NASA discovers three Earth-sized planets right in the habitable zone

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For the past three years, NASA’s Kepler space observatory has been pushing back the boundaries of our knowledge of the universe. The telescope has generated enormous amounts of data and is expected to continue doing so through 2016. As of the last update, Kepler has detected 2,740 planetary candidates across 2046 stars. If Hubble brought us visions of the cosmos from the dawn of creation, Kepler has been vital in our search for other planets in our own backyard.

Today, NASA announced a new milestone in Kepler’s survey of the heavens — the confirmation of Kepler 62e and 62f as existing planets within the habitable zone of their parent star, Kepler 62. These discoveries are remarkable; this is the first time we’ve confirmed planets roughly the same size as Earth orbiting in the Goldilocks Zone. Kepler 62e is 1.61x Earth’s size and orbits every 122 days, while Kepler 62f is 1.41x Earth-size and orbits every 267 days.

There’s still a great deal we don’t know about the new planets, which is why the science teams, while excited, are taking a fairly neutral tone. It’s impossible to see whether or not the two worlds have atmospheres, or what the atmospheres might be made of. Both planets have more than enough mass to retain an oxygen atmosphere, but there’s no way to tell if carbon dioxide is also present, or to examine what other compounds might be in the air.

The constant rate of discoveries implies that some of our basic assumptions about planet formation are fundamentally correct. Before Kepler, there was some debate as to whether most stars had planets or not. The discovery of planets similar in size to Earth located in habitable zones doesn’t prove that life exists, but it does mean that some of the most basic building blocks for life — or at least, life that’s something like us on a structural level — exists in other places. Alternately, while the rocky planet explanation is more likely, it’s possible that these planets might be something we’ve never seen in our solar system: a water world.

From L to R: Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f, and Earth

A water world is a hypothesized type of world that begins as a ball of frozen ice at the edge of a solar system. As the planet migrates towards the inner portion of the solar system, temperatures would rise high enough to melt the outer core. This creates liquid oceans hundreds of kilometers deep, possibly with an exotic icy mantle at their very depths. Right now, the best candidate for this kind of planet is Gliese 1214b, but Kepler 62e and 62f could prove to be water worlds as well.

As Kepler’s mission continues, the telescope’s ability to see the regular dips in starlight as a planet passes across its sun will improve. Longer observation windows make it easier for the telescope to isolate small changes that were initially undetectable. According to NASA, the telescope will eventually be able to confirm the existence of true Earth-sized planets — moving us one step closer to understanding the shape of the rest of the galaxy.

The announcement also covered the discovery of a potentially habitable planet around Kepler-69. Unlike Kepler-62, which is a small, dim star that’s far older than our Sun, Kepler-69b is much more like Sol as far as size and luminance. Kepler-69c’s speed and distance from its star make it more analogous to Venus than Earth, and it’s larger than the Kepler-62 planets, at 1.7x Earth-size. It’s not necessarily as well-suited to life, but it’s a useful data point for predicting what kind of planetary configurations should be expected around stars much like our own.