Japanese scientists have announced initial results from the Hayabusa2 mission to the asteroid Ryugu, finding that the space rock is a dry and porous “pile of rubble” that formed into its unusual spinning-top shape during a period of rapid rotation at some point in its 100-million-year history.
The spacecraft Hayabusa2, which launched in December 2014, arrived at Ryugu in June last year. Its aim is to take samples from the asteroid and return them to Earth, allowing scientists to probe the conditions that existed when the planets were first forming.
About 4.6 billion years ago, the solar system was just a massive cloud of gas and dust. Part of the cloud eventually collapsed in on itself, creating a spinning disk. Hydrogen atoms started to fuse together, creating fusion reactions that would lead to the birth of the sun. While our star took up over 99 percent of the dust, most of the leftovers started to clump together to form the planets. Asteroids are the rocks that remained.
Because they have changed very little since the start of the solar system, asteroids still carry the materials that could have led to life on Earth.
Ryugu, which was first discovered by U.S. scientists in 1999, is a 3,000-foot-wide asteroid that is thought to have broken off of a larger parent body. In February, officials from the Japan Aerospace Exploration Agency (JAXA) said it had fired a bullet into the asteroid’s surface and collected the dust produced in the process. Next, the space agency plans to drop a small explosive onto Ryugu to get samples from beneath its surface. JAXA is planning to get the samples back to Earth in 2020.
In three studies published in Science , researchers working on the Hayabusa2 have announced more details about the asteroid’s composition. They say that its interior is porous and that its surface is largely uniform. The rocks that form Ryugu are loosely clustered, and its shape is the result of it spinning twice as fast as it does now.
To their surprise, they found Ryugu to be very dry—far more so than expected. Because the asteroid is thought to have broken away only 100 million years ago (not a long time in astronomical terms), it is thought that Ryugu’s parent body was also devoid of water. This has important implications for the origin of water on Earth, most of which is thought to have been delivered to our planet via asteroids and distant comets. If asteroids are largely dry rocks, scientists will have to change their models about what the early solar system looked like.
“[Studying Ryugu allows us to] reconstruct the delivery system of water and organics from the main asteroid belt to Earth,” study author Sei-ichiro Watanabe told Newsweek , adding that the samples delivered back to Earth will help the researchers identify Ryugu’s formation process.
In a statement, Seiji Sugita from the University of Tokyo’s Department of Earth and Planetary Science said Hayabusa2 discoveries have implications for finding life elsewhere in the universe. “There are uncountably many solar systems out there, and the search for life beyond ours needs direction,” he said. “Our findings can refine models that could help limit which kinds of solar systems the search for life should target.”
Thomas Seccull from the U.K.’s Queen’s University Belfast, who was not involved in the study, told Newsweek the latest findings provide a “fascinating insight into the surface properties of Ryugu, how it formed and, crucially, where the Hayabusa2 team should be looking to take a sample of the asteroid.”
He said that Ryugu, like other asteroids, appears to be the product of the solar system’s violent past and that it formed through a collision between two far bigger objects. “These collisional fragments likely collapsed under gravity to form a loosely bound pile of boulders, pebbles and smaller grains, which is why Ryugu looks like exactly that, a rubble pile.”
The next stage, where samples from the asteroid’s interior are returned to Earth, will finally give scientists a better view of what the solar system was like when the planets were forming, Seccull said.
“During this early period, it is predicted that important materials such as water and complex carbon molecules were being delivered from the outer solar system to Earth, and the other inner planets, by asteroids like Ryugu. As a result, understanding this material has important implications for our understanding of the early development of our own planet as well as the asteroids themselves,” he said. “I eagerly await further results from this fantastic mission.”
JAXA’s Hayabusa2 mission precedes NASA’s OSIRIS-REx mission to the asteroid Bennu. The two scientific teams are sharing information on the two asteroids to determine in what ways they are similar and different, potentially providing an even better view of the solar system’s origins.
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