When a NASA mission finally arrives at the vaunted Psyche asteroid in six years, it may find its target coated in a rust-like substance.
Previous glimpses suggests the asteroid, which measures 140 miles (225 kilometers) in diameter and is 2.2 billion miles away from Earth, contains a substantial amount of metals such as iron and nickel. Other prior research found that Psyche does not reflect light and may not be as dense as a largely metallic object should be. To get to the bottom of this celestial mystery, NASA, along with several prominent universities, used the James Webb Space Telescope to further examine Psyche.
In the resulting paper, currently available as a pre-print and slated to run in the American Astronomical Society’s Planetary Science Journal, scientists suggest that the unusual reflection could be due to the presence of hydroxyl—a group of chemicals that are just one hydrogen atom away from becoming water. Among these chemicals is hydroxide, which, combined with iron, forms rust. The data also hints at the presence of water on Psyche’s surface. The JWST is equipped with instruments that measure light in the infrared range, which isn’t visible to humans.
Because of Psyche’s composition, scientists have theorized that it may be the remnant of a planetesimal—an early planetary building block. However, the potential presence of hydroxyl and water introduces uncertainty about this theory.
“Hydration that is endogenous [internally sourced] could suggest that Psyche is not the remnant core of a protoplanet,” said Anicia Arredondo, a planetary physicist at the Southwest Research Institute and co-author of the study, in a statement. “Instead, it could suggest that Psyche originated beyond the ‘snow line,’ the minimum distance from the Sun where protoplanetary disc temperatures are low enough for volatile compounds to condense into solids, before migrating to the outer main belt.”
The data is far from conclusive, as it’s not clear if the hydroxyl and water are native to Psyche, or if they arrived during impacts from other celestial objects.
Psyche has been a subject of fascination due to its metallic makeup and possible origins. NASA launched a spacecraft, also named Psyche, in October 2023 to study the asteroid. Once at its destination, the Psyche probe will perform extensive examinations of its namesake target, searching for evidence of an ancient magnetic field and determining its chemical and mineral composition. The hope is that Psyche can be a case study for how terrestrial planets, like Earth, form in their infancy.
“Our understanding of solar system evolution is closely tied to interpretations of asteroid composition, particularly the M-class asteroids that contain higher concentrations of metal,” said Stephanie Jarmak, a physicist at the Harvard & Smithsonian’s Center for Astrophysics who led the research.
It’s going to be a while before scientists get their close up with Psyche to double check the JWST data. Despite traveling at over 27 miles (44.5 kilometers) per second, Psyche (the spacecraft) won’t meet up with Psyche (the asteroid) until August 2029.
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