|Discovered by R. H. McNaught|
MPC designation (5645) 1990 SP
Minor planet category Apollo · NEO
Discovered 20 September 1990
Discoverer Robert H. McNaught
Asteroid group Apollo asteroid
|Discovery date 20 September 1990|
Alternative names 1990 SP
Observation arc 40.89 yr (14,935 days)
Discovery site Siding Spring Observatory
|Similar Solar System, 3362 Khufu, 2212 Hephaistos, 1865 Cerberus, 4183 Cuno|
(5645) 1990 SP is an eccentric and tumbling asteroid, classified as near-Earth object and Apollo asteroid, approximately 1.7 kilometers in diameter. It was discovered on 20 September 1990, by Scottish–Australian astronomer Robert McNaught at the Siding Spring Observatory in Canberra, Australia.
The asteroid orbits the Sun at a distance of 0.8–1.9 AU once every 1 years and 7 months (576 days). Its orbit has an eccentricity of 0.39 and an inclination of 14° with respect to the ecliptic. The first precovery was taken at the discovering observatory during the Digital Sky Survey (DSS) in 1974, extending the asteroid's observation arc by 16 years prior to its discovery. This near-Earth asteroid has an Earth minimum orbit intersection distance of 0.055 AU (8,200,000 km), only slightly above the threshold minimum distance of 19.5 lunar distances (0.05 AU) to make it a potentially hazardous object. It also makes close approaches to Mars. On 14 April 1969, it passed the Red Planet at only 0.013 AU (1,900,000 km).
The stony S-type asteroid is also classified as a P-type asteroid, based on post-cryogenic observations by the Spitzer Space Telescope, while observations at the NASA Infrared Telescope Facility using its SpeX instrument during a follow-up campaign of the Spitzer-observed objects between 2009 and 2012, gave it a C/X/T spectral type.
In April 2002, Czech astronomer Petr Pravec obtained a rotational light-curve from a photometric observations, which gave a relatively long period of 7001303900000000000♠30.39±0.04 hours with a brightness variation of 0.7 in magnitude (U=2). The observations have also shown that the body is most likely in a tumbling motion.
Estimates for the body's diameter range from 1.6 to 2.2 kilometers with an albedo for its surface between 0.06 and 0.12, according to observations made by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer and by the Spitzer Space Telescope. The Collaborative Asteroid Lightcurve Link takes the revised WISE data – an albedo of 0.0872 and a diameter of 1.65 kilometers – as the best of all available results.