Found: lost planet

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Apr 3, 2017

Lost in space, a new exoplanet recently surfaced from the darkness—but how can a Neptune-size orb only 3,000 light-years away possibly stay in the shadows?

While Kepler-150 f was never really “lost” (you can’t lose something you never knew existed), it was overlooked when the other four planets in the Kepler-150 system were identified.  Most exoplanet discoveries are made by artificial brains. Computer algorithms use their virtual vision to make out any planetary transit signals as alien planets orbit and temporarily occult (hide) their stars as they pass by, at least depending on the point of view of the observer. What these computers don’t always take into account that one planet may also end up occulting another. Seems like even AI was left in the dark this time.

"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," said Yale graduate student Joseph Schmitt, lead author of a paper on the discovery published in the Astronomical Journal. "Essentially, it was hiding in plain sight in a forest of other planetary transits."

Schmitt and his colleagues realized there was literally a hole in the process. An object is identified in the Kepler pipeline when the computer indicates a transit signal and removes any data points associated with said transit. Eliminating these signals results in a light curve with more holes than Swiss cheese, to the point that transit subtraction is actually called “Swiss cheesing” by scientists. That same curve is then used and reused to detect multiple transits. When Schmitt’s team tried to figure out how a planet could ever get lost in the search, they realized the holes created by the computer’s removal of transit signals could black out the possibility of spotting an undiscovered planet if another one is in transit of (appears to move across) it.

“The probability that a transiting planet is lost due to the transit masking is low, but non-negligible,” said Schmitt. Meaning, never rule out anything.

It was a follow-up visual search through all the “Swiss-cheesed” data that revealed where Kepler-150’s was lurking. What didn't exactly help was that this planet has a particularly long, 637-day orbit around its star, which is one of the longest ever for any planet in a system of five or more planets.

So what can we expect from Kepler-150 f? Before you think “aliens,” little is known even about its neighbor planets. What we do know is that they orbit a star very similar to our sun. Kepler-150 b is a super-Earth—again, no known biosignatures, just a mass higher than Earth’s but lower than that of Uranus or Neptune—and Kepler 150-c is an ice giant.

The Kepler space telescope has been able to confirm over 1,000 exoplanets, so who knows what may still be hiding out there.

(via Yale News)

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