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Wednesday, August 25, 2004

Baby steps...

I caught sight of this while checking my e-mail and had to blog about it. It appears that some European astronomers have identified an extra-solar (i.e. beyond the limit of our solar system. As I've indicated before this limit is usually considered to be the heliopause) planet that is rocky, or terrestrial, in composition. This differs from the extra-solar planets detected previously, which tended to be gas giants like Jupiter, Saturn, Uranus, and Neptune. This is being touted as evidence that solar systems similar to our own may be quite common.

Don't get your hopes up too much, though. The planet in quesiton is 14 times the mass of the Earth, which puts it roughly into the same ballpark as Uranus. Moreover, it orbits its system primary (i.e. host star) every 10 days. That's pretty damned quick. Since the time required to orbit is proportional to the distance of the orbit from the star, we're basically faced with a huge rocky planet that's almost on top of its parent star. Why is this relevant?

Well, one of the dominant theories for why gas giants formed way the hell out yonder in the solar system, and terrestrial worlds formed in here, has to do with the radiant energy of the sun. Basically the inverse square law states that the amount of energy falling in any area decreases with the square of the distance. So, the amount of energy from the sun that falls on a huge planet farther out may be substantially less than that falling on a much smaller planet closer in. Since gas giants are largely composed of volatile, low-mass materials (hydrogen, helium, etc.) it doesn't take much energy to excite them to the point that they can escape from a host body. So, gas giants shouldn't last long close to a star because they simply can't hold onto their huge envelopes of gas.

So, this newly discovered planet isn't so much terrestrial, as it is the core of a gas giant that either went bald, or never developed a gas-envelope in the first place. Not quite so revolutionary, and not quite such strong evidence that our own solar system is typical.

On the other hand, the techniques we've used so far to detect such planets largely only work with very big planets. That being the case, as soon as we started using these techniques to try to find planets we started turning them up (We've found in excess of 120 so far) so there's good reason to think that as our technology improves, we'll find that there really are some genuinely terrestrial planets out there.

Baby steps, people. Baby steps.


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