Origins of the Snowballs

Comet orbits come in two varieties, long and short period. There are about 600 comets with known orbits. About 100 have orbits that lie within the solar system with periods less than 200 years. The majority of comets have long elliptical orbits that are randomly oriented in space. These are the long period comets.

These long period comets come from a place called the Oort cloud. Far beyond the orbit of Pluto is a vast cloud of comets that extend over a third of the way to the nearest star. It is estimated that there are over 200 billion objects in this cloud.

Way out in the Oort cloud, the comets do not display tails or comas. They are merely dirty snowballs tumbling around in their orbits. It is believed that these comets formed in the same cloud as did the planets and Sun. They were probably ejected out into the Oort cloud by the gas giants Jupiter and Saturn as they increased to their present size.

A passing star, or collison with other comets disturbs the orbit of one of these bodies and sends them into the inner solar system. The other planets often alter the comet's orbits, sometimes such that they change to a short period orbit.

All comets are ancient unchanged objects. They are not large enough to have melted from radioactive decay and they would not have differentiated. It is likely the only changes these bodies have undergone is break ups and craters from impacts. Comets, are the senior citizens of the solar system!

• The Best Way to Watch a Meteor Shower
• Where to Look for the Leonids
• Star Charts
• Leo
• Photographing Meteor Showers
• Other Meteor Showers
• What are Meteors and Meteorites
• Origin of Meteorites
• Thunderstones and Shooting Stars: Meteors and Meteorites in Folklore
• Asteroids and Comets: Proud Parents of Meteors
• Target Earth
• Links to other good sites about the Leonids
• More images

Constellations

The Solar System