title: Radar imaging of binary near-Earth asteroid (66391) 1999 KW4.
abstract: High-resolution radar images reveal near-Earth asteroid (66391) 1999 KW4 to be a binary system. The approximately 1.5-kilometer-diameter primary (Alpha) is an unconsolidated gravitational aggregate with a spin period approximately 2.8 hours, bulk density approximately 2 grams per cubic centimeter, porosity approximately 50%, and an oblate shape dominated by an equatorial ridge at the object's potential-energy minimum. The approximately 0.5-kilometer secondary (Beta) is elongated and probably is denser than Alpha. Its average orbit about Alpha is circular with a radius approximately 2.5 kilometers and period approximately 17.4 hours, and its average rotation is synchronous with the long axis pointed toward Alpha, but librational departures from that orientation are evident. Exotic physical and dynamical properties may be common among near-Earth binaries.
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USA. ostro@reason.jpl.nasa.gov
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Ostro
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Margot
authors.forename: Lance A M
authors.initials: LA
authors.lastname: Benner
authors.forename: Jon D
authors.initials: JD
authors.lastname: Giorgini
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Scheeres
authors.forename: Eugene G
authors.initials: EG
authors.lastname: Fahnestock
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Broschart
authors.forename: Julie
authors.initials: J
authors.lastname: Bellerose
authors.forename: Michael C
authors.initials: MC
authors.lastname: Nolan
authors.forename: Christopher
authors.initials: C
authors.lastname: Magri
authors.forename: Petr
authors.initials: P
authors.lastname: Pravec
authors.forename: Petr
authors.initials: P
authors.lastname: Scheirich
authors.forename: Randy
authors.initials: R
authors.lastname: Rose
authors.forename: Raymond F
authors.initials: RF
authors.lastname: Jurgens
authors.forename: Eric M
authors.initials: EM
authors.lastname: De Jong
authors.forename: Shigeru
authors.initials: S
authors.lastname: Suzuki