If a giant Asteroid perhaps a quarter of the size of earth narrowly missed a collision with us...

[Diceroller]

I'm talking a very near miss maybe a mile or two over the ocean. How would the Asteroids gravity affect earths gravitational field, the ocean and anything else?

[Diceroller]

I forgot to add it passes over the ocean for as long sustained period of time as possible before carrying on into space.

[rowanwitch]

heat generated would evaporate a significant amout of water affecting weather syystems I think.... potentially trigger for earthquakes and volcanic activity

[Frank97]

I'm no expert, but I don't think something that size would pass by that close without being pulled into the planet itself.

[nightmare]

An asteroid a quarter the size of Earth - and that is a seriously big asteroid - passing a few miles over the ocean's surface would significantly disrupt Earth's orbit for a start.

[MarkRae]

It would largely depend how fast it was travelling. Just as a rocket has to be travelling at a certain speed in ratio to its mass in order to escape from Earth's gravity, the same would apply to an asteroid. However, an asteroid a quarter of the size of Earth would have to be travelling at an incredible speed.

There are simply too many variables, though. There are two reasons that our planet is not bombarded by space objects much more often. Firstly, our atmosphere keeps most of the smaller ones out because the heat generated as they fly through it more often than causes them to burn up and disintegrate. The other reason is Jupiter, whose gravitational pull is so great (because of its size) that most of the larger objects entering our planetary system get pulled into Jupiter.

Of course, some don't...

[beso]

The outcome would depend on the direction the asteroid was traveling and the type of interaction. There would certainly be some major transfer of momentum and the Earth's orbit would be moved.

Most likely Earth would gain momentum because the asteroid would probably have come into the inner solar system from the Oort cloud and hence have very high momentum.

If so the Earth's orbital velocity would probably increase and the orbit move further from the Sun.

[jomifl]

Mark..escape velocity has no relationship with the mass of the escaping object.

[argorstran]

An object that size (1/4 earth ) and that close ( 1 or 2 miles ) wouldn't miss , it would hit because gravity would pull the two together . An object that size coming as close as it could without actually hitting would cause massive tidal waves and atmospheric disruption ( wind , weather ) . It could also have an effect on the earth's period of rotation (day length ) and possibly also slightly change its orbit .

[mibn2cweus]

Any gravitationally bound body (short of a neutron star) would be ripped apart passing that close to the Earth.

http://www.world-buil.../less/les1/roche.html