The surprises keep coming for NASA’s Lucy mission, on its way to study the Trojan asteroids in the orbit of Jupiter. Lucy recently passed by a small asteroid called Dinkinesh and took this opportunity to test out some of its systems — but Dinkinesh turned out to be a fascinating system all of its own.
Last week photos from the flyby revealed that Dinkinesh had a tiny companion asteroid, making it part of a binary. Now, more photos reveal that the smaller moonlet is itself an interesting object, as it is a type of asteroid called a contact binary. That means it is made up of two objects touching each other, forming a double-lobed shape.
“Contact binaries seem to be fairly common in the solar system,” said Lucy deputy project scientist John Spencer of the Southwest Research Institute in a statement. “We haven’t seen many up close, and we’ve never seen one orbiting another asteroid. We’d been puzzling over odd variations in Dinkinesh’s brightness that we saw on approach, which gave us a hint that Dinkinesh might have a moon of some sort, but we never suspected anything so bizarre!”
This image was taken around six minutes after Lucy made its closest approach to the asteroids, coming within 1,010 miles of Dinkinesh. As the spacecraft traveled away from Dinkinesh, it was able to take this image from a previously unseen vantage point which revealed the strange double-lobed structure of the smaller moonlet.
“It is puzzling, to say the least,” said SwRI’s Hal Levison, the Lucy principal investigator. “I would have never expected a system that looks like this. In particular, I don’t understand why the two components of the satellite have similar sizes. This is going to be fun for the scientific community to figure out.”
Dinkinesh is located within the main asteroid belt of the solar system, between Mars and Jupiter. This region is thought to contain more than 1 million asteroids which are larger than 1 km (0.6 miles) across, plus millions more which are smaller in size. Contact binaries like the smaller moonlet observed by Lucy can form when small asteroids collide and stick together, often creating a loose “rubble pile” style of asteroid rather than a more solid object.
The unusual part of this recent finding is the fact the system is made up of not two but three parts: the larger Dinkinesh and the two parts of the smaller moonlet. It’s not clear how this contact binary came to orbit Dinkinesh itself.
“It’s truly marvelous when nature surprises us with a new puzzle,” said Tom Statler, Lucy program scientist at NASA. “Great science pushes us to ask questions that we never knew we needed to ask.”
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