SF State professor, researchers make landmark discovery in search for planets similar to Earth 

A professor at San Francisco State University was among an international team of researchers who recently reached a milestone in galactic exploration: finding a planet very similar to Earth that could harbor life.

Stephen Kane, an astronomer and professor at SFSU, told The San Francisco Examiner on Wednesday that the discovery of Kepler-186f marks the closest scientists have come to finding a potentially habitable planet other than our own. He called the discovery “more exicting moments of my research history.”

Kepler-186f, the fifth and outermost planet found to be orbiting the dwarf star Kepler-186, is both similar to the Earth’s size and within the habitable zone of its star — criteria that until this finding have never before been known to overlap in another planet, Kane said.

“The difference between this planet and other discoveries from the Kepler mission [is that] although Kepler has discovered planets about the size of the Earth before and it has also discovered planets in the habitable zone before, this is the first time when we’ve been able to put those two pieces together,” said Kane, who was tasked with determining whether the planet’s orbit was indeed inside the habitable zone.

The planet is also believed to be rocky and contain liquid water, two additional characteristics that could allow it to harbor life, Kane said.

Researchers have been looking for Earth-size planets in our corner of the Milky Way Galaxy with NASA’s Kepler telescope since 2009. Previously, they have found planets either around the same size as Earth or in a habitable zone — meaning the planet orbits its star at a distance where any water on the surface could be liquid.

“This is getting us increasingly closer in finding something that is very similar to the Earth,” Kane said.

Astronomers discovered Kepler-186f, which is 500 light-years away from Earth, using what’s called the transit method. The process detects potential planets as their orbits cross in front of their star, causing a tiny but periodic dimming of the star’s brightness. Once it was confirmed that Kepler-186f was a planet, researchers used the transit information to determine that it’s about 10 percent bigger than Earth.

Kane noted additional differences between Kepler-186f and Earth, including that the newly discovered planet takes 130 days to orbit its star — about a third of Earth’s orbital period around the sun.

The star orbited by Kepler-186f is also “much smaller than the sun,” and is the most common type of star in the universe, Kane said.

“Our sun is often described as an average star, but these kinds of stars are extremely common,” Kane said. “That’s good news, because if you have these systems of five terrestrial planets orbiting a common star, it really does mean that planets like this are everywhere.”

Kane emphasized that there’s still a lot more research to be done, such as finding out if Kepler-186f’s atmosphere is similar to that of Earth.

Kane, who moved to San Francisco last summer to teach astronomy at San Francisco State, has been studying exoplanets — aka extra-solar planets — since the field developed in 1995.

Prior to the Bay Area, Kane lived in Los Angeles for five years, working as a research scientist at the NASA Exoplanet Science Institute. Part of the reason he moved to San Francisco, he said, was to return to teaching.

Next spring, Kane plans to introduce a new class at SFSU specifically on the topic of exoplanets.

Kane developed an interest in space as a teenager after watching the Voyager missions capture images of Jupiter, Saturn and other planets.

“Just seeing these planets close up for the very first time got me really excited about planets, and I knew that’s what I wanted to do,” he said.

About The Author

Laura Dudnick

Laura Dudnick, a Bay Area native, covers education and planning for The San Francisco Examiner. She previously worked as a senior local editor for Patch.com, and as the San Mateo County bureau reporter and weekend editor for Bay City News Service.
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