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UC Berkeley researchers predict galaxy may hold 40 billion habitable Earth-like planets

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NOVEMBER 07, 2013

The search for extraterrestrial life may no longer require examining galaxies far, far away or the pages of science fiction novels, according to a study released Monday.

After the completion of a project by researchers from UC Berkeley and the University of Hawaii using NASA’s Kepler space telescope, astronomers believe as many as 40 billion Earth-sized planets in habitable zones may exist in our galaxy.

There are two possible implications to the findings, according to UC Berkeley graduate student Erik Petigura, who co-authored the study published in the Proceedings of the National Academy of Sciences.

“Either life is exceptionally rare — and by rare, we mean not one in a thousand or even one in a million, but in one in billions — or the galaxy is teeming with life,” Petigura said.

A common estimate of the number of stars in our galaxy is 200 billion, according to Petigura. Of those stars, about 50 billion are sunlike, and about 22 percent of those harbor Earth-sized planets that could host life, he said.

The projection of 40 billion habitable Earth-like planets links Petigura’s calculations, which estimate about 10 billion of such planets, with data from work by Harvard University researchers David Charbonneau and Courtney Dressing, who found that about 15 percent of the most common type of star in our galaxy, red dwarfs, also have similar planets.

Petigura, who studied physics and astrophysics as an undergraduate at UC Berkeley, developed software to analyze four years of measurements of sunlike stars taken by the Kepler telescope, using a technique to monitor the momentary dimming sometimes produced by a planet periodically passing across a star’s face.

Geoffrey Marcy, a co-author of the report and a UC Berkeley professor of astronomy, said the next question concerns the existence of intelligent life and has yet to be answered.

“Even if life occasionally does get started on habitable planets, how often does that life evolve by Darwinian evolution to intelligent life?” Marcy said. “We’re fooled a little bit because we all watched Star Trek and Avatar, which makes it seem like intelligent civilizations spring up routinely.”

In addition to assisting the search for intelligent life, the recent findings may help build on the theory of how solar systems formed, according to UC Berkeley astronomy professor Burkhard Militzer, who was not involved with the project.

The study has helped Petigura realize his dreams of conducting research with Marcy, an idea that began when the professor handed him keys to the student observatory during Welcome Week of his freshman year.

“As scientists, we have to stay rooted in the facts, but in our quiet moments, we always wonder if there are other beings out there,” Petigura said. “It’s our science fiction imaginations that inspire us to go off and spend over three years working on this stuff.”

Contact Chloee Weiner at 

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NOVEMBER 07, 2013


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