Newly Discovered Exoplanet Almost Avoided Detection with its Inconsistency

A newly discovered planet apparently won't stick to a schedule. Astronomers have spotted a low-mass, low-density planet that's so inconsistent that automated computer algorithms have trouble picking it up as they search for stellar light curves.

The new planet is called PH3c, and is located about 2,300 light-years from Earth. Its atmosphere is loaded with hydrogen and helium and has a highly inconsistent orbit around its sun. It's this irregular orbit in particular that has allowed it to nearly avoid detection.

"On Earth, these effects are very small, only on the scale of one second or so," said Joseph Schmitt, first author of the new paper, in a news release. "PH3c's orbital period changed by 10.5 hours in just 10 orbits."

The inconsistency actually kept the planet from being picked up by automated computer algorithms that search stellar light curves and identify regular dips caused by objects passing in front of their stars. So how was this planet detected? A program that began in 2010, called Planet Hunters, is largely responsible for detecting the planet. This program, which has found more than 60 planet candidates since 2010, uses citizen scientists to check survey data from the Kepler spacecraft.

"It harnesses the human dimension of science," said Debra Fischer, co-author of the new study. "Computers can't find the unexpected, but people can, when they eyeball the data."

Planet Hunters didn't just find PH3c, either. They also enabled astronomers to better characterize two others planets to either side of PH3c.

"Finding the middle planet was key to confirming the others and allowing us to find their masses," said Schmitt. "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 findings reveal a bit more about this new planet and show the importance of citizen science. Not only that, but it paves the way for future discoveries using Planet Hunters.