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NASA's Kepler Discovers Multiple Planets Orbiting a Pair of Stars
DevotedSkeptic writes "Kepler has continued its stellar (pun intended) discovery spree, this time locating multiple planets orbiting a binary star system. This is especially interesting because it proves that more than one planet can form under the stresses of a binary star system. The system is known as a circumbinary planetary system, a mechanism where a planet orbits two stars. Prior to this discovery, having multiple planets in a circumbinary system was unproven. Named Kepler-47, the system consists of a pair of orbiting stars that eclipse each other every 7.5 days. One star is similar in size to our Sol, however it only provides approximately 84% of Sol's light, the other is smaller, measuring one third of the size of Sol and emits less than 1% of Sol's light. Kepler-47b is the closer planet to its two suns, orbiting in 50 Earth days. Kepler-47c is further out and orbits every 303 days, within the Goldilocks zone. 'Unlike our sun, many stars are part of multiple-star systems where two or more stars orbit one another. The question always has been — do they have planets and planetary systems? This Kepler discovery proves that they do,' said William Borucki, Kepler mission principal investigator at NASA's Ames Research Center in Moffett Field, Calif. 'In our search for habitable planets, we have found more opportunities for life to exist.'"
You win for now...nerd
That's a compliment. Of course, even the mainstream news sites are saying this is "like Tatooine". Of course it isn't Tatooine itself, since Tatooine is long ago in a galaxy far, far away. This is in our own galaxy only 5000 light years away; the Mayans and Egyptians were still building pyramids when the light we're measuring left those stars.
What's exciting about this isn't that it's like Tatooine (or a lot of other science fiction star systems) but that it exists at all. It was formerly thought impossible for a binary star system to have planets. TFA I read earlier this morning said one of them was the size of Neptune and in the goldilocks zone, and wondered if the Neptune-sized planet had moons, and how strange it would be to be standing on one of those moons.
It seems likely that the outer, Neptune sized planet would have moons, since all the gas giants in our system do. Imagine, two suns, a HUGE GIANT moon (the planet) taking half the sky, and other moons visible as well.
Too bad it's impossible to get 5k light years away, I'd love to see the place.
Free Martian Whores!
There are those who think that tidal forces are part of the reason complex and even intelligent life arose on Earth, and that without our highly-unlikely over-sized moon, we wouldn't be here to talk about it. We have temperature variations on the order of 20% (absolute) and call it "seasonal".
With that thought in mind, I've wondered if looking for a small rocky planet in the Goldilocks zone is the best way to look for life. I've wondered if a small rocky moon orbiting a gas giant might be a more likely place to find complex life. On the other hand it was disappointing to hear that there would never be colonies on Ganymede because of radiation near Jupiter, though I know nothing of the intensity, or whether a planetary magnetic field and atmosphere would shield it, etc.
The living have better things to do than to continue hating the dead.
Using Kepler's 3rd Law, a^3 = p^2, with a = average orbital separation in AU (Earth to Sun distance), and p the orbital period in years: a = (7/365)^(2/3) = 0.07 AU. 1 solar radius is about 0.0046 AU. Go to the original paper here: http://www.sciencemag.org/content/early/2012/08/27/science.1228380.abstract and you see the larger star is about the size of our Sun, the smaller star 1/3 the size. 0.07 AU/0.0046(AU per radius) = 15.2 Solar radius separation between the stars. So, close but not close to overlapping.
Looks like I'm fielding the astronomy numbers today. Ok, look at my response to the 7.5 days question. The stars are separated by 0.07 AU (distance Earth to Sun in our system). The center of gravity's closer to the more massive star, so let's say the center of mass is 1/4(0.07 AU) from the larger star. Assume a circular orbit (not a bad assumption). Then, v = 1/4*2PiR/(t) = 2*Pi*(1/4*0.07AU*1.15x10^11 m/AU)/4*(7 days*24*60*60) = 390,000 m/s = 3.9*10^5 m/s, a tiny fraction of c, which is 3*10^8 m/s. Fast, not that fast. 0.001 c