Ryugu is a C-type asteroid, thought to be a remnant from the early days of the Solar System. These types of asteroids are known to contain significant amounts of water and other volatiles, and thus could have been an important source of water for the terrestrial planets, like Earth.
The Hayabusa2 mission, launched by the Japanese space agency JAXA, arrived at Ryugu in June 2018 and spent more than a year exploring the asteroid. During its stay, the probe deployed two small rovers, MASCOT and MINERVA-II, and collected samples from the asteroid's surface, which were returned to Earth in December 2020.
In the new study, a team of researchers analyzed data collected by the probe's onboard remote sensing instruments, including a thermal infrared imager and a near-infrared spectrometer. The results show that Ryugu's surface is extremely heterogeneous, with some regions depleted in water-bearing minerals and others enriched in them.
The team found that the water depletion is likely due to impact-induced heating, which caused water-rich material to be ejected from the asteroid's surface. The modeling suggests that the impact that caused this heating event occurred very early in Ryugu's history, when the asteroid was still relatively young and hot.
"Our results suggest that Ryugu was severely dehydrated throughout most of its history, which is in contrast with the view of a pristine, volatile-rich asteroid that has persisted in the literature up until now," said lead author Dr. Takuya Kouyama, a researcher at Japan's National Institute of Advanced Industrial Science and Technology (AIST). "The impact that caused this dehydration likely played a major role in shaping Ryugu's geological and chemical evolution."
The study also provides new constraints on the properties of Ryugu's interior, including its thermal structure and porosity. The team found that Ryugu's interior is likely very porous, with a large amount of void space between the mineral grains. This porosity may be due to fracturing caused by the impact event that dehydrated the asteroid.
The results of this study have implications for our understanding of the formation and evolution of asteroids and other Solar System bodies. They suggest that impact-induced heating events may be common in the early evolution of small bodies, leading to the loss of water and other volatiles. This could have important implications for the origin of water and other volatiles on terrestrial planets, as well as for the understanding of asteroid-related hazards.
