Close Calls: Planet Earth and Asteroid Flybys

Scientists believe that about 400,000 small Near Earth Objects or NEOs, up to 1,000 meters wide = could strike Earth with little or no warning. In the accompanying image, an artist's concept of a catastrophic asteroid impact with the early Earth. Scientists believe that several gigantic asteroids collided with the Earth during our planet's youth.

Scientists believe that an asteroid measuring 500 kilometers in diameter would effectively sterilize the Earth if it were to collide into our planet.

An artist's representation of a possible "Dino killer." The remains of an impact crater in the Northwestern Yucatan is believed to have been the impact site of a global catastrophic event at the boundary of the Cretaceous and Tertiary periods in Earth's geologic history.

On January 9 2002, the asteroid 2001 YB5 came within 830,000 km. from the earth. At 300 meters in diameter, the approach of this asteroid caused some worry and it was classed as "potentially hazardous." If an asteroid that size ever does collided with earth, NASA says it would excavate a crater (on land) the size of a small city, and the blast would cause considerable damage on the scale of a country like France.

Asteroid 243 Ida was 58 kilometers long and 23 kilometers. Photographed by the Galileo spacecraft as it passed by the asteroid on August 28, 1993.

Asteroid 253 Mathilde is constructed from four images acquired by the NEAR spacecraft on June 27, 1997. The part of the asteroid shown is about 59 by 47 kilometers.

Asteroid 1999 AN10 photographed by the Palomar Digital Sky Survey. The faint streak is the trail left by the asteroid. The image has been contrast-enhanced.

With an average diameter of about 3.5 kilometers JM8 is the largest of the so-called potentially hazardous asteroids ever studied in detail, photographed August 26, 1999. The asteroid came within 5.3 million miles of Earth.

On October 2, 1998, the Jet Propulsion Laboratory observed asteroid 1992 KD in a background of stars. In July 1999, NASA's Deep Space 1 technology flew by 1992 KD at a distance of 188 million kilometers from Earth.

This 2005 montage of the asteroid Eros was assembled from images acquired by the Near Earth Asteroid Rendezvous spacecraft on Dec. 23 of that year as the spacecraft flew by the asteroid at a distance of 4,100 kilometers.

Montage of 11 images taken by the Galileo spacecraft as it flew by the asteroid Gaspra on October 29, 1991. Gaspra is roughly 17 kilometers long and 10 kilometers wide.

The asteroid Geographos photographed August 30, 1994 when the asteroid was 7.2 million kilometers from Earth. Its overall dimensions are about 5.1 by 1.8 kilometers.