Astronomers Have Spotted A "Lost" Planet The Size Of Neptune

Artist's impression of Kepler-150 f. Michael S. Helfenbein

If it weren't for a newly developed algorithm, a Neptune-sized exoplanet would have eluded astronomers. 

The newly discovered planet is part of a system discovered by the Kepler observatory in its K2 mission. The system, Kepler-150, already sports four other worlds: Kepler-150 b, c, d, and e. The new planet, Kepler-150 f, was further out than its planetary siblings and thus its signal was overlooked for many years. 

However, as reported in the Astronomical Journal, astronomers at Yale gave the system, located 3,000 light-years away, another look. The algorithm takes into account the variability of the stars and the signals of known planets, which means what's left should be caused exclusively by new objects. The team was able to apply the new technique to 114 different stars, uncovering evidence of 33 potential exoplanets around 24 stars. 

The researchers were able to confirm the existence of Kepler-150 f using some clever statistical tools on the data available. Based on the fact that Kepler-150 already has planets, the likelihood of a false positive, and how long the potential planet took to orbit, the team confirmed the discovery with 99.998 percent confidence. 

“Only by using our new technique of modeling and subtracting out the transit signals of known planets could we then actually see it for what it really was,” lead author Joseph Schmitt said in a statement. “Essentially, it was hiding in plain sight in a forest of other planetary transits.”

Kepler-150 f orbits its star in about 637 days, making it one of the widest orbits of a planet discovered with the transit method. This is where planets move in front of their stars and cause mini-eclipses, blocking some of the light. The change is usually a fraction of a percent, but it's enough for the sophisticated instruments onboard Kepler.  

Exoplanets continue to be discovered around new stars every week, and even known systems could be hiding some more surprises. 


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