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A Strange New Planet

  • Teacher Resource
  • Posted 12.17.05
  • NOVA

Scientists have been looking for extra-solar planets for decades, but only recently, with better equipment and improved techniques, have they finally unveiled new and unusual planets. Since 1995, over 155 planets have been discovered orbiting stars other than our Sun. In this video segment adapted from NOVA, two of the most successful planet-hunters discuss the search for extra-solar planets.

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NOVA A Strange New Planet
  • Media Type: Video
  • Running Time: 3m 09s
  • Size: 9.4 MB
  • Level: Grades 6-12

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Source: Origins, A NOVA Presentation: "Where are the Aliens?"

This resource was adapted from Origins, A NOVA Presentation: "Back to the Beginning."


Looking for a planet outside our solar system is difficult, but not impossible. For years, scientists failed to find any extra-solar planets. However, since the discovery and confirmation of one such planet in 1995, the daunting task has become more possible. Once astronomers found a successful technique, they continued to discover extra-solar planets at an increasing rate.

The discovery of the first extra-solar planet confused the scientific community. A massive planet, roughly the size of Jupiter, seemed to be orbiting its star in just four days. Such a short orbit indicates that the planet is very close to the star, but according to the most accepted theory of solar system formation, such a massive planet should have a fairly large orbit. Our solar system neatly fits the formation theory, with smaller rocky planets near the Sun while larger gaseous planets reside in the cooler distant regions. It seemed impossible to have a Jupiter-sized planet orbiting so closely to its star. As the observations were confirmed, astronomers questioned their understanding of solar system formation. They have since realized that the formation theory may still be correct, but that massive planets may be able to migrate inwards some time after the initial formation.

Most of the discovered extra-solar planets have been massive — ranging from the size of Neptune to ten times the size of Jupiter. Rather than indicating that large planets are more common than small ones, these findings may just be a result of massive planets being easier to find. Our instruments are not yet advanced enough to detect smaller, Earth-like planets, but new technology is being developed to improve the search.

Current research techniques rely on indirect evidence of planets. Indirect searches rely on observations of effects caused by the planet. The majority of planets have been found with the radial velocity, or Doppler, technique, which looks for a back-and-forth shift in the star's spectra due to the gravitational pull of the planet as it orbits the star. Other methods of detection include: the astrometric technique, which looks for a side-to-side wobble against the background stars; the gravitational lensing technique, which looks for a change in the positions of background stars; and the transit technique, which looks for the periodic dimming of the star by the crossing of a planet.

To learn more about the planets in our solar system, check out All Planet Sizes.

To learn more about the search for extrasolar planets, check out The Search for Another Earth.

To learn more about another surprising astronomical discovery, check out Pulsars: Jocelyn Bell.

To learn more about the Doppler Effect, check out Stellar Velocity: The Doppler Effect.

Learn in this NOVA classroom activity how planetary spectra can be used to search for life on other worlds.

Questions for Discussion

    • Why is it so difficult to see planets around other stars?
    • Why did the Americans think it was impossible for a gas giant to have a 4-day orbit?
    • Discuss how it was possible for planets to be "hiding" in the astronomers' data. What did the American scientists find when they re-analyzed their own data, which they had been collecting for years?
    • At the beginning of the video, our Sun is shown as being very close to its planets (including Earth) and barely larger than them. Considering proportions, distance, and the imaginary blue lines, what is wrong with the representation? How might it be shown more accurately?
    • What does this video tell you about the processes of science?

Resource Produced by:

					WGBH Educational Foundation

Collection Developed by:

						WGBH Educational Foundation

Collection Credits

Collection Funded by:

						National Science Foundation

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