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|
|National Geographic Society|
|Apollo, PHA, Mars-crosser|
|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)|
|1.39 yr (507.61 d)|
Average orbital speed
|Earth MOID||0.029311 AU (4.3849 Gm)|
|Jupiter MOID||3.45265 AU (516.509 Gm)|
|Dimensions||5.0×2.0×2.1 ± 0.15km|
|1.28 ± 0.075 km|
|5.22204 h (0.217585 d)|
|0.3258 ± 0.051|
The asteroid 1620 Geographos // 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 ±5.7 m yr−1, while the 27.4YORP effect is increasing the asteroid's rotation at the rate of ±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. (1.5
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). Its orbit is well-determined for the next several hundred years.
- "JPL Small-Body Database Browser: 1620 Geographos (1951 RA)". Retrieved 26 March 2016.
- 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.