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Dec. 07, 2011

Not Quite Earth's Twin, But Getting Closer

by Kaitlyn Gerber

By Kaitlyn Gerber, Carleton College

Artist's conception of Kepler-22b. Credit: NASA/Ames/JPL-Caltech

NASA's Kepler mission, which seeks to detect and analyze extraterrestrial planets of near-Earth size, has confirmed the existence of a planet that could be suitable for life. With a radius that is 2.4 times that of Earth, Kepler-22b is the smallest confirmed planet in the "habitable" zone, the region around a star where conditions could permit liquid water to form.

Two other planets had previously been identified within habitable zones, but because they were located on the fringes of the regions, they were likely to be too hot or too cold to feasibly sustain life. The stars near which the other planets were spotted are also much cooler than our sun, making them unlikely to support life. Kepler-22b's star is in the same class as our sun, although it is slightly smaller and cooler; as a result, the planet is about 15% closer to its star than we are to our sun.

Modeling also suggests that Kepler-22b may have a similar temperature to Earth's. At its ongoing Kepler Science Conference, Bill Borucki, Kepler Principle Investigator at the NASA Ames Research Center, explained that if Kepler-22b had similar greenhouse warming, its surface temperature "would be something like 72 degrees Fahrenheit, a very pleasant temperature here on Earth." The surface temperature of a planet is extremely important, because an earth-like temperature allows water to remain in a liquid state, increasing the chances that the planet can support life.

Launched in 2009, the Kepler observatory orbits the sun and uses a telescope lens called a photometer to measure the brightness of light. It detects planets through a method known as the transit method, which detects changes in the brightness of stars. When a planet crosses in front of the face of a star, it blocks some of the star's light, causing a minute dip in the star's brightness of about 1/10,000. This dip lasts between two and sixteen hours. Three of these dips, or transits, are needed before Kepler flags the potential extraterrestrial planet. The planet's existence is then verified using large, ground-based telescopes and NASA's Spitzer Space Telescope to review the observations. Although these dips can sometimes be caused by binary stars rather than planets, a team of researchers, led by Jean-Michel Desert of the Harvard-Smithsonian Center for Astrophysics, announced at the same conference that the probability of these "false positives" is less than one percent.

The Kepler team also announced that it has discovered an additional 1,094 potential planet candidates. Of these, 207 are near-Earth sized, and 48 are located in the hospitable zone (down from 54 in February, as the team has refined its criteria). At 600 light-years away, Kepler-22b is the first planet to be confirmed in the region.

"This is a major milestone on the road to finding Earth's twin," said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Kepler's results continue to demonstrate the importance of NASA's science missions, which aim to answer some of the biggest questions about our place in the universe."

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Kaitlyn Gerber is a sophomore at Carleton College, where she plans to major in biology. Originally from Ridgefield, CT, she likes soccer, reading, and science, especially ecology and astronomy.

About Kaitlyn Gerber

The views expressed are those of the author and are not necessarily those of Science Friday.

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