2000 SG344

2000 SG344 is a small Aten asteroid first observed in 2000. It is assumed to have a diameter of approximately 37 meters (120 feet) – or roughly twice that of the Chelyabinsk meteor – and an assumed mass of 7.1×107 kg (71,000 tonnes).[3] But the size is only known within about a factor 2. It is the largest object known to have a better than 1/400 chance (0.25%) of impacting Earth. The next good chance to observe the object will be in May 2028 when it passes 0.02 AU (3,000,000 km; 1,900,000 mi) from Earth.[2]

2000 SG344
2000 SG344 seen on 29 September 2000, as a dim streak in the center of the image, moving against the background field of stars
Discovery[1]
Discovered byD. J. Tholen
R. J. Whiteley
Discovery siteMauna Kea Obs.—UH88
Discovery date29 September 2000
(first observation only)
Designations
NEO · Aten
Orbital characteristics[2]
Epoch 2020-May-31 (JD 2457400.5)
Uncertainty parameter 3
Observation arc507 days (1.39 yr)
Aphelion1.0429 AU (156.02 Gm)
Perihelion0.91199 AU (136.432 Gm)
0.97744 AU (146.223 Gm)
Eccentricity0.06696
0.97 yr (352.96 d)
35.680°
1.0198°/day
Inclination0.112202°
191.91°
275.35°
Earth MOID0.0008 AU (120,000 km)
Physical characteristics
Mean diameter
37 m (assumed)[3]
15–70 meters[4]
Mass7.1×107 kg (assumed)[3]
24.7[2]

    Because of its very Earth-like orbit and because it would have been near the Earth in 1971 (coinciding with the Apollo program), there was speculation that 2000 SG344 might not be an asteroid but a man-made object such as an S-IVB booster stage from a Saturn V rocket which would make it about 15 meters in diameter and much less massive.[4][5] (cf. J002E3, the S-IVB booster of Apollo 12 which was mistaken for an asteroid.)

    Possible impacts with Earth

    Until December 2004, it was considered to have the highest (though still very low) likelihood of any near-Earth object to impact Earth in the next 100 years. It is ranked a zero on the Torino scale of impact risk because of its small size (the scale is 0–10) and is listed on Sentry Risk Table.[3][6] It was briefly surpassed in December 2004 by 99942 Apophis (which at the time was known only by its provisional designation 2004 MN4). Smaller asteroids such as 2006 JY26 and 2010 RF12 have a greater chance of impacting Earth.

    Based on 31 observations of 2000 SG344 made from May 1999 to October 2000, there is about a 1 in 380 chance that it will collide with Earth between 2069 and 2113.[3] The greatest chance of impact is on 16 September 2071 with a 1 in 1100 chance of impact. Assuming the object is a rocky asteroid, the impact energy released would be an estimated 1.1 megatons of TNT, which could create an impact crater approximately 100 feet (30 m) wide assuming it does not explode in the atmosphere.

    Virtual impactors
    Date Impact
    probability
    (1 in)    		 JPL Horizons
    nominal geocentric
    distance (AU)    		 NEODyS
    nominal geocentric
    distance (AU)    		 uncertainty
    region[7]
    2069-09-1859 million0.07 AU (10 million km)0.08 AU (12 million km)[8]± 32 million km
    2070-09-1771000.18 AU (27 million km)0.14 AU (21 million km)± 275 million km
    2071-09-1077000.43 AU (64 million km)0.35 AU (52 million km)± 462 million km
    2071-09-1611000.44 AU (66 million km)0.36 AU (54 million km)± 475 million km

    Planned NASA mission

    In 2008, NASA considered this asteroid as a possible target for a manned mission (Artemis 2) using the Orion spacecraft, prior to a projected 2030 push to Mars.[9][10] Those plans were since abandoned. 2000 SG344 will be observable in May 2028 at an apparent magnitude of 19.[11]

    References
    1. "IAU Circular: MPEC 2000-U19". 24 October 2000. Retrieved 18 May 2008. Cite journal requires |journal= (help)
    2. "JPL Small-Body Database Browser on 2000 SG344". NASA. Retrieved 18 May 2008.
    3. "2000 SG344 Earth Impact Risk Summary". 7 April 2017. Archived from the original on 24 October 2004. Retrieved 12 November 2004.
    4. "Much Ado about 2000 SG344". NASA. 7 November 2000. Archived from the original on 17 January 2009. Retrieved 19 May 2008.
    5. Chodas, P. W.; Chesley, S. R. (November 2001). "2000 SG344: The Story of a Potential Earth Impactor". Bulletin of the American Astronomical Society. 33: 1196. Bibcode:2001DDA....32.0803C. hdl:2014/12396.
    6. "NASA Near Earth Object Program: Current Impact Risks". Archived from the original on 29 May 2013. Retrieved 12 November 2004.
    7. Go to JPL Horizons. Table Settings: only need "20. Observer range & range-rate" AND "39. Range & range-rate 3-sigmas".
      RNG_3sigma = uncertainty range in km.
    8. "2000SG344 Ephemerides for 18 September 2069". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 9 December 2020. Retrieved 9 December 2020.
    9. Sample, Ian (7 May 2008). "Closer encounter: Nasa plans landing on 40m-wide asteroid travelling at 28,000mph". The Guardian. Archived from the original on 9 May 2008. Retrieved 9 May 2008.
    10. Into the Beyond: A Crewed Mission to a Near-Earth Object – text slides
    11. "Near-Earth Object Human Space Flight Accessible Targets Study (NHATS)". NASA/JPL Near-Earth Object Program Office. Retrieved 8 June 2012.

    Further reading
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