The closest rocky, Earth-like world could be as close as 6.5 to 7 light years away, according to new research. New Scientist magazine reported Tuesday that Penn State University astronomer Ravi Kopparapu's estimates put these types of potentially life-sustaining worlds half as distant from Earth as previously believed.
In February, Courtney Dressing and David Charbonneau of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts announced their findings that the nearest Earth-like planet is probably orbiting a small red dwarf star at a distance of 13 or so light years from Earth. "Earth-like" means a small, rocky planet, rather than a gas giant like Saturn or Jupiter.
Using data gathered by NASA's Kepler telescope, Dressing and Charbonneau analyzed fluctuations in the light reaching Earth from nearby red stars. Planets passing between the stars and Earth cause the light from that star to waver.
Small planets create smaller disturbances in the light and are therefore harder to find, but the scientists were able to count 95 dim, red dwarf stars nearby which host possible planets, including three Earth-sized worlds located within the "habitable zone," meaning at enough distance from their respective suns to allow for the existence of liquid water.
The two scientists then estimated how many red dwarf stars could have a planet half as large as Earth to one and a half times the size of Earth orbiting within their habitable zones, arriving at approximately 15 percent. Looking at the distribution of red stars through the Milky Way, they calculated that the nearest Earth-like planet to be about 13 light years away.
Light years are the distance that light travels in one year. Light travels at 186,000 miles per second and a year contains 31,536,000 seconds, making a light year about 6 trillion miles.
Penn State astronomer Ravi Kopparapu looked at Dressing and Charbonneau's calculations and realized that the scientists were operating on slightly outdated information.
"I noticed that they were using old definitions of habitable zones, and so they did not count all the planets that should be in the habitable zone," said Kopparapu. The boundaries of a habitable zone are determined by the temperature of a star and how well a planet's atmosphere absorbs light and transfers it to the surface.
These parameters, Kopparapu noted, had not been updated since 1993, meaning that valuable knowledge scientists have gained since then about how sunlight reacts with Earth's atmosphere was not included, as well as greater knowledge about the variation in the temperatures of different stars. Kopparapu and the scientist who composed the original 1993 guidelines updated the formulas for determining habitable zones and found that habitable planets could be much closer than Dressing and Charbonneau thought.
Half of the red dwarf stars in the Milky Way could have Earth-like planets in their orbits, said Kopparapu, and the average distance to one is more likely to be 6.5 to 7 light years. This could potentially place rocky, water-bearing worlds close enough to currently be receiving TV and radio signals broadcast on Earth in 2006.
"This is a good sign," Kopparapu said, "for detecting extraterrestrial life."
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