Four hundred years ago, an astronomer named Giordano Bruno was burned at the stake for suggesting the existence of other Earth-like worlds. Today we know that there are potentially billions of extra solar planets in the Milky Way. None found so far resemble Earth. Indeed, many are shockingly different from our world. Although none of the planets investigated so far have shown any signs of life, many astronomers believe that it is only a matter of time before Earth’s twin planet is discovered.
Our solar system is just one specific planetary system—a star with planets orbiting around it. Our planetary system is the only one officially called “solar system,” but astronomers have discovered more than 2,500 other stars with planets orbiting them in our galaxy. That’s just how many we’ve found so far. There are likely to be many more planetary systems out there waiting to be discovered! Our Sun is just one of about 200 billion stars in our galaxy. That gives scientists plenty of places to hunt for exoplanets, or planets outside our solar system. But our capabilities have only recently progressed to the point where astronomers can actually find such planets.
Even our closest neighboring stars are trillions of miles away. And all stars are enormous and extremely bright compared to any planets circling them. That means that picking out a planet near a distant star is like spotting a firefly right next to brilliant lighthouse miles away.
So far, the planets outside our solar system have proven to be fascinating and diverse. One planet, known as HD 40307g, is a “super Earth,” with a mass about eight times that of Earth. The force of gravity there would be much stronger than here at home. You would weigh twice as much there as you do on Earth! Another planet, called Kepler-16b, turns out to orbit two stars. A sunset there would provide a view of two setting stars!
In another planetary system, called TRAPPIST-1, there are not one…not two…but seven Earth-sized planets that could be covered in liquid water. The planets are relatively close together, too. If you were to stand on the surface of a TRAPPIST-1 planet, you might see six other planets on the horizon!