Giant impactA Russian astronomer turned a few heads earlier this month when he published a paper noting that a dwarf star, currently 63 light-years away, will very likely dip into the outer edge of our solar system in fewer than two million years.

Vadim Bobylev of the Pulkovo Observatory in Russia presented in the March issue of Astronomy Letters a survey of nearby stars that are likely to make close encounters, past or future, with our solar neighborhood. He found that Gliese 710, a star with about half the mass of the sun, has an 86 percent chance of plowing through the Oort cloud, a spherical swarm of comets at the solar system's outermost fringe, in about 1.5 million years. Given that the Oort cloud is one of two major reservoirs of comets that buzz and occasionally collide with Earth, the natural concern is that stirring up the Oort cloud would be like shaking an interplanetary hornet's nest.

The paper spurred a few dramatic headlines, but as Bobylev himself carefully noted, Gliese 710's future approach was known more than a decade ago. And, as was pointed out then, the encounter may well prove relatively harmless.

Back in 1999 a team of researchers crunched data from the European Hipparcos satellite, which catalogued the position and motion of nearly 120,000 stars in the Milky Way. Their survey, published in the Astronomical Journal, found that Gliese 710 would likely swing past the sun at a distance of about 1.1 light-years, well within the Oort cloud, in about 1.4 million years' time. This estimate very closely mirrors Bobylev's later prediction, also based on Hipparcos data, of an encounter of about one light-year in 1.5 million years.

The authors of the 1999 study concluded that Gliese 710's cruise past the sun at 1.1 light-years would indeed scatter millions of comets, but they would trickle into the inner solar system over two million of years, providing only a marginal and probably undetectable bump to the impact rate at Earth.

Paul Weissman, a senior research scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who co-authored the original paper, says he stands by what he and his colleagues wrote in 1999 and in a follow-up 2001 study. It would take a much closer approach to the sun for Gliese 710 to stir up a major comet shower at Earth, Weissman adds. That's not an impossibility given our uncertainty about the star's motion, but Bobylev's research indicates that it's unlikely. And Weissman notes that a good deal of uncertainty remains regarding Gliese 710's motion; an improved measurement on that front later could rule out a truly threatening encounter entirely.

But even if future generations millions of years hence did find the dwarf star bearing down on them, who's to say that a mitigation strategy wouldn't be close at hand? One and a half million years ago, our species did not yet exist, and the technological state of the art for Homo erectus was stone tools and possibly controlled fire. One would hope that, if humankind can hang on for another million or two years, a few comets thrown Earth's way would elicit nothing more than a yawn and the press of a button from whatever hyper-evolved technician happened to be on duty at the apocalypse mitigation facility that day.

Image credit: NASA