57 Mnemosyne

57 Mnemosyne is a large main belt asteroid. It is a stony S-type asteroid in composition. This object was discovered by Robert Luther on 22 September 1859 in Düsseldorf. Its name was chosen by Martin Hoek, the director of the Utrecht Observatory, in reference to Mnemosyne, a Titaness in Greek mythology.

This asteroid is orbiting in the outer main belt at a distance of 471.082 Gm from the Sun with an eccentricity (ovalness) of 0.118 and a period of 2041.056 d. The orbital plane is inclined at an angle of 15.2° to the ecliptic. The orbital period of this asteroid is close to a 2:1 commensurability with Jupiter, which made it useful for perturbation measurements to derive the mass of the planet.

Photometry measurements made at the Oakley Observatory during 2006 produced a lightcurve with a rotation period of and an amplitude of in magnitude. Subsequent observations at Organ Mesa Observatory in 2019 showed this period was not a good fit to a longer light curve. A period of was adopted; roughly double the original period. It has an estimated span of and a mass of .