This image shows the outline of the asteroid Geographos viewed
from above its north pole. It was created from radar images
obtained August 30, 1994 when the asteroid was 7.2 million
kilometers (4.5 million miles) from Earth. A planetary radar
instrument at the Deep Space Network's facility in Goldstone,
California was used. The tick marks on the borders are 1
kilometer (0.62 mile) apart. The central white pixel locates the
asteroid's pole. The grayscale is arbitrary and no meaning is
attached to brightness variations inside the silhouette.
Geographos's overall dimensions are about 5.1 by 1.8 kilometers
(3.2 by 1.2 miles). Its pole-on silhouette has the largest
length-to-width ratio of any solar system object imaged so far.
It is not known whether the asteroid is a single body or made up
of several distinct pieces. Geographos was discovered at Palomar
Observatory 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 radar
observations were done a few days after Geographos passed 5
million kilometers (3.1 million miles) from Earth, its closest
approach for at least two centuries.
August 30, 1994
Geographos is called an Earth-crossing asteroid because its orbit
can evolve to intersect Earth's orbit. Fewer than 300 Earth-
crossing asteroids have been found, but the total is thought to
include several hundred objects larger than Geographos as well as
thousands more than half a mile across and a few hundred thousand
larger than a football field. Earth-crossing asteroids include
the cheapest destinations of piloted and robotic spacecraft
missions beyond the Earth-Moon system.
The Geographos radar observations, made by Dr. Steven J. Ostro of
NASA's Jet Propulsion Laboratory and colleagues, were part of the
Planetary Astronomy Program of NASA's Office of Space Science.
The image was one of two accompanying a paper published June 8,
1995, in Nature magazine.