 Geographos
is classified as an Earth-crossing asteroid because its orbit can
evolve to intersect Earth's orbit. Scientists have found fewer than
300 Earth-crossing asteroids; however, they believe hundreds of thousands
of objects might exist. The asteroids probably include several hundred
objects larger than Geographos, thousands larger than half a mile
across, and a few hundred thousand that are larger than a football
field.
Geographos is an irregular body with dimensions of about 5.1 kilometers
by 1.8 kilometers (3.2 miles by 1.2 miles). It has the largest length-to-width
ratio of any solar system object ever imaged to date. Scientists
do not know whether the asteroid is a single coherent body or consists
of several distinct pieces. Geographos was discovered at Palomar
Observatory near San Diego, California, in 1951. The asteroid's
name, which means geographer, was chosen to honor the National Geographic
Society for its support of the Palomar Mountain Sky Survey.
The above image shows the outline of asteroid Geographos
viewed from above its north pole. Researchers obtained radar images
of the asteroid on August 30, 1994, when the asteroid was 7.2 million
kilometers (4.5 million miles) from Earth. They used a planetary
radar instrument to image the asteroid from the Deep Space Network's
facility at Goldstone, California. The tick marks on the borders
are 1 kilometer apart. The central white pixel locates the asteroid's
pole. The gray scale is arbitrary and no meaning is attached to
brightness variations inside the silhouette. Scientists conducted
the radar observations a few days after Geographos passed 5 million
kilometers (3.1 million miles) from Earth, its closest approach
in at least two centuries.
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