A Closer Look: Extrasolar Planets

It has long been suspected that the Sun is not the only star in the galaxy that has planets orbiting it, but it is only recently that astronomers have had the tools necessary to successfully search for them. Since 1995, over 100 extrasolar planets have been detected, and new telescopes and satellites that employ a variety of techniques are being created to find more. One way to find a planet orbiting a distant star is to continually monitor the amount of light coming from the star. If a planet's orbit brings it between the Earth and the star, the planet will block some of the light and, from Earth, it will look like the star becomes briefly dimmer. By determining how often this happens, the period of the planet's orbit and its distance from the star can be determined. By measuring how much light the planet blocks, it is possible to determine its size, because a larger planet will block more light.

One problem with this method of detecting planets is that only large planets that orbit very close to their host star will block enough light for astronomers to be able to measure the fluctuations in the brightness of the star. As a result, the planets found with this or any other method developed thus far are all very large (about the size of Jupiter), and many of them orbit closer to their stars than the Earth is to the Sun. Since in our solar system the largest planets all orbit the Sun much farther out than the Earth, it is a challenge to understand why these systems are so different from our own. With the next generation of telescopes and satellites, astronomers hope to be able to detect Earth-like planets at Earth-like distances from their stars. At that time, scientists will be able to determine how common or rare it is for such massive planets to be able to form so close to their stars.

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