However, since it's 60% bigger than Earth and somewhere around 5 times Earth's mass, it may not experience a runaway greenhouse effect for another 500 million years.īut that’s not all the team knows about this system. If Kepler-452b had the same mass as Earth it would be on the verge of experiencing the runaway greenhouse effect and the loss of its water inventory. As Jenkins put it in a press conference today, “This planet has a somewhat better than even chance of being rocky.” Kepler-452b receives 10% more energy from its parent star than Earth receives from the Sun. The size measurement and mass estimate put the planet smack in the middle of the dividing line between super-Earths, planets slightly bigger than Earth with rocky surfaces, and sub-Neptunes, planets slightly bigger than Earth with a significant gaseous envelope. Even then, Jenkins adds, “we'll have a better idea, but it will still be a statistical estimate and not a direct measurement.” The planet’s size measurement depends on the star’s size, and measuring that depends on knowing the star’s precise distance, something which the Gaia space telescope will return in a year or two. But what the team can do is refine the planet’s size still further. “We probably won't be able to make a direct mass measurement of this planet anytime soon,” says Jenkins. Jon Jenkins (NASA Ames Research Center) and colleagues and others compared that size to other small exoplanets whose size and mass are known, and estimated the planet’s mass to be between 3 and 7 Earth masses. What the Kepler team does have is the planet’s physical size. Its fifth planet, Kepler 186-f, is an Earth-size planet in the habitable zone, but its star is a dimmer M dwarf and the planet is probably tidally locked, with a permanent dayside and nightside. Kepler-186 is a miniature solar system that would fit entirely inside the orbit of Mercury. (The planet candidate was confirmed using statistical methods rather than observations.) This size and scale of the Kepler-452 system compared alongside the Kepler-186 system and the solar system. There’s no way to measure mass directly from Kepler data, and the planet is too small and faint for ground-based follow-up. To even begin guessing about a planet’s composition, you have to start with its density, and for that you need its mass. This is the first planet to meet all three criteria (Earth-size, habitable-zone orbit, and Sun-like star), making it the closest cousin to Earth found so far.īut is Kepler-452b really Earthlike? That remains to be seen. That puts it well within the stars’ habitable zone, that fuzzy theoretical region where a planet’s hypothetical surface could support water. This exoplanet has a radius 1.6 times that of our home world and orbits its Sun-like (read: G-type) star every 385 days. The planet isn't guaranteed to be rocky, but if it is, it's probably 5 Earth masses and has twice Earth's surface gravity. But is it Earthlike? Kepler-452b, as imagined by planetary geologists and atmospheric scientists. The Kepler team announced today the discovery of Kepler-452b, an Earth-size planet in the “goldilocks” zone around a Sun-like star.
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