Extrasolar planets are planets orbiting stars other than our Sun. Finding and studying extrasolar planets will help astronomers learn more about the formation of our solar system, and the possibility of life in the universe since life would probably develop on planets, not stars or the emptiness of space. Many astronomers believe that almost every Sun-like star has a solar system at some point in its development.

Astronomers need techniques to locate extrasolar planets. The stars these planets orbit around are millions or billions of times brighter than the planets, and the planets are close to the stars. This will make it hard to see the planets, and even the most powerful telescopes cannot pick out a planet against the glow of the star. Astronomers can sometimes detect the dimming of a star as its planet passes in front of it.

Astronomers have developed a different way to detect extrasolar planets. They look at the stars to see if they wobble. Stars wobble because of the gravitational pull between the star and the planet. Even though the star is much larger than the planet, the planet still has some pull on the star, causing the star to wobble.

All the extrasolar planets that have been found have been very large. Some of these planets are several times larger than Jupiter, the largest planet in our solar system.

Astronomers also use radio telescopes to find new solar systems. When a solar system is forming, radio waves are formed from the hot gas and dust. Radio telescopes on Earth can detect these radio waves, helping to find and map new solar systems.

In the 1900s astronomers found that our solar system was not in the center of the galaxy, and that our galaxy was not the center of the universe. Earth is just a tiny planet orbiting one star out of billions. This made it seem more likely that other stars had a solar system and that some of those solar systems might have planets similar to Earth.

In 1995, astronomers discovered the first extrasolar planet, 51Pegasi B, orbiting a star 45 light-years from Earth. Between 1996 and 1998, American astronomers Geoffrey Marcy and Paul Butler found 13 more solar systems with planets.

In May 1998, the Hubble Space Telescope took a picture of what is probably the first extrasolar planet ever photographed.