CAMBRIDGE, Mass., Sept. 8 (UPI) -- U.S. researchers say they've detected a distant planet that alternately runs late and early in its orbit, proof that a second, "invisible" world tugs on it.
Astronomers say this is the first time an unseen planet has been detected in this fashion and that no other technique could have discovered the hidden world.
"This invisible planet makes itself known by its influence on the planet we can see," astronomer Sarah Ballard of the Harvard-Smithsonian Center for Astrophysics said.
"It's like having someone play a prank on you by ringing your doorbell and running away," she said. "You know someone was there, even if you don't see them when you get outside."
Both the visible and the invisible planets orbit a Sun-like star located 650 light-years from Earth in the constellation Lyra, a Harvard-Smithsonian release said Thursday.
Astronomers used NASA's Kepler space telescope to observe and record the variations in the orbital times of the visible planet that revealed the presence of its invisible neighbor.
"This method holds great promise for finding planets that can't be found otherwise," Harvard astronomer David Charbonneau said.