Geographos

Named for a map of the sky

Geographos was discovered on 14 September 1951 by Albert George Wilson and Rudolph Minkowski at Palomar Observatory.^[2] It was named after the National Geographic Society, which funded the National Geographic Society – Palomar Observatory Sky Survey, a photographic atlas of the northern sky led by Minkowski.^[2][3]

The Greek word geographos means geographer — from “Earth” and “drawer or writer”.^[2]

Stretched to the limit

Geographos measures about 5.0 × 2.0 × 2.1 km.^[1] Its brightness changes by one to two full magnitudes as it rotates, a sign of extreme elongation.^[2] Radar images from Goldstone during its 1994 approach showed it to be the most elongated object in the Solar System known at the time.^[2][5]

The flyby that never happened

The Clementine spacecraft, launched in January 1994, was meant to map the Moon and then fly past Geographos at under 100 km.^[4] On 7 May 1994, a malfunction fired a thruster for 11 minutes, using up its fuel and leaving it spinning at about 80 rpm. The asteroid flyby was cancelled.^[4]

Orbit and close approaches

Geographos orbits between 0.83 and 1.66 AU every 1.39 years, crossing the orbits of Earth and Mars.^[1][2] It is a potentially hazardous asteroid by definition — larger than 150 m with an Earth MOID under 0.05 AU — but its orbit is well determined for centuries.^[2][6]

In 1994 it passed 5.0 million km from Earth, its closest approach in two centuries, which will not be bettered until 2586.^[2]

Sunlight is slowly moving it

Measurements show the Yarkovsky effect shrinking Geographos’ orbit by about 27 m per year, while the YORP effect speeds up its spin.^[2][7]

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