Wednesday, February 22, 2006

New Moons Confirmed

Dammit! - two new moons for Pluto, from Hubble

9 comments:

Kirsten said...

...moons bad?

Also, if Pluto is smaller than the moon, and Pluto still gets to be a planet, does the moon get to be a planet, too? I mean, it's only fair.

Dr. Lisa said...

See, this is where the fun begins. Jupiter's moon Ganymede, the largest moon in the solar system, is larger than Pluto, larger than Mercury! Why isn't it a planet? Because it orbits Jupiter. Pretty much the only thing that astronomers agree on is that planets orbit stars. Plunk down Ganymede into orbit around the Sun, and we'd have do difficulty calling it a planet. (Titan is even more convincing, with that lovely thick atmosphere.)

What intrigues me is, if we're still going to call Pluto a planet and not a Kuiper Belt object, why not call it a double planet? Its largest moon, Charon, is half its size! Seriously, this discussion will probably be settled within the year, because more moons for Pluto and the unfortunately nicknamed "Xena" are pushing the issue.

I devote a whole lecture to this rant. Consider this the mini-lecture. :)

David Moles said...

Maybe this is a way out for that lazy-ass IAU committee —  “Planet: Must be larger than 4500km in diameter or have at least three moons. Take that, 2003 UB313!”

Kirsten said...

Sorry, I wasn't clear. If Pluto is larger than the Moon, as in ours...and doesn't the Moon orbit the Sun, too?

Dr. Lisa said...

The IAU really has to tighten up their guidelines. Right now, it has devolved into a "well, it feels like a planet" debate. Since we all get to voice our opinions, I think we have 8 planets and a schload of KBOs. But I guess we could have fun making up dozens of new planet names!

The Moon kinda orbits the Sun, if you count its motion around the Sun as the Earth drags it along. Guess that might count.

Let's just call all the tidbits planets, even the dust grains!

Jackie M. said...

I still advocate my "drop it into the Sun and see if it grows a tail" test...

(A quadruple comet! Consider the possibilities, people!)

Dr. Lisa said...

I like that test, Jackie. I guess since it isn't mandatory for a planet to have an atmosphere, it might be allowed to sublimate an atmosphere, though.

Jackie M. said...

Hmm! I think the way I got around that before was to argue that anything large enough to qualify as a "planet" would possess a gravitational well deep enough to hold onto most its atmosphere well inside of the Earth's orbit... and so no tail would be visible to the naked eye.

(Mostly I just want to drop Pluto into the Sun. It's a "go away kid, ya bother me" kind of thing.)

Dr. Lisa said...

I wanna drop Pluto into the Sun just to see what it's made of! :)