If you’re looking for life on other worlds, a good place to start would be finding planets that are similar to Earth. Earth’s orbit around our star, the Sun, keeps us within a “habitable zone” that allows water to stay liquid, a key life ingredient.
If our orbit were too close, Earth would be too hot and water would boil away. If our orbit was too far from the sun, our water would freeze.
Earth is also just the right size. If a planet is too big, it’s likely become a gaseous giant like Jupiter. If it’s too small, it wouldn’t have the gravity necessary to hold an atmosphere close to it. An atmosphere is necessary to trap some of the heat we get from our just-the-right-distance-away star.
These are some of the factors that astronomers use when when scouring the universe for habitable planets. Unfortunately, the distances to other solar systems from Earth makes finding just-right “Goldilocks” planets like these a real challenge. In addition, little planets are much harder than big, bright stars to see in the darkness of space.
Recently, NASA scientists have used the Kepler spacecraft, a special telescope in orbit around the Sun, to discover habitable zone planets that are similar in size to Earth in two different solar systems. A few other habitable zone planets have been found before, but these are the smallest yet. Scientists don’t know if these planets are actually capable of supporting life, but these discoveries are a step towards identifying actual Earth-like planets.
Kepler discovers planets in other solar systems by pointing at one area in space for a long time and measuring the brightness of stars. Kepler watches to see if the stars temporarily dim, which is a sign that a planet is passing in front of the stars and blocking some of the light. Using a calculation that includes how much the starlight dimmed and how long it dimmed for, scientists are able to determine the mass of the planet and the size of its orbit.