Wednesday, November 07, 2007

Five planets and counting...

Yesterday, one of the most productive teams hunting planets outside our own Solar System announced that they had discovered a fifth planet around a star already known to hold four planets.

The star, 55 Cancri, is about 20% smaller than the sun, is about 41 light-years away, and is in the constellation Cancer. So, it is a pretty normal star.

Before this announcement, the star had four planets, including one discovered by astronomers here at the University of Texas. Three of these planets are about the sized of Neptune and Saturn, and are pretty close to the star. The fourth is a whopping four times the mass of Jupiter, but is pretty far away from the star (about as far from Jupiter is from the sun).

The newest planet is about the same mass as Neptune, but it orbits its star at a distance of 80% the Earth-sun distance, and since its parent sun is 60% as bright as our sun, this means that the newest planet receives only a little less sunlight than the Earth does. In other words, the new planet, if it has a solid surface, could have liquid water on it. Or, if the planet is a bag of gas like Neptune, its moon (if it has one) could have liquid water. Maybe those aliens I was dissing a few posts back could have evolved on a moon of this planet?

To me, the most interesting part about the new find is not that the new planet may have liquid water, or even that it is the 5th planet in another solar system. After all, we have 8 or 9 planets, so our solar system is still #1 in that regard! No, I find most interesting the large variety in solar systems we are finding. Some stars don't have planets that we can detect. Some only have one as big as Jupiter that is orbiting right next to the parent star. Our solar system has four big planets, all pretty far from the star, and four small, rocky planets close to the star. 55 Cnc has four big planets close to the star, and one monster further out.

To me, this shows that extrapolating what we know about our solar system to planets across the Universe is no longer good science. For a while, it was all we could do, because it was the only example we had! But now we have hundreds of planets, and dozens of multiple-planet systems that we can study, and they exhibit a wider range of variety than we had though possible. This also tells us that making planets is easy -- you don't need a special configuration like our solar system for planets to form and stay put. A wide variety of conditions make planets, giving rise to a wide variety of solar systems.

And maybe, just maybe, this means that we shouldn't be surprised to find that our Galaxy is teeming with life. After all, if planet systems come in many shapes and sizes that look nothing like our own solar system, maybe life can come the same way, too.

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