LOS ANGELES, California (AP) -- The astronomers who claim to have discovered the 10th planet in the Earth's solar system have made another intriguing announcement: it has a moon. While observing the new, so-called planet from Hawaii last month, a team of astronomers led by Michael Brown of the California Institute of Technology spotted a faint object trailing next to it. Because it was moving, astronomers ruled it was a moon and not a background star, which is stationary. The moon discovery is important because it can help scientists determine the new planet's mass. In July, Brown announced the discovery...