2009 SH2

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.[3]

2009 SH2
Discovery[1][2]
Discovered bySiding Spring Survey
Discovery siteSiding Spring Obs.
Discovery date18 September 2009
Designations
2009 SH2
Earth co-orbital[3] · NEO
Aten[4]
Orbital characteristics[4]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 4
Observation arc14 days
Aphelion1.085 AU
Perihelion0.8978 AU
0.991 AU
Eccentricity0.09423
0.99 yr (360.46 d)
193.262°
0° 59m 55.362s / day
Inclination6.811°
6.674°
13 November 2020 22:52 UT
101.725°
Earth MOID0.0006 AU (90,000 km)
Physical characteristics
Mean diameter
30–60 m (assumed albedo 0.05–0.25)[5]
1.26 h[4]
18.8 (at discovery)[1]
24.9[4][2]

    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.[1] The asteroid was moving at an on-sky rate around 2.5 arcseconds per minute, from a distance of 0.030 AU (4.5 million km; 2.8 million mi) from Earth.[6] 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.[1]

    Orbit
    Orbit diagram of 2009 SH2 and the inner planets

    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 0.0006 AU (90,000 km; 56,000 mi) from Earth's orbital path and periodically makes close approaches to Earth.[4]

    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.[3]

    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.[2][5] A rotation period of 1.26 h has been tentatively measured from its lightcurve.[4]

    See also

    References
    1. "MPEC 2009-S51 : 2009 SH2". Minor Planet Electronic Circular. Minor Planet Center. 19 September 2009. Retrieved 12 February 2021.
    2. "2009 SH2". Minor Planet Center. International Astronomical Union. Retrieved 12 February 2021.
    3. de la Fuente Marcos, C.; de la Fuente Marcos, R. (September 2013). "A resonant family of dynamically cold small bodies in the near-Earth asteroid belt". Monthly Notices of the Royal Astronomical Society: Letters. 434 (1): L1–L5. arXiv:1305.2825. Bibcode:2013MNRAS.434L...1D. doi:10.1093/mnrasl/slt062.
    4. "JPL Small-Body Database Browser: 2009 SH2" (2009-10-02 last obs.). Jet Propulsion Laboratory. Retrieved 12 February 2021.
    5. Bruton, Dan. "Conversion of Absolute Magnitude to Diameter for Minor Planets". Department of Physics, Engineering, and Astronomy. Stephen F. Austin State University. Archived from the original on 23 July 2011. Retrieved 12 February 2021.
    6. "2009SH2 Ephemerides". Near Earth Objects – Dynamic Site (Ephemerides at discovery (obs. code E12)). Department of Mathematics, University of Pisa, Italy. Retrieved 12 February 2021.
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