Los Angeles, Oct. 2 (AP): The astronomers who claim to have discovered the 10th planet in the 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 spotted a faint object trailing next to it. Because it was moving, astronomers ruled it was a moon and not a background star.

The discovery will help scientists determine the planet’s mass. In July, they discovered the icy, rocky object larger than Pluto on the Kuiper Belt, a disc of icy bodies beyond Neptune, and labelled it a planet and nicknamed it Xena after the lead character of the TV series Xena: Warrior Princess.