is an Aten

Aten asteroid

The Aten asteroids are a group of near-Earth asteroids, named after the first of the group to be discovered . They are defined by having semi-major axes of less than one astronomical unit...

 and Mercury-crosser asteroid discovered by LINEAR

Linear

In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...

 in 1999.

has a moon

Asteroid moon

A minor planet moon is an astronomical body that orbits a minor planet as its natural satellite. It is thought that many asteroids and Kuiper belt objects may possess moons, in some cases quite substantial in size...

 orbiting it. The moon, designated S/2001 (66391) 1 or '1999 KW4 Beta' is ~360 m in diameter, and orbits 'Alpha' in 0.758 d (16 hours) at a distance of 2.6 km. The presence of a companion was suggested by photometric observations made June 19-27, 2000 by Petr Pravec

Petr Pravec

Petr Pravec is a Czech astronomer, born in Třinec, a prolific discoverer of binary asteroids using lightcurve photometric studies. He is leading the effort of a large consortium of stations called BinAst to look for multiplicity in the NEA and inner main-belt populations...

 and Lenka Šarounová

Lenka Šarounová

Lenka Kotková is a Czech astronomer.She is a prolific discoverer of asteroids. She works at Observatoř Ondřejov , located near Prague...

 at Observatoř Ondřejov (Ondřejov Observatory) and was confirmed by radar observations from Arecibo Observatory

Arecibo Observatory

The Arecibo Observatory is a radio telescope near the city of Arecibo in Puerto Rico. It is operated by SRI International under cooperative agreement with the National Science Foundation...

 from May 21-23, 2001 by Lance A. M. Benner, Steven J. Ostro

Steven J. Ostro

Steven J. Ostro was an American scientist specializing in Radar Astronomy. He worked at NASA's Jet Propulsion Laboratory. Ostro led radar observations of numerous asteroids, as well as the moons of Jupiter and Saturn, Saturn's rings, and Mars and its satellites...

, Jon D. Giorgini, Raymond F. Jurgens, Jean-Luc Margot

Jean-Luc Margot

Jean-Luc Margot is a Belgian-born astronomer and a Professor at UCLA. He specializes in planetary sciences. He was awarded the H. C. Urey Prize by the American Astronomical Society in 2004....

 and Michael C. Nolan, announced on May 23, 2001.

The shapes of the two bodies and their dynamics are complex. Among other bizarre properties, the equatorial regions of Alpha are very close to breakup: raising a particle a meter above the surface would put it into orbit around the object.