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One was more red, while the other was more blue. Now, based on a new analysis of the observations captured by the spacecraft, scientists know why.
Ryugu, like Icarus in Greek mythology, strayed too close to the sun at some point in its history.
Hayabusa2 landed in Ryugu on February 21, 2019 to collect a sample that is currently on its way to Earth and will return in December 2020 after leaving the asteroid in December 2019. This landing also allowed the spacecraft’s camera You will observe the asteroid’s surface in detail.
This landing event also caused the spacecraft’s thrusters to send a spray of material. It altered a layer of dark fine-grained material on the asteroid similar to the reddish materials on the asteroid’s surface. This was compared to the position of the asteroid’s craters.
And that was when Tomokatsu Morota, study author and associate professor at the University of Tokyo, and his colleagues determined “that the red and dark fine grains lifted by the thrusters immediately after landing were produced by solar heating,” Morota said in an email to CNN
“We also discovered that the alteration of the surface by solar heating occurred over a short period of time based on the stratigraphic relationship between the identified craters and the redder material. These results suggest that Ryugu underwent an orbital excursion near the sun.”
Asteroids don’t just go rogue and head towards the sun. Their movements are governed by the orbits of the planets.
“In general, near-Earth asteroids are believed to be transported from the main asteroid belt to near-Earth orbits by orbital resonance with Jupiter and Saturn,” Morota said. “We believe Ryugu underwent an orbital excursion near the sun when Ryugu was transported from the main belt to a near-Earth orbit.”
This could also have happened once Ryugu became a near-Earth asteroid, said Patrick Michel, co-author of the study and director of research at the French National Center for Scientific Research in Paris.
“When an asteroid becomes close to Earth, close encounters with planets disrupt its trajectory and undergo a sort of random walk at its mean distance from the sun,” Michel wrote in an email to CNN. “In Ryugu’s case, the planetary disturbances were such that they brought him closer to the sun at some point and then back to his current orbit.”
Michel added that asteroids do not undergo typical evolution. Their unique trajectories are controlled by planets.
Fortunately, the sample returned to Earth contains a mixture of materials from the asteroid’s surface, including evidence of the asteroid’s excursion to the sun.
The sample may contain clues to Ryugu’s history, which are otherwise difficult to understand.
“Unfortunately, there is no way to track the evolution of this asteroid by starting the calculations from its current orbit and calculating it over time,” said Michel. “This is not possible for asteroids like Ryugu that have a very chaotic evolution due to their close approaches with planets.”
This will help scientists not only better understand Ryugu, but also other aspects of the history of our solar system.
“How those molecules change chemically by solar heating is important for understanding the chemical evolutions of organic molecules, which may have been transported to early Earth,” said Morota.
Since visiting Ryugu, Hayabusa2 has returned a large amount of data for scientists to study and analyze before the samples return to Earth.
Ryugu is a dark top-shaped asteroid that is approximately 3,000 feet wide. The surface is covered with rocks. It is also incredibly dry.
Photos captured by the spacecraft have revealed a uniform distribution of dark, rough rocks, as well as those that are shiny and smooth. Scientists believe that there are two types of material on the asteroid because it probably formed from the debris left over after its parent body was hit.
The rocks are similar to carbonaceous chondrites, which are primitive meteorites. Some of the rocks contain small, colored materials called inclusions that could contain minerals such as olivine. This is also found in carbonaceous chondrites.
The researchers also determined that the asteroid is primarily made up of highly porous material. This could explain why carbon-rich meteorites are rarely found on Earth; our atmosphere protects them and makes them break into fragments.
Information like this, obtained by sending a spacecraft to the asteroid, will be compared to data collected by NASA’s OSIRIS-REx mission that visits another near-Earth carbonaceous asteroid called Bennu.
“All the knowledge we are acquiring with Hayabusa2 could not be obtained from ground observations,” said Michel. “So detailed characterization of an asteroid definitely needs these space adventures!”
