Earth Science: Geology, the Environment, and the Universe

Chapter 14: Climate

Problem of the Week

Life: What’s Eccentricity Got To Do With It?

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Most of us know that the Sun is a star and that the planets in our solar system revolve around it. Most of the planets in our solar system have a fairly eccentric orbit, especially Earth. Eccentricity refers to how close to being circular a planetary orbit is. The closer to circular an orbit is, the more eccentric the orbit. The more elliptical (oval-shaped) an orbit is, the less eccentric the orbit. The range of eccentricities for the planets in our solar system is Venus (whose orbit is nearest a circle) with an eccentricity of 0.007 to Pluto with an eccentricity of 0.248. Earth’s eccentricity is 0.017.

*To plot various eccentricity values and see the shape of the resulting orbit, go to http://www.bridgewater.edu/departments/physics/ISAW/PlanetOrbit.html.

More than 40 planets outside our solar system have been inferred from the indirect gravitational effects on the stars that they revolve around. The six most recently discovered planets are believed to have highly elliptical orbits. In addition, 18 of the planets that were discovered prior to these six also have highly elliptical orbits. This is a significant statistical majority. Scientists are interested in eccentricity because if this pattern holds, then the nearly circular orbits of the planets within our solar system will not be the norm–they will be the exception. This may be a major blow to scientists who are seeking evidences of life outside our solar system.

Think about this:

In your text, Earth’s orbit is discussed as a factor affecting climate. Your text explains that the more elliptical Earth’s orbit becomes, the warmer the climate becomes. This is due to the nearness of Earth during portions of the orbit (see page 372 of the text).

Problem:

How is a circular orbit more conducive to providing an environment that is able to support life on Earth?

If the nearly circular orbits of the planets in our solar system are the exception, how might this affect the possibility that life would occur on other planets?

Of course, eccentricity is not the only factor that determines the possibility of life on a planet. If all other factors are favorable, what would you hypothesize about the relationship between eccentricity of a planet’s orbit and the development of life on that planet?