Stephan Ulamec is in charge of the lander. He works for the German space agency. He says that right up until the summer when spacecraft started to catch up to the comet, they were expecting the landing would be fairly easy.
ULAMEC: But the more we saw the terrain and how rough the terrain is, we saw, of course, this is an extremely difficult target to land on.
BRUMFIEL: They're not even sure what the ground is like. It might be hard or it might be soft and sandy. And that's why this lander comes with harpoons.
ULAMEC: We've chosen the harpoons for anchoring because they would work in hard material just like in soft material.
BRUMFIEL: Moments after its feet touch down, the harpoons will fire, along with some thrusters to keep the lander grounded. Then screws in the feet will try to get a grip. It's a good plan, but only if the lander comes down on a flat spot. There are random cliffs and boulders scattered throughout the target zone, and the lander can't steer, it just falls. The descent will take seven hours. Karl Battams says the wait will be excruciating.
BATTAMS: There's going to be a lot of sweaty palms and tapping of feet, of fingers on desks, like, well, did it, did it, did it?
BRUMFIEL: By the end of tomorrow, we should know if it did. Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.