65803 Didymos

65803 Didymos
	Didymos (bottom left) and Dimorphos (top right) photographed by the DART space probe
Discovery
Discovered by	Spacewatch
Discovery site	Kitt Peak National Observatory
Discovery date	11 April 1996
Designations
MPC designation	(65803) Didymos
Pronunciation	/ˈdɪdɪmɒs/
Named after	Greek word for "Twin"
Alternative designations	1996 GT
Minor planet category	NEO · PHA; Apollo (2022)
Orbital characteristics
	Epoch 21 January 2022 (JD 2459600.5)
	Uncertainty parameter 0
Observation arc	24.82 years (9,066 days)
Aphelion	2.2753 AU
Perihelion	1.0131 AU
Semi-major axis	1.6442 AU
Eccentricity	0.38385
Orbital period (sidereal)	2.11 yr (770 days)
Mean anomaly	232.01
Mean motion	0° 28m 2.28s / day
Inclination	3.4079°
Longitude of ascending node	73.196°
Argument of perihelion	319.32°
Known satellites	1 (Dimorphos)
Earth MOID	0.0403 AU (15.7 LD)
Mars MOID	0.02 AU (7.8 LD)
Physical characteristics
Dimensions	851 × 849 × 620 m; (± 15 × 15 × 15 m)
Mean diameter	765±15 m
Mass	(5.4±0.4)×1011 kg (system); ≈ 5.2×1011 kg (primary)
Mean density	2.40±0.30 g/cm3
Synodic rotation period	2.2600±0.0001; 2.2593±0.0002 h
Axial tilt	174°±20°
Pole ecliptic latitude	−84°±20°
Pole ecliptic longitude	310°±20°
Geometric albedo	0.15±0.04
Spectral type	S · SMASS = Xk · X
Absolute magnitude (H)	18.0 · 18.16; 18.16±0.03

65803 Didymos (provisional designation 1996 GT) is a sub-kilometer asteroid and binary system that is classified as a potentially hazardous asteroid and near-Earth object of the Apollo group.^[a] The asteroid was discovered in 1996 by the Spacewatch survey at Kitt Peak, and its small 160-meter minor-planet moon, named Dimorphos, was discovered in 2003. Due to its binary nature, the asteroid was then named Didymos, the Greek word for 'twin'.

Didymos's moon, Dimorphos, was the target of the DART mission to test the viability of asteroid impact avoidance by collision with a spacecraft, while the impact was witnessed by LICIACube, a flyby CubeSat component of the mission.

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[2] "didymous". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

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