51 Pegasi b (Dimidium)

exoplanet · first discovery · space exploration · hot Jupiter

First exoplanet found. In 1995, scientists discovered 51 Pegasi b orbiting a star called 51 Pegasi, about 50 light-years away in the constellation Pegasus. This was the first time anyone had ever found a planet around a Sun-like star beyond our solar system.

A hot Jupiter. 51 Pegasi b is a giant planet similar in size to Jupiter, but it orbits incredibly close to its star, much closer than Mercury orbits our Sun. This surprised astronomers because they thought giant planets should be far from their stars, like Jupiter is in our solar system.

Super scorching world. Because it orbits so close to its star, 51 Pegasi b is extremely hot, earning planets like it the nickname 'hot Jupiters.' The planet is so close to its star that its year is only about 4 Earth days long.

Changed astronomy forever. This discovery proved that planets exist around other stars and that planetary systems can be very different from ours. It opened up the entire field of exoplanet science and led to finding thousands of other worlds beyond our solar system.

Official name is Dimidium. The planet was officially named Dimidium, which means 'half' in Latin, because it has about half the mass of Jupiter.