Physical Cosmology

How do scientists find planets outside our solar system?
Answered by Discovery Channel and Dr. Jeff Hall
  • Discovery Channel

    Discovery Channel

  • Dr. Jeff Hall

    Dr. Jeff Hall

  1. Scientists use two methods to chart planets outside our solar system, called exoplanets. In the wobble method, scientists look for stars that appear to wobble because of the gravitational pull of their orbiting planets; most exoplanets were discovered using this technique. When a planet passes between the light from its star and Earth, it partially blocks that light; in the transit method, scientists take advantage of this phenomenon to determine the location of the planet. This method also provides much more information than the wobble method, such as the planet's size, chemistry and orbital path.

    In 2007, the Trans-Atlantic Exoplanet Survey (TrES), a network of three telescopes located in Arizona, California and the Canary Islands, discovered its fourth exoplanet (named TrES-4), located 1,435 light years from Earth. By that time, 220 other exoplanets had already been discovered by teams of scientists known as planet hunters.

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  2. Dr. Jeff Hall Astronomer, Director, Lowell Observatory


    We've talked about how technology has revolutionized many areas of astronomy. It's certainly made a huge difference in our understanding, in solar research, of solar variability. Likewise, the precision of modern instrumentation has made it possible to not only look for but find planets around other stars. Because they're very small and faint, they're extremely hard to detect next to the brilliant star next to them.

    There's several ways you can try to find them, but it's really only been within the past decade or a little more that significant numbers of exoplanetary discoveries have been made. It's a very new and very exciting frontier in modern astrophysics. The first planets that were discovered were great big ones, the so-called "hot Jupiters," massive planets close to their parent stars, where their effect is relatively large and they're easier to see. The story of exoplanet discovery since then has been one of finding progressively less massive planets, planets more like Earth and less like Jupiter, and now we are pretty close to finding and characterizing planets in the area around a star like the sun where liquid water and life as we know it might exist. The Kepler spacecraft just announced one a couple of weeks ago, and no doubt, many more await.

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