This image is a schematic of a comet. The center part of the comet, or nucleus, is represented by the flame. The solar wind particles are shown as green dots with arrows. And the ionized particles are shown as green/red dots with arrows. Neutral particles are shown by the other dots (without arrows).
Click on image for full size
The Comet Coma
As the ices of the comet nucleus evaporate
, they expand rapidly into a large cloud around the central part of the comet.
This cloud, called the coma, is the atmosphere of the comet and can extend for millions of miles. The cloud is very thin, however, with only a 100 particles in a cubic centimeter. By comparison, a cloud in the Earth's atmosphere might contain millions of particles per cubic centimeter.
Just as in any atmosphere, there are electrically charged particles present, called ions, as well as electrically neutral particles. Ions are formed when the cloud of neutral particles collides with the solar wind. A continual stream of neutral particles is produced as long as the nucleus is evaporating, and these neutral particles are continually converted to ions. These ions are what help form the comet tail.
Shop Windows to the Universe Science Store!
Our online store
on science education, classroom activities in The Earth Scientist
specimens, and educational games
You might also be interested in:
Plasma is known as the fourth state of matter (the first three states being solid, liquid and gas).Matter in ordinary conditions on Earth has electrons that orbit around the atomic nucleus. The electrons...more
When evaporation begins, the gas is propelled from the nucleus at supersonic speed (depicted by arrows in the figure). Because of the low gravity in space, this means that the molecules from the nucleus...more
Comets are disturbed from their orbits in the Oort Cloud and begin a passage into the solar system, spinning and tumbling as they come. The trajectory which they acquire can be hyperbolic, parabolic, or...more
The image on this page shows the best views we've ever had (so far) of the nucleus of a comet. On January 2, 2004, the Stardust spacecraft flew past Comet Wild 2 at a relative speed of roughly six kilometers...more
In August 2009, scientists reported finding a type of amino acid in a sample returned from a comet. Amino acids are the building-blocks of proteins, one of the key molecules in living creatures. The comet...more
Hale-Bopp continues to offer surprises as astronomers study the comet. Using the Hubble Space Telescope and the International Ultraviolet Explorer, astronomers have found that there are distinctly different...more
Six spacecraft flew by Halley's comet in 1986. There were two spacecraft launched from Japan, Suisei and Sakigake, and two from the Soviet Union, Vega 1 & 2. One spacecraft, ICE, from the United States...more