(66391) 1999 KW4

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Categories: Aten asteroids | Binary asteroids | Earth-crosser asteroids

The correct title of this article is (66391) 1999 KW₄. It features superscript or subscript characters that are substituted or omitted because of technical limitations.

**(66391) 1999 KW₄**
Discovery
Image:1999 KW4 animated.gif Simulated animation of 1999 KW4's rotation and moon.
Discovered by	LINEAR
Discovery date	May 20 1999
Designations
Alternative names	none
Minor planet category	Aten asteroid, Mercury-crosser asteroid, Venus-crosser asteroid
Orbital characteristics
Epoch July 14, 2004 (JD 2453200.5)
Aphelion	162.228 Gm (1.084 AU)
Perihelion	29.943 Gm (0.200 AU)
Semi-major axis	96.085 G m (0.642 AU)
Eccentricity	0.688
Orbital period	188.017 d (0.51 a)
Average orbital speed	37.16 km/s
Mean anomaly	168.533°
Inclination	38.890°
Longitude of ascending node	244.934°
Argument of perihelion	192.597°
Physical characteristics
Dimensions	1.2 km
Mass	2.33×10¹² kg
Mean density	2.6 g/cm³
Equatorial surface gravity	0.000 43 m/s²
Escape velocity	0.000 72 km/s
Rotation period	0.1152 d
Albedo	0.3
Temperature	~326 K
Spectral type	?
Absolute magnitude	16.5

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

1999 KW₄ has a moon orbiting it. The moon, designated S/2001 (66391) 1 or '1999 KW4 Beta' is ~360 m in diameter, and orbits 1999 KW₄ '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.^[2] 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.

Image:Asteroid 1994 KW4.jpg

Radar images of asteroid 1999 KW₄ and its moon. The 'streaks' on the image are the moon's trail as it moved while the images were created.

References

^ [1]
^ NASA Jet Propulsion Laboratory Asteroid Radar Research, retrieved May 3 2007

Johnston, Wm. Robert, ed. (66391) 1999 KW4 January 7 2007, retrieved May 3 2007
Margot, Jean-Luc, Another radar image of 1999 KW₄ November1999, retrieved May 3 2007

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