Oct 2, 2005
Scientists discover moon orbiting '10th planet'
LOS ANGELES - The astronomers who claim to have discovered the 10th
planet in the solar system have made another intriguing
announcement: it has a moon.
This artist's concept, released by Nasa, shows the so called 10th
planet at the lonely outer fringes of our solar system. Our Sun can
be seen in the distance. -- AP
While observing the new, so-called planet from Hawaii last month, a
team of astronomers led by Mr 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, Mr Brown announced the
discovery of an icy, rocky object larger than Pluto in the Kuiper
Belt, a disc of icy bodies beyond Neptune. He labelled 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.
The moon is about 250km wide and 60 times fainter than Xena, the
farthest-known object in the solar system. It is currently 14
billion km away from the sun, or about three times Pluto's current
distance from the sun.
But the newly discovered moon, nicknamed Gabrielle after Xena's
faithful travelling 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.
Possessing a moon is not a criteria of planethood since Mercury and
Venus are moonless planets.
Scientists believe Xena's moon was formed when Kuiper Belt objects
collided with one another. The Earth's moon formed in a similar way
when Earth crashed into an object the size of Mars.
Scientists expect to learn more about the moon's composition during
further observations with the Hubble Space Telescope in November.
-- AP
