22_Kalliope

22 Kalliope

22 Kalliope (Καλλιόπη) is a large main belt asteroid of the M-type, discovered by J. R. Hind on November 16, 1852. It is named after Calliope, the Greek Muse of epic poetry.

Characteristics

Kalliope is somewhat elongated, approximately 180 km in diameter, and slightly asymmetric, as evidenced by resolved images taken with the VLT at the European Southern Observatory .

While its spectrum is an M-type, Kalliope does not appear to be metallic, similarly to other M-types such as 21 Lutetia, for example. Firstly, its density, which is known with confidence from its satellite's orbit, is far too low to agree with any plausible metallic substance, even a rubble pile. It would have to be 70% porous, which is inconsistent with packing considerations. Furthermore, spectroscopic studies have shown evidence of hydrated minerals and silicates , which indicate rather a stony surface composition. Kalliope also has a low radar albedo , which is again inconsistent with a metallic surface.

Lightcurve analysis indicates that Kalliope's pole most likely points towards ecliptic coordinates (β, λ) = (-23°, 20°) with a 10° uncertainty , which gives Kalliope an axial tilt of 103°. Kalliope's rotation is then slightly retrograde.

Satellite

Kalliope has one known natural satellite, Linus, or (22) Kalliope I Linus. It is quite large being 30-40 km in diameter, and would be a sizeable asteroid by itself. It orbits about 1065 km from Kalliope, equivalent to about 12 Kalliope radii. Linus was discovered on August 29, 2001 by Jean-Luc Margot and Michael E. Brown, while another team lead by William Merline also independently detected the moon 3 days later.

First Stellar Occultation

On November 7 2006, the first stellar occultation by the satellite of an asteroid (Linus) was successfully observed by a group of Japanese observers according to a prediction that was made just one day before by Berthier et al. based on more than 5 years of regular observations of Kalliope binary system using adaptive optics systems on ground-based telescopes. The observed chords of Linus give a unique opportunity to estimate the size of the moonlet which was estimated to 20-28 km.