Halley's Comet

[TwigtheWonderkid]

Probably another of my daft questions, but do we know where it goes on its 76 yr orbit? Do we follow it? If it hit another planet or something tomorrow, would we know, or would we just be disappointed by its failure to turn up next time?

[Einion Yrth]

These were its orbital elements at the time of its last apparition. If anyone cared they could be solved forward as far as necessary. I imagine someone will have given the current orbit a once over at the time to see if it was likely to hit anything, otherwise no, there's not much to follow; comets that aren't outgassing due to solar heating have a tendency to be very low albedo, and thus, at distance, pretty hard to see.

[Eric Mc]

We do roughly know where comets go to in their orbits around the sun. For 90% of the time they are at very great distances from the sun in long elongated orbits, either on the way out or on the way in. They only become visible once they start coming in past the orbit of Saturn or Jupiter. Their visibility depends on how reflective their surfaces are (albedo) or the amount of gas and dust they are jetting out. They start emitting dust and gas as they get closer to the sun and start warming up.

Even though we can calculate the orbits of comets, sometimes these orbits are changed because the comet may get tugged or pushed by the gravitational field of a planet. Jupiter is the main cause of cometary deviations. Back in 1994 Jupiter managed to deviate comet Shoemaker-Levy 9 so much that it broke the comet up and the remnants plunged into Jupiter's atmosphere.