Astronomers are convinced that asteroids Bennu and Ryugu came from the same much bigger space rock that split apart. Both of these asteroids, which orbit between Earth and Mars, are believed to have been formed following the creation of two centers of gravity.
Bennu was discovered in September of 1999 by astronomers in Socorro, New Mexico. The asteroid measures 1,610 feet in diameter. Astronomers in Socorro also discovered Ryugu a few months before in May of 1999 and that asteroid measures 3,280 feet in diameter.
Rock samples from both of these asteroids will need to be analyzed in order to know for sure if they came from the same space rock. Samples have already been taken from Ryugu and are currently on their way back to Earth on Japan’s Hayabusa2 spacecraft which is scheduled to return to our planet later this year.
No samples have been taken yet from Bennu, although NASA’s OSIRIS-REx is expected to land on the asteroid on October 20th of this year to collect the specimens. The spacecraft will land on a site called “Nightingale” located in the northern hemisphere of the asteroid and it will then collect samples about 0.8 inches in diameter.
Astronomers from the University of Arizona and Laboratoire Lagrange, Ivory Coast, simulated different collisions that could have taken place in the Mars-Jupiter asteroid belt. In their models, they found that pieces of asteroids would be ejected from the rock but would assemble back together in a spinning-top shape which is similar to both Bennu and Ryugu.
Even though the asteroids are different in regards to their hydration levels, they could very well still be from the same space rock. Once the samples from both asteroids come back to Earth, experts will be able to verify for certain if they’re related by determining their age as well as what they are composed of. Pictures of both asteroids can be seen here.
A really interesting fact about the pictures that Hayabusa2 took of Ryugu is that some of the rocks on its surface are reddish in color, suggesting that at some point it traveled pretty close to the sun.
In their paper, planetary scientist Tomokatsu Morota from the University of Tokyo as well as his colleagues wrote in part, “Immediately after touchdown, Hayabusa2’s thrusters disturbed dark, fine grains that originate from the redder materials.” They went on to say, “The stratigraphic relationship between identified craters and the redder material indicates that surface reddening occurred over a short period of time,” adding, “We suggest that Ryugu previously experienced an orbital excursion near the Sun.” The study was published in Nature Communications and can be read here in full here.