"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.
The moon discovery is important because it can help scientists determine the new planet's mass. In July, Brown announced the discovery of an icy, rocky object larger than Pluto in the Kuiper Belt, a disc of icy bodies beyond Neptune. Brown labeled the object a planet and nicknamed it Xena after the lead character in the former TV series "Xena: Warrior Princess."
By determining the moon's distance and orbit around Xena, scientists can calculate how heavy Xena is. For example, the faster a moon goes around a planet, the more massive a planet is.
But the newly discovered moon, nicknamed Gabrielle after Xena's faithful traveling sidekick in the TV series, likely will not quell the debate over what exactly is a planet and whether Pluto should keep its status. The problem is there is no official definition for a planet and setting standards like size limits potentially invites other objects to take the "planet" label."