SF State professor part of team that unlocks new way to find Earth-like planets 

click to enlarge The Venus Zone is the area around a star where a planet is likely to show similar conditions to Venus, researchers say. - COURTESY CHESTER HARMAN
  • courtesy Chester Harman
  • The Venus Zone is the area around a star where a planet is likely to show similar conditions to Venus, researchers say.

As scientists continue to search the stars for habitable planets, they can thank a San Francisco astronomer for helping develop a new tool to use in that galactic quest.

Stephen Kane, a professor at San Francisco State University, and two other scientists have reached a milestone in predicting what planets are most like Venus, which down the road could help determine the real difference between Earth and its sister planet.

Considered sister planets because of their similar size and appearance, and likely having formed the same way, Venus and Earth actually have dramatically different surface conditions. The surface temperature of Venus is nearly 900 degrees Fahrenheit -- the hottest surface location in our solar system -- and its atmospheric pressure is about 90 times that of Earth.

"The atmosphere [of Venus] has gone a completely different path than Earth," said Kane, who is the lead author of a study on Venus-like planets that was published Wednesday online in the Astrophysical Journal Letters. "What we want to do is understand, how did things go so wrong on Venus?"

On Wednesday, Kane revealed the first step in establishing what might have happened to Venus to place it on the "opposite end of the spectrum of habitability" from Earth.

Kane's research, which involves looking for Earth-size planets in our corner of the Milky Way Galaxy with NASA's Kepler telescope since 2009, led to the landmark identity of the Venus Zone, the area around a star in which a planet is likely to exhibit the uninhabitable conditions found on Venus.

Previously, because Venus and Earth are so similar in size, there was no way to distinguish in another planet which atmosphere was more closely mirrored. The Venus Zone allows scientists to determine the frequency of such unlivable planets in other solar systems.

"Our estimate for stars like the sun is that about half of those have a planet like Venus," Kane said. Specifically, of stars like the sun, about 45 percent -- or 43 of the more than 4,000 planetary candidates discovered by the Kepler mission -- have planets similar to Venus.

The Venus Zone is calculated by determining where a planet like Venus or Earth would actually start to lose its atmosphere because it's so close to a star.

With this new method, scientists can look at the atmospheric conditions of those planets and determine whether they have runaway greenhouse effects like Venus, where liquid water has long since evaporated due to the high temperatures.

"That means ... we can start to really get a feel for what conditions a planet needs in order to become like Venus," Kane said.

Last spring, Kane's research helped lead to the discovery of the planet Kepler-186f. It is the closest scientists have come to finding a potentially habitable planet other than Earth.

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 was never before known to overlap in a planet outside our solar system.

However, the transit method -- which scientists used to identify Kepler-186f by detecting potential planets as their orbits cross in front of their star, causing a tiny but periodic dimming of the star's brightness -- doesn't verify a planet's atmosphere.

The Venus Zone marks the first step in helping scientists discern what living conditions such a planet might offer -- mostly oxygen, like Earth, or carbon dioxide, similar to Venus.

Kane, who moved to San Francisco in 2013 to teach astronomy at SFSU, has been studying exoplanets, or extra-solar planets, since the field developed in 1995.

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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