Asteroids and Comets

Of the thousands of known comets in the solar system, Halley's comet is one of some 200 that are periodic. Halley's comet orbits Earth every 76 years; the next flyby will occur in 2061.

Comet C/2001 Q4, also known as NEAT, emits a blue-and-purple glow as it moves through the cosmos in May 2004. Its coma, or head, and a portion of its tail are visible in this shot, as are myriad stars. This image was taken by telescope from Kitt Peak National Observatory near Tucson, Arizona.

viMory: myriad  无数的

This image shows ejected material that was propelled into space when NASA's Deep Impact probe collided with comet Tempel 1 at 1:52 a.m. ET on July 4, 2005. It was taken by the spacecraft's medium-resolution camera 16 seconds after impact.

Seen here in a 2004 composite image, the intensely active surface of comet Wild 2 ejects dust and gas streams into space, leaving a trail millions of kilometers long. Other than the sun, Wild 2 is currently the most active planetary surface in our solar system, astronomers say.