Are there any other Earths out there? Is there another planet like ours, maybe one where we could live? One goal in the search for exoplanets, planets orbiting stars other than our own sun, is to find Earth-like planets. NASA’s Kepler mission just found the closest match yet!
This planet is called Kepler-452b. It’s not exactly a catchy name, but it’s informative: the name tells us the planet was found by the Kepler mission, and gives a number to the star system and a letter to each object. This planet got the letter “b” because it’s the second object found in the system, after the star.
A planet in its star’s habitable zone? We’ve found a few, but that’s still pretty cool—or rather, just the right amount cool for liquid water to potentially exist on the planet. This is the definition of the habitable zone. Without liquid water, we wouldn’t find a planet habitable, and in order to have liquid water, a planet would need to be warm enough for water not to freeze and cold enough for water not to boil. The temperature on the surface of a planet depends largely on its distance from its sun. The closer they are, the warmer the planet is. However, being not too close to and not too far from its star doesn’t tell you everything about a planet. It could be large or small, and made of all sorts of different materials. It could be dense and rocky like Earth or Mercury, or it could be fluffy and gaseous like Jupiter or Neptune.
So, being in the habitable zone isn’t enough to make a planet habitable. It would be hard to live on a planet without a surface you could stand on, so if you’re looking for a new planet to inhabit, pick out a rockier one. The size of the planet would also make a difference. The smaller a planet is, or even a moon for that matter, the harder it is to hold on to an atmosphere. Less mass means less gravity, which means less pull on the gases which make up an atmosphere. Gas particles can fly away over time until there are hardly any left. More mass means more pull, so it’s harder for particles to escape. So, more massive planets are more likely to have a thick atmosphere.
What about Kepler-452b? Where does this recent discovery fit in? It’s 60% larger than Earth in diameter, which is actually pretty close in size. For comparison, Kepler-452b is about 1.6 times the diameter of Earth, and Earth is about 1.9 times the diameter of Mars. Kepler-452b is considered a super-Earth in size. That’s what we call planets near in size to Earth, but on the large side.
While we know all this about Kepler-452b, there is also a lot we don’t know. We don’t know exactly what it looks like. We don’t know how close it is to actually being habitable. We certainly don’t know its whole story—yet. As technology improves, telescopes get better, and we think up cleverer ways to learn more about far-off places, we keep finding out more and more about distant worlds like this one.