Neptune, Pluto... Xena and Gabrielle?
Sun, 02 Oct 2005 - CBC News

Astronomers say Saturday that an icy, rocky object that might be the solar system's 10th planet has its own moon. Scientists have dubbed the possible planet Xena and its much smaller satellite, Gabrielle.

They made the discovery on Sept. 10 using the Keck Observatory on Mauna Kea in Hawaii. "Since the day we discovered Xena, the big question has been whether or not it has a moon," Michael Brown, of the California Institute of Technology, said in a statement.
"Having a moon is just inherently cool -- and it is something that most self-respecting planets have, so it is good to see that this one does too."
Xena also goes by the more prosaic name 2003 UB313. It was discovered 2003, in an ongoing survey at Palomar Observatory's Samuel Oschin telescope.
Proclaiming a heavenly body a planet is controversial because there is no official definition of what a planet is.
A planet does not need to have a moon in order to deemed a planet. Neither Mercury nor Venus have moons. But the moon's discovery is significant because it can help determine the mass of the possible planet.

The moon is about 250 kilometres wide. It is currently 15 billion kilometres away from the sun, or about three times Pluto's current distance from the sun.
Astronomers know that Xena is bigger than Pluto but they don't know what it is made of, so they can't calculate its mass. But the discovery of the moon Gabrielle means Xena has at least enough mass to keep a satellite circling it.

Gabrielle was the name of the sidekick and pal in the former television series, Xena: Warrior Princess. This isn't the first discovery of a so-called 10th planet. In 2000, 2000 EB173 was discovered using the CIDA observatory in Merida, Venezuela.
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