Scientists using the James Webb Space Telescope (JWST) have discovered a component of water on the metal-rich asteroid Psyche, suggesting the presence of rust. This finding could provide insights into the asteroid's formation.
Asteroid 16 Psyche, located in the main asteroid belt between Mars and Jupiter, spans 173 miles (280 kilometers) at its widest. Initially believed to be entirely metallic, Psyche's shiny surface led researchers to theorize that it might be the iron-rich core of a planetesimal, potentially offering clues about the formation of Earth and other terrestrial planets. Some estimates place the value of Psyche's metal components at an astonishing $100,000 quadrillion.
The hypothesis about Psyche's composition inspired NASA's ongoing Psyche mission, launched in October 2023, with plans to reach the asteroid by 2029 for a detailed study.
Recent data has revealed that Psyche might not be purely metallic. Over the past decade, new information about the asteroid's density and reflectance spectra indicates that it is likely a mix of silicate and metal.
In 2017, researchers detected traces of water on Psyche. Infrared spectra revealed the presence of hydroxyl units (OH molecules), a component of water. However, the results were inconclusive, as the data collected from Earth-based telescopes might have been contaminated by Earth's atmosphere.
To confirm the presence of water, planetary scientist Stephanie Jarmak and her team used two of JWST's infrared instruments — the Near Infrared Spectrograph (NIRSpec) and the Mid-Infrared Instrument (MIRI). In March 2023, they directed these instruments toward Psyche, capturing spectra from the asteroid's north pole. Their findings showed a hydroxyl signature consistent with rust-bearing, carbon-rich meteorites, suggesting that hydroxyls are bonded to metals on Psyche, forming rust.
While the MIRI data did not show a conclusive signature of water, researchers cannot rule out its presence. Water might be located in areas of Psyche that JWST could not observe or exist in concentrations too low for MIRI to detect.
Psyche's hydroxyl groups also offer clues about its origins. If these groups formed within the asteroid, it could indicate that Psyche originated in the cold outer regions of the solar system. However, current evidence suggests that water-bearing asteroids collided with Psyche, contributing to its current composition.
Future research aims to map the distribution of hydrated metals on Psyche's surface, including observations of its south pole, which features a large crater possibly formed by a collision with a water-bearing impactor.