After successful landings on Ryugu, Hayabusa-2 passed Earth in 2020. The Japanese satellite then dropped a probe with the dust that had been collected.

Luleå University of Technology was responsible for the calibration of the thermal imager that was present during the landings on Ryugu. It measured the thermal inertia of the material on the surface – and the researchers discovered that the stones cooled very quickly. It showed that Ryugu’s surface layer has more in common with a very porous material than one might have thought.

– It was an unexpected discovery. We knew that asteroids can be porous, but not to this degree – and this has significant consequences for science, says Axel Hagermann, professor of atmospheric science at Luleå University of Technology, to Ny Teknik.

He also participated in the work with the thermal imager on board the spacecraft that has revolved around the asteroid.

The latest study of LTU researchers has been published in Nature Astronomy. According to their calculations, a comparable porosity would be more than 70 percent, which Axel Hagermann describes as “a very fluffy material”. A comparable porosity of pumice is found, but the professor notes that the comparison is lame in that the pumice has a much higher mechanical strength than the material on Ryugu.

LTU’s heat measurements indicate that science must rethink the relationship between the most common type of asteroid – type C, and meteorites.

– We have previously believed that asteroids such as Ryugu have a connection to the meteorites called carbonaceous chondrites that we find on Earth, and which in themselves are very fragile. But our conclusion is that the material on Ryugu is so fragile that it would not survive an entry into the atmosphere. This means that the meteorites we find on Earth cannot consist of the same material, he says.

– We need to rethink and come up with new ideas as asteroids are obviously more diversified, and there are materials on the asteroids that we can not find on Earth, says Axel Hagermann.

“Pretty surprising”

He says that the visit surprised in many ways. Among other things, Ryugu has the shape of an asteroid that should rotate much faster than it does. Another area is that Ryugu has materials and boulders with very different porosity mixed. This means that the planet’s body was in various stages of consolidation when it was destroyed by a collision.

Asteroids consist of remnants of planetesimal, the very early building blocks that formed the solar system. Collisions between larger bodies have thrown away materials which are then attracted to each other and form the asteroids. They can be described as rubbish heaps, with debris from different places.

– When Ryugu broke loose, that body must have begun to form a denser material in the core, and the material we see on the surface today originates from both the inside and the outside. We see material at different degrees of consolidation, which is quite surprising. We can also see what are parts of the mantle from early bodies. Finding all those kinds of materials in a body is quite unusual, he says.

Axel Hagermann believes that we now need to rethink how we explore asteroids, and realize that size is not everything when it comes to the bumblebees that can threaten the earth.

– There is a lot of talk about mining on asteroids, and we must be prepared for a wide range of materials. We must also think new about how to dispel meteorites that have these properties so that they do not hit the earth, says Axel Hagermann.