90 Antiope

The most remarkable feature of Antiope is that it consists of two components of almost equal size (the difference in mass is less than 2.5%[12]), making it a truly "double" asteroid.

Its binary nature was discovered on 10 August 2000 by a group of astronomers using adaptive optics at the Keck Telescope on Mauna Kea.

[citation needed] Complementary observations using adaptive optic observations on 8–10 m class telescopes and mutual events photometric lightcurve over several months have served as input quantities for a derivation of a whole set of other physical parameters (shapes of the components, surface scattering, bulk density, and internal properties).

The shape model is consistent with slightly non-spherical components, having a size ratio of 0.95 (with an average radius of 42.9 km), and exhibiting equilibrium figures for homogeneous rotating bodies.

A comparison with grazing occultation event lightcurves taken in 2003 suggests that the real shape of the components do not depart much from Roche equilibrium figures (by more than 10%).

[citation needed] Observations from the VLT-UT4 telescope equipped with an adaptive optics system in 2007 and lightcurve data analysis suggest that one of the components appears to have a 68 km bowl-shaped impact crater that may be the result of a violent collision that broke proto-Antiope into two equisized bodies.

This implies they may have a common origin, such as being formed from the breakup of a larger rubble-pile asteroid, but other formation scenarios cannot be ruled out.