Psyche

A metal-rich asteroid that may be the exposed iron core of an ancient protoplanet — target of NASA's Psyche mission.

Orbits Sun

One of the most massive M-type (metallic) asteroids known.
Estimated 30-60% metal by volume.
Target of NASA Psyche mission (launched October 2023, arriving August 2029).
May be the exposed iron-nickel core of a differentiated protoplanet whose mantle was stripped by collisions.

Physical Properties

Mean radius113 km

Mass2.29e19 kg

Density3.88 g/cm³

Rotation period4.196 h

Bond albedo0.16

Orbit

OrbitsSun

Semi-major axis2.923 AU

Eccentricity0.134

Inclination3.095°

Orbital period5 yr

Sources & Further Reading

Numerical values (radius, mass, orbital elements, temperatures) are drawn from NASA NSSDC Planetary Fact Sheets, JPL Horizons, and the JPL Small-Body Database. Last refreshed: 2026-04-18 18:19:26.

16 Psyche is one of the most massive M-type (metallic) asteroids in the main belt. Radar and spectral measurements suggest it contains substantial amounts of iron, nickel and other siderophile metals. One hypothesis is that Psyche is the exposed core of a differentiated protoplanet whose mantle was stripped away in early Solar System collisions. NASA’s Psyche mission, launched 13 October 2023 on a Falcon Heavy, will arrive at the asteroid in August 2029 and begin orbital mapping to test that hypothesis.