An international team of astronomers, led by San Diego State University researchers, has discovered a third transiting planet in the Kepler-47 (K-47) circumbinary system - a system where the planets orbit two stars instead of one.
According to the team, this newly discovered planet, dubbed K-47d, is sized somewhere between Neptune and Saturn, and orbits between two previously known planets, named Kepler-47b and Kepler-47c.
Kepler-47 is the first circumbinary multi-planet system discovered by the NASA's Kepler mission. It is located in Cygnus constellation and lies approximately 4,900 light-years away from Earth.
According to NASA, the pair of stars in K-47 eclipse each other every seven-and-a-half days from the vantage point of Earth. One of these stars is similar to the Sun in size, but is less bright.
The second star in the system measures just one-third of the size of the Sun.
The first planet of this system, K-47b, was discovered in 2011 by NASA's Kepler mission. This planet orbits the pair of stars in less than 50 days, and its radius is three times the radius of the Earth.
The second planet, Kepler-47c, is believed to be a gas giant. It is slightly bigger in size than Neptune and orbits binary stars in 303 days.
The third planet, Kepler-47d, is the largest of all three planets in the star system, according to the latest observations.
Astronomers said they used the "transit method" to discover K-47d. Although they got a hint of the planet back in 2012, its presence could not be confirmed at the time due to its weak transit signals.
More recently, the obit of the planet became more aligned for astronomers on Earth, enabling them to detect stronger transit signals from the planet.
"With an additional transit, the planet's orbital period could be determined, and we were then able to uncover more transits that were hidden in the noise in the earlier data," said Jerome Orosz, the lead author of the study paper.
Researchers say they never expected the third planet to be the largest planet in the system and orbiting in the middle of the two previously known planets.
The findings of the study are published in the Astronomical Journal.
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