(CN) – A hunch paid off for two Arizona State University cosmochemists, who became the first to find water in dust samples from an asteroid – providing evidence that similar asteroids striking a young Earth could have delivered up to half its ocean water.
The pair analyzed sample grains half the thickness of a human hair using ASU’s Nanoscale Secondary Ion Mass Spectrometer (NanoSIMS).
“We found the samples we examined were enriched in water compared to the average for inner solar system objects,” said Ziliang Jin, lead author of the paper published Wednesday in Science Advances.
The samples were collected by the Japanese space probe Hayabusa which landed on Itokawa, a small, peanut-shaped asteroid that is a remnant of a much larger parent body, and some of the samples were shared with ASU researchers.
“It was a privilege that the Japanese space agency JAXA was willing to share five particles from Itokawa with a U.S. investigator,” said Maitrayee Bose, study co-author. Out of the five particles shared with ASU, two of them contained pyroxenes, a rock-forming mineral.
The discovery of pyroxenes acted as the catalyst for finding the water, because on Earth pyroxenes contain more water than other anhydrous mineral phases.
“Pyroxenes ordinarily should contain tiny amounts of water in its crystalline structure,” Bose said, adding when the team ran thermal-diffusion models to mimic heating and impacts from other objects on pyroxenes, they found “the amount of water loss is minimal, and therefore we hypothesized that Itokawa pyroxenes or Itokawa material contains water that we should be able to measure. So the hunch and this study were initiated on an educated guess."
Not only did they find water within the pyroxenes, Bose said, it was the right kind of water to match what is found on Earth.
Itokawa, an S-type asteroid linked with stony meteorites, was originally part of a 12-mile-wide parent body.
“When it formed, it incorporated water from the solar nebula,” Bose said.
A destructive impact shattered the body into smaller boulders and pebbles, some of which reformed to become Itowaka.
Jin said, “Although the samples were collected at the surface, we don’t know where these grains were in the original parent body. But our best guess is that they were buried more than 100 meters deep within it.”
The simulations the team ran showed if grains were less than 10 meters deep in the original asteroid surface, they would lose their water, said Bose.
Because these particles were first buried deep within the asteroid before it shattered, they were able to retain water despite long-term exposure to radiation and impacts by smaller celestial bodies, the study authors said.
This latest discovery will provide valuable insight into the intricacies of our solar system and the terrestrial bodies within.
“There is enough evidence to show that these building blocks made Earth, and possibly other planets like Mars,” said Bose, who is also interested in “understanding organic delivery to planets in the form of carbonaceous meteorites and interplanetary dust particles.”
The ASU research team is making preparations to study samples from two other asteroids, Bennu and Ryugu. NASA launched a spacecraft as part of its OSIRIS-REx mission to bring back samples from Bennu in 2023, and Japan’s space center JAXA will provide samples from Ryugu in late 2020.
Asteroids are a valuable resource for planetary scientists and cosmochemists as they add to the picture of how the solar system was formed. Bose explained they preserve materials from early in the history of the solar system, and are necessary for in-depth study of planetary objects.
"The Hayabusa mission to Itokawa has expanded our knowledge of the volatile contents of the bodies that helped form Earth. It would not be surprising if a similar mechanism of water production is common for rocky exoplanets around other stars,” Bose said.
She aims to uncover some of the secrets that gave us this beautiful planet full of life.
“We find ourselves in this ‘pale blue dot,’ a planet full of water, rich in organics and supportive of life. We know of no other such planet.”
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