Investigating Asteroid (16) Psyche with HST Ultraviolet Observations

The Main Belt Asteroid (16) Psyche is considered the archetype for the M-class of asteroids due to its relatively featureless, red-sloped spectrum at visible and near-infrared wavelengths. Its high radar albedo and mass suggest that its composition is dominated by iron-nickel. We observed Psyche using the Hubble Space Telescope at ultraviolet (UV) wavelengths (170 nm–310 nm) to further assess its composition. We find that the UV spectrum is very red, consistent with the presence of iron on the surface; however, our models show that only a small amount of iron (10 percent) would be needed to reproduce the spectrum of Psyche if the iron particles are intimately mixed with other materials. We find two weak absorption features in the UV spectrum that may be attributable to metal-oxide charge transfer bands. Some hemispheric differences were detected in the spectra, possibly due to variations in composition, grain size, or exposure to space weathering. The arrival of NASA’s Psyche mission in 2026 may better explain these observed differences.