A research team led by San Francisco State University astronomer Stephen Kane has obtained new observations of Wolf 1061, known to host at least three super-Earth exoplanets. The team’s findings will appear in the Astrophysical Journal (arXiv.org preprint).
An artist’s rendering of the exoplanet Wolf 1061c. Image credit: NASA / Ames / JPL-Caltech.
The very dim M-dwarf star Wolf 1061 is one of our closest neighbors. It is located in the constellation Ophiuchus, approximately 14 light-years away.
Also known as GJ 628, the star was recently discovered to host three super-Earths.
One of these planets, Wolf 1061c, is entirely within the habitable zone.
“The Wolf 1061 system is important because it is so close and that gives other opportunities to do follow-up studies to see if it does indeed have life,” Dr. Kane explained.
Dr. Kane and co-authors were able to measure the star to gain a clearer picture of whether life could exist on Wolf 1061c.
“We present the results from direct measurements of stellar properties for one of the closest known exoplanet host stars, Wolf 1061,” they said.
“Our observations from the Center for High Angular Resolution Astronomy interferometric array provide a direct stellar radius measurement of 0.3207 solar radii.”
“We also obtained seven years of precise, automated photometry that reveals the correct stellar rotation period of 89.3 days.”
According to the team, Wolf 1061’s luminosity is only about 1% that of the Sun and the star’s effective temperature is around 5,490 degrees Fahrenheit (3,032 degrees Celsius).
“Using the updated stellar parameters, we estimate the inner and outer boundaries of the conservative habitable zone to be 0.11 AU and 0.21 AU, respectively.”
“When scientists search for planets that could sustain life, they are basically looking for a planet with nearly identical properties to Earth,” Dr. Kane explained. “Like Earth, the planet would have to exist in a sweet spot often referred to as the ‘Goldilocks zone’ where conditions are just right for life.”
“Simply put, the planet can’t be too close or too far from its parent star,” he added.
“A planet that’s too close would be too hot. If it’s too far, it may be too cold and any water would freeze, which is what happens on Mars. Conversely, when planets warm, a ‘runaway greenhouse effect’ can occur where heat gets trapped in the atmosphere.”
“Planetary researchers believe this is what happened on Venus. They believe Venus once had oceans, but because of its proximity to the Sun the planet became so hot that all the water evaporated. Since water vapor is extremely effective in trapping in heat, it made the surface of the planet even hotter.”
“The surface temperature on Venus now reaches a scalding 880 degrees Fahrenheit (471 degrees Celsius).”
Since Wolf 1061c is close to the inner edge of the habitable zone, it could be that the planet has an atmosphere that’s more similar to Venus.
“It’s close enough to Wolf 1061 where it’s looking suspiciously like a runaway greenhouse,” Dr. Kane said.
He and his colleagues also observed that unlike Earth, which experiences climatic changes such as an ice age because of slow variations in its orbit around the Sun, Wolf 1061c’s orbit changes at a much faster rate, which could mean the climate there could be quite chaotic.
“It could cause the frequency of the planet freezing over or heating up to be quite severe,” Dr. Kane said.
“These findings all beg the question: Is life possible on Wolf 1061c? One possibility is that the short time scales over which Wolf 1061c’s orbit changes could be enough that it could actually cool the planet off,” he added.
“But fully understanding what’s happening on the planet’s surface will take more research.”
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Stephen R. Kane et al. 2017. Characterization of the Wolf 1061 Planetary System. ApJ, accepted for publication; arXiv: 1612.09324
