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The Solar System is surrounded by thousands of stars, but until recently it wasn’t at all clear where they were all heading.

In 1997, however, astronomers published the Hipparcos Catalogue giving detailed position and velocity measurements of some 100,000 stars in our neighbourhood, all gathered by the European Space Agency’s Hipparcos spacecraft. It’s fair to say that the Hipparcos data has revolutionised our understanding of the ‘hood.

In particular, this data allowed astronomers to work out which stars we’d been closer to in the past and which we will meet in the future. It turns out that 156 stars fall into this category and that the Sun has a close encounter with another star (meaning an approach within 1 parsec) every 2 million years or so.

In 2007, however, the Hipparcos data was revised and other measurements of star velocities have since become available. How do these numbers change the figures?

Today, Vadim Bobylev at the Pulkovo Astronomical Observatory in St Petersburg gives us the answer. He’s combined the Hipparcos data with several new databases and found an additional nine stars that have either had a close encounter with the Sun or are going to.

But he’s also made a spectacular prediction. The original Hipparcos data showed that an orange dwarf star called Gliese 710 is heading our way and will arrive sometime within the next 1.5 million years.

Of course, trajectories are difficult to calculate when the data is poor so nobody has really been sure about what’s going to happen.

What the new data has allowed Bobylev to do is calculate the probability of Gliese 710 smashing into the Solar System. What he’s found is a shock.

He says there is 86 percent chance that Gliese 710 will plough through the Oort Cloud of frozen stuff that extends some 0.5 parsecs into space.

That may sound like a graze but it is likely to have serious consequences. Such an approach would send an almighty shower of comets into the Solar System which will force us to keep our heads down for a while. And a probability of 86 percent is about as close to certainty as this kind of data can get.

The good news is that Bobylev says the chances of Gliese 710 penetrating further into the Solar System, inside the Kuiper Belt, are much smaller, just 1 in a 1000. So that’s all right, then.

Keep calm and carry on.

Ref: arxiv.org/abs/1003.2160: Searching for Stars Closely Encountering with the Solar System

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