more (at source): Right now, says Chakrabarti, the galaxy is roughly 300,000 light years away from us - about twice as far away as the LMC. But the simulations suggest it follows a highly elongated elliptical path, and about 300 million years ago it swept through our own galaxy just 16,000 light years from the galactic centre - closer in than Earth - disturbing the Milky Way's outskirts as it went.

"Overall, it is a very plausible scenario," says Abraham Loeb at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who was not part of the study. "Of course, the fact that we don't see such a massive satellite is an issue."