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Stars, Planets, Life, and the Universe

What is a planet?
web seminar player window The second of two Web Seminars on NASA's Stars, Planets, Life, and the Universe was held on Wednesday, June 21, 2006, from 6:30 p.m. to 8:00 p.m. Eastern time. The presenter was Dr. Natalie Batalha, astronomer at NASA's Ames Research Center. Dr. Batalha's presentation focused on planets in the solar system, planets orbiting around other stars, and the definition of the word: planet. Among the participants were a few teachers who had attended the face-to-face symposium at the NSTA National Conference in Science Education in Anaheim, CA.

The session started with a general overview of the NSTA Web Seminar tools and how they can be used to facilitate interaction between the participants and the presenters. Forty-six participants were present in addition to the presenter and the NSTA staff. Participating educators represented the states of Arizona, California, Florida, Georgia, Illinois, Iowa, Louisiana, Maine, Maryland, Michigan, Minnesota, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, Tennessee, Texas, Washington, Wisconsin, and Wyoming.

Batalha started the presentation with a review of the solar system. Participants were introduced to terms, like the Kuiper Belt and the Oort cloud. The Kuiper Belt, Dr. Batalha explained, is a reservoir of icy asteroids that orbit the Sun beyond the orbit of Pluto. Some astronomers believe Pluto belongs to this new category of objects. The Oort cloud, however, is composed of comet-like objects with highly eccentric orbits. To define the word planet astronomers consider several different criteria, Dr. Batalha said. For example, size and shape of the object. Objects with a critical amount of mass are shaped round. Most asteroids do not have this critical mass, and hence have irregular shapes. Planets are round in shape. Dr. Batalha explained that for an object to be considered a planet, it has to be at least as big as planet Pluto. This is why asteroid Ceres is not considered a planet, though it is a round object. Another criterion to be considered for being a planet is orbital characteristics. A planet must orbit its parent star and not another planet, like natural satellites do.

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Recent discoveries of large Kuiper Belt objects are forcing astronomers to re-consider the number of planets in our solar system. About a dozen Pluto-size objects have been discovered within the last 15 years. UB313, discovered by Dr. Mike Brown and his team, is one of these Pluto-size objects. Dr. Batalha described UB313 as an object located in the Kuiper Belt measuring about 1,500 miles in diameter. It is the responsibility of the International Astronomical Union to decide if UB313 will be known as the 10th planet in our solar system. Throughout the presentation there were several opportunities for the participants to interact with each other and with the presenters by answering poll questions, chatting, stamping, and marking.

Here are some comments provided by the participants at the end of the Web Seminar:

  • "Learned a LOT about Pluto & the classification of what is/not considered a
    planet. I had no idea there were actual guidelines for defining a planet
    - although now it does not come as a surprise."
  • "The seminar was outstanding. I learned that it takes the mass of 13 Jupiter planets for an object to start fusion and to become a star."
  • "Great way to help science teachers have the latest information. How
    impressive it will be for me to say that I "chatted" directly with a NASA
    scientist. The illustrations were excellent - easy to understand. The
    presenter was excellent."
  • "I think one of the outstanding aspects of these seminars is the current-
    -cutting-edge--content. This is just what classroom teachers need to stay in
    touch with the newest information/data."

Thanks to the participants and Dr. Batalha for the learning opportunity, the interactions, and a job well done!

Web Seminar II Resources


See a recorded version of the Web Seminar.

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Underwritten in part by
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