C-type asteroids are the key to understanding how water from the Earth's oceans and organic matter from the sources of life were brought to Earth, and how the rocks that form the Earth took in water and organic matter and mutually traced their evolutionary history. By acquiring information on the topography, materials, and internal structure of a C-type asteroid, and by taking samples (asteroid fragment) from several locations back to the earth, we will examine the history of the formation of the C-type asteroid, the characteristics of water and organic substances that are believed to exist on the object, and the relationship between the C-type asteroid and water and organic substances on the earth, using state-of-the-art analytical equipment on the ground. Analysis of return samples reveals where water and organic matter were formed in the solar system, how much material evolved on the asteroid, and whether such water and organic matter could be transported to Earth and become the source of water and organic matter on Earth.
What is Ryugu?
Ryugu is an asteroid discovered by Lincoln Research Institute in 1999. It was known to be a C-type asteroid by observation with a telescope on the ground. The asteroid is classified as a near-earth asteroid with an orbit close to the earth, and it was considered one of the asteroids that the probe can reach with less energy (fuel). JAXA set the target for the next sample return mission following Hayabusa as a C-type asteroid, which is different from the S-type asteroid (This is the type of asteroid Itokawa that the Hayabusa spacecraft explored.), and selected the asteroid 1999 JU3 (name of the time) as the target for Hayabusa2. Until Hayabusa2 conducted a near-field survey, we knew only its orbit, its approximate size (1 km), and its rotation period (7.6 hours).
Results of the Field Survey
After Hayabusa2 arrived at Ryugu, the size, shape, and gravity of the asteroid were precisely examined using onboard scientific observation equipment, and at the same time, surface materials were examined. And as a result,
The shape is "spinning-top" like, and the average radius is about 450 m.
The bulk density is 1.19 ± 0.03 g/cm3, and assuming the density of carbonaceous chondrite, the total should have a porosity of 50 ~ 60%.
Large blocks of rock larger than 10 m are abundant throughout the surface, and the reflectance of the Agave surface material is only about 4.5%, which is darker than typical carbonaceous chondrites.
The absorption of 2.72 micro-meter is observed in the whole surface area, but the absorption is weaker than that of carbonaceous chondrites containing hydrous minerals.
Ryugu
Average radius: about 450 m
Bulk density: 1.19±0.03g/cm3
Porosity: 50-60%
Reflectance: about 4.5%
Absorption of 2.72 micro-meter is observed in the whole surface area
and so on. An experiment on the generation of an artificial crater was conducted using a collision device called as the Small Carry-on Impactor (SCI). We obtained information on the physical properties of asteroid surface materials, and at the same time, we exposed surface and underground materials to reveal differences from surface materials. After the creation, a sample have been successfully collected from the area near the artificial crater where emissions from the crater have accumulated, raising expectations for the analysis of the return sample.
In December 2020, the Extraterrestrial Samples Curation Center (ESCuC) received a sample from the asteroid Ryugu retrieved by the Hayabusa2 spacecraft.
