A Japanese spacecraft is on its way to Earth with samples of an asteroid called Ryugu. And an American craft is scheduled to gather samples of the asteroid Bennu in a few days. When scientists examine the samples, they won’t be surprised if they find that the asteroids were separated at birth.

The asteroids look alike. Both of them are shaped like spinning tops, with a ridge around the equator. Ryugu is twice the size of Bennu — about two-thirds of a mile in diameter. But Bennu appears to contain more water-bearing minerals.

A study released a few months ago said the two asteroids could have been born when a larger asteroid was hit by another space rock. The impact blasted debris into space. Some of the debris coalesced to form smaller bodies — including Ryugu and Bennu.

The difference in water suggests they formed from different parts of the parent asteroid. Bennu might have come from material near the surface, for example, with Ryugu coming from deeper inside. On the other hand, Ryugu might have formed from debris close to the impact site, with Bennu from debris on the opposite side of the parent.

Scientists will know more about the heritage of the two asteroids when the samples are brought to Earth. The Japanese craft is scheduled to return home in early December. And the American craft, Osiris-Rex, will gather samples from Bennu as soon as next week, and bring them to Earth in late 2023.

More about Osiris-Rex tomorrow.

Script by Damond Benningfield

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