A recently discovered planet seems to have trouble sticking to a schedule.
The low-mass, low-density planet PH3c has an inconstant orbit time around its host star because of the gravitational influence of other planets, Yale University reported.
"On Earth, these effects are very small, only on the scale of one second or so," said Joseph Schmitt, a Yale graduate student and first author of the paper. "PH3c's orbital period changed by 10.5 hours in just 10 orbits."
The inconsistency of the planet's orbit is what kept it from being picked up by radar that looks for dips in light caused by objects passing in front of stars. Members of a program called Planet Hunters discovered PH3c by looking at data from the Kepler spacecraft.
"[The project] harnesses the human dimension of science," said Debra Fischer, who leads the exoplanets group at Yale and is a co-author of the paper. "Computers can't find the unexpected, but people can, when they eyeball the data."
The findings will help researchers to better characterize the planets on either side of PH3c. The outer planet, dubbed PH3d, is believed to be slightly larger than Saturn while the inner planet PH3b most likely has a rocky composition.
"Finding the middle planet was key to confirming the others and allowing us to find their masses," Schmitt said. "The outer planet's orbital period also changes slightly, by about 10 minutes. You need to see both planets' changing orbital periods in order to find out the masses of the planets. One planet doesn't give enough information."
The outer planet's year is 1.91 times longer than PH3c's , which has a year 1.91 times longer than the inner planet's.
"We're not sure if this is just a coincidence or whether this might tell us something about how the planets were formed," Schmitt said.
The findings were published Oct. 29 in The Astrophysical Journal.
