In October 2018, the Hayabusa 2 satellite released a small robot, Mascot, on the asteroid Ryugu's surface. The mission was to map and photograph the dark and extraterrestrial world for 19 hours. During that time, three days and two nights passed in Ryugu.

- I think it's really cool that we can get such nice close-ups on the asteroid, especially nice are the night pictures. You can see how the robot's lamp lights up the dark environment, says Sanna Alwmark, a planetary geologist at Lund University.

The darkest object of the solar system

Ryugu is in orbit around the sun in the inner solar system. It has a diameter of just 900 meters and contains large amounts of carbon, making it one of the darkest solar bodies in the solar system.

In a study published in this week's Science, Japanese and German researchers have analyzed the images and found that the asteroid's rock bumps contain millimeter-sized drop-shaped bullets.

- This indicates that the rock has not been subjected to a major transformation in space, which in turn means that it is a very primitive type of stone, says Sanna Alwmark.

From the sunblock

The constituents of the asteroid consist of the same type of stones that were found in the solar blob from which our planetary system was formed nearly 4.6 billion years ago. It is significantly older than the earth's rocks that have been subjected to countless crashes and alterations.

The researchers now want to examine this rock carefully to better understand how it went when the planetary system was formed. That is why the Hayabusa 2 satellite landed on the asteroid in February this year and collected rock samples to be transported home to Earth.

The study was published in this week's Science.