Hubble Confirms Pluto's New Moons


(courtesy of NASA)

I've heard that the IAU is meeting to discuss whether the debate of Pluto as a bonifide planet will finally be resolved. Some have suggested that Pluto should be classified as just a Kuiper Belt Object. Xena (10th planet), and it's moon are also considered to be KBO's.

Maybe now this will get ironed out...

Pluto is still part of the Kuiper Belt. It just becomes a question now of how complex the belt is, and whether Pluto and her moons are more than just icy chunks.

Nice find though

There are those that contest the Kuiper Belt is part of our solar system. Some deny, and others abstain. I think it stands to reason that any larger planetoids and planetesimals that reside in the system should be encompassed accordingly. And if such an object has an orbiting moon, that should differentiate it from the other junk floating around...

There are Jovian moons that are literally nothing but icy chunks!

Ok. So if we aren't defining "moon" by composition, are we defining it by size, or merely that it is orbiting another body?

Not composition, for the various moons of existing 'defined' planets vary. By definition, moons have to orbit. Concentric (or nearly so) used to be the norm. Elliptical give some cause for debate. But as to size, Pluto is an enigma because Charon is respectively so large. The astro-phys guys are still chewing on that one.

And 'Xena' (if that's what the finally name it) is larger than Pluto. So if size becomes a quantifiable condition- if Pluto becomes a planet, then Xena must.

The IAU is like the UN. They have a difficult time deciding on things...

Pluto is smaller than the moon right? Which makes the whole thing more confusing. The only bodies we can say for certain are planets ends with Neptune IMO. The discovery of these moons just adds to the puzzle.

It is still cool though. I think we need Hubble 2 now.

Correct. The Moon is 3476 km, and Pluto is 2360 km. Xena is 3000km.

I think somewhere along the line, someone qualified a planet as such if it had an orbiting moon, or natural formed satellite. If that criteria is followed, then both Pluto and "Xena"(2003UB313) would qualify as planets. Pluto was an enigma until Charon was discovered, then the debate was off to the races as to whether Charon was actually a moon, or at one time part of Pluto- since it was uncharacteristically large. With all the junk floating around in the Kuiper Belt, a collision is a possibility.

Okay- here is the latest skinny I found on the IAU meeting... (BBC)

I think using gravity as a determining factor is kind of strange, but that's just my opinion.

It seems there are a couple different variants of that proposal floating around... some stricter then others. See: http://z4.invisionfree.com/Popular_Technol...?showtopic=1629

I think gravity is a great determinant. Because it's not just an arbitrary number like "x kilometers wide", but, instead a characteristic that has meaning. A "planet" needs to be orbiting a star and have sufficient gravity to make itself a nearly spherical shape. That's excellent!

It's a bit hard to argue that anything with those characteristics *ISN'T* a planet. The queerness comes when we have "planets" smaller then "moons". To deal with that, I'd just draw a size line and say anything smaller then the earth's moon is a minor planet. Sounds like what they're already doing with "plutons".

I think it's cool that Ceres will finally get some recognition (it actually used to be considered a planet, long ago), and that Pluto-Chiron might be considered a twin planet.

Really, if you were looking at things objectively this is the classification you'd come up with, but people are so used to "the solar system has 9 planets" they are very reluctant to add or subtract from that number.

Yeah ... "to make itself" is an interesting turn of phrase. It would imply that spherical meteriods in the belt are not "planets" but things of comparable size could be, if they were dense enough to self-form.

The only problem I have with this definition is we need to know how a body formed ... something that we are still learning about, particularly in the case of "plutons".