For most of human history, planets beyond our solar system belonged to speculation. Today, thousands of exoplanets are known, and the possibilities are stranger than many early imaginings.

How do you find a planet beside a star?

Stars overwhelm planets with light, so astronomers often detect worlds indirectly. A planet crossing in front of its star can cause a tiny repeating dip in brightness. A planet’s gravity can also make its star wobble. Other techniques add more pieces to the puzzle.

There is no single kind of solar system

Researchers have found giant planets close to their stars, compact systems with several worlds, rocky planets and objects with sizes unlike the familiar categories in our own neighborhood. Each discovery reminds us that nature was under no obligation to copy our solar system.

The careful search for habitability

A planet lying in a star’s habitable zone is not the same thing as discovering life. Size, atmosphere, temperature, chemistry, geology and the behavior of the host star all matter. Scientists search for evidence step by step rather than treating one promising measurement as proof.

A sky suddenly full of destinations

We cannot yet visit these worlds, but we can begin to characterize some of them from across interstellar distances. That alone changes the night sky: stars are no longer merely lights. Many are suns with worlds of their own.