Citizen scientists spot 14 exoplanet candidates – including 7th in first 7-planet system

The Planet Hunters citizen science project has submitted a paper to the Astronomical Journal reporting on their discovery of 14 planet candidates in the Kepler space observatory data: Seventh heaven with our sixth exoplanet paper – Planet Hunters.

See the outline here of how the Planet Hunters project takes advantage of human pattern recognition abilities to spot the changes in brightness of a star as a planet crosses in front of it.

In the Planet Hunters blog:

The most exciting result involves KOI-351, a system with six known planet candidates identified by the Kepler team, two of which had also been independently discovered by Planet Hunters before the Kepler identification.  We have identified a seventh candidate, marking KOI-351 as the first Kepler seven planet system.  While we cannot yet confirm the candidates in KOI-351, gravitational interactions between the planet candidates overwhelmingly point to their planetary nature.  It is also known that false positives in multiple candidate systems are extremely rare.

All of this together makes KOI-351 the strongest case for the first seven planet system known (apart from our own Solar System, of course!) The new planet is the fifth furthest from its parent star, orbiting with a period of nearly 125 days. With a radius of 2.8 times that of the Earth (+/- 1.1) it fits snugly into a family that now includes two roughly Earth sized worlds, three ‘super-Earths’ and two larger bodies.

In total, we announce the discovery of 14 planet candidates, all of which were identified by volunteers through the Planet Hunters Talk page.  Of these, eight reside in their host star’s habitable zone, but none of them approach Earth or super-Earth size.  Additionally, five of these new candidates met the requirements to have been detected by the Kepler team’s automated Transit Planet Search algorithm, but were undetected, including KOI-351.07, the newly discovered seventh candidate.

Here is the paper that they have submitted and its abstract: Planet Hunters VI: The First Kepler Seven Planet Candidate System and 13 Other Planet Candidates from the Kepler Archival Data – J.A. Schmitt et al

We report the discovery of 14 new transiting planet candidates in the Kepler field from the Planet Hunters citizen science program. None of these candidates overlap with Kepler Objects of Interest (KOIs), and five of the candidates were missed by the Kepler Transit Planet Search (TPS) algorithm. The new candidates have periods ranging from 124-904 days, eight residing in their host star’s habitable zone (HZ) and two (now) in multiple planet systems. We report the discovery of one more addition to the six planet candidate system around KOI-351, marking the first seven planet candidate system from Kepler. Additionally, KOI-351 bears some resemblance to our own solar system, with the inner five planets ranging from Earth to mini-Neptune radii and the outer planets being gas giants; however, this system is very compact, with all seven planet candidates orbiting ≲1 AU from their host star. We perform a numerical integration of the orbits and show that the system remains stable for over 100 million years. A Hill stability test also confirms the feasibility for the dynamical stability of the KOI-351 system.

The paper will need to pass the peer review process before it can be published. There may be changes suggested by the reviewers as well. If accepted, this will be the sixth paper from Planet Hunters to be published.