Pluto and Charon - Planets?

Question

So it looks as if the IAU have finally decided that Pluto should be a Planet. But the criteria they have come up with seem (I've not had time to read them carefully) to imply that a heck of a lot of other objects should now count as planets, including Pluto's erstwhile moon, Charon. Are they right??

Ah - they are saying that if the Barycentre of a system lies beyond the surface of the primary body, the secondary counts as a planet too! So the old logic of charon being a moon 'cos it orbits Pluto doesn't count!

Answer 1

They could not be judged as right or wrong, just setting a standard for their so-called definition of a "planet". They would need to include a heck lot of other Kuiper Belt Objects if they want to include Pluto, so I suggest that they completely ignore Pluto altogether. (That would make memorisation much much easier...)

Answer 2

I believe the scientist have a clue as to what they are doing. My understanding is that Charon and Pluto have a shared center of gravity, they both kind of orbit around the same place. I think it's great that they are finally deciding on a definition for planet and making the necessary changes in classification. Up until now, they identified these large bodies (what we call planets) and said all those big things up there, we'll call them planets. They did not have a definition of planet. Where now they are saying, we have this specific information and any body that fits this classification will be called a planet.

"Under the proposed definitions, a celestial body is considered a planet if its mass is sufficient for its self-gravity to pull it into a roughly spherical shape, and if it orbits the sun but is neither a star itself nor the satellite of another planet. These definitions would immediately make planets of Ceres (beyond Mars, formerly considered an asteroid), Charon (formerly considered a moon of Pluto) and the object 2003 UB313, nicknamed Xena upon its discovery in 2003 but not yet formally named. Charon and Pluto form a double planet system, spinning together around a point in space between them—and because this barycentre isn’t under Pluto’s surface, Charon wouldn’t be considered a satellite of Pluto the way the moon is a satellite of Earth. A dozen more objects also are considered strong candidates for classification as planets, and [Linda] French has heard projections of up to 50 planets total, once objects in the Kuiper Belt near Pluto are sorted out." http://www2.iwu.edu/newsrelease06/fac_FrenchPluto_0806.shtml

Answer 3

They've classed them as "plutons" however, I disagree with making Charon a planet (I am half convinced by Ceres and 2003 UB313) Because Charon is a satellite around pluto (although they are calling it a twin planet) but the moon is a satellite around earth, so by the new definition, the moon should be a planet, or Charon remains as a satellite - not one of each as they are suggesting.

However, it needs to be ratified, although I think it will be. There are a further dozen or so objects that they are clling into question as planets or "plutons".

Answer 4

Apparently they're going to be something like "Level 2 planets" (i cant remember the exact name

This will also include the astroid belt between mars and jupiter, and another random planet further out with a really random name (Something like e4020 or some rubbish.)

I dont understand why they're counting these as planets, but they have a habit of doing things like this then not following through (Remember the 13th sign of the zodiac they found??)

Answer 5

Their criteria seems pretty simple but I could be totally off that their suggesting that a planet has to have enough of its own gravity to create a spherical planet and orbit a star? I have no idea

Answer 6

Charon orbits a planet, so it's a moon.

Answer 7

pluto is the planet and charon is the moon of pluto..

Answer 8

Ok fair enough its just a small piece of rock and ice. But it has feelings!

Answer 9

they're putting scanning bars an a price on it