What would happen if another star were to come fairly close to our Sun, say a trillion km away? Would that be bad? Well maybe, sorta.
Stellar density is our neighborhood is about 0.1 stars pc^-3 (1 parsec is about 30 trillion km). The nearest stars are about a parsec and a half from us. So one would expect considerably closer encounters from time to time. Is anybody headed our way right now?
Well, yes. It seems that the catchily named HIP 85605 might have our name on it.
The latest study was conducted by Coryn Bailer-Jones of Germany's Max Planck Institute for Astronomy, and accepted for publication in the journal Astronomy & Astrophysics. He used Monte Carlo statistical simulations to analyze the galactic orbits of tens of thousands of stars tracked by the European Space Agency's Hipparchos satellite. Bailer-Jones wanted to find out how many of those stars could conceivably come within 2 parsecs (6.5 light-years) of our own sun.
The answer to the question was 42.
Out of those 42 alien suns, HIP 85605 appeared likely to have the closest encounter. Today the star is 4.9 parsecs (16 light-years) away, but hundreds of thousands of years from now, it's judged to have a 90 percent probability of passing through at a distance of 0.04 to 0.2 parsecs (767 billion to 3.8 trillion miles).
That may not sound all that close, but it's close enough to disrupt the vast repository of comets in the solar system's Oort Cloud, which is thought to extend about 0.5 parsecs (1.6 light-years) from the sun. "That would really tear it up, and I'm guessing you would have a pretty big comet shower, potentially pretty disastrous," Adrian Melott, a physicist at the University of Kansas, told NBC News.
Don't panic, though. We should have a few hundred thousand years to think about it. And:
"If I were a gambling man, I would bet that we'd still be safe, or that a comet shower caused by this star would not be the reason why we're not around," Bochanski said. "Global warming or a world war would probably knock us out a lot sooner than that."