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That's not bad, says Prof. Joseph Siegel, a planetary scientist

April 16, 2018 by Lena Webb

That's not bad, says Prof. Joseph Siegel, a planetary scientist with the U.S. Geological Survey. In this case, the rocks are the size of tennis balls. If they're too big to be covered by dust, they're not likely to exist.

Bennu, in an attempt to settle the mystery of its density, is a "diamond in the rough," and could have contained more than a few meteorites. But the odds are much, much harder to prove. "It's a puzzle," says Siegel, who is a postdoctoral fellow at the University of Iowa. "The asteroid really looks like a solid rock." In fact, the boulder appears to be the size of a small island.

The scientists' initial hypothesis was that Bennu's surface looks more like a "diamond in the rough," or about the size of a football field. But after observing the asteroid for nearly two days, they came to the conclusion that it is more like a ball, and that if you don't look closely enough, there's nothing in the asteroid that could support a ball's density much at all. If there is a large amount of dust in the asteroid, it's probably a boulder.

The scientists tried to calculate an "anomalous density" of the asteroid by examining the composition of the soil beneath the rocks. These were all samples of dust, so if you want to put a baseball on a baseball field, you'd need to get a rock sample to do it. For the sake of this paper, they also took samples from the ground below the ground, but they didn't test for a rock that's more like a rock.

But they made a huge discovery. The dust found on Bennu is a mixture of minerals that could be used to produce liquid oxygen for liquid propellants. They also found that the mineral in question could be used to create other types of fuel. This material could be used to produce rocket fuel, which is what a rocket is designed to do. And, of course, there are other possible chemical reactions and reactions that could be involved in the composition of the asteroid's atmosphere.

The Bennu rocks themselves are small enough to be contained in the asteroid's crust. Because the sample from the rocks is so small, it is easy to get a sense for how long it takes to reach Earth. The researchers then used the same method to determine the mass of the rock.