Chapter 18
A Family of Planets
Comets, Meteors and Asteriods
Comets are small, fragile, irregularly shaped bodies composed of a
mixture of non-volatile grains and frozen gases. They have highly
elliptical orbits that bring them very close to the Sun and swing them
deeply into space, often beyond the orbit of Pluto.
Asteroids are rocky and metallic objects that orbit the Sun but are too
small to be considered planets. They are known as minor planets.
Asteroids range in size from Ceres, which has a diameter of about
1000 km, down to the size of pebbles. Sixteen asteroids have a
diameter of 240 km or greater. They have been found inside Earth's
orbit to beyond Saturn's orbit. Most, however, are contained within a
main belt that exists between the orbits of Mars and Jupiter. Some
have orbits that cross Earth's path and some have even hit the Earth
in times past. One of the best preserved examples is Barringer Meteor
Crater near Winslow, Arizona.
Meteors, Meteoroids and Meteorites
A meteor is the visible path of a meteoroid that enters the Earth's (or
another body's) atmosphere, commonly called a shooting star or
falling star. The visibility is due to the heat produced by the ram
pressure (not friction, as is commonly assumed) of atmospheric
entry. A very bright meteor, brighter than the apparent magnitude of
Venus, may be called a fireball
Information on the PlanetsComets, Meteors and AsteriodsThe Moons of the Solar SystemAssignment Sheets, Games and Practice Tests