The power of radar is really hard to understand until you compare the best images we have of an asteroid. The asteroid 216 Kleopatra is a 217-kilometer across dogbone of an asteroid that regularly gets fairly close to Earth. Between 2017 and 2019, astronomer Franck Marchis used the world’s best ground-based imaging system, the Very Large Telescope (VLT) in Chile, to observe Kleopatra as it passed, and the images we got back look a bit like an unusual biological experiment. While low on the “Glamour Shot” beauty scale, these images allowed researchers to create more detailed shape models of the asteroid than were possible with earlier radar data, and they also allowed the orbits of Kleopatra’s two moons, AlexHelios and CleoSelene, to be better determined.
This science is awesome, and for full disclosure, Franck and I work together on a lot of projects like the Grudge Report YouTube series. I just need to show you the radar images of Kleo because it’s from the radar images that you can get a real appreciation of the dogbone nature of this asteroid.
See that? Dogbone! (You can see the images in our show notes at DailySpace.org.)
Observed with the Arecibo Radio Telescope and radar system, these images were released in a paper in 2000. The combination of these original radar images and the new VLT images allows us to understand that like Ryugu and Bennu, Kleopatra is likely a rubble pile asteroid. Its density is half that of iron, but it’s thought to be metallic in composition! This implies that there is a lot of empty space in there. What’s more, it is rotating so fast that it is just barely balanced between gravity holding it together and the spin trying to tear it apart. These latest observations lead researchers to believe Kleo’s two moons may be the result of impacts knocking things off Kleopatra but not knocking things off hard enough that they escaped the asteroid’s gravity.
While no spacecraft is slated to visit Kleo in the immediate future, this curiously shaped asteroid is something I hope we’ll one day be able to visit and explore in detail.
ESO press release
“(216) Kleopatra, a low density critically rotating M-type asteroid,” F. Marchis et al., 2021 September 9, Astronomy & Astrophysics