Give Pluto the boot!

[ciphergoth]

Check out this list of solar system object by mass.

The Sun is by far the most massive object in the solar system, making up over 98% of the mass of the entire system. After that come the planets, starting of course with Jupiter, and finishing with Mercury. Then there's seven of the larger satellites: Ganymede, Titan, Calliso, Io, the Moon, Europa, and Triton. After that comes the newly-discovered trans-Neptunian object, 2003 UB 313, better known as "Xena".

After all that, you get Pluto. Less than one-twentyfifth of the mass of the next-smallest official planet, Mercury. Its orbit is so weird it crosses the orbit of Neptune for years at a time, and it's not in the ecliptic plane. Its likely composition: a big lump of cold rock.

It only barged its way into the planetary club because the presence of its moon Charon caused astronomers to believe that Pluto was much larger than it turned out to be. In fact Charon is practically as big as it is, with the result that rather than one orbiting the other, it makes more sense to describe it as a binary system, with both orbiting a single point in space, faces locked towards each other.

If Pluto is allowed to stay in the club, we'll have to allow in all sorts of dull riff-raff - not only Xena, but Ceres, Charon, and possibly others like Quaoar and Sedna. No-one will be able to remember the names of all the planets.

I implore the IAU to strip Pluto of planet status as soon as possible. It should count itself lucky that we allow it to stay in the solar system at all.

Comments

[emarkienna.livejournal.com]

Have you seen this? http://planetary.org/news/2006/0816_The_IAU_Redefines_Planet__Pluto_is_a.html - If the vote passes, on 24 August not only will Pluto remain a planet and Xena become a planet, but so will Charon and Ceres (the latter which was a planet once before, I believe).

A possible list of potential new planets after that is at: http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601c.html , so that could soon be 24 planets.

It does sound rather silly if 'By the end of this century, there could well be "up to 200 new planets,"' But in some sense, no one being able to remember all the names would put an end to this controversy of "how many planets we have", which isn't really something you can well-define - e.g., no one worries about the exact definition of a mountain, because no one could remember all the names of mountains, but if we only used "mountain" to refer to a few big ones, we'd have problems everytime we discovered a new one close to the boundary.

This is an interesting read on how not just Ceres, but also Vesta, Juno, and Pallas were considered planets at one time, before they all lost their status when more were discovered. Perhaps that will eventually happen again? - though the IAU do seem prepared that their definition will result in large numbers of planets.

Was Pluto not considered a planet before Charon was discovered in 1978?

[ciphergoth.livejournal.com]

Was Pluto not considered a planet before Charon was discovered in 1978?

That's what I mean - before astronomers realised that they were looking at a double planet system, they accounted for what they saw as being a much larger single body.

[emarkienna.livejournal.com]

Ah of course, yes that makes sense.