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Wednesday, May 11, 2005

Earth is a very special planet

Is the Earth just “Nowheresville”? Check out some of the planets in other solar systems in our galaxy? (Planets that orbit stars other than our sun. )

BALTIMORE - Of the more than 130 planets found around distant stars, a large number have highly elliptical orbits, crazy oblong shapes that have surprised theorists who try to explain the configurations with near collisions or perturbing disks of gas.

An elliptic orbit is characterized by the eccentricity, which is how much a planet’s distance from its star varies as it carves out a year. Most of the planets in our solar system have relatively low eccentricities, less than about 5 percent (tiny Pluto being a notable exception and considered not really a planet by some astronomers).

By contrast, the average eccentricity of extrasolar planets is about 25 percent. And these are not Plutos. They are typically more massive than Jupiter.

Eccentricity is bad for a planet because it leads to summers that are hotter than the boiling point of water and winters that are 100 degrees below zero. Many life forms, including me, could not stand that.
Our solar system is apparently an exception, not a rule, and earth is very unusual. Contrary to the Principle of Mediocrity (we must assume we are not special), we are actually very lucky.

Learn more about my book By Design or by Chance?

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