Coma

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The comet Ikeya-Zhang exhibiting a bright, condensed coma (March 2002)

In astronomy, a coma (from the Latin word for "hair") is the nebulous envelope around the nucleus of a comet. It is formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublimate.

Comets may be more than just simple conglomerations of ice, dust and gases.^[1]

Larger charged dust particles are left along the comet's orbital path while smaller charged particles are pushed away from the Sun into the comet's tail by light pressure.

This gives a comet a "fuzzy" appearance when viewed in telescopes and distinguishes it from stars. Stardust was a NASA mission to recover samples of a comet's coma.

In some cases, such as the Great Comet of 1882, a comet develops a visible antitail or dust tail, which points in a different direction and when the viewing angle and parallax are just right may appear to point in the opposite direction from the normal ion tail.

See also

• Comet nucleus
• Extraterrestrial atmospheres

References

v • d • e Comets General Comet · Comet nucleus · Comet Coma  · Comet tail  · Antitail (dust trail)  · Comet dust Types Extinct comet  · Lost comet  · Great Comet  · Main-belt comet  · Sungrazing comet (Kreutz Sungrazers)  · Interstellar comet Lists List of periodic comets  · List of non-periodic comets See also Comets in fiction  · Asteroids  · Centaur  · Extraterrestrial atmospheres

v • d • e Atmospheres Major Sun · Venus · Earth · Mars · Jupiter · Saturn · Titan · Uranus · Neptune · Triton · Pluto · HD 209458 b Tenuous Mercury · The Moon · Io · Europa · Ganymede · Enceladus See also Stellar atmosphere · Coma (cometary) · Extraterrestrial atmospheres

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