(66391) 1999 KW4
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| Discovery A (http://cfa-www.harvard.edu/iau/lists/NumberedMPs.html) | |
|---|---|
| Discoverer | LINEAR |
| Discovery date | May 20 1999 |
| Alternate designations | B (http://cfa-www.harvard.edu/iau/MPDes.html) |
| Category | Aten asteroid, Mercury-crosser asteroid, Venus-crosser asteroid |
| Orbital elements C (http://asteroid.lowell.edu/) Epoch July 14, 2004 (JD 2453200.5) | |
| Eccentricity (e) | 0.688 |
| Semi-major axis (a) | 96.085 Gm (0.642 AU) |
| Perihelion (q) | 29.943 Gm (0.200 AU) |
| Aphelion (Q) | 162.228 Gm (1.084 AU) |
| Orbital period (P) | 188.017 d (0.51 a) |
| Mean orbital speed | 37.16 km/s |
| Inclination (i) | 38.890° |
| Longitude of the ascending node (Ω) | 244.934° |
| Argument of perihelion (ω) | 192.597° |
| Mean anomaly (M) | 168.533° |
| Physical characteristics | |
| Dimensions | 1.2 km |
| Mass | 2.33×1012 kg |
| Density | 2.6 g/cm³ |
| Surface gravity | 0.000 43 m/s² |
| Escape velocity | 0.000 72 km/s |
| Rotation period | 0.1152 d |
| Spectral class | ? |
| Absolute magnitude | 16.5 |
| Albedo | 0.3 |
| Mean surface temperature | ~326 K |
(66391) 1999 KW4 (also written 1999 KW4) is an Aten and Mercury-crosser asteroid discovered by LINEAR in 1999. It is interesting for two reasons.
First, 1999 KW4 is one of the few asteroids whose orbit crosses that of Mercury, the innermost planet (another is 1566 Icarus). Its unusual, eccentric orbit suggests that the asteroid may in fact be a comet that has lost its surface ice and can no longer produce a tail.
Second, despite its small size (about 1.2 km in diameter), 1999 KW4 has a small moon orbiting it. The moon, designated S/2001 (66391) 1 is only 360 m in diameter, and orbits 1999 KW4 in 0.758 d (16 hours) at a distance of 2.6 km and a leisurely speed of 0.25 m/s (0.9 km/h). The companion was first suggested by an apparent eclipsing binary signal in photometric observations made June 19-27, 2000 by Petr Pravec and Lenka Šarounová at Ondrejov Observatory. It 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.
References
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