Shop Windows to the Universe

Ready, Set, SCIENCE!, by the National Research Council, focuses on K-8 science classsrooms. Check out the other publications in our online store, as well as classroom materials.
Sedna is a large Trans-Neptunian Object discovered in 2003. Here's how an artist thinks Sedna might look.
Click on image for full size
Image courtesy NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

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 Objects (TNOs).

There are different classes of TNOs. The region of space just outside Neptune's orbit, but largely near the same plane in which the planets revolve, is called the Kuiper Belt. Much further out is the Oort Cloud, which is scattered into a gigantic sphere around the Sun. Some astronomers recognize a third class of TNOs called scattered disc objects (SDOs), which may be in transition between the Kuiper Belt and the Oort Cloud. SDOs have orbits intermediate between the Kuiper Belt and the Oort Cloud, in terms of both size of orbit and amount of tilt of orbital plane.

This region is the main source of comets that visit the inner Solar System. When the orbits of TNOs are disturbed, the objects can be flung out of the Solar System or they can plunge inward towards the Sun.

TNOs hold clues to the origin and evolution of our Solar System. Some Kuiper Belt Objects (KBOs) may have formed near their current positions, and may thus be deep frozen samples of material from the earliest days of our Solar System. Many KBOs, Oort Cloud objects, and SDOs have been scattered into their current locations by past gravitational interactions with large planets, particularly Jupiter. Their orbits provide clues about possible changes in positions of the gas giant planets throughout the history of our Solar System.

The planet Pluto and its large moon Charon are examples of the Kuiper Belt subset of TNOs. Quaoar, Orcus, and Varuna are some other KBOs you might have heard about. The "tenth planet", 2003 UB313 (nicknamed "Xena"), seems to be a scattered disc object. Sedna might be an extreme innermost fringe member of the Oort Cloud.

Last modified January 31, 2006 by Randy Russell.

Shop Windows to the Universe Science Store!

Learn about Earth and space science, and have fun while doing it! The games section of our online store includes a climate change card game and the Traveling Nitrogen game!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Cool It! Game

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

What is a planet?

It may surprise you, but astronomers don't really have a good definition of a "planet". Because of this, Pluto is at the heart of a controversy about its status. Is Pluto a planet, or isn't it? Scientists...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

Solar System Formation

Scientists believe that the solar system was for med when a cloud of gas and dust in space was disturbed, maybe by the supernova of a nearby star. Shock waves from the explosion compressed the cloud of...more

Pluto

Pluto is a frigid ball of ice and rock that orbits far from the Sun on the frozen fringes of our Solar System. Considered a planet, though a rather odd one, from its discovery in 1930 until 2006, it was...more

Charon - largest moon of Pluto

Charon is by far the largest of Pluto's // Call the moon count function defined in the document head print_moon_count('pluto'); known moons. Charon was discovered by the American astronomer James Christy...more

Eris - a dwarf planet

Eris is a dwarf planet that was discovered in 2005. Eris is a trans-Neptunian object (TNO) that orbits the Sun on the frozen fringes of our Solar System beyond the Kuiper Belt. Eris takes 557 years to...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

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF