The possible tenth planet, 2003 UB313, which takes 540 years to circle the sun, in a highly eccentric orbit, has now acquired a satellite. The new moon was discovered two months after 2003 UB313 by the Keck observatory on September 10th and the findings will be published tomorrow. The existence of a moon ensures that Xena will be seriously considered as a tenth planet, since it has the mass to acquire orbiting bodies.
“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.”
The possible 10th planet moves in a highly eccentric orbit, tilted some 45 degrees above the orbital plane of the other planets. Its orbit is also elliptical, zooming in as close as 3.5 billion miles from the sun and moving out to as far as 9 billion miles away.
And, as you know, the self-respecting companion of Xena, could only have been called Gabrielle.
I suspect the existence of a moon won’t tip the planet-or-not decision one way or the other. There are a number of asteroids with moons, and I don’t think anyone’s calling for their promotion to planet status. The only way the moon might help (or hinder) 2003 UB313’s case is by helping astronomers determine its mass much more precisely.
Shameless self promotion: I wrote a post a couple of months ago speculating about possible names for 2003 UB313 if it does qualify as a planet.
At least one prominent astrophsyicist told me years ago that Pluto was not really a planet, just a Kuiper belt object.
We are going to have to be careful about who we let into the planetary club.
When a couple more Kuiper belt objects are found I’m in no doubt that any enthusiasm to call them planets will fade. However, whether we call them planets or not is irrelevant. They will still be solid objects orbiting the Sun just as they always have been, and our semantic arguments over their classification won’t alter this fact.
The obvious thing to do is to modify our definition of “planet” to either exclude or include these bodies. This sounds easy, but I suspect that a heated debate will rage for some time to come, particularly if Pluto is to become a casualty.
Please don’t discriminate against Pluto or 2005 UB313, I’m sure the planetry club is open, inclusive and diverse in its membership.
‘We’re all planets now.’
I’ve never quite understood the opposition to calling big spherical Kuiper Belt Objects “planets”. I can remember when Jupiter was only thought to have about a dozen moons; now it’s known to have at least 63, and we still think of them as moons, even though we know Jupiter has rings (and therefore very many satellites with some logarithmic distribution of sizes).
If an object orbits the sun and is big enough to pull itself into a sphere, it’s a planet as far as I’m concerned. I’d even be willing to see Ceres promoted, or an exception declared for main belt asteroids, as you prefer. Just don’t demote Pluto!
Thorough agreement with Tensor. The “sphere” argument has one overriding advantage: consistency.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and…Xena?
I really hope that’s not it’s final designation.
If Neptune was the god of the sea, and Pluto the god of the underworld, then the planet should be named for the god of Earth’s inner core.
The Commissar suggests the gods of the blogosphere underworld:
Well some 40 years ago Arthur C. Clark pretended that the solar system had ten planets. The tenth planet was supposed to be twice far away from the sun than Pluto. And he called it Persephone.
As he is such a popular science fiction writer, I think we should call this planet Persephone.