Thursday June 16th 2011


Passing Stars and Interstellar Speculations

Watching how exoplanet news hits the press is always interesting, but I was surprised at how the discovery of CoRoT-9b (discussed here yesterday) was received. The scientific reward could be significant, which is why one scientist referred to the find as a ‘Rosetta stone,’ but the fact that we had a gas giant that was both analyzable through transits and not a ‘hot Jupiter’ evidently needed to be ginned up in some media circles. What emerged were headlines seeing similarities to our Solar System (New Exoplanet Like One of Ours) and making bizarre extrapolations: Corot-9b: Extra Solar Planet Proffers Hope of Inhabitation.

I suppose CoRoT-9b is like a planet in our Solar System in being a gas giant in a stable orbit not hugging its star, but it’s hardly alone in that regard. What makes it special is that we can study it both by radial velocity and transit methods, gaining insights into the composition of such ‘temperate’ gas giants. I suspect the headlines left many readers disappointed when they read the ensuing story and realized it wasn’t about a terrestrial world just like the Earth. As for colonizing a gas giant, well, I leave that to your imagination.

And what to do about Gliese 710? Here is a dwarf star that may, in approximately 1.5 million years, pass through the Oort Cloud, with all the disruptive effect that seems to describe. A rain of comets moving into the inner system? Headlines like Rogue Star to Hit the Solar System are lively, to be sure, and send a chill up the spine of that dedicated band that is convinced we’re all about to be destroyed by runaway celestial objects in 2012. News on a million-year time cycle is not something that sells papers, but ‘rogue stars’ just might.

As to Gl 710, Vadim Bobylev (Pulkovo Astronomical Observatory, St Petersburg) used revised Hipparcos data to make the call on its future near-miss. Looking at stars within 30 parsecs of the Sun, Bobylev found nine new candidates to add to previously known close encounters (the astronomer defines a ‘close encounter’ as passing less than 2 parsecs from the Sun). And here’s the scoop on the closest of these:

For the star GL 217.1, a well-known candidate for a passage close to the Sun, the new observational data were shown to change noticeably its previously known encounter parameters with the Sun. The encounter parameters found here are: dmin = 1.28 ± 0.06 pc and tmin = −(861 ± 40) thousand years. Improving the radial velocity for the white dwarf WD 0310–688 (HIP 14754) whose orbit passed at a distance dmin = 1.61 ± 0.19 pc from the solar orbit about 300 thousand years ago is of current interest. Our statistical simulations showed that the star GL 710 has not only a high probability of penetrating into the Oort cloud, P1 = 0.86, but also a nonzero probability, P2 = 1 × 10−4, of penetrating into the region where the influence of the passing star on Kuiper Belt objects is significant.

Gliese 710, then, may well penetrate the Oort Cloud, potentially causing the kind of disruption there that could bring comets into an Earth-crossing orbit. Of all the stars the astronomer studied, this is the only one with a high probability of entering the Oort region. Interestingly enough, apart from what Bobylev has given us, we know about 156 Hipparcos stars within a radius of 50 parsecs that either have or will encounter the Solar System within a distance of less than 5 parsecs in a window from 10 million years in the past to ten million years in the future. One revised study shows the frequency of encounters closer than one parsec to be roughly 11.7 events per million years (plus or minus 1.3).

A New Scientist article goes to work on the Gl 710 encounter (Hurtling Star on a Path to Clip Solar System), saying the star will almost certainly send comets toward the Earth, and speculating on possible changes to Neptune’s orbit, which could occur if the one in ten thousand probability of such a close penetration comes to pass. So Gl 710, now ‘hurtling’ 63 light years from us in the eastern part of the constallation Serpens, becomes an object of concern for our remote posterity.

Does interstellar travel occasionally get such nudges for those species fortunate enough to have the technology to exploit them? A star closing to these distances is potentially in range for a civilization able to make a 10,000 AU journey (roughly the distance between Proxima Centauri and Centauri A and B). It’s useful to remember that the vast distances between the stars are themselves changeable as the galaxy continues to evolve and as our Sun continues its passage around it. It’s also useful to keep a cosmic perspective, one that reckons that on a galactic scale, civilizations may find innumerable ways to spread.

There’s your headline: ‘Civilization Jumps onto Passing Star.’ If we wait long enough, we may get to read it. The paper is Bobylev, “Searching for Stars Closely Encountering with the Solar System,” Astronomy Letters, Vol. 36, No. 3 (2010). Abstract available.

This article was originally posted on Centauri Dreams