2009 SH2 is a sub-kilometer near-Earth asteroid of the Aten group, discovered by the Siding Spring Survey at Siding Spring Observatory, Australia on 18 September 2009. It is in a co-orbital configuration with Earth, a type of 1:1 orbital resonance where the asteroid appears to librate around Earth's path in a horseshoe orbit when viewed in a corotating reference frame with Earth. The co-orbital state of 2009 SH2 is only temporary as it has entered it about 30 years ago and will leave it in about 100 years into the future.
Discovery.
2009 SH2 was discovered by the Siding Spring Survey at Siding Spring Observatory, Coonabarabran, New South Wales, Australia on 18 September 2009. It was first observed in the constellation Fornax at an apparent magnitude of 18.8. The asteroid was moving at an on-sky rate around 2.5 arcseconds per minute, from a distance of from Earth. Follow-up observations of the asteroid were carried out by the Rio Cuarto Observatory (I20) on the following day. The asteroid was then confirmed by the Minor Planet Center and announced as 2009 SH2 on 19 September 2009.
Orbit.
2009 SH2 orbits the Sun at an average distance of 0.99 AU once every 360 days, or approximately 0.99 years. Its orbit has an eccentricity of 0.09 and an inclination of 7° with respect to the ecliptic plane. Over the course of its orbit, its distance from the Sun ranges from 0.90 AU at perihelion to 1.08 AU at aphelion, crossing the orbit of Earth. Since its orbit crosses that of Earth's while having a semi-major axis less than 1 AU, 2009 SH2 is classified as an Aten asteroid. Its nominal orbit has a small minimum orbit intersection distance approximately from Earth's orbital path and periodically makes close approaches to Earth.
In 2013, astronomers Carlos and Raúl de la Fuente Marcos identified 2009 SH2 to be in a co-orbital configuration with Earth, a type of 1:1 orbital resonance where the asteroid appears to librate around Earth's path in a horseshoe orbit when viewed in a corotating reference frame with Earth. The co-orbital state of 2009 SH2 is only temporary as it has entered it about 30 years ago and will leave it in about 100 years into the future.
Physical characteristics.
Based on an magnitude-to-diameter conversion and a measured absolute magnitude of 24.9, 2009 SH2 measures between 30 and 60 meters in diameter for an assumed geometric albedo of 0.25 and 0.05, respectively. A rotation period of has been tentatively measured from its lightcurve.
References.
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