Wrapped in dark matter, an object known as the Smith Cloud is hurtling toward the Milky Way at more than 150 miles per second. Now 8,000 light-years away, the gassy clump of hydrogen is expected to smash into the galaxy in about 30 million years.
But that won't be the first time this blob of gas has met our galaxy: Scientists think it's been here before, millions of years ago.
Normally, gas clouds don't easily survive such encounters without being torn apart; to make it through, a cloud would need to be incredibly dense. Smith's Cloud is not.
Astronomers initially proposed that the cloud's strong magnetic field ...