海角大神

Two years after astronomers found a 鈥渟uper-Earth鈥� in our cosmic neighborhood, another scientist sees reason for caution.

In December 2015, a research team at Australia鈥檚 University of New South Wales announced the discovery of three rocky planets orbiting the star Wolf 1061. One of these planets, dubbed Wolf 1061c, fell within the circumstellar habitable zone, sometimes called the "Goldilocks zone": the area not too hot and not too cold for liquid water, considered an essential ingredient for life.

Located about 14 light years from Earth, Wolf 1061c is close by cosmic standards.聽Proxima Centauri b, discovered in August 2016, is the closest rocky exoplanet at 4 light years.

Discoveries of these 鈥淓arth-like鈥� worlds聽have stirred hopes of discovering life beyond our solar system. But after taking a closer look at Wolf 1061c, Stephen Kane has his doubts about whether we鈥檒l find it there.

鈥淚t鈥檚 close enough to Wolf 1061 where it鈥檚 looking suspiciously like a runaway greenhouse,鈥� Professor Kane, an astrophysicist at San Francisco State University, told Sci News on Friday.

A 鈥渞unaway greenhouse鈥� effect took place on Venus. Scientists believe that Earth鈥檚 inner neighbor once had oceans of its own, but the planet's massive volcanoes flooded the air with carbon dioxide. Intense sunlight could then heat the planet until the oceans boiled away, leaving a thick atmosphere that keeps the planet鈥檚 temperature at a toasty 880 degrees Fahrenheit.

Kane thinks that a similar process may be at work on Wolf 1061c. His research, whose results will be published in an upcoming issue of the Astrophysical Journal, examined the planet鈥檚 host star.

"The previous estimate used models of what the [star鈥檚] radius could be," he explains in a phone interview, "whereas this is a direct estimate of what the radius is."

Kane and his team measured Wolf 1061 using six networked telescopes at the Center for High Angular Resolution Astronomy in California. They used their measurements to revise previous estimates of its 鈥淕oldilocks zone.鈥�

The Australian team that first discovered the three planets estimated 鈥渃onservative habitable zone limits of 0.092 to 0.18 AU and optimistic limits of 0.073 to 0.19 AU.鈥� (1 AU, or astronomical unit, equals the distance from Earth to the sun, about 93 million miles.)

Kane鈥檚 group pushed the habitable zone鈥檚 boundaries outward, estimating them at 0.11 to 0.21 AU. That, he explained, means that Wolf 1061c is dangerously close to the inner edge, and prone to a Venus-like fate.

Even if Wolf 1061c escaped a 鈥渞unaway greenhouse鈥� effect, it might pose other obstacles to life. 鈥淚f we find a planet in the habitable zone, it doesn鈥檛 mean everything is as it seems,鈥� Kane tells 海角大神. He explains that the planet displays 鈥渧ery interesting oscillations in its orbit鈥� that make it difficult to determine what kind of climate 鈥� if any 鈥� it could have.

But those hoping to find extraterrestrial life may not want to write off Wolf 1061c just yet. A new generation of telescopes could reveal more about the planet. A solar system this close, Professor Kane explained, 鈥減resents an opportunity for direct imaging of the planet. That鈥檚 something that will have to wait until the 2020s.鈥�

He mentioned two upcoming NASA missions 鈥� the James Webb Space Telescope and the Wide Field Infrared Survey Telescope 鈥� that will make it possible to examine the light reflected through nearby planets鈥� atmospheres for the chemical signatures of life.

鈥淭he planets will appear as nothing more than a speck of light,鈥� he predicts. 鈥淎nd that鈥檚 all we really need.鈥�