Ice on ancient asteroids like Ryugu could have been crucial to the emergence of life on Earth. Researchers at Imperial and their colleagues analyzed the asteroids’ rocks and found cracks caused by freeze-thaw cycles. These processes likely delivered water and essential organic materials to our planet, providing the necessary building blocks for the emergence of life billions of years ago.

The role of water in the evolution of asteroids

The research was led by Dr Matt Genji from Imperial’s Department of Earth Science and Engineering, with staff from the Natural History Museum, the University of Kent and the Japan Space Agency (JAXA). This indicates that there is evidence that rocks are being broken up by ice on asteroid Ryugu, which was returned to Earth by JAXA’s Hayabusa2 mission.

The research team discovered that these cracks are filled with clay and sulfur minerals that form in the presence of water. These mineral-filled cracks appear to be the result of a freeze-thaw process in which ice expands and contracts as it melts and refreezes, causing the rock to break down.

This suggests that water played a crucial role in changing the composition of the asteroid in the early solar system. Scientists believe these changes may have allowed essential organic materials, as well as clay, sulfur minerals and water, to reach Earth when the asteroid hit our planet billions of years ago. This delivery could be an important factor in the emergence of life on Earth.

How did freeze-thaw cycles lead to life on Earth?

Dr Genge said: “Our findings suggest that repeated melting and refreezing of ice on asteroids may have contributed to the emergence of life on Earth.

“Our calculations show that the pressure exerted by the ice as it grows is sufficient to shatter asteroids down to their cores and allow water to spread through them. The water then interacted with minerals within the asteroid, creating essential organic matter that would be transported to early Earth, forming oceans and the organic building blocks of life.”

While collisions with other asteroids can also shatter asteroids, the team concluded that certain rift patterns on asteroid Ryugu may have formed solely through the freeze-thaw process. These freeze-thaw cycles not only fractured Ryuga, but also allowed water to escape through these cracks, creating geysers on the asteroid’s surface. The article was published on: Nature Astronomy.

Ryugu’s tiny shards are deciphered

The team examined a millimeter-sized piece of Ryugu sent to Earth by JAXA. To analyze the sample, they used X-ray computed tomography (XCT), which is similar to medical computed tomography but allows seeing the three-dimensional shapes of asteroid fractures for rocks.

In addition to the hairline cracks that indicate the role of ice in breaking the asteroid, the researchers also found “veins” containing framoid magnetite (tiny spherical crystals of magnetic iron oxide), providing further evidence of the presence of water.

Researchers noticed that the faults and veins had strange curved shapes and looked like a series of bumps. It was the characteristic shape of the veins that helped them understand the role of ice: The team experimented with ice grains embedded in clay and discovered similar spikes forming around the ice.

“It was the destruction of asteroids through freeze-thaw that enabled the asteroids to completely replace water. Without it, these life-giving materials would have been much rarer. The cosmic Rock, Scissors, Ice game may well have been integral to the emergence of life,” concluded Dr. Genge.