A team of astronomers has discovered a new planet orbiting two stars, and not only is this new world the 10th so-called circumbinary planet discovered to date by the NASA Kepler Mission, it is also located squarely in the habitable zone of its host stars.
Stephen Kane, an assistant professor of physics and astronomy at San Francisco State University, and San Diego State University Professor William Welsh have dubbed the world Kepler-453b. Its discovery is detailed in a paper set to be published in The Astrophysical Journal and will be officially announced Friday at the annual IAU meeting in Honolulu.
Kane, who is the head of NASA’s Kepler Habitable Zone Working Group, explained that he and his fellow astronomers were fortunate to have made the discovery when they did, because if they were observing the area where Kepler-453b was located any earlier or later, they would not have seen anything and would likely have just assumed that there was no planet in the vicinity.
A really lucky discovery
In most instances, astronomers spot exoplanets by observing the decrease in starlight as a planet transits or passes between its host star and Earth. In Kepler-453b’s case, though, it is affected by the gravitational pull of two stars, not just one, Kane explained in a statement.
As a result, its orbit is more erratic in nature, and the transits of such planets are visible just nine percent of the time. Had researchers not discovered the new planet now, they would not have had another chance at spotting it for more than 50 years.
“Yes, there was a certain amount of luck involved for this discovery,” Kane told redOrbit via email. “The Kepler spacecraft monitored the stellar system for about four years but it was only in the latter part of the observations that we saw the signature of the planet.”
“The reason for this is that the axis of the system slowly moves around like a spinning top with a period of 103 years. That means that sometimes the planet passes between us and the stars of the system but most of the time we would not see any signature,” he added. “Kepler just happened to be viewing the system at the right time for us to make the detection.”
Planet likely a gas giant, but may have rocky moons
During its transit, Kepler-453b blocked 0.5 percent of its host stars’ light, allowing researchers to observe that the new planet has a radius about 6.2 times the size of the Earth, or about 60 percent larger than Neptune. Based on the size measurements, they determined that it is not a rocky planet but a gas giant. Thus, despite being in its stars’ habitable zone, it is unable to support life.
However, it may have rocky moons orbiting it that could still be home to living organisms, and the nature of the discovery suggests that there are a lot more of these kinds of planets than we are thinking, according to Kane. Astronomers are just looking at the wrong times, he noted.
“We calculated that the planetary transits are only visible from Earth nine percent of the time, which means (for similar systems) there around 11.5 systems that are not showing signs of transits during the course of Kepler observations,” he told redOrbit. “This means that there is a lot of value to continuing to monitor such systems since there’s many planetary systems that are avoiding detection simply because we’re not looking at the right time.”
A vastly different stellar binary than you’d see in Star Wars
Kane added that there were “a few other really interesting things about this system,” including the fact that the stellar binary contained a star that is “quite similar” to the Sun (approximately 94 percent the size of our solar system’s central star) and a smaller second star that is just 20 percent the size of the sun and emits only one percent of the larger star’s energy.
“That means that the primary star vastly outshines the secondary star and would be an interesting view from the planet,” he explained. “By contrast, the view of the double stars from the surface of Tatooine in Star Wars shows them as being more or less identical. In the case of Kepler-453b, one would see a bright star like the Sun along with a fainter red star.”
(Image credit: Mark Garlick)
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