Ryugu

Japan's Hayabusa2 mission brought back 5.4 g of material from Ryugu in December 2020, far more than the 0.1 g it had aimed for.^[1] Part of it came from beneath the surface, dug out by an impact the spacecraft made itself.^[1]

A spinning top

Ryugu is about 900 m across, a little under a kilometer.^[2] Its shape resembles a spinning top, wider at the equator than at the poles, a form seen in many small, fast-rotating asteroids, among them Bennu and Didymos.^[2] It turns once about every 7.5 hours, in the opposite direction to Earth's rotation.^[2] It is a C-type asteroid, a carbon-rich kind thought to be the parent bodies of carbon-rich meteorites.^[3]

The first artificial crater on an asteroid

Hayabusa2 launched on 3 December 2014.^[1] At Ryugu, it touched down on 22 February 2019 and collected surface material.^[1] On 5 April it fired an impactor into the surface, making the first artificial crater on an asteroid, and on 11 July it touched down a second time to collect material from below the surface.^[1] It left Ryugu on 13 November 2019 and released its return capsule on 5 December 2020; the capsule was recovered in Australia the next day.^[1]

What the sample showed

Among known meteorites, the sample is most similar to CI chondrites, whose composition is the closest to the average of the solar system, although Ryugu's material is less dense and reflects less light.^[3] It is rich in minerals that formed in water and in organic matter.^[3] Analysis found about 20,000 kinds of organic molecules, including amino acids in equal left- and right-handed forms, a sign that they formed without life.^[4] A separate study found uracil, one of the four bases of RNA.^[5]

Isotope measurements suggest that the material Ryugu formed from came from the outer solar system and that the asteroid later moved inward.^[6] Hayabusa2 itself is continuing on an extended mission, scheduled to explore the asteroid 1998 KY26 in 2031.^[1]