An unmanned Japanese spacecraft orbiting an asteroid has made surprising discoveries that scientists say will improve understanding about the origin’s of the Earth’s water and help search for life in other solar systems.
Scientists working on Japan’s Hayabusa 2 space mission said that by using a wide range of cameras and instruments to collect images and data about the near-Earth asteroid Ryugu, they had made some “tantalizing discoveries.”
“The primary one being the amount of water, or lack of it, Ryugu seems to possess,” said Seiji Sugita of the University of Tokyo’s Department of Earth and Planetary Science in a press statement as the mission released its initial findings.
“It’s far dryer than we expected, and given Ryugu is quite young (by asteroid standards) at around 100 million years old, this suggests its parent body was much largely devoid of water too,” Sugita added.
The finding is significant, he said, because of all of Earth’s water is thought to have come came from local asteroids, distant comets and the nebula or dust cloud that became our sun.
“The presence of dry asteroids in the asteroid belt would change models used to describe the chemical composition of the early solar system,” he added.
The discovery also has implication for finding extraterrestrial life. “There are uncountably many solar systems out there and the search for life beyond ours needs direction,” Sugita said. “Our findings can refine models that could help limit which kinds of solar systems the search for life should target.”
The mission’s three initial papers published in the journal Science on Tuesday described the mass, size, shape, density, spin and geological properties of the asteroid, a porous “pile of rubble” shaped like a spinning top.
The Japanese space agency, JAXA, research has also benefited from cooperation with NASA, which has its own probe, OSIRIS-REx, exploring a different asteroid known as Bennu.
NASA and JAXA share data from their respective missions and this cooperation has thrown up a further surprise.
Both Bennu and Ryugu are extremely dark, spinning-top shaped asteroids that are covered in large boulders, but the latest findings show that Ryugu is a lot drier.
Researchers had expected the two asteroids to have similar levels of water, but the discrepancy has opened up new avenues for future research.
“Thanks to the parallel missions of Hayabusa2 and OSIRIS-REx, we can finally address the question of how these two asteroids came to be,” Sugita said. “That Bennu and Ryugu may be siblings yet exhibit some strikingly different traits implies there must be many exciting and mysterious astronomical processes we have yet to explore.”
Other scientists shared Sugita’s optimism. “It seems that the asteroid formed as a spinning rubble pile from a previous generation of asteroidal parent bodies, and that those parent bodies had undergone thermal or shock metamorphism,” said John Bridges from the space research center at UK’s University of Leicester.
“This is far from the old stereotype of a potato-shaped, inert and perhaps rather dull, gray asteroid,” he added. “Ryugu shows that asteroids have recorded an incredibly rich history.”
Some scientists echoed Sugita’s initial reaction to the discovery of the asteroid’s lack of water, which he surmised by saying, “what felt limiting is now enlightening.”
Matthew Genge, an earth and planetary scientist from Imperial College London, said Hayabusa 2 had aimed to be the first to sample a C-type asteroid rich in water and carbon-rich objects because they are thought to preserve the best record of the earliest stages of the solar system.
He added that Ryugu appeared to be a type of asteroid that had had its history of the early solar system “overwritten” by a heating experience.
“It’s like mounting an expedition to find the world’s largest elephant, and instead finding the world’s smallest,” he said. “Not what you expected, but perhaps just as valuable. How did that elephant become so small?”
“Understanding how and why asteroids lose water is… a very important question in understanding how rocky planets become habitable,” he added.
In February, Hayabusa 2 touched down on the surface of the asteroid and fired a “bullet” into its surface in order to disturb material which was then collected by a “sample horn” on the underside of the probe.
These samples will be analyzed when the craft returns to Earth by the end of 2020.
“When we bring back the samples to Earth, we will know the answer. The greatest news is that we have already obtained the samples in the spacecraft. We are very excited about this,” Sugita said.