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What is an Exoplanet?

With all the talk of exoplanets in the news, we take a look at what exactly is an Exoplanet?

By , 11th November 2008 in Astrobiology

Exoplanet is a relatively new word used to describe a planetary body orbiting a star other than our own Sun. The word is a combination of Extra-Solar Planet.

The first exoplanet was detected in 1988 by the Canadian astronomers Bruce Campbell, G. A. H. Walker, and S. Yang. Their radial-velocity observations suggested that a planet orbited the star Gamma Cephei. They remained cautious about claiming a true planetary detection, and it wasn't until 1996 that the discovery was confirmed.

In early 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of planets around pulsar PSR 1257+12. This discovery was quickly confirmed, and is generally considered to be the first definitive detection of an exoplanet.

Artist's impression of the extrasolar planet HD 189733 b
Image Credit: NASA
Artist's impression of the extrasolar planet HD 189733 b

More information: How to Find an Exoplanet

Since then Exoplanets have been discovered at an ever increasing rate, and as of November 2008, 322 exoplanets have been detected and confirmed.

HD189733b is the third planet of the red dwarf star Gliese 581 and is roughly the size of Jupiter. It is now known to contain methane and water in its atmosphere, the first time organic molecules have been detected in an extrasolar planet. Astronomers used the Hubble Space Telescope with the help of the Spitzer Space Telescope and studied how light from the host star filters through the planet's atmosphere using a process called spectroscopy.

In April 2005 astronomers using the NACO adaptive optics facility at the 8.2-m VLT Yepun telescope at the ESO Paranal Observatory photographed the first image of an exoplanet orbiting a star.

The planet is near the southern constellation of Hydra and approximately 200 light years from Earth.

The Brown Dwarf 2M1207 and its Planetary Companion
Image Credit: NASA
The Brown Dwarf 2M1207 and its Planetary Companion

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