Ever since astronomers figured out that the stars in the sky are just like our sun,

they began wondering if those stars had planets just like our sun.

For centuries, this remained an unanswerable question.

Telescopes and techniques weren't advanced enough to get an answer one way or the other.

Eventually, however, astronomers develop these methods to detect if there were planets outside

of our solar system, and when they did, they found them everywhere.

Learn more about exoplanets, planets that orbit other stars,

on this episode of Everything Everywhere Daily. The idea that other stars had planets has been around a long time.

As early as the 16th century, the Italian astronomer Giordano Bruno posited that there might be planets orbiting around other stars and he was also the first person to seriously raise the idea that those other planets might have life just like Earth.

It was a philosophical point for centuries because no one had any way of detecting

if there were planets around other stars. There were several claims of planets having been

found around other stars in the late 19th and early 20th centuries, but those claims were

never substantiated. Because we had no data, astronomers were stuck

speculating. The big question was if our solar system was typical or

atypical. If there were other solar systems

around other stars would they look roughly like our solar system or would they be

totally different? For example in our solar system small rocky planets are the inner planets, and gas giants are the outer planets.

No one knew if this was a rock-solid law of planet formation or if this was just particular

to how our solar system happened to develop.

Imagine an alien encountering a single human being and from that one example trying

to figure out if every human being was like that one.

Did we all have four limbs? Did we all have black hair? There's no way to know from a single

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