How did water originate on Earth? Data from asteroid Ryugu deepen mystery

Asteroid Ryugu was chosen for sending and returning a mission as it "belonged to a class of asteroids that are dark in colour and suspected to have water-bearing minerals"

As astronomers, the world over, continue looking for answers to the origin of the universe, one major curiosity is how water was formed or brought on Earth. The Hyabusa-2 spacecraft that recently returned with rock, soil samples from what is believed to be a part of water-bearing asteroid Ryugu is piquing interest globally even as the analysis of its capsule continues. 

While scientists hoped Ruygu would answer some of those questions, analysis of equipment onboard Hayabusa-2 mission reveals the asteroid was not rich in water-bearing minerals as some other asteroids. A study published in Nature Astronomy suggests that the ancient parent body from which Ryugu was broken had likely dried out before Ryugu came into being.

Ralph Milliken, a planetary scientist at Brown University and co-author of the study in a statement said, “One of the things we are trying to understand is the distribution of water in the early solar system, and how that water may have been delivered to Earth. Water-bearing asteroids are thought to have played a role in that, so by studying Ryugu up close and returning samples from it, we can better understand the abundance and history of water-bearing minerals on these kinds of asteroids." 

The Hayabusa-2 capsule entering Earth's atmosphere after travelling 300 million km in deep space. (Bloomberg)

It is to be noted that Ryugu was initially chosen for sending and returning a mission as it "belonged to a class of asteroids that are dark in colour and suspected to have water-bearing minerals and organic compounds." Scientists believe that these asteroids are parent bodies of water and carbon-bearing meteorites found on Earth. 

The Hayabusa-2 spacecraft plucked two sets of samples last year from two locations on the asteroid, more than 300 million kilometres from Earth. The first landing collected samples from Ryugu's surface and the second from underground. Each was stored separately. 

During its touchdown with Ryugu, the Hyabusa-2 fired a small projectile into the asteroid’s surface creating a small crater and exposing the rock buried underground. The near-infrared spectrometer onboard the spacecraft was activated to detect water-bearing minerals so that water content of surface rock with that of the underground surface could be compared. The spacecraft had initially made observations of the upper surface during its flybys and revealed that it was not water-rich as expected by scientists on Earth. 

The Hayabusa capsule after it landed on Earth with samples from Asteroid Ryugu. (JAXA)

"The data showed the underground water signature to be quite similar to that of the outermost surface. That finding is consistent with the idea that Ryugu’s parent body had dried out, rather than the scenario in which Ryugu’s surface was dried out by the sun," Brown University said in a statement.

"You would expect high-temperature heating from the sun to happen mostly at the surface and not penetrate too far into the underground surface. But, what we see is that the surface and subsurface are pretty similar and both are relatively poor in water, which brings us back to the idea that it was Ryugu’s parent body that had been altered,”  Milliken added.

While the study so far only takes into consideration the data received from the equipment on board, analysts of the deep space samples are yet to be released. JAXA is continuing the initial examination of the asteroid samples ahead of deeper studies in 2021. Scientists hope the samples will provide insight into the origins of the solar system and life on Earth.

After the completion of the set-up of the clean booth, a test run being undertaken. (JAXA)

Earlier in December 2020, officials from the Japanese space agency had said that they found more than the anticipated amount of soil and gases inside the small capsule that Hayabusa-2 brought back from deep space. As the analysis continues, scientists are hoping that samples from the asteroid's subsurface can provide information from billions of years ago that are unaffected by space radiation and other environmental factors.

While further studies and research into the samples will continue on Earth, Hayabusa-2, is already on an 11-year expedition to another small and distant asteroid, 1998KY26, to try to study possible defences against meteorites that could fly towards Earth.