16 Psyche

16 Psyche (sye'-kee) is the 13th-largest Main belt asteroid, measuring 250 kilometers in diameter.

It was discovered by Annibale de Gasparis on March 17, 1852 from Naples and named after the Greek nymph Psyche.

Spectral and other analyses indicate a fairly pure iron-nickel composition. Psyche and other class M asteroids originate from the metallic core of a large differentiated planetesimal similar to asteroid 4 Vesta.

Psyche is massive enough that its perturbations on other asteroids can be measured, which enables accurate mass and density values. Its density turns out to be extremely low, indicating extreme porousity or (less likely) a non-metallic composition. In other words, the asteroid is probably a gigantic rubble pile. (1)

Only one stellar occultation event by Psyche has so far been observed (from Mexico on March 22, 2002). Lightcurve variations indicate a non-spherical body.