One is redder, while the other is bluer. Now, based on new analysis of observations captured by spacecraft, scientists know why.
Ryugu, like Icarus in Greek mythology, got lost a little too close to the sun at some point in its history.
Hayabusa2 landed at Ryugu on February 21, 2019, to collect samples that are currently on their way to Earth and will return in December 2020 after leaving the asteroid in December 2019. This touchdown also allows spacecraft cameras to observe the surface of the asteroid in detail.
This landing event also caused the spacecraft’s propulsion to send material sprays. It interferes with the dark, fine-grained material on the asteroid similar to the reddish material on the surface of the asteroid. This is compared to the position of the asteroid crater.
And that’s when Tomokatsu Morota, study author and professor at the University of Tokyo, and his colleagues determined “that fine red granules are lifted by the booster immediately after touchdown is produced by solar heaters,” Morota said in an email to CNN.
“We also found that surface changes by solar heating occur in a short time based on the stratigraphic relationship between the identified craters and the redder material. These results indicate that Ryugu underwent an orbital journey near the sun.”
Asteroids don’t just become naughty and head for the sun. Their movements are regulated by planetary orbits.
“In general, near-Earth asteroids are thought to be transported from the main asteroid belt to near-Earth orbit by orbital resonance with Jupiter and Saturn,” Morota said. “We think that Ryugu traveled near the sun when Ryugu was transported from the main belt to near-Earth orbit.”
This can also happen once Ryugu becomes an asteroid near Earth, said Patrick Michel, study co-author and research director at the French National Center for Scientific Research in Paris.
“When an asteroid gets close to Earth, a close encounter with the planets interferes with their path, and they experience a kind of random journey in their average distance to the sun,” Michel wrote in an email to CNN. “In the case of Ryugu, the planet’s disturbances are such that they bring it closer to the sun at some point, and then to its current orbit.”
Michel added that the asteroid did not experience a typical evolution. Its unique trajectory is controlled by planets.
Fortunately, the sample returned to Earth contained a mixture of material from the surface of the asteroid – including evidence of the asteroid’s journey towards the sun.
Samples can contain clues about Ryugu’s history, which are otherwise difficult to understand.
“Unfortunately, there is no way to trace back the evolution of this asteroid by starting the calculation from its current orbit and counting again in time,” said Michel. “It’s not possible for an asteroid like Ryugu which has a very chaotic evolution because of its close approach to the planet.”
This will help scientists not only to understand Ryugu better, but also other aspects of the history of our solar system.
“How such molecules change chemically with solar heating is important for understanding the chemical evolution of organic molecules, which may have been transported to ancient Earth,” Morota said.
Since visiting Ryugu, Hayabusa2 has returned a lot of data for scientists to study and analyze before the sample returns to Earth.
Ryugu is a dark asteroid that rotates about 3,000 feet wide. The surface is covered by large stones. It’s also very dry.
Photos taken by the spacecraft have revealed an even distribution of dark and rough rocks, as well as bright and smooth ones. Scientists believe there are two types of material in the asteroid because it is likely formed from the debris left after the mother’s body was hit.
The rock is similar to carbon-containing chondrites, which are primitive meteorites. Some stones contain small colored ingredients called inclusions which can contain minerals such as olivine. This is also found in carbon chondroitite.
The researchers also determined that the asteroid was made mostly of very porous material. This could explain why carbon-rich meteorites are rarely found on Earth; our atmosphere protects them and causes them to break into pieces.
Information like this, obtained by sending a spaceship to an asteroid, will be compared with data collected by NASA’s OSIRIS-REx mission visiting another asteroid near Earth called Bennu.
“All the knowledge we gained with Hayabusa2 cannot be obtained from observations on land,” said Michel. “So, the detailed characterization of the asteroid definitely requires this space adventure!”