Extrasolar Planets

Topics: Star, Planet, Binary star Pages: 1 (363 words) Published: May 17, 2013
Astronomers can identify extrasolar planets using “direct” and “indirect” methods. Indirect methods include the use of the radial velocity method and the transit method which all rely on the detection of a planet’s effect on its parent star. Direct methods on the other hand involve finding images or the spectra of a planet and are very difficult to obtain. When a object moves the wavelength of the light emitted it is shifted along the spectrum, if the object is moving towards the Earth the light will be shifted towards the shorter, blue wavelengths whilst light from a object moving away will be shifted towards the longer, red wavelength. Astronomers study the light of spectral lines of stars to see if they are moving back and forth, this indicates whether they have a planet orbiting them. As the planet orbits the star, it pulls on its gravitational field causing the star to “wobble”, the star will at times be moving towards earth and at other times be moving away and this results in the Doppler effect. [1] The transit method is based on the observation of a star’s brightness. As a planet orbits the star, it passes in front of the star causing there to be a drop in brightness. By observing the repeated occurrence of the drop in brightness astronomers can determine if the drop is really from a planet.[2] The direct method of finding an extrasolar planet is much more difficult than using the indirect method, as planets further away are usually dimmer compared to their parent stars. However new techniques are being created such as the use of interferometry where the light of various telescopes are combined to “overcome the diffraction-limit of an individual telescope.” [3] This technique allows clearer pictures as well as better lighting, which is required to directly view far away objects which may be extremely faint without the use of interferometry [4] [1] http://burro.astr.cwru.edu/stu/advanced/esol_find.html

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