The first extrasolar planet was discovered in October 1995 by Michael Mayor and
Didier Queloz, a pair of astronomers working in Switzerland. The planet
the found was orbiting around the star 51 Pegasus, in the Pegasus constellation.
They found this planet by measuing the regular change in the star's doppler shift
(that is as a light source moves away from you, the light's spectra will
shift towards the blue, if the light moved towards you, the light will shift towards the
red).
The planet around 51 Pegasus has a period of only 4.2 days, which translates into
almost 300,000 mph. (The Earth moves around the Sun at about 75,000 mph.)