Water Discovered In Samples From Asteroid Itokawa

Asteroid Itokawa. Japan Aerospace Exploration Agency (JAXA)

There are currently two missions collecting material from asteroids, Hayabusa-2 and OSIRIS-REx. But before them, there was Hayabusa (the original), which brought back small samples of space rock to be analyzed on Earth in 2010.

The latest set of tests has given us an important new insight into the samples. Researchers at Arizona State University (ASU) found that Itokawa has water-rich materials, which has a big consequence for water on Earth. Asteroids like this, according to the team, might be responsible for delivering as much as half of our planet’s ocean water. The findings are reported in Science Advances.

The team found the mineral pyroxene in two out of five samples. On Earth, this mineral contains water molecules in their crystal structure and the researchers hoped this would be the case for Itokawa too, despite the asteroid's expected dryness.

"We found the samples we examined were enriched in water compared to the average for inner Solar System objects," lead author Dr Ziliang Jin, a postdoctoral scholar at ASU, said in a statement.

Itokawa is a peanut-shaped asteroid with a maximum diameter of 535 meters (1,800 feet) and a width of 209-294 meters (700-1,000 feet). It has quite a history. It has experienced multiple impacts, heating, shocks, and fragmentations. These events would certainly raise the temperature of the asteroid and lead to a loss of water. Finding water has important implications for the class of asteroids to which Itokawa belongs (the S-types).   

"S-type asteroids are one of the most common objects in the asteroid belt," explained co-author Assistant Professor Maitrayee Bose. "They originally formed at a distance from the Sun of one-third to three times Earth's distance."

Itokawa appears to be the end product of a 19-kilometer (12-mile) parent body, which reached temperatures of up to 800°C (1,500°F) and was broken apart by impacts, with one final massive one that broke it apart completely. Some of the fragments eventually merged into what we see today.

"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 [328 feet] deep within it," Jin explained.

The mystery of the origin of Earth’s water is fascinating. While some water was released by volcanic processes, a large fraction is believed to have come from space. Comets and C-type asteroids, which formed further out and are ice-rich, have been thought to be culprits, but the isotopic composition of their water doesn’t match Earth’s. In contrast, the samples from Itokawa are indistinguishable from samples of water on Earth.

Hayabusa was a mission by the Japanese Space Agency.

The two samples from Itokawa that contain water. JAXA

 

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