New analysis suggests asteroid Ryugu is likely the result of the destruction of a much larger asteroid. Observations conducted by the Japanese Hayabusa-2 spacecraft indicate the celestial body is a pile of rubble from at least two different objects.
As reported in Nature Astronomy, the team used the spacecraft's instruments to study the composition of the asteroid from above. They found that the vast majority of the asteroid is carbonaceous, rich in carbon and water, similar to C-type asteroids. However, there is also material that's water-poor and silicate-rich that likely belongs to an S-type asteroid.
“We used the optical navigation camera on Hayabusa2 to observe Ryugu’s surface in different wavelengths of light, and this is how we discovered the variation in rock types. Among the bright boulders, C and S types have different albedos, or reflective properties,” lead author Dr Eri Tatsumi, from the University of La Laguna, said in a statement.
Based on the data available at this time, the team believe the asteroid formed between 10 million and 20 million years ago, practically yesterday in cosmic time. Ryugu is 435 meters (1,430 feet) in radius and would have formed from the debris left over from the collision between its parent bodies.
“Ryugu is too small to have survived the whole 4.6 billion years of solar system history,” added co-author Professor Seiji Sugita from the University of Tokyo. “Ryugu-sized objects would be disrupted by other asteroids within several hundred million years on average. We think Ryugu spent most of its life as part of a larger, more solid parent body. This is based on observations by Hayabusa2 which show Ryugu is very loose and porous. Such bodies are likely formed from reaccumulations of collision debris.”
There’s more to understand about the history of Ryugu, but fortunately we don’t have to wait long for more data. Hayabusa-2 collected several samples of surface and sub-surface soil, which will arrive on Earth in December.
“I eagerly await the analysis of the return samples, as this will confirm theories and improve the accuracy of our knowledge about Ryugu. What will be really interesting is knowing how Ryugu differs from meteorites on Earth, as this could in turn tell us something new about the history of Earth and the solar system as a whole,” added Tatsumi.
Asteroid Bennu, currently orbited by NASA’s OSIRIS-REx, is also a pile of rubble. The NASA mission will collect a sample next month to see if the object is the result of a collision too.
“When I was a child, I felt the other planets were always out of reach. But with the power of the instruments on our spacecraft, the images are so sharp and clear it feels like you could almost touch the surface of these asteroids,” said Tatsumi. “Right now, I’m studying asteroids with giant telescopes in the Canary Islands. And one day, I hope to also explore icy comets and trans-Neptunian objects such as dwarf planets. In this way, we may soon fully understand and appreciate how our solar system began.”