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Sedna, Planet Wannabe (March 19, 2004, One)

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Program Summary

Long, long ago, in a galaxy far, far away—Wait, that’s another story. But it could be the opening line in this month’s announcement that a tenth planet may be added to the solar system. Astronomers have found the coldest, most distant object ever observed orbiting the Sun.

Sedna, officially known as 2003 VB12, is estimated to be about 1,100 miles in diameter, slightly smaller than Pluto (1,400 miles across) but larger than all other non-planet objects. Its highly elliptical orbit around the Sun takes 10,500 years to complete, bringing it no closer than 8 billion miles away from our star and 84 billion miles away at its farthest point. Now that’s a road trip! Scientists theorize that Sedna was formed closer to the Sun billions of years ago, but was thrown outward by gravitational forces from the giant planets. Interaction with even more distant stars may be what’s keeping it in its current position.

Mystery surrounds Sedna. What is it made of? Why is it red? Does it have a moon? Can it be classified as a planet? This last question makes for lively debate among the astronomical community. One faction states that Sedna is indeed a planet since it is so much like Pluto. Another faction believes that Sedna is just a planetoid and that Pluto should never have been considered a planet in the first place. They claim that Pluto is simply the largest object in the Kuiper belt, a thick collection of small objects that orbits the Sun in the space beyond Neptune. They also assert Sedna is either a large object on the outskirts of the Kuiper belt or the inner edge of the hypothetical Oort cloud, from whence astronomers believe certain comets originate.

So what exactly is the definition of a planet? That’s another good question, the one that leads to the debate as to whether or not Pluto and Sedna qualify. While the debate rages, Sedna is slowly getting nearer and brighter. It will take 72 years to reach its closest point to the Sun. Then it will proceed on its centuries-long journey. The last time Sedna came this close, Earth was emerging from the Ice Age. Who knows what Earth will be like next time around?

Guests

Mike Brown, associate professor of planetary astronomy at the California Institute of Technology in Pasadena

Related Links and Resources

BBC News, March 15, 2004: "Astronomers Discover 'New Planet'"
California Institute of Technology Geological and Planetary Studies: Sedna (2003 VB12)
NASA.gov, March 15, 2004: “Planet-Like Body Discovered at Fringes of Our Solar System"
Space.com, March 15, 2004: "Scientists Find Another Huge Mini-World in Outer Solar System"

For Discussion:

• How was Sedna discovered?
• What is the definition of a planet? Is Sedna a planet? How does its discovery affect the status of Pluto?
• How was Sedna formed? How long is its orbit around the Sun? What makes the orbit so elliptical?
• What are the Kuiper belt and the Oort cloud?
• A generation is considered to be 25 years. What generation of astronomers will be studying Sedna 10,500 years from now?
• Who is Sedna named after? What would you call it? Why?

Activities

Nine or not. You’ll find one definition of a planet at Sedna (2003 VB12) and find out why Sedna and Pluto don’t qualify in some scientists’ eyes. You’ll also find explanations of the Oort cloud, Kuiper belt, and many other terms that you’ll be hearing a lot. One of the most interesting and detailed explorations of the solar system is The Nine Planets. Everything you ever wanted to know about them is at your fingertips, with facts, images, discussion questions, and links galore for the planets, moons, asteroids, comets, and much more. Chronology of Solar System Discovery traces the history of solar system theory and discovery; Planetary Linguistics lists the names of the planets in dozens of languages and has other fun facts. What really sets this site apart, though, is that sound bites from Holst’s musical suite “The Planets”accompany each chapter.

All aboard. Take a 3-D tour of the universe at Runaway Universe, companion site for an espisode of PBS’s “NOVA.” This fascinating site also offers an interactive history-of-the-universe timeline, online activities, and wonderful animations. Poke into every corner or you’ll miss something great.

Fasten your seat belts. For a truly eye-popping trip through space, visit NASA’s Solar System Exploration, a lively, well-written site with fantastic graphics, slide shows, multimedia, a kids’ section, educational resources, and intriguing information, of course.

The NASA Jet Propulsion Laboratory’s (JPL’s) Planet Quest presents the search for another Earth-like planet that may have harbored (or does harbor) life. The New Worlds Atlas section is a 3-D simulation of planets that revolve around stars other than our Sun. Educator Resources lists some unusual activities and many NASA and related sites dealing with space education.

Get a window seat. Windows to the Universe, a terrific site from the University Corporation for Atmospheric Research at the University of Michigan, is available in English and Spanish. Colorful, well written, and well designed, it mixes science, art, and history for a delightful experience. Students can play games, keep a journal, pose questions to scientists, and much more.

Photo op. JPL’s Welcome to the Planets provides dozens of photographic images from NASA missions. At How to Make Your Own Eye-Popping 3-D Pictures, students can learn how to create images like the ones being sent back from Mars by the rovers.

Patch it together. More resources, lesson plans, and activities can be accessed at JPL’s Education Gateway.

What’s in a name? Sedna is named after the Inuit goddess of the sea; the discovery team felt is was appropriate to give a frozen planet a name from people who inhabit the Arctic Circle. Find out more about Sedna and other Inuit beliefs at Inuit Myths. Until now, celestial objects have been given names from Greek and Roman mythology. Learn why at How Do Planets and Their Moons Get Their Names?, then find out who actually decides on the formal names at "How Do Planets Get Their Names?" (BBC News). Students can think of alternative names for Sedna.

Use the search box below to perform a Google search within any of the specifc sites or general domains mentioned in this Activities section.

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