20 years ago, discovery of exoplanet changed how scientists viewed solar systems

On Oct. 6, 1995, the discovery of 51 Pegasi b in the constellation Pegasus – a planet about half the size of Jupiter approximately 50 light years away – was announced in the magazine Nature.

Unofficially, the planet is called Bellerophon, after the Greek hero who tamed Pegasus. Original observations were made at the Haute-Provence Observatory in southern France by Michel Mayor and Didier Queloz. Confirmation was provided six days later with observations from the Lick Observatory near San Jose, Calif.

The discovery marked a turning point in astronomy research and changed the way we think about solar systems beyond our own. While not the first exoplanet discovered, it was the first found orbiting a sun like our own.

In the 20 years since, nearly 1,900 exoplanets in nearly 1,200 planetary systems have been confirmed. In 2012, astronomers estimated that stars in the Milky Way are host to an average 1.6 planets each based on observations from the Kepler space observatory.

Researchers did not find 51 Pegasi b by observing it directly, but rather the gravitational effects it has on its parent star 51 Pegasi and dimming effect the planet created as it passed in front of the star. Measuring tiny wobbles in the star revealed not only the presence of the gas giant but also it’s approximate mass (about 150 times that of Earth) and length of its year (about 4 Earth days). Astronomers also estimate surface temperatures of this “hot Jupiter” like planet to be around 1000 degrees Celsius.

In April of this year, 51 Pegasi b became the target of another first. The La Silla Observatory in Chile made the first-ever spectroscopic detection of visible light reflected off an exoplanet.

You can celebrate the break in the clouds this week by discovering 51 Pegasi b for yourself. Look high in the eastern sky for the square of Pegasus, then find the faint star about halfway along the top line of the square. The hot mini-Jupiter is orbiting that star and the light you are seeing left there over 50 years ago.