ESA Science & Technology08-Jul-2005 11:28:42

Extrasolar Planets


When light is reflected by a planet it is not just the wavelength that can be changed. Being a wave, each light ray oscillates in a particular direction. Light rays emitted by a star are said to be unpolarized because the oscillation direction of each ray is random. When light rays bounce off the planet, however, the oscillations are forced into a preferred direction because of the way the light interacts with the atoms and molecules in the planet's atmosphere. Light rays lined up like this are said to be polarized.

Astronomical devices known as polarimeters are capable of detecting just polarized light and rejecting the unpolarized beams. New, highly accurate polarimeters are currently being made, in the hope that they will be able to pick out the faint polarized light beams coming from the extrasolar planets.

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