Avatar and Lithium

Avatar and Lithium. What the heck does a movie and an element used to treat bipolar disorder have in common? The answer is planets. But first, let's talk about Avatar, a most pleasant surprise for this SF bunny. Yes, this review is kinda late but it's not like a lot of people read this blog anyway.

I had the opportunity to watch it in 3D at IMAX, which was terrific. As it was subtitled, I had Japanese floating in front of me and when the Nav'Ri spoke I had to struggle to read the kanji to figure out what they were saying. Mostly guesswork. I'll have to wait for the DVD.

The arrival sequence at Pandora was most gratifying, because the interstellar transport was actually a well-designed vessel, not something created by a 7-Up gulping graphic designer with no understanding of engineering and far too much Gundam influence.

You can read Winchell Chung's rave review here.

Pandora itself is a fascinating planet, or rather, moon. It orbits a gas giant around Alpha Centauri B, although the interesting thing is that astronomers have watched the Alpha Centauri system and are pretty sure that there are no gas giants in orbit around either. Theory says that there may be some planets tucked in there, and the two stars are far apart that planets in the "Goldilocks" zone won't get ejected by the stars' gravitational tug.

Now here's the interesting part. We know that stars that have planets appear to be depleted in lithium, including, of course, our sun. How lithium depletion relates to all this, we're not sure. th Alpha Centauri A and B have high levels of lithium depletion. There are two interesting possibilities here:

First, about a third of all stars seem to have lithium depletion. So as many as 1 in 3 stars may have planets. Of course, so far this means planets we can detect, not terrestrial-sized planets. Normal (lithium-rich) stars may be swarming with asteroids and terrestrial planets, which we can't we can't yet detect.

Second, Alpha Centauri A and B may well harbour small rocky planets. Maybe quite a few, since they are both heavily depleted compared to our own sun. But that remains to be seen, since there are so many other factors that could influence planet formation. For all we know, the planets may have been ejected into space by tidal forces long ago. It seems likely that a giant planet did not form close in and gobble up all the newly formed planets, because that giant planet would have wound up dumping its lithium back into its parent star as it continued inwards on its death spiral (computer simulations of "hot jupiters" indicate that they are so big that drag from solar wind decays their orbits and dumps them into their star).