Itokawa: Water Discovered in Asteroid Samples for First Time—And It Could Reveal Origins of Earth's Oceans

Itokawa asteroid
Asteroid Itokawa is the much-battered remnant of a larger parent body. Working with samples provided by the Japan Aerospace Exploration Agency, scientists have discovered that despite Itokawa's tumultuous history, this rubble-pile asteroid still contains significant amounts of water in its minerals. Japan Aerospace Exploration Agency (JAXA)

Researchers have taken the first measurements of water in samples collected from an asteroid—and the findings cast new light on the mysterious origin of the substance on Earth.

Analysis of the samples—which were collected from the asteroid Itokawa by the Japanese space probe Hayabusa—suggests that similar objects could have delivered up to half of our planet's ocean water earlier in its history via impacts, according to a study published in the journal Science Advances.

"Itokawa became the first asteroid from which samples were captured and brought to Earth for analysis," Ziliang Jin, lead author of the study from Arizona State University, told Newsweek. "Hayabusa touched down twice on the asteroid and collected a small amount of dust, despite the failure of the mechanism designed for the purpose. It delivered the sample to Earth on 13 June, 2010."

The asteroid is a peanut-shaped object measuring around 1,800 feet long and up to 1,000 feet wide, orbiting the Sun every 18 months in an elliptical path. This orbit brings it both closer to and further away from the star than the Earth-Sun distance. Itokawa belongs to a class known as S-type asteroids, which are one of the most common types of objects in the asteroid belt.

When the team investigated the samples collected from Itokawa, they found a high quantity of water inside its minerals, indicating that S-type asteroids—which formed in the inner solar system—contained the substance, despite their volatile history. These objects were often subject to heating, multiple impacts and fragmentation, and other processes that could drive off the water.

"We found the samples we examined were enriched in water compared to the average for inner solar system objects," Jin said in a statement. Thus it's possible that S-type asteroids could have been a source for Earth's water, he argues.

Furthermore, the team found that the Itokawa samples were extremely similar—in certain characteristics—to those of rocks found on Earth and other inner solar system bodies, lending weight to the hypothesis that such bodies share the same source of water.

"We report in our paper that Itokawa is water-rich, which has important implications: Itokawa formed in the inner solar system and is water-rich, hence [S-type asteroids] are not as 'dry,' as is often suggested," Jin said.

"More importantly, several Itokawa-like bodies may have collided with the proto-Earth and provided water to the planet," he said. "In other words, small asteroid bodies in the inner solar system could be a source of water for Earth and other planets. You can think of these small bodies in the inner solar system as being the fundamental building blocks of planets, bringing water and other materials, like organics."

According to the researchers, the latest findings provide an alternative explanation to previous hypotheses of where water on Earth came from.

"The source of water on Earth and other planets like Mars is hotly debated in the planetary science community," Jin said. "The most popular scenario is that water on Earth was delivered by water-rich asteroids from the outer solar system (C-type asteroids) during different periods of planetary formation, i.e., early, when Earth was not as big as it is now (proto-Earth) or late, after the Earth had completely formed."

Other suggested sources are comets, ice accumulating on pebble-sized bodies and influxes of molecular hydrogen into growing planets.

Cristina Thomas, an assistant professor from Northern Arizona University who was not involved in the study, said that the latest results were a "real game-changer" for how we think about water in the inner Solar System.

"We think of many inner Solar System materials, those that comprise S-type asteroids in particular, as being essentially dry," Thomas told Newsweek. "As stated in the paper, this completely changes how we think about water delivery on Earth. Of particular interest to me as a small body astronomer, this changes how we think about this type of object and what we assume about how they form and have evolved."