The Eleventh PlanetHunters Habitable Zone Candidate

Manual reviews of the light curve for Kepler target star KIC 9886255 have revealed the presence of some intriguing transits on a ~106 day period, visible in the public data for Quarters 3 through 9.

A transit in corrected flux for Quarter 3

The Kepler Input Catalog calls out 9886255 as a Type K star of 15.8 apparent visual magnitude, 5137(K) and an assumed radius of  0.6 compared to Sol.

A potential follow up issue exists with this target due to another source close in the field, identified as KIC 9886258 and seen with tag '#2" in the Skyview image below:

Currently this neighboring source is not a monitored target and no light curve exists on record for it. Preliminary investigation suggests no active pixel offset is occurring that might indicate the noted transits actually belong to this star as opposed to 9886255, however the close proximity and risk of blended flux is a cause of concern c/t analysis of this candidate.

If we take the data at face value, the depth and duration suggest a potential habitable zone exoplanet, albeit one that may be in a slightly eccentric orbit around its host star.

 Discussion Source

"Here's close-up of the transit, and although the flux values are spread quite widely and individual transits show a lot of variation, the averaged plot with a polynomial fit shows a U-shape and flat-bottom . The measured depth is 2500ppm with a duration of 7.37hr. This is at odds with a computed central transit of 5.6hr. If this is planetary this could be explained by an eccentric orbit. Using the stellar parameters provided in MAST, I estimate a 3.26x RE planet, at 0.4 AU and a Teq of 274K, putting this in the HZ." -Kianjin

Like most of the other habitable zone candidates we've seen at Planethunters, this exoplanet would weigh in far heavier than Earth; if the calculated radius is accurate it belongs to the Neptune or sub-Neptune domain as opposed to a Super-Earth, and likely has a thick, high pressure atmosphere. Additional Kepler data is going public soon so it will be interesting to see if any longer period transits show up for this system that may have been lost previously in time series data breaks and gaps.

Latest numbers have the official Kepler count at 2405 exoplanet candidates awaiting follow up and amongst confirmed systems 127 of the 834 known!