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. (Courtesy Dr. Steven J. Ostro, JPL/NASA).