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.
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.