an area much brighter than the mean. Radar observations with the Arecibo Radar Telescope revealed that Psyche's "background" radar albedo is , comparable to other M-type asteroids like 21 Lutetia. This value is consistent with a silicate (rocky) regolith enriched in metal phases. However, in at least three locations, Psyche's radar albedo is nearly twice this value, suggesting high concentrations of metal phases in these regions. One of these locations corresponds with the optically bright Panthia crater, while the other two correspond with regions that have been reported as optically bright. This apparent correlation between optical and radar albedos on Psyche has led to the hypothesis that there is a link between the process(es) that create regions of high metal content and brighter terrain. Composition The bulk density of Psyche () places constraints on its overall composition. The iron-nickel found in most iron meteorites has a bulk density of . If Psyche were the remnant core of an early planetesimal, it would have to have an overall porosity of 50%. Given Psyche's size, this is considered highly improbable. However, there are other metal-rich meteorite types that have been suggested as Psyche analogs, each of which have bulk densities that are similar to Psyche's, including enstatite chondrites, bencubbinites, and mesosiderites. Several observers have reported the presence of silicate minerals on the surface of Psyche. Spectra taken in October 2016 at the NASA Infrared Telescope Facility at the Mauna Kea Observatories showed evidence (~3 μm absorption feature) of hydroxyl ions on the asteroid that may suggest the presence of hydrated silicates. Since Psyche is thought to have formed under dry conditions without the presence of water, the hydroxyl may have reached Psyche via past impacts from smaller carbonaceous asteroids. Psyche's radar albedo varies considerably over the surface, ranging from 0.22 to 0.52, values that are two to four times as high as most main-belt asteroids. Models of radar reflection equate this range of values with regolith bulk densities of 2.6 to 4.7 . This range is consistent with most of the metal-rich meteorite classes noted above and the spectroscopic detection of silicate minerals. It is inconsistent with a pure iron-nickel regolith unless it is highly porous. Origin Several possible origins have been proposed for Psyche. The earliest of these was that Psyche is an exposed metallic core resulting from a collision that stripped away the crust and mantle of an originally larger