Planet Hunters has reported a second confirmed exoplanet discovery, along with 42 additional candidates and possible candidates.

Planet Hunters is an online project that allows citizen scientists to help find exoplanets in archived data from NASA’s Kepler space telescope. The new discovery, designated PH2-b, is a Jupiter-sized planet in the habitable zone of a Sun-like star. A paper on the discovery has been submitted to the Astrophysical Journal and made available to the public at arxiv.org.

PH2-b has an estimated surface temperature 46 Celsius, which is right for liquid water, but the planet is believed to be a gas giant with no solid or liquid surface. To rule out the possibility of a false-positive detection, Planet Hunters used Keck telescope’s HIRES spectrograph and NIRC2 adaptive-optics system to obtain high-resolution spectrum and high-spatial-resolution images.

Planet Hunters also announced the detection of 31 long-period (>100-day) candidate planets, 15 of which are located in the habitable zone. The majority of these candidates are believed to be Neptune- to Jupiter-sized.

A significant number of exoplanet candidates are now being discovered by citizen scientists. These discoveries increase the number of long-period planet candidates by more than 30% and almost double the number of gas-giant candidates in the habitable zone, some of which might have habitable moons.

Planet hunters also announced a watch list of nine possible candidates, which have been observed for only two stellar transits. The Kepler science team has established a criterion that requires three observed transits for a detection to be considered a planet candidate.