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Scientists discover 10th planet's moon
(AP)
Updated: 2005-10-02 09:11
LOS ANGELES - The astronomers who claim to have discovered the 10th planet in
the solar system have 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 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." The moon was
nicknamed Gabrielle, after Xena's faithful traveling sidekick.
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 discovery of the moon is not likely to quell debate about what
exactly makes a planet. 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.
Possessing a moon is not a criteria of planethood since Mercury and Venus are
moonless planets. Brown said he expected to find a moon orbiting Xena because
many Kuiper Belt objects are paired with moons.
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