Once more on the search for exoplanets, and Alpha Centauri

Excuse me for the absence of regular science posts, but my brain has turned to mush from writing fantasy. Isn’t it easy when you’re allowed to make everything up and as long as it makes sense, no one cares about accuracy? But, yes, I will return to where I left my characters in the Jupiter system, or in a space station orbiting the fictional gas giant Sarasvati, in the not-too-distant future.

This morning I came across this very interesting article on the Centauri Dreams website. By the way, Centauri Dreams, the website of the Tau Zero Foundation, is a very rich source for writers of realistic SF, especially in relation to planetary exploration and interstellar travel.

The article summarises results and speculation arising from new planets discovered by the European Southern Observatory’s HARPS spectrograph, which provides the most accurate Radial Velocity measurements we currently have (see an earlier post on how planets are discovered). Because of its increased sensitivity, HARPS can detect smaller planets. The smallest planet found at this point in time is a mere 1.5 times Earth’s mass. One of the, perhaps expected, outcomes of the spectrograph’s bevy of newly found low-mass planets (super-Earths or near Earth-mass) is that there are many of these smaller planets, a lot more than there are very large planets, and that the previous bias was merely a product of larger planets being easier to detect. The galaxy is swarming with smallish rocky planets. It is quite likely that some will be found inside the habitable zone.

We may already have found some of these planets. Much was made last year of the ‘discovery’ of Gliese 581g, supposedly in the habitable zone of an M class star. However, further analysis has so far failed to confirm the existence of this planet. But the star has two other planets which orbit at the edge of the habitable zone, and out of these, Gliese581d looks the most promising. The width of the habitable zone is not absolute, but varies with the planet’s albedo (basically, how much light it reflects) and composition and (if any) atmosphere composition (see another post on that here). So a newly discovered planet, HD85512b, at 3.6 Earth masses, may also fit the bill. It is a little close to its K class parent star, but could harbour liquid water on its surface if certain conditions of composition and atmosphere are met (see original paper by Kaltenegger et al. here).

Using the HARPS spectrograph, another group of researchers report on the search for planets orbiting sun-like stars within 40 light years from our solar system. (original paper by Pepe et al here). This work has resulted in a the discovery of a number of planets, again, most in the smaller size category. One of the main targets for the hunt is Alpha Centauri B, but there are some problems, one of the main ones being that it is part of a triple star system, and that any model the describes the wobble of the star that is caused by an orbiting planet must take into account that there are two other stars in the system, and as you could understand that is tricky business.

Image depicting an exoplanet system snarfed from NASA JPL


10 comments on “Once more on the search for exoplanets, and Alpha Centauri

  1. It is possible, though. Really, in the end, computers do all of the heavy lifting with calculations. http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=140 is a brief snipped article about a planet in a binary system (actually, the hardest thing is finding a stable orbit in a binary system, I think, for a planet to exist in).

    I also remember reading something about Kepler finding a triple star system (here we go: http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=119 ). There’s a lot of crazy stuff out there and I, personally, look forward to writing stories about it ;-p

    • I have a paper somewhere (‘somewhere’ being the vast and chaotic repository of PDFs on my hard drive) that details a model (yay, models!) doing just this. I think–from memory–a star in a binary system can have planets if the other star is further away than Neptune is from the Sun. I’d imagine such stars would each have to be smallish and the planets in close orbit, but there you go. Now if I could find that reference….

  2. I suspect it would all depend on masses of both stars and planets. One of the labs I was teaching back home involved computing possible stable orbits (or at least, non-fatal ones) around binary stars. One day, I’ll get around to blogging about this…

    • I’m reasonably sure this unfindable paper I have covered Alpha Centauri. Sure it depends on masses. I mean–can you name anything in astronomy (or, for that matter, space flight) that doesn’t depend on mass 😉

      • My cheeky (and only half correct answer) to that is the speed of light in a vacuum. ;-p

        The stable orbits in binaries thing has risen on my to do list for once I finish the current (not that) short story.

      • Heh. I’m not one for poetry, but Geoff Landis, one of my favourite writers who regularly publishes in Asimov’s wrote a poem about light with the weight of a kitten striking the Earth every… whatever (forgot the units, sorry–could be seconds or minutes. Meh stoopid brain).

        It was a gorgeous comparison.

  3. “Excuse me for the absence of regular science posts, but my brain has turned to mush from writing fantasy. Isn’t it easy when you’re allowed to make everything up and as long as it makes sense, no one cares about accuracy?”

    Ouch 🙂

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