11885 Summanus

11885 Summanus (prov. designation: 1990 SS) is a dark asteroid and large near-Earth object of the Apollo group. It was discovered by astronomers with the Spacewatch programm at Kitt Peak Observatory on 25 September 1990. The object has a rotation period of 7.3 hours and measures approximately 1.3 kilometers (0.8 miles) in diameter.^[3] It was named after Summanus, the Roman deity of nocturnal lightning and thunder.^[1]

11885 Summanus

Discovery[1]
Discovered by	Spacewatch
Discovery site	Kitt Peak Obs.
Discovery date	25 September 1990
Designations
MPC designation	1990 SS
Pronunciation	/sʌˈmeɪnəs/[2]
Named after	Summānus
Minor planet category	NEO · Apollo[3]
Orbital characteristics[3]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	20.54 yr (7,504 days)
Aphelion	2.5119 AU
Perihelion	0.8950 AU
Semi-major axis	1.7035 AU
Eccentricity	0.4746
Orbital period (sidereal)	2.22 yr (812 days)
Mean anomaly	346.75°
Mean motion	0° 26m 35.88s / day
Inclination	19.419°
Longitude of ascending node	359.89°
Argument of perihelion	116.07°
Earth MOID	0.0689 AU (26.8 LD)
Physical characteristics
Mean diameter	1.298±0.446 km[3]
Synodic rotation period	7.358 h[4]
Geometric albedo	0.033±0.029[3]
Absolute magnitude (H)	18.5[3]

Discovery and naming

Summanus was discovered on 25 September 1990, by Spacewatch survey at the Kitt Peak Observatory, southwest of Tucson, Arizona, United States. It was the first fully automatic discovery of a near-Earth asteroid.^[5][6] The name Summanus is symbolic of the discovery of the asteroid by software running on a (lightning-fast) computer.^[1]

Orbit

The orbit is well-established with over 20 years of observations. Summanus orbits the Sun in the inner main-belt at a distance of 0.9–2.5 AU once every 2 years and 3 months (812 days). Its orbit has an eccentricity of 0.47 and an inclination of 19° with respect to the ecliptic.^[3]

The closest approach to the Earth in the years 1900–2200 is 0.102 AU (15,300,000 km; 9,500,000 mi) on 17 March 1991, and 17 March 2011. For comparison, the distance to the Moon is about 0.0026 AU (390,000 km; 240,000 mi).