1620 Geographos

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1620 Geographos
1620Geographos (Lightcurve Inversion).png
A three-dimensional model of 1620 Geographos based on its light curve
Discovered by Albert George Wilson, Rudolph Minkowski
Discovery date 14 September 1951
MPC designation (1620) Geographos
Named after
National Geographic Society
1951 RA
Apollo, PHA,[1] Mars-crosser
Orbital characteristics[1]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 0
Observation arc 23558 days (64.50 yr)
Aphelion 1.6630 AU (248.78 Gm)
Perihelion 0.82764 AU (123.813 Gm)
1.2453 AU (186.29 Gm)
Eccentricity 0.33541
1.39 yr (507.61 d)
25.92 km/s
Inclination 13.338°
Earth MOID 0.029311 AU (4.3849 Gm)
Jupiter MOID 3.45265 AU (516.509 Gm)
Physical characteristics
Dimensions 5.0×2.0×2.1 ± 0.15km[1]
Mean radius
1.28 ± 0.075 km
5.22204 h (0.217585 d)[1]
0.3258 ± 0.051[1]
Temperature ~249 K

The asteroid 1620 Geographos /ˈɡræfɒs/ was discovered on September 14, 1951, at the Palomar Observatory by Albert George Wilson and Rudolph Minkowski. It was originally given the provisional designation 1951 RA. Its name, a Greek word meaning "geographer" (geo– 'Earth' + graphos 'drawer/writer'), was chosen to honour geographers and the National Geographic Society.

Geographos is a Mars-crosser asteroid and a near-Earth object belonging to the Apollos. In 1994, during the asteroid's closest approach to Earth in two centuries at 5.0 Gm – which will not be bettered until 2586 – a radar study of it was conducted by the Deep Space Network at Goldstone, California. The resultant images show Geographos to be the most elongated object in the solar system; it measures 5.1×1.8 km.

Geographos is an S-type asteroid, meaning that it is highly reflective and composed of nickel-iron mixed with iron- and magnesium-silicates. The light curve shows a high amplitude, indicative of its elongated shape. The Yarkovsky effect is causing a decrease in the orbital semimajor axis of 27.4±5.7 m yr−1, while the YORP effect is increasing the asteroid's rotation at the rate of (1.5±0.2)×10−3 rad yr−2. The interior of the asteroid probably has a rubble-pile structure. The asteroid's high thermal inertia indicates the surface is most likely a mix of fine grains and large rocks and boulders.[2]

Geographos was to be explored by the U.S.'s Clementine mission; however, a malfunctioning thruster ended the mission before it could approach the asteroid.

1620 Geographos is a potentially hazardous asteroid (PHA) because its minimum orbit intersection distance (MOID) is less than 0.05 AU and its diameter is greater than 150 meters. The Earth-MOID is 0.0304 AU (4,550,000 km; 2,830,000 mi).[1] Its orbit is well-determined for the next several hundred years.


  1. ^ a b c d e f g h "JPL Small-Body Database Browser: 1620 Geographos (1951 RA)". Retrieved 26 March 2016. 
  2. ^ Rozitis, B.; Green, S. F. (August 2014), "Physical characterisation of near-Earth asteroid (1620) Geographos. Reconciling radar and thermal-infrared observations", Astronomy & Astrophysics, 568: 11, Bibcode:2014A&A...568A..43R, doi:10.1051/0004-6361/201323090, A43. 

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