Radar imaging of binary near-Earth asteroid (66391) 1999 KW4.
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.
Ostro
Steven J
SJ
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USA. ostro@reason.jpl.nasa.gov
Margot
Jean-Luc
JL
Benner
Lance A M
LA
Giorgini
Jon D
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Scheeres
Daniel J
DJ
Fahnestock
Eugene G
EG
Broschart
Stephen B
SB
Bellerose
Julie
J
Nolan
Michael C
MC
Magri
Christopher
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Pravec
Petr
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Scheirich
Petr
P
Rose
Randy
R
Jurgens
Raymond F
RF
De Jong
Eric M
EM
Suzuki
Shigeru
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