In 2020, the Japanese space probe Hayabusa2 returned soil samples from the asteroid Ryugu. Analyzes of the samples now reveal the composition of the asteroid. It turns out to be a fragment of the material that fused together and formed our sun 4.5 billion years ago.
The asteroid Ryugu was once part of a tens of kilometers of icy celestial body and raced around for a while like a mud ball. Researchers deduce this from the soil samples.
More than meteorites
The Hayabusa2 probe landed on Ryugu in 2018. It took over five grams of samples of rock, at and just below the surface. This particular package landed in the Australian outback in late 2020.
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Researchers are very happy about this. “We’ve really never had a monster like this. It’s spectacular,” said geochemist Andrew Davis of the University of Chicago.
The material could never have reached Earth without the protection of a space probe. “Normally, we can only study asteroids based on fragments large enough to land on Earth as meteorites,” Davis continues. “If you took this handful of Ryugu material and dropped it into the atmosphere, it would burn up and disappear.”
Scientists studied every microgram of the recovered material, from the gases trapped in the capsule and the asteroid to the chemical composition of each rock grain. Their findings were published last week in the journal Proceedings of the Japan Academy and Science.
Early last year, preliminary analyzes of the material suggested that the space rock was likely to have a primitive composition. This confirms the new research, which has largely looked at the relative amounts of different chemical elements and isotopes – variants of the same element.
The composition of Ryugu is similar to that of the sun. This means that the asteroid was born of the same material. The space rock, of which Ryugu is a fragment, was formed about 4.5 billion years ago when our solar system was a large, rotating cloud of gas and dust.
At that time, most of this cloud began to merge in the middle. From here the sun rose. The remnants of gas and dust in the disk around the young star also clumped together, forming the planets. Remaining fragments like Ryugu that roam the solar system are called asteroids.
wet mud ball
Reika Yokochi, also from the University of Chicago, describes the soil sample study as figuring out a recipe for soup based on the end result. “We can look at the soup and separate the ingredients and try to determine how much and in what order they have been treated and heated based on their condition.” A difficult but not impossible task.
For example, the researchers conclude that the soil samples were once soaked in water. This is striking as the space rock is now boned dry.
This is probably because Ryugu was part of a tens of kilometers of icy celestial body that lived in the cold outer parts of the young solar system. Due to collisions, this object broke. The temperature of Ryugu, one of these fragments, rose due to the energy released by the decay of radioactive elements in the rock. This melted the ice and turned the asteroid into a giant mud ball.
Collisions with other celestial bodies and gravitational effects eventually brought Ryugu closer to the sun. This evaporated the water and other volatiles, leaving the porous asteroid that visited Hayabusa2 in 2018.
This information on space rock Ryugu helps scientists map the history of the solar system. They hope to expand that knowledge with future missions that will collect samples from other asteroids, but also from the planet Mars and the moons on Mars.