57 Mnemosyne

57 Mnemosyne was discovered by Robert Luther on 22 September 1859 at Düsseldorf. The name was chosen by Martin Hoek, director of the Utrecht Observatory, referencing the Titaness Mnemosyne of Greek mythology; in the astronomical context the name functions as a catalogued proper name assigned during 19th-century minor-planet naming practice.

Physically, 57 Mnemosyne is reported as a stony S-type asteroid with an estimated diameter of 112.59 ± 2.8 km. Descriptions in the sources treat its appearance in observational terms (lightcurves and measured parameters) rather than anthropomorphic or supernatural qualities.

As a non-sentient astronomical object, documented behaviors are orbital and rotational: it orbits the Sun in the outer main belt at an average distance near 3.149 AU with eccentricity ≈ 0.118 and inclination ≈ 15.2°. Its orbital period is about 5.58811 years, a value near a 2:1 commensurability with Jupiter that has made it useful in perturbation studies to derive Jupiter's mass. Photometric studies reported a rotation period measurement of 12.06 ± 0.03 h in 2006 (amplitude 0.14 ± 0.01 mag), but subsequent 2019 observations indicated that period was a poor fit and adopted a longer rotation period of 25.324 ± 0.002 h.