For centuries, people have wondered whether distant stars had planets orbiting around them. Unfortunately, most stars are so far away that it was impossible to spot any planets. But modern instruments have now made it possible to detect planets, and more than 400 of them have already been found.

BABY PLANETARY SYSTEMS
Out in space, new solar systems are still forming. This is the Orion Nebula, where many stars are being born. Around each new star is a spinning disk of gas and dust. If material in this disk starts to clump together, it eventually forms planets that orbit the star.

Pulling power
The first exoplanet in orbit around a Sun-like star was discovered in 1995. The planet was detected from a tiny wobble in the motion of the star 51 Pegasi. As the planet, called 51 Pegasi b, orbited the star, its gravity sometimes pulled the star toward Earth and sometimes away from it. This wobble showed up as slight shifts in the spectrum of the starlight. Since then, hundreds of exoplanets have been found from the wobbles they create in nearby stars.


DUSTY DISKS
Planets form inside huge rotating disks of dust and gas. Even before the first exoplanets were spotted, dust disks were found around many young stars. The first was the disk around a star called Beta Pictoris. In 2008, scientists discovered an object very close to this star. They think it is a giant planet, located somewhere inside the disk.

A planet like Earth?
As planetary systems are fairly common, there may be many exoplanets similar to Earth scattered across the universe. We have not yet found one, but space observatories are expected to do so in the next few years. The system below, called HR 8799, was one of the first multiplanet systems to be recorded. Images like this prove that complex planetary systems do exist—systems that might just contain an Earth-like planet.

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