Largest m-type asteroid

The largest M-type asteroid is 16 Psyche, which has a mean diameter of 226 km (plus or minus 5 km) and a mass of approximately 22.87 x 10^15 tonnes (22.87 quadrillion tonnes; or about 0.03% of the mass of the Moon). Based on an estimated density of between 3,400 and 4,100 kg per m^3, Psyche is believed to be between 30% and 60% metal, with the remainder being silicate rock.

An M-type asteroid is one thought to contain a high quantity of metal (typically iron and nickel). It is one of the three major asteroid classifications along with C-type (carbon-rich) and S-type (silicate rich, or stony). Psyche is irregularly shaped, and measures 290 x 245 x 170 km across its principal axes. The NASA Psyche probe is scheduled to reach the asteroid in January 2026, following its launch in August 2022.

The prefix "16" refers to the fact that Psyche was the 16th minor solar system body to be discovered. It was discovered by the Italian astronomer Annibale de Gasparis on 17 March 1852.