Tuesday, October 23, 2007

Are we not the only Earth out there?

Howstuffworks "The Goldilocks Zone"

Other Possible Earths

One of the main goals of planet hunting is to find exoplanets that have the characteristics of Earth and may consequently contain life. One of the keys to this search is the Goldilocks Zone. Also called the habitable zone or life zone, the Goldilocks Zone is an area of space in which a planet is just the right distance from its home star so that its surface is neither too hot nor too cold. That means that the planet could possibly host liquid water.

Earth-like planet
Image courtesy NASA
In surveying potential candidates for "new Earths," astronomers
look for traces of biological activity, such as the presence of oxygen.

Few planets have been found in the Goldilocks Zone, but in April 2007, European astronomers announced the discovery of one. It was also, at that point, the most Earth-like planet ever found. The planet, called Gilese 581c, is 12,000 miles in diameter, or not much larger than Earth (8,000-mile diameter). It orbits a massive red star called Gilese 581, located in the Libra constellation, 20.5 light years from Earth. Gilese 581c orbits its star very closely, completing an orbit in just 13 Earth-days. This short orbit would make a planet too hot for life, except that Gilese 581's surface temperature is 1/50th that of our sun.

Because it lies in the Goldilocks Zone, Gilese 581c's surface temperature ranges from an estimated 32 degrees Fahrenheit to 102 degrees Fahrenheit. The research team that discovered it believes it has a developed atmosphere. The planet might not only have water -- it might be entirely covered by oceans.

Gilese 581c does have some things working against it. Its gravity is about twice as strong as Earth's, and it receives significant doses of radiation from its star. Both could inhibit life from developing. Even so, Gilese 581c is exciting not only for its Earth-like conditions, but also because of its relative proximity to Earth and its location in the elusive Goldilocks Zone.

As more powerful and precise telescopes go into space, future efforts will involve examining exoplanets' atmospheres for traces of oxygen and methane and looking for rocky planets that lie in the Goldilocks Zone. Scientists are also increasing their use of automated telescopes that are programmed to look for minuscule variations in a star's brightness caused by an orbiting planet passing in front of it. With a rapidly increasing pace of discovery of exoplanets and a practically infinite number of stars in the universe, many other exciting discoveries are ahead of us.

The ideal discovery would be a planet similar in composition to Earth that lies within the Goldilocks Zone and orbits a stable star. But it's important to keep in mind that popular depictions of extraterrestrial life are likely wrong. Some life forms may be no more advanced than bacteria. Others may be highly advanced but unrecognizable, a thought that has caused some scientists to advocate the search for so-called weird life.

For more information about Earth-like planets, planet hunting and related topics, please check out the links on the next page.

One of my friends happened to find this on howstuffworks.com and I thought it was pretty cool. I knew there was some range of distance in which planets would be habitable, I just didn't know it had a name.

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