In a solar system 1,200 light-years away from ours, there's a couple of planets that come so close to each other every 97 days they can see each other rise in the night sky. This odd duo, found thanks to data from the Kepler telescope, would stay within 1.2 million miles of each other at their closest approach — the closest two planets ever discovered.
One of the planets called Kepler-36b is a rocky world roughly 1.5 times the size and 4.5 times the weight of Earth. The other one, Kepler-36c, is a gas giant 3.7 times the size and 8 times the weight of our planet. What makes the duo unusual is that rocky planets like ours usually orbit close to the sun, while gas giants like Neptune or Jupiter tend to orbit their stars from a distance.
On the surface of 36c, rocky world 36b would look like a full moon in the sky. On the surface of 36b, on the other hand, 36c appears as a full moon 2.5 times the size of ours — a giant purple full moon, to be precise, due to the sodium and potassium content of 36c's atmosphere.
The discovery is unprecedented, according to Eric Agol, one of the lead researchers. "They are as different in density as Earth and Saturn (the highest and lowest density planets in our solar system), yet they are 30 times closer than any pair of planets in our solar system."
But even though 36b is a rocky planet, it most likely isn't habitable. Both planets stay too close to their star — three times closer than Mercury is to our sun, in fact. Add that to the likelihood that their star is hotter than ours and the possibility is that you'll find an abundance of flowing lava on 36b's surface.
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