Exoplanets are planets beyond our own solar system. Thousands have been discovered in the past two decades, mostly with NASA’s Kepler Space Telescope. These exoplanets come in a huge variety of sizes and orbits. Some are gigantic planets hugging close to their parent stars; others are icy, some rocky. NASA and other agencies are looking for a special kind of planet: one that’s the same size as Earth, orbiting a sun-like star in the habitable zone. The habitable zone is the area around a star where it is not too hot and not too cold for liquid water to exist on the surface of surrounding planets. Imagine if Earth was where Pluto is. The Sun would be barely visible (about the size of a pea) and Earth’s ocean and much of its atmosphere would freeze.
