One of the 15, a Jupiter-sized planet orbiting the solar-type star KIC 12735740, has been officially confirmed as a planet (with 99.9 percent certainty). Named PH2 b, it is the second confirmed planet to be found by Planethunters.org, part of the Oxford University-led Zooniverse citizen science project that turns raw data over to keen amateur researchers. The remaining 14 planet candidates are at least 90 percent likely to be planets.
Since 2010, Planethunters has been searching through the Kepler data NASA released into the public domain, allowing its 200,000-strong army of volunteers to seek out the telltale dip in the brightness of parent stars as planets pass in front of them.
Added to the 19 similar planets already discovered in habitable zones, where the temperature is neither too hot nor too cold for liquid water, the new finds present exciting possibilities for the discovery of regions that could potentially support life — not only on the planets themselves, but also on their moons.
Jupiter has several large water-rich moons. If a Jupiter planet in the habitle zone had Earth size moons, we would see worlds with rivers, lakes and all sorts of habitats. This scenario might be common.
We report the latest Planet Hunter results, including PH2 b, a Jupiter-size planet orbiting in the habitable zone of a solar-type star. PH2 b was elevated from candidate status when a series of false positive tests yielded a 99.9% confidence level that transit events detected around the star KIC 12735740 had a planetary origin. Planet Hunter volunteers have also discovered 42 new planet candidates in the Kepler public archive data, of which 33 have at least three transits recorded. Most of these transit candidates have orbital periods longer than 100 days and 20 are potentially located in the habitable zones of their host stars. Nine candidates were detected with only two transit events and the prospective periods are longer than 400 days. The photometric models suggest that these objects have radii that range between Neptune to Jupiter. These detections nearly double the number of gas giant planet candidates orbiting at habitable zone distances. We conducted spectroscopic observations for nine of the brighter targets to improve the stellar parameters and we obtained adaptive optics imaging for four of the stars to search for blended background or foreground stars that could confuse our photometric modeling. We present an iterative analysis method to derive the stellar and planet properties and uncertainties by combining the available spectroscopic parameters, stellar evolution models, and transiting light curve parameters, weighted by the measurement errors. Planet Hunters is a citizen science project that crowd-sources the assessment of NASA Kepler light curves. The discovery of these 43 planet candidates demonstrates the success of citizen scientists at identifying planet candidates, even in longer period orbits with only two or three transit events.