[Evanescence]

Hi all,
I have a question that’s been really baffling me and the rest of my science class at school.
Last year it was announced that a ‘10th planet’ was discovered in the outer solar system. It was named ‘Sedna’. It was believed to be red in colour, much smaller than Pluto, and had no moon.
However, recently I read an article in a newspaper that claimed that scientists had found a new 10th planet this year and called it ‘Xena’. It was this time bigger than Pluto and had a moon.
Can someone please explain what’s going on here? Is Xena Sedna under a new name? Is Sedna now not classed as a planet and therefore Xena is the 10th planet? Help!

[CraigD]

Originally Posted by Evanescence

Is Xena Sedna under a new name? Is Sedna now not classed as a planet and therefore Xena is the 10th planet? Help!

No, Sedna and Xena are completely separate objects. Whether one, both, or neither should be called a planet is under debate among professional astronomers, as is whether Pluto should continue to be called one.

For the past few years, about 3 or so objects Sedna’s size or bigger are being discovered every year. Occasionally, a discovery gets a lot of press coverage, such as Sedna or Xena, but more often, they do not. More than half or recent discoveries have yet to be given nice names, going by names like 2000 CR105, 90482, 003 EL61, and 2005 FY9. By my count, we’re up to about 25 objects that can make a reasonable claim to be called “planets”

I think the consensus among planetary scientists is that it was a mistake to grant Pluto “planet” status, since there are likely hundreds more like it, and we should go back to saying there are 8, stopping with Neptune. Some, like one of Xena’s discoverers, Mike Brown, argues that “planet” isn’t really a scientific term, but a cultural one, so, if the discovery is well known enough, we should go ahead and call it a planet, even if its small, or its orbit weird. A discussion of this can be found in the Space article “Defining 'Planet': Newfound World Forces Action”.

Scienceforums discussed this a few weeks ago in threads "New 10th Planet Discovered" and ”Sun's Tenth Planet Discovered”, if you want to read some of our thoughts on the subject.

However the argument about counting planets turns out, it seems that Xena has stolen Sedna’s moment of glory, and the title “tenth planet.” It’ll be interesting to see if it can hold on to the title, or if people will decide to stop counting at 9, or even back up one to 8.