A ball of rock and ice, often referred to as a “dirty
snowball.” Typically a few kilometers in diameter, comets orbit the Sun
in paths that either allow them to pass by the Sun only once or that repeatedly
bring them through the solar system (as in the 76-year orbit of Halley's Comet).
A comet’s “signature” long, glowing tail is formed when the Sun’s
heat warms the coma or nucleus, which releases vapors into space.
Comet Shoemaker-Levy 9 (SL-9)
A comet that became gravitationally bound to Jupiter,
colliding with the planet in July 1994. Prior to entering the planet’s atmosphere,
the comet broke into several distinct pieces, each with a separate coma and
When one body strikes another with great force. Some examples
include a meteor colliding with the Moon or a comet, such as Shoemaker-Levy 9,
slamming into Jupiter.
A collision between two solar system bodies that releases
exceptionally large amounts of energy. Some examples are the 1908 Siberian Tunguska
impact by a comet or an asteroid and the asteroid that struck Earth 65 million
years ago, which may have led to the extinction of the dinosaurs and other species
of the Cretaceous-Tertiary era.
A region in our outer solar system where many "short-period"
comets originate. The orbits of short-period comets are less than 200 years.
This region begins near Neptune’s orbit at 30 astronomical units (AU)
and extends to about 50 AU away from the Sun. An astronomical
unit is the average distance between Earth and the Sun. The Kuiper Belt may
have as many as 100 million comets.
A comet having an orbital period greater than 200 years
and usually moving in a highly elliptical, eccentric orbit. Comets have orbits
that take them great distances from the Sun. Most long-period comets pass through
the inner solar system only once. Hale-Bopp is an example of a long-period comet.
A vast spherical region in the outer reaches of our solar
system where a trillion long-period comets (those with orbital periods greater
than 200 years) reside. Comets from the Oort Cloud come from all directions,
often from as far away as 50,000 astronomical units.
A comet in a closed, elliptical orbit within our solar
system. These comets typically have orbital periods of less than 200 years.
Many comets have orbits that keep them in the inner solar system and allow their
trajectories to be calculated with great accuracy and precision. Perhaps the
best-known periodic comet is Halley’s comet, whose orbital period is 76 years.
A comet that orbits mainly in the inner solar system. Short-period comets usually orbit the Sun in less than 200 years. Halley’s comet is an
example of a short-period comet.