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Distant ‘Goldilocks’ world

Planet-hunters find a just-right world outside the solar system

Astronomers have discovered a small planet outside the solar system with a temperature that could be — but probably isn’t — hospitable to alien life. E.T., keep dialing. This is an artist’s interpretation of how the planet, called Kepler-22b, may appear. 

NASA, Ames, JPL-Caltech

On December 5, astronomers introduced a newly discovered planet that seemed habitable for extraterrestrial life. The faraway world is an exoplanet, or planet outside our solar system, called Kepler-22b. It looks E.T.-friendly because its temperature is neither too hot nor too cold for liquid water, which is essential to life as we know it. The planet orbits its star at just the right distance, sometimes called the “Goldilocks” zone.

Early studies suggested that the average temperature on the new planet hovers around 72 degrees Fahrenheit, room temperature for many places on Earth. Kepler-22b’s host star is a bit cooler than the sun, and the planet’s 290-day year is a bit shorter than Earth’s. This news left the scientific world abuzz.

“It’s a great gift,” space scientist Bill Borucki said at the conference introducing the planet. “We consider this sort of our Christmas planet.” Borucki works at NASA’s Ames Research Center, where he leads a team of scientists who look for planets using the Kepler Space Telescope.

Using this telescope’s data, scientists found that the planet’s radius is about 2.4 times Earth’s. (Radius is the distance from a sphere’s surface to its center.) That means Kepler-22b is larger than our planet but much smaller than giants like Jupiter and Saturn. Scientists don’t yet know if the planet is rocky, like Earth and Mars, or gassy, like Neptune and Uranus.

It didn’t take long after the discovery for other scientists to weigh in with doubts about the planet’s ability to support life. Planetary scientist Abel Mendez at the University of Puerto Rico in Arecibo studies and keeps track of possibly habitable planets. He told Science News that Kepler-22b doesn’t look promising.

Using data relayed from the space telescope, Mendez and his colleagues tested different possible combinations of size and mass for the planet. Mass is a measure of how much stuff is in an object. On Earth, objects with more mass weigh more. The scientists hoped to use mass as an indication of whether Kepler-22b might be even remotely Earthlike, and therefore able to support life.

Mendez thinks the new planet might support life if it were covered with water on its surface, like a giant ocean planet. But even then the chance of life is low, based on his team’s findings. “I’m not optimistic,” he said. “But I would love to be wrong.”

Sara Seager is a planet-hunting astronomer at the Massachusetts Institute of Technology in Cambridge. She told Science News that if the planet has an atmosphere, it should be hot and steamy and “too hot at the surface for life to survive.” Seager suspects the planet is gassy, like a miniature version of Neptune.

It’s still possible that the planet is rocky and surrounded by a thin atmosphere — or somewhat Earthlike. Scientists can’t know that, however, without further observations. But if Kepler-22b isn’t hospitable for E.T. or other life forms, that would be all right, too. Scientists have identified more than 2,000 possible planets using the new telescope’s data. Each planet has to be confirmed by follow-up studies, and 22b has already passed that second test. Perhaps another, more Earthlike planet is just waiting in the data.

Scientist Natalie Batalha from San Jose State University in California works on the Kepler telescope mission. She told Science News that of the thousands of potential planets just identified, hundreds might be small. “Not only do we have Earth-size planets, we have planets that are significantly smaller than Earth.


(adapted from the New Oxford American Dictionary)

exoplanet A planet that orbits a star outside the solar system.

mass The quantity of matter that a body contains.

radius A straight line from the center to the circumference of a circle or sphere.

atmosphere The envelope of gases surrounding a planet.

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