There’s now proof that half of the world’s oceans came from outer space

The melting glaciers of AntarticaNASA

  • Samples collected from a sea-otter shaped asteroid named Itokawa contain water.
  • Itokawa and other asteroids like it might have brought water for half of the world’s oceans when they bombarded into Earth billions of years ago.
  • Finding water on the second most common type of asteroid in the Solar System makes them a "high priority target for exploration” according to one of the members of the team that made the discovery.

Normally, you wouldn’t think to look for water on an asteroid, especially in a nominally dry asteroid like Itokawa.

Samples from another asteroid, Ryugu, had nearly no water at all.


In 2005, JAXA's Hayabusa spacecraft landed on asteroid Itokawa (above) and collected samples that were returned to EarthNASA

Yet, two cosmochemists at the Arizona State University (ASU) followed their hunch to find that not only did Itokawa contain water but that half of the world’s oceans could be a by product of hundreds of asteroids just like it.

Until we proposed it, no one thought to look for water. I'm happy to report that our hunch paid off.

Maitrayee Bose, Assistant Professor, ASU’s School of Earth and Space Exploration

Finding water on asteroids isn’t just about determining Earth’s origins but also about finding alternative sources for a resource that is increasingly becoming scarce on Earth.

That makes these asteroids high-priority targets for exploration.

Maitrayee Bose, Assistant Professor, ASU’s School of Earth and Space Exploration

Itokawa, having been in its current state for 8 million years, has been subject to multiple impacts, shocks and fragmentation. This, in turn, should raise its temperature to drive off water.

So, in order to see exactly how much water was in the sample collected from Itokawa — the first ever asteroid samples to return to Earth for examination — the team at ASU used a Nanoscale Secondary Ion Mass Spectrometer (NanoSIMS).


To the team’s surprise, the results indicated that the samples from Itokawa were unexpectedly rich in water — even though they came from the surface of the asteroid where they were the most susceptible to damage.

The minerals have hydrogen isotopic compositions that are indistinguishable from Earth.

Zilliang Jin, a postdoctoral scholar,ASU’S School of Earth and Space Exploration

Itokawa isn’t the only one of its kind. According to Maitrayee Bose, one of the authors of the discovery, "S-type asteroids are one of the most common objects in the asteroid belt.” In fact, they’re the second-most common type of asteroid in our Solar System.