A planet that never sticks to schedule found

Astronomers have discovered a new planet that has a highly inconsistent orbit time around its Sun.

The low-mass, low-density planet, known only as PH3c, which is 2,300 light years away from the Earth, has an atmosphere loaded with hydrogen and helium.

The planet nearly escaped detection as PH3c does not have a consistent orbit time around its Sun due to the gravitational influence of other planets on its system.

"On the Earth, these effects are very small, only on the scale of one second or so," said Joseph Schmitt, a graduate student at Yale University.

"PH3c's orbital period changed by 10.5 hours in just 10 orbits," explained Schmitt.

This inconsistency kept the planet out of reach for automated computer algorithms that search stellar light curves and identify regular dips caused by objects passing in front of stars, he said.

The researchers discovered the new planet with the help of Planet Hunters programme coordinated by Yale University and University of Oxford.

The programme, which has found over 60 planet candidates since 2010, enlists citizen scientists to check survey data from the Kepler spacecraft.

Not only did Planet Hunters spot PH3c, but the discovery also enabled astronomers to better characterise two other planets - one on each side of PH3c.

An outer planet PH3d is slightly larger and heavier than Saturn. An inner planet, PH3b may have a rocky composition like the Earth.

"Finding the middle planet was key to confirming the others and allowing us to find their masses," Schmitt explained.

The discovery appeared online in the Astrophysical Journal.