NASA’s planet-hunting Kepler spacecraft operating in a new mission profile called K2. Credit: NASA Ames/JPL-Caltech/T Pyle Read more at: http://phys.org/news/2015-08-astronomers-tenth-transiting-tatooine.html#jCp
Astronomers at the 29th International Astronomical Union General Assembly will announce on Aug 14 the discovery of a new transiting “circumbinary” planet, bringing the number of such known planets into double digits. A circumbinary planet orbits 2 stars, and like the fictional planet “Tatooine” from Star Wars, this planet has two suns in its sky. The discovery marks an important milestone and comes only 4 years after the first Kepler circumbinary planet was detected. Once thought to be rare or even impossible, these 10 discoveries confirm that such planets are common in our galaxy.
The new planet, Kepler-453 b, also presented astronomers with a surprising twist—the tilt of the orbit of the planet rapidly changes, making transits visible only 9% of the time. The change of orientation of the planet’s orbital plane, known as precession, brought it into proper alignment halfway through the space telescope’s lifetime, allowing 3 transits to be observed before the end of the mission. “The low probability for witnessing transits means that for every system like Kepler-453 we see, there are likely to be 11 times as many that we don’t see,” said Prof Jerome Orosz. The precession period is estimated to be ~103 yrs. The next set of transits won’t be visible again until the year 2066.
Kepler-453 b is the 3rd Kepler circumbinary planet found to lie in the habitable zone of its host pair of stars. In a binary star system, the habitable zone is more complex than around a single star, but it can be readily calculated once astronomers know the masses, radii, and temperatures of the stars. However, Kepler-453 b is a gas-giant planet and is unlikely to harbor life as we know it.
Based on the amount of starlight blocked during the transits, astronomers deduced that Kepler-453 b has a radius 6.2X Earth. The mass of the planet was not measurable with the current data, but is likely to be less than 16X Earth. The planet takes 240 days to orbit its parent stars, while the stars orbit each other every 27 days. The larger star is similar to our own Sun, containing 94% as much mass, while the smaller star contains only 20% as much mass and is far cooler and fainter. The system is in the direction of constellation Lyra, some 1,400 light-years away, and is ~1-2 billion years old, much younger than our solar system.
With known circumbinary planets now at 10, astronomers can begin to compare different systems and look for trends. The systems tend to be very compact and they come in a wide range of configurations. Their tendency to be in the habitable zone is a bonus, spurring astronomers to keep searching for Earth-size circumbinary planets in the Kepler archive.The finding complements SDSU’s previous success with Kepler data. In 2012, Welsh and Orosz discovered the first instance of a 2-planet circumbinary system: 2 planets orbiting a pair of suns. http://phys.org/news/2015-08-astronomers-tenth-transiting-tatooine.htmljCp
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