Water Detected on Largest Metallic Asteroid in Solar System

The asteroid, called Psyche, is 186 miles across and is made of almost pure nickel-iron metal. It is thought to be the remnant core of a planetary embryo that was mostly destroyed by impacts billions of years ago.

Previous observations of Psyche had shown no evidence for water-rich minerals on its surface. However, new observations from the NASA Infrared Telescope Facility in Hawaii show evidence for water and/or hydroxyl on its surface. Results are published in The Astronomical Journal.

While the source of these water molecules on Psyche remains a mystery, scientists propose a few possible mechanisms for their formation. It is possible that water-rich minerals detected on Psyche might have been delivered to its surface by carbonaceous asteroids that impacted Psyche in the distant past.

“We think that Psyche may not be entirely exposed metallic core,” says Driss Takir, lead author and scientist at the USGS Astrogeology Science Center in Flagstaff, Arizona. “What we see might instead have been a core-mantle boundary of a differentiated body that was disrupted via impacts. Solar radiation is another mechanism that can produce hydroxyl, which is a molecule consisting of one oxygen atom and one hydrogen atom, by interacting with the surface of Psyche.”

"This work underscores how much more we have to learn about asteroids,” says Laszlo Kestay, Director of the USGS Astrogeology Science Center. “It will take more of this kind of careful work with telescopes on Earth, and spacecraft visiting asteroids, before we understand what treasures await us in space."

Takir is a member of NASA’s OSIRIS-REx mission and JAXA’s Hayabusa2 mission to collect carbonaceous samples from the water-rich asteroids, Bennu and Ryugu.

“We are excited to continue studying Psyche, and other water-rich asteroids, to give us further insight into the distribution of potential resources in space,” said Takir.

This research on Psyche is funded by the USGS/NASA Eugene M. Shoemaker Fellowship, NASA Planetary Science Division Planetary Geology and Geophysics and Solar System Observations Programs.