Asteroid Itokawa
The asteroid samples studied by Jin and Bose came from the area called the Muses Sea, which is the smooth area in the middle of Itokawa. JAXA

How did our planet end up with vast oceans? Did they appear over thousands of years on their own or was there some cosmic force behind their formation? Scientists believe that half of the Earth's oceans may have come from space, thanks to water-rich asteroids.

Samples of the Itokawa asteroid, obtained using Japan's Hayabusa probe, contained water. For the first time ever, researchers were able to measure the water content in an asteroid. Scientists believe that water-rich asteroids bombarded Earth millions of years ago, and this in turn helped form some of Earth's oceans.

"We found the samples we examined were enriched in water compared to the average for inner solar system objects," Ziliang Jin, a postdoctoral student at the Arizona State University's (ASU) School of Earth and Space Exploration and the lead author of the study, said in a statement.

"Until we proposed it, no one thought to look for water," Maitrayee Bose, the co-author of the study, who serves as an assistant professor at ASU, said. "I'm happy to report that our hunch paid off. It was a privilege that the Japanese space agency JAXA was willing to share five particles from Itokawa with a U.S. investigator."

Itokawa is an S-type asteroid that is around 1,800 feet long and around 700 - 1,000 feet wide. It circles the sun every 18 months and its orbit path brings it within Earth's own orbit. "S-type asteroids are one of the most common objects in the asteroid belt," Bose said. "They originally formed at a distance from the sun of one-third to three times Earth's distance."

Two of the five samples of asteroid Itokawa, when analyzed, were found to contain the mineral pyroxene. This mineral, when found in space rocks, contains water in its crystaline structures. The scientists discovered that the asteroid contained a surprisingly significant amount of water.

Asteroid Itokawa
Ziliang Jin (left) and Maitrayee Bose prepare Itokawa samples for analysis at ASU. Jin and M. Bose/ASU

According to the researchers, Itokawa may have originally been around 12 miles wide. However, the original asteroid likely collided with other space rocks at some point, which resulted in it breaking into smaller pieces. The aftermath of this impact is believed to have created two large fragments, which eventually merged and formed Itokawa as it exists today. Researchers believe that the asteroid likely reached its current size around 8 million years ago.

"The particles we analyzed came from a part of Itokawa called the Muses Sea," Bose said. "It's an area on the asteroid that's smooth and dust-covered."

"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," Jin added.

Jin said that despite the original collision and the asteroid having been exposed to radiation, the asteroid's minerals still contained water. "The minerals have hydrogen isotopic compositions that are indistinguishable from Earth," Jin said.

"This means S-type asteroids and the parent bodies of ordinary chondrites are likely a critical source of water and several other elements for the terrestrial planets," Bose explained."And we can say this only because of in-situ isotopic measurements on returned samples of asteroid regolith — their surface dust and rocks. That makes these asteroids high-priority targets for exploration."

"The Hayabusa mission to Itokawa has expanded our knowledge of the volatile contents of the bodies that helped form Earth," Bose added. "It would not be surprising if a similar mechanism of water production is common for rocky exoplanets around other stars."