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Exploring the Comets

COMETS      SEEING      FAMOUS      EXPLORATION      STARDUST      ROSETTA      DEEP IMPACT      HALE-BOPP      DEEP SPACE 1
DID A COMET BRING SARS TO EARTH?       COULD A COMET HIT EARTH?       COMET RESOURCES

The interplanetary probe ISEE-3/ICE
ISEE-3/ICE made the first-ever comet encounter in 1985 [NASA art]
Comets have been known since antiquity. Often described as dirty snowballs and icy mudballs, comets are water ice and frozen gases mixed with dust samples from the earliest history of our Solar System.

Nearly 900 comets have been cataloged over the years. Of those, 184 are listed as periodic comets which circle the Sun every so often, up to at least once every 200 years.

Most comets are in highly eccentric orbits, which take them around the Sun and out beyond the orbit of the planet Pluto. Such long-period comets usually are seen once and then disappear for thousands of years. On the other hand, short-period and intermediate-period comets like Comet Halley stay within the orbit of Pluto for most of their orbits.

After it swings in through the inner Solar System and around the Sun a few hundred times, most of a comet's ice and gas will have been lost. It is left as a rocky object looking very much like an asteroid. In fact, some astronomers say half of the so-called near-Earth asteroids may be "dead" comets.

A comet in an orbit near the Sun might crash into one of the planets or even the Sun itself. On the other hand, the powerful gravitational force of the Sun could fling a comet out of the Solar System altogether.

Human beings have wanted to know more about comets since the Chinese recorded Comet Halley in 240 BC. Several robot explorers have been sent out toward comets to take a closer look. Here is a compilation of all of the deep space missions from Earth that have made contributions to the study of comets, even though some of the missions, such as Galileo and Ulysses, have not had comets as their primary targets.

Current and Proposed Comet-Related Missions Past Comet Missions Lost Comet Missions
Star: The Sun
Inner Planets: Mercury Venus Earth Mars
Outer Planets: Jupiter Saturn Uranus Neptune Pluto
Other Bodies: Moons Asteroids Comets The Voyagers
Comet Stories: History Explorers Hale-Bopp Global Links

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