Slashdot Mirror
Two Planets Found Sharing One Orbit
dweezil-n0xad writes "Buried in the flood of data from the Kepler telescope is a planetary system unlike any seen before. Two of its apparent planets share the same orbit around their star. If the discovery is confirmed, it would bolster a theory that Earth once shared its orbit with a Mars-sized body that later crashed into it, resulting in the moon's formation."
Quick, we need to redefine the meaning of "planet" yet again.
Win a signed Stephen Carpenter ESP Guitar from the Deftones: http://def-tag.com/?r=0008781
This is more liberal lies. Bill O'Reilly told me that you can't explain that!
What a fool believes, he sees, no wise man has the power to reason away.
Check Wikipedia.
That there's a duplicate Earth on the exact opposite side of the Sun!
OK, just for the fun of it: what would be the most efficient method to check this hypothesis?
That would be STEREO.
That there's a duplicate Earth on the exact opposite side of the Sun!
OK, just for the fun of it: what would be the most efficient method to check this hypothesis?
By checking how its gravity would effect other planets in the same star system. For background: Counter-Earth on Wikipedia, Lagrangian point L3 on Wikipedia, and Counter-Earth on TV Tropes. Executive summary: We don't have one, and we know this because if we did, we'd be able to detect its pull. Furthermore, such an orbit would be unstable.
It's not clear that this is anything new. A number of astronomers have suggested that we should treat the Earth/Luna and Pluto/Charon pairs as "double planets" sharing an orbit. And there's a pair of Saturn's moons that share an orbit. Of course, whether these are counterexamples depends on the picky, legalistic details of how you define the term "planet", which we've discussed to death here on /. already. Fun as such pseudo-arguments may be, the fact is that they're not terribly significant.
Thus, for the Pluto/Charon pair, reclassifying Pluto as a "dwarf planet" make it especially an edge case, since it still includes the term "planet" in its classification. But they're both large, spherical bodies in a single orbit around the sun, while also orbiting each other.
The Earth/Luna pair is a bit of a mathematical curiosity. One of the arguments supporting calling our moon a "planet" orbiting the sun is that its orbit is everywhere convex with respect to the sun. You'd expect a "moon" to have a much more wiggly orbit, parts of which are curved away from the sun, and this is true of the other objects in the solar system that we call moons. OTOH, the barycenter of the Earth/Luna pair is (slightly) inside the Earth, which can be used with some definitions to say that it's really a satellite of the Earth.
And, of course, Saturn's two moons in a single orbit can be disqualified because they're obviously not "planets". They're not even big enough to be spheroidal, which is required by most definitions of a planet.
But the fact remains that our solar system contains at least three example of paired bodies sharing an orbit about their primary, and periodically exchanging the lead position. The mechanics of such orbits have been long understood, and astrophysicists can tell you when such orbits are stable. So while this may be "news" in the sense that it's about such orbits around another star, it's hardly news in the astrophysics sense.
What'll be interesting news is the discovery of three astronomical bodies in a "Scottish reel" orbit, which was proved possible several years ago, but to my knowledge hasn't actually been observed yet. Possible places to find them are in the asteroid belt, in Jupiter's "Trojan" asteroid clumps, and in the Kuiper Belt.
Those who do study history are doomed to stand helplessly by while everyone else repeats it.
The problem with the planet detection methods used by the Kepler team is that it is all calculated based on occultations; the slight dimming of the star's light as a planet passes between that star and the Kepler satellite. This only works if the planet in question is 1) HUGE or 2) very close to the star or 3) the Earth just HAPPENS to be in the plane of the planet's orbit around the star. That's why we're discovering so many enormous planets with orbital periods in the range of only a few days. But the nice thing about the Kepler data seems to be that it's eliminating many of the "it could NEVER have happened that way!" explanations. With upwards of 500 billion stars in the Milky Way galaxy and we've looked only at a few thousand, it looks more and more that ANYTHING is possible when it comes to planetary formation.
Oh, sorry, typed it wrong...
.htraE ylno eht si sihT .tuoba gniklat er`uoy tahw wonk t'nod I .uoy rof taht dexiF
Don't tell me to get a life. I had one once. It sucked.