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Comets are small Solar System bodies composed of ice and dust. They have thin, temporary atmospheres called comas and tails made of dust and gas.

en.wikipedia.org/wiki/Comet

A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces  ...

www.qrg.northwestern.edu/projects/vss/docs/space-environment/1-what-is-a-comet.html

Comets are often referred to as "dirty snowballs." They are left over from the formation of stars and planets billions of years ago. Before zipping around the Sun ...

coolcosmos.ipac.caltech.edu/ask/178-What-is-a-comet-

Comets are basically dusty snowballs which orbit the Sun. They are made of ices, such as water, carbon dioxide, ammonia and methane, mixed with dust.

www.planetsforkids.org/what-is-a-comet.html

What is a comet? A comet is basically a big ball of ice and rock. Where do they come from? They are leftovers from the beginning of the solar system. Why dose  ...

solarviews.com/eng/comet/whatis.htm

Comets are small, fragile, irregularly shaped bodies composed of a mixture of non-volatile grains and frozen gases. They usually follow highly elongated paths  ...

www.space.com/53-comets-formation-discovery-and-exploration.html

Nov 15, 2014 ... Learn about the composition and orbit of comets, as well as the history of their discovery, famous comets and space missions to analyze them.

cse.ssl.berkeley.edu/SegwayEd/lessons/findplanets/find_comet/WhatsAcomet.html

Sep 26, 1996 ... What's A Comet? A comet is a small body in our solar system that orbits the Sun much as do the Earth and the planets, except that comets ...

www.kidsastronomy.com/comets.htm

What are comets? A comet is a small world which scientists sometimes call a planetesimal. They are made out of dust and ice, kind of like a dirty snow ball.

www.skyandtelescope.com/astronomy-resources/what-is-a-comet

Jul 15, 2014 ... Comet ISON was discovered by two amateur astronomers in 2012. Despite high anticipation, it fizzled and broke apart while making its first ...