The New York Times
Q&A
Tuesday, December 12, 1989, p. C11

Planet X

	Q. Is there a 10th planet, called Chiron, beyond Pluto?

	A. "Chiron is an icy and rocky object in the outer solar system a couple of
hundred kilometers across," said Eugene Levy, director of the Lunar and
Planetary Laboratory at the University of Arizona.

	It is in orbit beyond Pluto, but it is not a planet, he said.

	But he added: "There are a lot of undiscovered objects in the solar system,
and we do not know whether there is something as large as a planet. It is
conceivable that there is something out there."

	Speculation about a so-called Planet X arose because of unexplained 11
gravitational perturbations that affect planetary orbits," Dr. Levy said.
However, he said, there is also speculation that the cause is an inward
extension of the comet cloud, the billions of comets believed to be in orbit
trillions of miles from the Sun, which might also create enough gravitational
force to affect planetary orbits.