Star’s flying visit could fling comets at Earth
Nearby stars hurtling through the Milky Way could send a rain of comets careening toward Earth – but it won’t happen for at least a quarter of a million years.
At the moment, our closest stellar neighbour is Proxima Centauri, a red dwarf a little over 4 light years away. But all stars in the galaxy are constantly moving around, and in the future some will come even closer to the sun. That could be a problem for Earth: the outer reaches of the solar system are littered with comets in a region called the Oort cloud, and the gravitational pull of a passing star could send one flying our way.
Coryn Bailer-Jones of the Max Planck Institute for Astronomy in Heidelberg, Germany, decided to assess the risks Earth faces by simulating the past and future motion of 50,000 stars, using data from the European Space Agency’s Hipparcos spacecraft, which scanned the entire sky in the 1990s. He found 14 stars predicted to come within one parsec, or slightly more than three light years, of the sun over the next few million years.
The star that is set to come closest is called Hip 85605, and has a 90 per cent chance of reaching between 0.13 and 0.65 light years away from us in the next quarter to half a million years – although its current position data isn’t entirely clear so the estimate may be wrong. The next closest is GL 710, which has a 90 per cent chance of reaching 0.32 to 1.44 light years in the next 1.3 million years.
Either one would be close enough to influence the Oort cloud, which extends from 0.0065 to around 1.63 light years from the sun. “I think we can safely predict that comet orbits would indeed be disrupted by the closest encounters,” says Bailer-Jones. He is now working on a follow-up study to determine the probability of Earth being hit by a comet as the result of a star passing by.
A new star map from the European Space Agency’s Gaia spacecraft, a sequel to Hipparcos launched last year, should help nail down the odds, he says.
Could one of those stars bring a planet close enough for us to visit? Data from NASA’s Kepler space telescope tells us that most stars come with a gaggle of exoplanets, so you might think a close approaching star would provide a shortcut. But Bailer-Jones says their fast speed as they swing by the sun would make reaching those planets as difficult as traveling to more distant star systems.
In any case, the close approaches are too far down the line to hold out for, he says. “If we can ever achieve interstellar travel, I don’t suppose it would take that long, so why wait?”