Editing 16 Psyche (section)

=== Composition ===
The bulk density of Psyche ({{val|3.9|0.3|u=g/cm3}}) places constraints on its overall composition. The iron-nickel found in most [[iron meteorite]]s has a bulk density of {{val|7.9|u=g/cm3}}. If Psyche were the remnant [[Planetary core|core]] of an early [[planetesimal]], it would have to have an overall porosity of 50%. Given Psyche's size, this is considered highly improbable.<ref name="Elkins-Tanton_2020" /> 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 chondrite]]s, [[bencubbinite]]s, and [[mesosiderite]]s.<ref name="Gaffey_asteroidsII" /><ref name="Viikinksk-Vernza-etal-2018" /><ref name="Elkins-Tanton_2020" />

Several observers have reported the presence of [[silicate mineral]]s on the surface of Psyche.<ref name="Hardersen-Gaffey-Abell-2005" /><ref name="Ockert-Bell"/><ref name="Sanchez"/> Spectra taken in October&nbsp;2016 at the [[NASA Infrared Telescope Facility]] at the [[Mauna Kea Observatories]] showed evidence (~3&nbsp;μm absorption feature) of [[Hydroxy group|hydroxyl]] ions on the asteroid that may suggest the presence of hydrated silicates.<ref name=Takir-Reddy-etal-2016/> 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 asteroid]]s.<ref name=Takir-Reddy-etal-2016/><ref name="Shepard2015" />

Psyche's [[Albedo#Radar Albedo|radar albedo]] varies considerably over the surface, ranging from 0.22 to 0.52,<ref name="Shepard2021" /> values that are two to four times as high as most main-belt asteroids.<ref name="Magri2007"/> Models of radar reflection equate this range of values with regolith bulk densities of 2.6 to 4.7 {{val|u=g/cm3}}.<ref name="Shepard2015" /> This range is consistent with most of the metal-rich [[Meteorite classification|meteorite]] classes noted above and the spectroscopic detection of silicate minerals. It is inconsistent with a pure [[Iron meteorite|iron-nickel]] regolith unless it is highly porous.

[[File:16 Psyche orbit.png|thumb|The orbit of Psyche, between Mars and Jupiter, with eccentricity of 0.140: much higher than most planets, but typical for an asteroid.]]