Billions of Icy Bodies Beyond Neptune

^{The discovery images of the Kuiper Belt object 1993 SC.
Image Credit: Dr. Alan Fitzsimmons, Queen's University of Belfast.}

Billions of icy bodies beyond Neptune's orbit may be a cold-storage reservoir for comets that periodically visit the inner part of the solar system.

How do we know? Look at the two images above of a small section of the night sky. They were taken about four and a half hours apart. Most of the objects in these images are fixed, distant stars or galaxies. But one (marked by lines) moved during the time the images were taken. This object is a very faint, cold, icy body that orbits the Sun at a distance slightly beyond that of Neptune.

Astronomers named the faint body 1993 SC. It is about 150 miles across and a member of a family of objects that orbit the Sun at distances beyond the orbit of Neptune. Collectively, this family of objects is called the Kuiper Belt, after Gerard Kuiper, a Dutch-born American astronomer.

A few of the Kuiper Belt objects are as large or larger than 1993 SC. But most are much smaller, similar to the sizes of comets. Their total number has been estimated at several billion. Computer simulations show that the Sun's outer planets can perturb the orbits of Kuiper Belt objects and send them toward the inner part of the solar system. There we see them as comets, with a bright gaseous coma (ices evaporated by the Sun) and a tail.

Object 1993 SC was discovered in 1993 by a group of astronomers led by Dr. Alan Fitzsimmons of Queen's University of Belfast using the one-meter Jacobus Kapteyn telescope at the Observatorio del Roque de los Muchachos on the island of La Palma in the Canary Islands.

More Cool Stuff

We obtained the above images by going to Dr. Alan Fitzsimmons' homepage and clicking on "Kuiper Belt Objects":

http://star.pst.qub.ac.uk/~af/af.html

The homepage of the Jacobus Kapteyn telescope used in the discovery of object 1993 SC is at:

http://www.ast.cam.ac.uk/~lpinfo/

In 1995 astronomers detected a Kuiper Belt object using the Hubble Space Telescope. For information on this discovery, go to this page of the Space Telescope Science Institute:

http://www.stsci.edu/pubinfo/PR/95/26.html

For information on the most recent bright comet to visit the inner part of the solar system, go to our Observation of the Week of March 20, 1996:

http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960320/ob960320.html

For information about comets and other small bodies in the solar system, go to the following pages of "Using Science and the Internet as Everyday Classroom Tools," a NASA-funded project at the Smithsonian Institution. Click on "Table of Contents," and then on "Chapter 5 -- Planetesimals":

http://hea-www.harvard.edu/ECT/the_book/

To learn about another recent comet, comet Shoemaker-Levy 9, which collided with Jupiter in July 1994, go to the Public Connection Web site of Rice University and the Houston Museum of Natural Science:

http://space.rice.edu/hmns/sl9/sl9.html

The Kuiper Belt objects are not to be confused with the objects of the Sun's Oort cloud. For a discussion of the differences between these two families of objects, go to a Web site of the Students for the Exploration and Development of Space (SEDS) at the University of Arizona:

http://www.seds.org/nineplanets/nineplanets/kboc.html

Check out other observations in the Observation of the Week Archive.