Scientists baffled by discovery of mystery gullies on an asteroid

Contributed by
Jun 25, 2015

The most exciting thing we can usually think of when we think of asteroids is how we might stop one from crashing into Earth someday, but now scientists have given us another bit of asteroid intrigue. A NASA probe just sent us images from one of the biggest space rocks in the asteroid belt, and they show some pretty strange topography.

The NASA Dawn probe spent more than a year mapping the surface of Vesta, the asteroid belt's second-largest object, and along with the usual craters and barren plains, the probe found something else: gullies.

The gullies ran down the sides of Vesta's craters, and researchers have divided them into two types. The first type, Type A, are shallower and shorter and were likely created by solid material falling down into the craters. The second type, Type B, are something else entirely. Their formations are very similar to gullies on Earth that are formed by water. That's right, we might have just found evidence of water on an asteroid.

"We want to hear what other people's opinions are," said Jennifer Scully, a researcher from UCLA. "We're just putting it out there to the community; we're not suggesting anything hard and fast at this stage."

Though Scully and her fellow researchers aren't keen to declare this evidence of water on an asteroid, they're not denying that these gullies are puzzling. Only 11 instances of Type B gullies were observed in more than 60 observations, but that's enough to make this very interesting.

"The first group we call Type A. They're very typical of dry-mass wasting; the sort of thing you would get on Earth's Moon and on other, smaller asteroids," Scully said. "But the Type B gullies are the ones we think may have this liquid water origin; they have quite distinct morphologies. They are longer and narrower. They also interconnect, branching off one another."

But if these gullies really were made by some kind of liquid, how did the liquid get there? Vesta's not known for any volatile materials that could produce liquid, and while comets and other objects could deposit liquid on the surface at some point, asteroids don't have the atmospheric pressure to hold water on their surfaces. So how would liquid hang around long enough to carve geographic features?

"[It] would be cool enough just a few meters or even some centimeters beneath the surface that water could be preserved for a long time," said Professor Chris Russell, the principal investigator on the Dawn mission. "So we have some mechanisms like comets that might bring water to the surface - then it could be stored for some period of time."

If that's true, and Vesta's holding water under its surface, the water would have to be freed from beneath the surface by an impact or some other temperature-changing event to create the gullies. Still, it's a possibility.

But whatever the explanation, the Dawn team is not jumping to conclusions about the Vesta gullies. They're waiting for more evidence.

"We want to be very, very sure on any statement or pronouncement we make about the gullies or water or anything like that, because it turns out that there are a lot of different interpretations - we have to work our way through them," Russell said.

(Via BBC News)