The Hayabusa2 mission was launched in 2014, arriving at Ryugu in 2018.
REPUBLIKA.CO.ID, JAKARTA — Observations from Japan’s Hayabusa2 mission have astronomers questioning its origin asteroid Ryugu. The Hayabusa2 mission launched in 2014, arrived at Ryugu in 2018 and returned samples of asteroid material to Earth in 2020.
In addition to collecting these samples, the mission is collecting important data about cosmic bodies remotely. While rock samples are still being studied, remote observations reveal three important features about Ryugu: its composition, shape and possible origin, according to a statement from Nagoya City University in Japan.
Remote observations show that instead of a single monolithic rock, Ryugu is a debris-heap asteroid made up of tiny pieces of new and solid material that clumped together by gravity. According to the statement, Ryugu is also shaped like a spinning top, possibly due to its fast rotation.
Lastly, observations show that Ryugu has a very high organic matter content, suggesting that it did not originate from the debris left over from a collision between two larger asteroids, as previously thought. Instead, the researchers say Ryugu may be the remnant of an extinct comet that has lost most of its water ice.
Comets are made up of water ice, rock and dust left over from formation solar system about 4.6 billion years ago. They form in the cooler outer parts of the solar system.
However, when a comet travels to the inner solar system, it heats up very quickly as it approaches the sun, causing solid ice to turn directly into gas through a process called sublimation. This process leaves only rocky debris, which, in turn, is compacted by gravity, forming a debris pile asteroid.
“Ice sublimation causes the comet’s core to lose mass and shrink, which increases its rotational speed,” lead author Hitoshi Miura, a professor at Nagoya City University, said in a statement. SpaceMonday (4/4/2022).
As a result of this spin-up, the comet’s nucleus can acquire the rotational speed necessary for the formation of the swirling shape.
“In addition, comet ice components are thought to contain organic matter generated in the interstellar medium,” Miura added.
This organic material will be deposited in the rocky debris left behind as the ice sublimates. Using physical models, the researchers simulated how long it would take Ryugu’s ice to sublimate, as well as estimate the resulting increase in the asteroid’s rotational speed.
Their simulations suggest that Ryugu likely spent tens of thousands of years as an active comet before moving into the inner solar system, where Ryugu’s ice evaporated, turning it into a debris-heap asteroid, according to the statement.
Further analysis of the Ryugu sample will help confirm its origin. In turn, similar debris-stack asteroids with high organic content might be referred to by astronomers as comet-asteroid transition objects (CATs). The OSIRIS-REx mission, which aims to return samples from another near-Earth asteroid known as Bennu, will provide additional insight into this type of object.
“CATs are small objects that were once active comets but have become extinct and appear to be indistinguishable from asteroids,” Miura said in a statement. “Because of their similarities to comets and asteroids, CATs can provide new insights into our solar system.”
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