Would it be possible for a comet to be caught in and orbit around the Earth?

Question

I can't solve that one, but suspect the interaction of the Earth, Moon and a comet COULD capture a comet.

If so, would the comet be close enough to the Earth to generate a tail? How long would that last?

edit: If it were LIKELY we would have a whole flock (what's the collective noun for moons?) of dead comets circling the Earth. I know its UNLIKELY, is it POSSIBLE? Many comets ended up as moons to the outer planets, for just the reasons you guys stated... their orbits start way out there and at aphelion they ain't moving too fast (like me in the morning). The POINT is (was) using the Moon/Earth/random comet as a three body problem, could a comet be slowed into an Earth stable orbit?

Answer 1

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Answer 2

Brant is correct. When comets reach into the interior of the Solar System where the Earth hangs out, they are generally moving too fast to get caught. The Earth will perturbe the orbit of a comet that comes close, but not capture it.

As far as a tail is concerned, most comets when they get within the orbits of the inner planets, sprout a tail. It is the sun's energy that causes the comet to grow a tail, not the proximity of planets.

Hundreds of asteroids come close to the Earth. They are much more common than comets, but don't generally get captured in an orbit. However, I read somewhere that Earth has had a ring, like Saturn only much thinner. This would have been a captured body that was subsequently disintegrated by Earth's gravity.

Answer 3

With some difficulty it would be just possible.

The trouble is that the Earth moves in a circular orbit at around 30km/sec relative to the sun. To be captured into orbit a comet would need to be moving tangential to the Earth, not too far away and at no more than the escape velocity which would be around 7km/sec. Hence the comet would need a rather finely tuned trajectory, moving at about 37km/sec relative to the sun as it overtakes the Earth.

Trouble is that comets come plummeting in towards the sun on very long orbits and are travelling well above the necessary velocity by the time they reach the Earth. Obvious when you think about it. If they were travelling at the Earth's velocity near the Earth then they would be in circular orbits!

A long and complicated capture manouvre involving the cooperation of the various planets and moon might just work. Yes it would have a tail, and no the tail would not last long, perhaps only hundreds of orbits depending on the comet's constitution, and how long the capture took.

This is a tremendously improbable event. Therefore a comet in Earth orbit infers either deliberate action or many previous unsuccessful attempts. Hmm sounds like we are talking about the origin of the universe here!

Answer 4

Yes, it's theoretically quite possible. The moons of Mars probably started out as asteroids and were captured in such a fashion.

Comets are mostly ices that evaporate inside the ice line, however, so an Earth-orbiting comet wouldn't last very long. The heat of the sun would quickly evaporate all the ice, either causing the comet to disintegrate or leaving behind a small rocky core. Until that happened, it would show a tail.

Answer 5

Yes, a comet could be captured by Earth's gravity, but the situation would have to be ideal, and several factors would come into play.

1-The comet would have to have a relatively low orbital speed, and would have to pass by Earth at a wide angle instead of head on so the gravitational attraction would be greater.

2-The comet would have to be relavitely small in order to be affected substantially by Earth's gravity.

3-A comet with a less elliptical orbit would be easier to capture, because comets(and planets) move fastest at perihelion.

A comet could not generate a tail when near Earth, because comet tails are caused by gas and dust reacting with solar wind and heat when the comet nears the sun. Some comets have tails as close to the Sun as Earth, but this is not extremely common. The Earth itself would not cause the comet to have a tail, but because the comet was captured, it might have an unstable orbit and would eventually break up due to tidal forces and create a ring around the earth; or the comet would eventually collide with Earth. The orbit of a captured satellite would be further complicated by the gravitational pull of the moon, which would severely disrupt the orbit of the new object.

Answer 6

Two-body gravity alone can never "capture" anything, ever, because the orbit is either bound or unbound, and there is no in between. The only way a body can be captured by another body is for some frictional or other process to extract energy from the orbit. In other words, the comet would have to either have exactly the right trajectory to aerobrake in the atmosphere without breaking up, or have an interaction with both the Earth and the Moon.

In other words, not bloody likely.

Answer 7

It is theoretically possible.

If the comet's orbit was first affected by one of the gas giants and placed on a less eccentric orbit, with little or no inclination to the plane of our orbit, and it passed in some "lucky" way a few times near us and Mars, it could eventually be caught in some highly elliptical orbit.

If the process does not take too long, the comet will still have a good supply of ices that could continue to evaporate under the influence of the Sun and produce a tail (the tail is the result of the Sun's action, not Earth).

There can be two tails (dust and ions); the dust tail (yellowish light) is sunlight reflected on the grains of dust that are pushed back from the comet by solar wind: they proceed on their own individual orbit, making the tail look curved.

The ion tail are molecules or atoms of gas evaporating from the comet and made to glow by charged particles (solar wind). When a comet goes through areas of reversal of the sun's magnetic field,it can turn on and off.

I have no idea how the ion tail would behave within Earth's magnetosphere, if the comet gets in close enough.

Answer 8

Jose´ has the right answer here. There has to be a mechanism by which the comet could lose energy in order to be "captured" in earth orbit. Just the right sort of encounter with the moon could do it, I suppose, but things that are "just right" don't happen by accident very readily.

Answer 9

Yes it would be possible. It would be a rare view, for earthlings the moon a comet and conjunctions between them. With time the tail would disappear and there would be a ball of rock and ice turning around the Earth and and reflecting the sun, if the orbits cross we eventually could have a crash among them, if not we would have two moons, with time.

Answer 10

It might be capture-able, but with the Moon out there to perturb its orbit, it might not remain captured for very long.

Proximity to the Earth has nothing to do with the appearance of a tail, that is caused by teh combined effects of solar heating and solar wind.

Answer 11

I'm guessing no, unless it happens to be at perihelion near the earth's orbit. Otherwise, they are traveling too fast to get captured.

That would be cool, though.

Edit, on second thought, since they all come from so far out, I'll bet there's no place where they could be going slow enough for capture.