Astrophysics (Index)About

comet

(Sun-orbiting object with coma and possible tail)

A comet is an object orbiting the Sun that displays a visible coma (a fuzzy surrounding region which is the comet's atmosphere) and in some cases, a tail that is pointed in the direction away from the Sun. They are icy, i.e., they include solid substances that turn to gas at temperatures reached during the inner part of their orbits (i.e., volatile material substances), also releasing embedded dust, together creating the coma and possible tail. Classically, they have long orbital periods (tens to thousands of years) that are highly eccentric, with only a brief portion of the orbit visible to us. They display the coma- and tail-effects (active comet) when the comet is nearest the Sun, the activity generally becoming evident around the time it comes within Mars's orbit. The coma and tail consist of plasma pushed directly away from the Sun by the charged solar wind (gas tail), dust pushed away somewhat less by radiation pressure and not directly in the comet's shadow (dust tail), and in some cases a third neutral tail of neutral atoms/molecules. A cometary hydrogen cloud forms around the comet during its active phase.

At the far end of their orbits, they move slowly such that they remain in that region for a very long time (decades to thousands of years or more), and it is thought that there are always many long-period comets in that state, which together are known as the Oort Cloud.

The solid portion is known as the comet's nucleus. Inspection has revealed rocky surfaces. Volatiles such as water, carbon dioxide, carbon monoxide, methane, and ammonia make up the ice, which may be inside.

Two well-known comets are Comet Halley (Halley's Comet, recognized in 1705 by Edmund Halley as orbiting approximately every 76 years) and Comet Shoemaker-Levy 9 which was observed colliding with Jupiter in 1994.


(solar system,object type,eccentricity)
Further reading:
https://en.wikipedia.org/wiki/Comet
https://astronomy.swin.edu.au/cosmos/C/Comet
http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/comet.html
https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/
https://astronomy.swin.edu.au/cosmos/C/Cometary+Coma

Referenced by pages:
67P/Churyumov-Gerasimenko (67P)
AMPTE
apsis
asteroid belt
Bok globule
C/2014 UN271
CAESAR
Caldwell Catalog
Catalina Sky Survey (CSS)
centaur
Chicxulub crater
cloud
coma
comet planet
Comet Shoemaker-Levy 9
cosmic dust
Crab Nebula (M1)
damocloid
Deep Impact
Deep Lens Survey (DLS)
Deep Space 1 (DS1)
dwarf planet
eccentricity (e)
electron pressure
EPOXI
ESO/Uppsala Survey of the ESO (B) Atlas
extended source
falling evaporating body (FEB)
fluorescence
Giotto
glycine (Gly)
gravitationally bound
gravity assist
Hills Cloud
hydrogen cyanide (HCN)
International Cometary Explorer (ICE)
ion engine
Kuiper Belt (K Belt)
LINEAR
LONEOS
long-period comet
mass spectrometer
Messier Catalog (M)
meteoroid
minor planet
Minor Planet Center (MPC)
near-Earth object (NEO)
nebula
Nice model
occultation observations
Oort Cloud
Origins Space Telescope (OST)
Oumuamua
Parker wind
Pioneer Venus Orbiter (PVO)
planet
planetary science
planetesimal
planetoid
provisional designation
reflection nebula
Rosetta
Smith Cloud
solar system
solar system object (SSO)
SPACEWATCH
SPARTAN
SSSB
Stardust
striae
transient (AT)
Ulysses
Uppsala-ESO Survey of Asteroids and Comets (UESAC)
water (H2O)

Index