According to NASA astronomers, the next major galactic event to hit up our Milky Way will be an epic pile-up of galaxies — our Milky Way with the Andromeda galaxy. Lucky for those of us alive today, that won't happen for another 4 billion years, but such certainty over an event so far into the future makes the prognostication even more amazing.

Truth is, scientists have known that Andromeda was destined to cross paths with the Milky Way for some time now. What they didn't know, however, was whether the galaxies will slip by each other, just clip each other or crash head-on into one another. Now, with amazingly detailed data from the Hubble Space Telescope, they can peg the event: They are certain it will be head-on.

So what happens when the galaxies meet? Will Earth be doomed? [Cue Aerosmith song.]

Well, not quite. Since these aren't cars, this won't be so much a collision as a merging of the galaxies — the Milky Way, Andromeda and possibly a smaller, third galaxy called Triangulum. Using the Hubble data, NASA created computer simulations showing that it will take another two billion years for the galaxies to fully join.

"In the worst-case-scenario simulation, M31 (Andromeda) slams into the Milky Way head-on and the stars are all scattered into different orbits," says Gurtina Besla of Columbia University. "The stellar populations of both galaxies are jostled, and the Milky Way loses its flattened pancake shape with most of the stars on nearly circular orbits. The galaxies' cores merge, and the stars settle into randomized orbits to create an elliptical-shaped galaxy."

This series of photo illustrations shows the predicted merger between the Milky Way and Andromeda as seen from Earth. The first frame is the present day; the last frame is 7 billion years from now.

Obviously, in all this, the Milky Way as we know it will definitely be re-jiggered. The sun may be slung to a different corner of the new galaxy, but our Earth and solar system will probably survive this event. Whether that means it will still be habitable, though — well, that might be another story.

[via NASA]