The news from NASA’s Kepler mission just keeps getting better. The space telescope, which launched in March of 2009, spends its time staring at 150,000 stars in a patch of Milky Way. It monitors their brightnesses, looking specifically for dips in the light caused by a planet passing in front of it. This transit method has found 115 planets and more than 2,740 candidates. And this week Kepler added two more to the candidate list: the two of the most Earth-like exoplanets yet in one system. We might have a planetary vacation spot yet.The planets in question orbit the star known as Kepler 62. It’s a fairly ordinary star, 1,200 light years away in the northern constellation Lyra. It’s Sun-like but slightly smaller, cooler, and more orange than our own star, making it more or less the same as tens of billions of stars in our galaxy. But this one has planets. Five of them. And two orbit squarely in that magical zone around the star where water can exist in a liquid form, the so-called Goldilocks zone.The two planets are named after their star: Kepler-62e and Kepler-62f. They’re both slightly bigger than the Earth, about 1.6 and 1.4 times the Earth’s diameter respectively. And they’re close to their star. Kepler-62e orbits about 37 million miles from the star, giving it a 122-day long year while Kepler-62f orbits about 65 million miles from the star with a 267-day long year. These orbits are roughly equivalent to the orbits of Mercury and Venus in our solar system; because Kepler 62 is cooler than our star, the planets aren’t fried like they would be around the Sun. But it is interesting that the Kepler 62 system resembles our own solar system. We also have two planets in out star’s habitable zone: Earth and Mars, which had the conditions for life early in its history but lost them. It’s just too small to hold on to an atmosphere.Taking what we know about the Earth and applying it to the possible Earth-like Kepler-62e and Kepler-62f, astronomers suspect both these planets could be habitable. But there are–and here’s the refrain no one likes to hear in exoplanet news–a lot of unknowns. Astronomers don’t know the masses of these planets yet, or their compositions, or whether they have appreciable atmospheres that could sustain life. They could be more Venus- or Mars-like, just too hostile for life.
And these all-important details are the ones we’re going to have to wait on. The system is far too far away for astronomers to measure the masses of these planets directly. Astronomers have measured similar-looking planets around other stars, so we can infer some details about the two Kepler 62 planets, but it’s an inference only.Neither of Kepler 62’s possible habitable worlds are small enough to be considered twin Earths, but it is another piece of evidence pointing to a galaxy littered with billions of Earth-size planets. And it means astronomers are probably getting closer to finding a twin Earth. With every discovery of a small planet, it seems increasingly likely that it’s only a matter of time.But for now Earth-bound astronomers will have to do some ground-based observations to confirm the Earth-like-ness of Kepler 62’s habitable planet candidates. And if it turns out that these planets could support life, well, that would be awesome. Not so much for us, but for our possible interplanetary descendants and the inhabitants of the Kepler 62 system. Imagine how easy interplanetary travel would be when you’ve got planetary neighbours to go visit.
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