This question is inspired by the recent “does the moon rise and set” thread. I was wondering, given that ‘luna’ is so large, relative to the earth, if the earth had another, (presumably smaller), satelite, would it be locked into one of the trojan points, assuming its orbital distance was close to ‘luna’s’ to start out with? Any astronomers and/or other dopers that can give me the straight stuff? As I recall, the trojan points would be 120 degrees in front and behind luna in it’s orbit. Thanks in advance for any thoughts.
A body at one of the Earth-Moon Trojan points would be stable. Whether or not a body would wind up there is a much more complex question.
More formally, the Trojan points are the fourth and fifth Lagrange points, L4 and L5. From Lagrange Points:
“The L4 and L5 points are home to stable orbits so long as the mass ratio between the two large masses exceeds 24.96. This condition is satisfied for both the Earth-Sun and Earth-Moon systems, and for many other pairs of bodies in the solar system. Objects found orbiting at the L4 and L5 points are often called Trojans after the three large asteroids Agamemnon, Achilles and Hector that orbit in the L4 and L5 points of the Jupiter-Sun system.”
IIRC, there is a society that proposes putting a space station at one of the trojan points of the Earth-Moon system. I think Jerry Pournelle is active in that society.
jonF quoted:
“Objects found orbiting at the L4 and L5 points are often called Trojans after the three large asteroids Agamemnon, Achilles and Hector that orbit in the L4 and L5 points of the Jupiter-Sun system.”
Yeah, but only Hector was Trojan. Agamemnon and Achilles were both Greek.
Shouldn’t they be “Greek points” instead.
Damn astronomers!
That would be, significantly, the L5 Society. However, when I do a web search for same I get local chapters calling themselves the L5 Society but listing themselves as members of the National Space Society. Maybe they changed their name.
It’s also possible for a body orbiting at L4 or L5 (L1, L2 and L3 are dynamically unstable) to be perturbed by other bodies and moved. If the perturbations are small they will return but they could be removed from the Lagrange point permanently by a large disturbance. So even if a moon were orbiting there it would not necessarily stay there. (Of course a large enough disturbance could take the moon (Luna) out of orbit, too. Then how would we know it was Easter?)
I read once that a Trojan point would be a bad spot for a space station because “garbage” would automatically collect there so there is a high chance of collisions. True? False?
The Trojan points lead and trail the Moon by 60 degrees, not 120, and junk does tend to accumulate there. I’ve heard that on a clear night, far from light pollution, you can actually see a couple of hazy patches in the sky from the dust accumulated there, but I’ve never seen this phenomenon myself.
The minor planets in these two points were named after participants in the Trojan War. Those at one point were named for Greeks, at the other for Trojans. However, they weren’t completely consistent and one from each point is from the wrong camp.
Some out there may wonder how multiple asteroids (and there’s over 400 trojans) can be at a single Lagrange point. It turns out that none of them are actually at the point 60 degrees ahead or behind Jupiter. Rather their orbits oscillate about those points.