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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.'"
I just wanted to have the first Tattoine reference
"Pun Intended". Either people get it, or they don't. It's not clever if you have to point it out.
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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.
Seems like a bit of a degenerate case to me. The two stars orbit each other each 7.5 days. I wouldn't be surprised if their atmospheres practically overlapped with that kind of distance. The planets essentially would be orbiting the center of mass of the two stars as a result. I wonder if they'd eventually merge, and what would happen then.
I think that this situation is likely to be a lot more stable than having another star orbiting further out than the planets.
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
Not possible given the orbital periods. Both planets orbit outside the orbits of the twin stars. (That's the definition of circumbinary, also.)
We only have one known planet where life has occurred and is sustained. There is no prof, yet, that life ever occurred on Mars or any other planet in our system. At this point with what we actually know about life I think the "habitable zone" graphics on some of these press releases are overly optimistic. I hope we can find evidence of life on Mars so we can actually expand our "known" habitable zone.
It all starts at 0
Unlike our sun, many stars are part of multiple-star systems
IIRC from my star fighter days, most stars, the vast majority of them, are part of multiple-star systems. Sol is very weird and a rare counter-example in that regard.
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At those distances tides would be extremely minor. The Sun does have tidal effects on the Earth, but they are quite minor. The tidal effects of a binary star would be about the same (they would vary according to the orbit more than it does on Earth, but not enough to be an issue).
The much bigger problem would be the fact that the planet would vary in distance from a star according to it's orbit, much more so than the Earth does, even if the orbit isn't eccentric, simply because the suns are orbiting each other (probably fairly rapidly) and would therefore be closer and farther from the planet in turns. Depending on the separation, mass, and orbit of the stars, it is possible there isn't even a "goldilocks" zone, because the radiation in any orbit varies from high to low extremes too much as one star gets closer and farther. Most likely, though, one star is much smaller and will have little effect, or the radiation won't vary so much from the average that it will make a difference. It's hard to say because any such arrangement is a three-body gravity problem, so the solution is very complex (although you could model it as a 2 body assuming the planet is a point-mass to calculate the stars orbits, and the stars are a single body to calculate the planet's orbit, which is in most cases quite accurate).
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