This is an illustration of what the Oort cloud might be like.
Click on image for full size

Where do comets come from?

Mathematical theory suggests that most comets may come to the solar system from very far away, as far away as 100,000 AU. In this picture, the solar system is buried deep within the cloud.

An AU is the distance from the earth to the sun and is roughly equivalent to 100,000,000 miles. Mars is 1.5 AU from the sun, Jupiter is 5 AU from the sun, and Pluto is 39 AU from the sun. So comets come from very far away indeed.

Comets are observed to come to the solar system from all directions, therefore the place from which the comets come is thought to be a giant sphere surrounding the solar system. This sphere is called the Oort cloud after Jan Oort who postulated its existence in 1950. Thus comets are said to come from the Oort cloud.

(It is natural to ask How did comets get so far away? Astronomers are presently working to understand the answer to that question.)

But some comets may come to the solar system from closer in. The place where these comets come from is called the Kuiper Belt, which is located past the orbit of Pluto.

Kuiper Belt objects are suspected to be the source of the Jupiter family, a group of comets whose orbits take them between Jupiter and the sun in a short period of time (3-10 years). Comet Shoemaker-Levy 9 may have been one of those.

Last modified March 17, 2004 by Randy Russell.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

The Jupiter family of comets

Comets are observed to go around the sun in a long period of time or a short period of time. Thus they are named "long-period" or "short-period" comets. One group of short-period comets, called the Jupiter...more

New planetoid named Sedna discovered

Astronomers have announced the discovery of a large new planetoid named Sedna. Mike Brown of the California Institute of Technology, Chad Trujillo of the Gemini Observatory in Hawaii, and David Rabinowitz...more

Trans-Neptunian Objects (TNO)

There are many icy and rocky planetoids on the outer edge of our Solar System. As a group, all bodies that orbit, on average, further from the Sun than the 8th planet Neptune are called Trans-Neptunian...more

What we learned from Comet Shoemaker-Levy 9

Scientists have learned a great deal from the crash of comet Shoemaker-Levy 9. Scientists traced the orbit of the comet backwards in time to guess its origin. This calculation, along with the discovery...more

The Perihelion Passage of a Comet

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

Stardust comet sample return mission

NASA's Stardust mission was the first spacecraft to collect samples of material directly from a comet and return them to Earth. Stardust was launched by a Delta 2 rocket from Cape Canaveral Air Station,...more

Comet Hale-Bopp

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

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA