An exoplanet is any planet that is outside our solar system. According to NASA, there are currently over 5,000 confirmed exoplanets and that amount continues to grow with even more exoplanet discoveries. Most of these are in our own Milky Way Galaxy!
Because these exoplanets are so far away, we cannot see them with a telescope. Instead, they are detected other ways: by robotic telescopes in outer space, or indirectly, like by measuring the dimming of a star as a planet passes in front of it.
Exoplanets come in all kinds of sizes, from gas giants like Jupiter, to small rocky planets like Earth. They can be boiling or freezing! Some may orbit a star or two, while others float freely in total darkness. Scientists have sorted them into 4 main groups: Gas Giants, Neptunian, Super-Earths, Terrestrial. These categories help us understand some of the characteristics they share with planets in our own solar system.
Our Milky Way Galaxy includes all of the stars you can see across the sky on clear nights. It also includes our Sun. If you think about it, each one of those stars we see could have a galaxy like ours around it, making the number of planets out there incredibly high! We have been guessing this might be true for thousands of years, but our generation is the first one to know for a fact that exoplanets really are out there!
How far away are they? Well, the star closest to us is called Proxima Centauri, and it is more than 25 trillion miles away! We know it has at least one rocky planet, but we have no way of traveling that distance to reach them. That won’t stop explorers from continuing to look at the sky, seeking what exists beyond our solar system!