(66391) 1999 KW4

Infobox Planet
discovery=yes
physical_characteristics = yes
bgcolour=#FFFFC0


caption= Simulated animation of 1999 KW4's rotation and moon.
name=(66391) 1999 KW₄
discoverer=LINEAR
discovered=May 20 1999
alt_names="none"
mp_category=Aten asteroid,
Mercury-crosser asteroid,
Venus-crosser asteroid
epoch=July 14, 2004 (JD 2453200.5)
semimajor=96.085 Gm (0.642 AU)
perihelion=29.943 Gm (0.200 AU)
aphelion=162.228 Gm (1.084 AU)
eccentricity=0.688
period=188.017 d (0.51 a)
inclination=38.890°
asc_node=244.934°
arg_peri=192.597°
mean_anomaly=168.533°
avg_speed=37.16 km/s
dimensions=1.2 km
mass=2.33×10¹² kg
density=2.6 g/cm³
surface_grav=0.000 43 m/s²
escape_velocity=0.000 72 km/s
rotation=0.1152 d
spectral_type=?
abs_magnitude=16.5
albedo=0.3
single_temperature=~326 K

mp|(66391) 1999 KW|4 (also written (66391) 1999 KW4) is an Aten and Mercury-crosser asteroid discovered by LINEAR in 1999.

mp|1999 KW|4 has a moon orbiting it. The moon, designated S/2001 (66391) 1 or '1999 KW4 Beta' is ~360 m in diameter, and orbits mp|1999 KW|4 '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 and Lenka Šarounová at Observatoř Ondřejov (Ondřejov Observatory) and was confirmed by radar observations from Arecibo Observatory from May 21-23, 2001 by Lance A. M. Benner, Steven J. Ostro, Jon D. Giorgini, Raymond F. Jurgens, Jean-Luc Margot and Michael C. Nolan, announced on May 23, 2001.

The shapes of the two bodies and their dynamics are complex. [NASA Jet Propulsion Laboratory [http://echo.jpl.nasa.gov/ Asteroid Radar Research] , retrieved May 32007] 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.

References

* Johnston, Wm. Robert, ed. [http://www.johnstonsarchive.net/astro/astmoons/am-66391.html (66391) 1999 KW4] January 72007, retrieved May 32007
* Margot, Jean-Luc, [http://astrosun2.astro.cornell.edu/~jlm/Sampler.html Another radar image of mp|1999 KW|4] November1999, retrieved May 32007