Another asteroid is giving up its secrets. At the end of January NASA found that asteroid Bennu contained 10,000 organic chemicals.
Now Japanese scientists studying rare samples from the asteroid 162173 Ryugu have discovered several types of salt crystals amongst the dust. The crystals help tell a story that Ryugu once belonged to a larger celestial body in the outer solar system—and this parent body hosted warm salty water.
Today, Ryugu is a 900m asteroid residing in the Apollo Belt, a group of asteroids that cross Earth’s orbit.
In a stunning bit of rocketry, in 2018, the Japanese Aerospace Exploration Agency (JAXA) landed the Hayabusa2 spacecraft on Ryugu. The spacecraft collected a 5.4g sample and returned it to Earth in 2020. Since then, laboratories around the world have been analysing the precious dust.
So far, research has determined that Ryugu is a rare type of carbon-rich asteroid and which carries a rich complement of organic materials, including one of the building blocks of RNA.
The team led by researchers at Kyoto University in Japan used a variety of analytical techniques, including X-ray tomography and scanning electron microscopy, to identify the salt minerals. Their results revealed sodium carbonate, halite and sodium sulphates clinging to grains of asteroid dust.
“Careful handling allowed us to identify the delicate salt minerals, providing a unique glimpse into Ryugu’s chemical history,” says corresponding author Toru Matsumoto of Kyoto University.
These kinds of salt crystals dissolve easily in water, so their presence suggests a limited amount of liquid that was already very salty.
Ryugu does not host any moisture today and questions remain about how its water was lost. But scientists have determined that Ryugu once belonged to a parent body that existed 4.5 billion years ago, shortly after the formation of the solar system. This parent body would have been heated by radioactive decay, supporting liquid saltwater.
“We hypothesized that as fractures exposed the saltwater to space or as the parent body cooled, this liquid could have either evaporated or frozen,” says Matsumoto. “The salt minerals we’ve found are the crystallized remnants of that water.”
Scientists are excited about comparing the salt minerals found on Ryugu to those on other rocky celestial bodies in the outer solar system that host water. These include dwarf planet Ceres in the asteroid belt, Jupiter’s moons of Europa and Ganymede, as well as Saturn’s moon Enceladus.
The comparisons will shine a light on the role of water in the development of these outer Solar System bodies, which are candidates for life outside of Earth.
The research is published in Nature Astronomy.
