Almost everything about an impact event – Earth hit by some form of space object – takes place at such long intervals, or the odds are so minimal that it’s almost embarrassing to describe. Still, it’s like winning the lottery (in reverse). Somebody wins. Shit happens. The odds are poor but asteroids, meteors and other objects have struck the Earth in the past, and will continue to do so – just not (probably) within any particular somebody’s lifetime. So, scientists are attempting to monitor those objects with orbits that might intersect that of Earth. NASA and other national space agencies are considering, seriously, how a projected impact event might be avoided.
In that line of thought, let us add a new menace: The orange dwarf (proto-star) Gliese 710 looks like it will crash through our Solar System in about 1.5 million years.
It’s that 1.5 million years, isn’t it? Why worry about something that far off?
Quite right. Gliese’s not to worry about. The information on Gliese 710, which is an orange dwarf – one of the cooler and smaller of stars, much smaller than our Sun, comes from a Russian astronomer, Vadim Bobylev at the Pulkovo Astronomical Observatory in St. Petersburg. He has been working with new data provided by the Hipparcos Catalog, a collection of information about 100,000 stars in our ‘neighborhood’ gathered by the European Space Agency’s Hipparcos spacecraft.
The Hipparcos Catalog has already made it possible for astronomers to identify stars that have done, or will, encounter our Solar System. They found 156 stars of ‘close encounter’ potential – a close encounter being within 1 parsec (that’s 31 trillion kilometers/19 trillion miles) – happening once every 2 million years or so. For one person or for the human race, that’s long odds. But in geological time, it’s not much. It would mean that we’ve had a stellar visitor in the neighborhood more than 2,000 times since the Earth formed.
“Having a stellar visitor in the neighborhood” makes it sound almost friendly. No, something the size of a star, even a small star or a brown dwarf, passing within one parsec of the Solar System will have a devastating effect. If nothing else, its gravitational disturbance will wreak havoc in the Oort Cloud, that vast conglomeration of small planets, asteroids, and other small objects, which exist by the billions in the outer region of our Solar System. Outer region = about .5 – 1 parsec. Even a ‘near miss’ could disrupt the orbits of millions of objects, sending many of them on inward trajectories toward the Sun. For Earth and the other planets, it would be worse than being a target in a shooting gallery on a Saturday night in summer.
Anyway, Bobylev combined the Hipparcos data with several new databases and found an additional nine stars with close encounter potential. One, in particular, caught his attention. That was Gliese 710 (Hipparcos ID: 89 825), a rather well-known star. According to his calculations Gliese is heading in the direction of our Solar System and will arrive within the next 1.5 million years. In fact, despite the relatively rough data and difficulty of calculating an accurate trajectory, there is an 86% chance that Gliese will plow through the Oort Cloud. To quote his paper’s abstract:
We show that, given the errors in the observational data, the probability that the well-known star HIP 89 825 (GL 710) encountering with the Sun most closely falls into the Oort cloud is 0.86 in the time interval 1.45-+0.06 Myr. This star also has a nonzero probability, 0.0001, of falling into the region d<1000 AU, where its influence on Kuiper Belt objects becomes possible.
Dryly put, of course, as it should be.
As I wrote, 1.5 million years is a big cushion – fuggedaboutit. No, the problem isn’t Gliese 710. It might be some other passing star, or even more likely a passing brown dwarf. The brown dwarf is the most problematic. They’re small, dark, and until very recently almost invisible. We could have many of them on a Solar System crossing trajectory, or not. We don’t know, and won’t know until the new space telescopes such as WISE and Kepler provide some knowledge. We are spending a considerable amount of money for these pieces of equipment – but consider it a small fee lottery ticket. The price of admission to advanced knowledge.