6979 days (19.11 yr)
11 April 1996
| 11 April 1996|
2.2755 AU (340.41 Gm)
| Kitt Peak National Observatory|
Solar System, Sun, 69230 Hermes, 3671 Dionysus, (66391) 1999 KW4
65803 Didymos (1996 GT) is an Apollo asteroid discovered on April 11, 1996 by Joe Montani at Spacewatch at Kitt Peak. It has a moon, whence the appellation "Didymos", meaning "twin". The primary is about 800 m in diameter and the moon 150 m in diameter. The moon is in an orbit about 1.1 km from the primary and with an orbital period of 11.9 hours. Didymos is the most easily reachable asteroid of its size from Earth, requiring a delta-v of only 5.1 km/s for a spacecraft to rendezvous, compared to 6.0 km/s to reach the Moon. It is the target of the proposed AIDA spacecraft, an unmanned mission that would test the possibility of changing an asteroid's orbit via impacting its surface.
65803 Didymos Wikipedia
Didymos was discovered by Joseph L. Montani using the Spacewatch 0.9-m telescope in 1996. The binary nature of the asteroid was discovered by others; suspicions of binarity first arose in Goldstone delay-Doppler echoes, and these were confirmed with an optical light-curve analysis, along with Arecibo radar imaging on November 23, 2003. It has been informally named "Didymoon".
Montani proposed a name to the International Astronomical Union only after the binary nature of the object was discovered: the name "Didymos" is Greek for "twin". The moon has been nicknamed "Didymoon".
Didymos's approach to Earth in November 2003 was especially close with a distance of 7.18 million km; it will not come that near until November 2123, with a distance of 5.9 million km. Didymos also passes very close to Mars: 4.69 million km in 2144.
The satellite has an orbital period of 11.9 hr.
Didymos rotates rapidly, with a period of 2.26 hours. Its density is 1.7±0.4 g/cm3.
Didymos is the target of the proposed Asteroid Impact & Deflection Assessment (AIDA) mission, a collaboration between ESA and NASA. This will be the first spacecraft to target an asteroid known to have a moon (243 Ida was visited by the Galileo spacecraft but its moon was a surprise). The mission is intended to test whether a spacecraft could successfully deflect an asteroid on a collision course with Earth; it would study Didymos from orbit, while also crashing a smaller spacecraft into Didymoon, in order to study the effect on its orbit.