People have been finding planets in distant space since Galileo first looked up at the stars with a telescope. By now though we can look much farther than just our solar system, we’ve even been able to see into the distant past. Astronomers find planets all the time as they look out into space with giant telescopes. The telescopes are usually in the middle of nowhere so other light does not interfere with them. XKCD describes well in one of his comic strips how amazing this is and also how much some people don’t care. Since finding planets is so common now it may seem easy to find one, like looking for a giant sphere of rock hurtling through space but it’s actually not as obvious as it seems.
There are many tactics to finding planets orbiting stars, most aren’t exactly for people in their backyards with a little telescope. One tactic called the transit method is to measure the light coming off of a star (the term is lumens). By keeping a consistent log of the light coming from a star, scientists can tell if there are planets orbiting it by noticing small variations in the brightness when the planet passes in front of our telescope. Another method came about by accident: scientists were studying the motion of a distant star and noticed, again, slight variations in their data. It was caused by something big pulling on the star, maybe a planet in orbit per-say.
Finding Earth-like planets is even more difficult though since the planet needs to be a certain distance from the star and even that is determined by the size and heat of it. Our planet Earth is in a place called the goldilocks zone around our sun. We aren’t too far where the planet will freeze to death and we aren’t too close where we will slowly burn and melt. The biggest reason this is the goldilocks zone is because it allows for liquid water. This is the biggest sign astronomers look for to find “Earth-like” or habitable planets. Also if there is little green men walking around on the surface it’s safe to assume the planet is habitable, that’s a bit of a larger hint.
Looking for other habitable planets like Earth may seem like a waste of time since our planet isn’t going anywhere anytime soon, but in a couple billion years when our sun turns into a red giant and engulfs our home in fiery radioactive fire, maybe everyone will be thankful that we did the research to find somewhere else to live and that the human race wasn’t born and then snuffed out but had the ability to expand and spread beyond our own home…or maybe we didn’t explore and instead burned to death on our own measly planet, who knows.