Facinated by the ‘could there be another moon’ thread, I recall seeing a movie a long time ago where there was another earth ‘behind’ the sun in our orbit and (I suppose) 180 degrees away from our earth (that reads horribly but hopefully you get the point).
If there was another planet shadowing us 180 degrees away and assuming that it mimicked our elliptical orbit in such a way that it was always hidden by the sun, would we ever be able to detect it and if so, how.
We would detect it by the gravitational effects it has on the other planets and stuff in our solar system.
Mlees Waits to get stomped by Chronos
No. If there were a duplicate earth that shared our orbit in such a way to always be occulted by the sun, we would still see the effects of it’s gravitation on other bodies in the solar system.
(One minute too late…)
The idea of a hidden Earth was first proposed by the Ancient Greeks–by Plato, if I recall correctly. From their perspective it was fully plausible, but to us it’s not. In addition to the gravitational effects, there’s also the fact that some of our spacecraft would have been able to see it.
Ah, Planet X at Lagrange point L3, also known as “Counter Earth.” No, L3 is unstable, and as mlees points out we’d see the gravitation effects.
We would be able to detect it because of its gravitational interaction with the sun, earth and other objects in the solar system. An undetected object of that size would create sufficient differences between calculated and observed behavior of the objects in the solar system, so that mathematically the size and location of the “mystery planet” could be calculated.
ETA: I gotta type faster.
If there were a Counter-Earth, it would be at an unstable Lagrange point, so it wouldn’t stay there for very long.
By Philolaus, if the semi-obligatory Wikipedia link is to be believed.
I prefer the Hollow Earth Theory, m’self.
YAY, PELLUCIDAR!
Old thread on the topic: [thread=337968] What if there was an opposite Earth[/thread]
Conclusion: no. Such an orbit would be unstable (technically metastable, but easily perturbed from a perfect arrangement, and then would rapidly devolve from there). Because of the (slight) eccentricity of the Earth’s orbit, Htrae wouldn’t even remain in direct opposition for most of the time, though it would be close (within a degree or so, I think). Don’t get any ideas about Klemperer Rosettes, either; they’re readily perturbed even without outside influence, as a simple Matlab simulation will demonstrate.
Upon review: damn, people crawled out of the woodwork to quash this one quick! My answers are thus redundant, but what the heck.
Stranger
[ZartennneX - Supreme High Tyrannist of CounterEarth]Suckers. I have you right where I want you.
Bwahahaha![/ZartennneX - Supreme High Tyrannist of CounterEarth]
From what I’ve read, we would see the effects of another earth’s gravitation on other things in our solar system.
Quick, someone with serious orbital mechanics fu, If there were an object in earth’s orbit, but exactly half an orbit behind, wouldn’t it’s variations of speed in the ellipse (which would be opposite from those of earth at every point) cause it to move into visible range ahead of and behind the sun?
Tris
Oh, you can rest assured that I will not! Since this is the first I’ve heard of them.
Wouldn’t it be the case that we would actually see the effects of the gravitational pull upon the Earth itself? I mean, we have a very clear idea what the rate of revolution around the sun is at any point in the ellipse, thanks to Kepler. Since Gor would be directly behind the sun, it would be moving faster when we are moving slower, and vice versa, normally. To stay stable, there has to be an effect upon us, slowing us down when we’d otherwise be faster, and again, vice versa. Id’ think that would become patently obvious, patently quickly, wouldn’t it?
The elliptical orbit of the Earth is about 0.017, which is enough to produce measurable variations in the Earth’s orbital speed (about 4% overall). This will cause it to be advanced ~7° from opposition at perihelion/aphelion. The Sun covers about 0.5° of arc of the sky. (These are rough, back of the envelope calculation; don’t go plotting any orbits from these numbers.) So yeah, an opposing planet won’t be ecclipsed by the Sun for a fair portion of the orbit, though you won’t be able to see it with the naked eye for obvious reasons, and not at night at all, except perhaps very shortly after sunset or right before sunrise.
Stranger
Even if there was, as long as we’ve got Gamera on our side, we’re safe.
So, in answer to the OP: nope, just look! It ain’t there! (Aphelion was just last week, in fact.)
Thanks.
Tris