[BRIEF NOTE] On the close encounter of HIP 85605 with Sol in a few hundred thousand years

[rfmcdonald]

io9's George Dvorsky was the first person I saw reporting on the news that we have discovered the stars next to make a close brush with our own planetary system, the binary HIP 85605. From New Scientist:

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.

Forbes' Bruce Dorminey had more.

Using Newton’s laws and standard numerical computations, Bailer-Jones traced each star’s trajectory backwards and forwards in time through “a sequence of a large number of very short line segments.” He says he also did the same for the Sun, since it, too, is moving around our galactic disk. Allowing for observational errors, he slightly changed each star’s initial coordinates some 10,000 times in order to build up what he terms a “probability distribution” of how close the stars actually came or will come to the Sun.

Such stellar interlopers can threaten life on Earth in three basic ways. Their gravity can cause the injection of Oort Cloud comets into our inner solar system. Passing massive hot stars could destroy Earth’s atmosphere via powerful ultraviolet (UV) radiation. And a very small fraction of passing stars might even go supernova over the estimated 30,000 year time-frame that they spend crossing through the Oort Cloud. Bailer-Jones says supernova remnants could induce long-term global cooling through the follow-on production of nitrogen dioxide (NO2)* in our atmosphere.

[. . . O]btaining these answers remains very much a work in progress. Bailer-Jones hopes that forthcoming data from the European Space Agency’s Gaia space observatory will allow astronomers to statistically investigate the link between such stellar close encounters and the Earth impact record.

But such encounters do happen over all timescales. Bailer-Jones notes that Van Maanen’s star, the closest known solitary white dwarf — a burned out stellar remnant — lies some 13 light years away in Pisces. It encountered our own Sun only 15,000 years ago.

The Dragon's Tales linked to a Universe Today article talking about the potential for visits.

[T]he most interesting question explored on his webpage is the possibility of using stellar close encounters as a shortcut for exploring exoplanets. According to current cosmological models, the majority of stars within our galaxy are believed to host exoplanets.

So if a star is passing us at just a few parsecs (or even with a single parsec) why not hop on over and investigate its planets? Well, as Bailor-Jones indicates, that’s not really a practical idea: “Traveling to a star passing our solar system at a distance of around 1 pc with a relative speed of 30 km/s is no easier than traveling the the nearby stars (the nearest of which is just over 1 pc away). And we would have to wait 10s of thousands of years for the next encounter. If we can ever achieve interstellar travel, I don’t suppose it would take that long to achieve, so why wait?”

Darn. Still, if there’s one thing this phenomena and Bailor-Jones study reminds us, it is that in the course of dancing around the center of the Milky Way, stars are not fixed in a single point in space. Not only do they periodically move within reach of each other, they can also have an affect on life within them.

Alas, the timescale on which such things happen, not to mention the consequences they entail, are so large that people here on Earth need not worry. By the time HIP 85605 or GL 710 come within a parsec or two of us, we’ll either be long-since dead or too highly evolved to care!