ESA Science & Technology08-Jul-2005 11:27:58
 

Extrasolar Planets

Imaging

The holy grail of this research is to obtain pictures of planets around other stars, so that astronomers can analyse the chemical composition and physical state of these distant worlds. This is an extremely challenging task. At visible wavelengths, a star like the Sun will outshine a planet like the Earth by a billion times. This is because planets do not emit visible light; they simply reflect some of the star's light. If, however, astronomers move to longer wavelengths, such as the mid-infrared, then the contrast between the star and the planet drops to a million, because the amount of infrared given out by the star goes down whilst the planet itself, begins to emit.

This mid-infrared radiation, however, is most easily viewed from space. At the Earth's surface, the signals can be swamped by the infrared waves our own planet gives out. Also, because planets and stars are usually close together, the Earth's atmosphere smears their light into a single fuzzy blob. So, astronomers have devised a number of techniques to work around these constraints and make direct detections collecting both visible and infrared light.



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