New Delhi, June 03, 2020.

A team of scientists led by the University of Arizona has discovered that the near-earth asteroids named Bennu and Ryugu might have originated from a collision in space. 

According to a report by the University, the Bennu which is the target asteroid for the OSIRIS-REx mission, and Ryugu that is said to be the target of the Japan Aerospace Exploration Agency’s Hayabusa2 asteroid sample return mission, are formed of parts of larger bodies that shattered upon colliding with other objects. This indicates that these two asteroids might have originated from the same body. 

Scientists earlier thought that their signature ‘spinning top’ was developed as the result of the YORP effect that boosts the speed of the asteroid’s spin and eventually leads to material accumulating on the equator after millions of years, forming a spinning-top shape. 

But, the new study published in Nature Communications suggests that the YORP effect may not explain the shape of Bennu or Ryugu asteroids. Scientists found that the Bennu got the top-like shape relatively early after its formation in the asteroid belt.

“Both asteroids have large impact craters on their equators, and their size suggests that these craters are some of Bennu’s oldest surface features. Since the craters cover the equatorial ridges, their spinning-top shapes must also have been formed much earlier,” explains the report by the University of Arizona. 

“Using computer simulations that model the impact that broke up Bennu’s parent body, we show that these asteroids either formed directly as top-shapes or achieved the shape early after their formation in the main asteroid belt.”

The presence of the large equatorial craters on these asteroids, as seen in images returned by the spacecraft, rules out that the asteroids experienced a recent re-shaping due to the YORP effect. We would expect these craters to have disappeared with a recent YORP-induced re-shaping of the asteroid,” said Ronald Ballouz, co-lead author and OSIRIS-REx postdoctoral research associate at Arizona. “

Besides their shape, scientists discovered that Ryugu’s surface material is less water-rich than Bennu’s, implying that Ryugu’s material has experienced more heating at some point.