If a new proposal of the International Astronomical Union is accepted, there will now be twelve planets in the solar system: Tauron, Gemenon, Scorpion, Saggitaron, Caprica . . . Oh, wait. No. Those are the twelve planets in Battlestar Galactica.
Our twelve planets will be: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon, and Xena. (See! There was a TV reference in there!)
And there may be more to come. Many, many more, potentially.
I’ve been meaning to blog about the definition of what a planet is for some time, but haven’t gotten around to it. Now the IAU is about to take action on the question, so here’s a quick version:
For the last few years there has been a debate going in astronomical circles over the definition of what a planet is. This is not a new debate–the discovery of what we now consider to be asteroids led to a similar debate. When Ceres–the largest object in the asteroid belt–was discovered, it was originally considered a planet. Later, when many, many more and smaller objects were discovered in a similar orbit, the category of "asteroid" was come up with, and the debate cooled off for a while.
Then in 1930 the planet YuggothPluto was discovered, and we’ve lived culturally with the idea of Pluto being a planet for going on 80 years now.
Problems is: Pluto turned out to be a lot smaller than we originally thought. Much of the mass originally attributed to it belongs to its moonsister-planet, Charon. And we started finding other objects similar to Pluto in similar, far-out orbits in what is known as the Kuyper belt. It looked like the asteroid belt problem all over again, and some folks started advocating that Pluto be demoted from the status of planet to something else, just as Ceres was. Only the new objects wouldn’t be called asteroids but "Kuyper-belt objects" or "trans-Neptunian objects" or something like that.
The thing that finally forced the issue was the discovery in 2003 of an object known as Xena. Actually, that’s just it’s nickname, and they’ll probably get around to giving it a more serious name–especially if it’s status as a planet is accepted. Technically, it’s known as 2003 UB313 and the thing about it that forced the definition of a planet debate is that it’s larger than Pluto.
As long as Pluto was the biggest of the things we knew about in the outer solar system, we could kinda let its status as a planet slide, but after we went and found something bigger, we needed to either classify it as a planet too or–if we didn’t want to do that–to vote Pluto out of the planet club. (Sorry, Pluto. That’s the way reality television works!) Of course, some folks speculated about grandfathering Pluto as a planet for sentimental reasons, while denying larger objects, but that’s excessively inelegant.
So the IAU has been debating what to do about defining a planet for some time, and a number of proposals have been developed.
The executive committee has now whittled it down to one proposed definition, which is as follows:
“A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.”
Under that definition, at least three bodies in the solar system would get counted as planets:
First, Ceres would get re-promoted to the status of planet. (Welcome back Ceres! Our reality TV show let’s people to get voted back in to the club! Try not to get any demerits this time!)
Second, Pluto’s "moon" Charon would get promoted to planet, too, since it’s mass relatie to Pluto is so large that the point the two orbit is not within either body but between them, meaning that neither orbits the other but they both orbit a common point. (I’m hinky about this one; more on that later.)
Third, Xena (as the largest of these three objects) would get planet status–and probably a more serious name, though I’d love to see the TV name become official.
And there might be more!
Under the new definition we’d have to further study other objects in the solar system to see if they, too, met the criteria about having enough gravity to create a stable shape for themselves, given their composition.
The proposal has been recommended by the executive committee of the IAU to the full body, which is currently meeting in Prague, and a vote is likely to be taken on it this week or next.
If the IAU accepts the proposal (as seems likely) then we’ll have to get used to living in a somewhat more accomodating planet club than we have been to date.
Oh, and non-scholar Zecharian Sitchin will have to find a new title for his dumb book The 12th Planet.
I’ll offer my own thoughts on the proposed definition of what a planet is in another post, but I wanted to use this one as a backgrounder to the current debate.
MORE.
AND MORE FROM THE IAU ITSELF.
Very interesting debate. I for one am more interested in whether certain moons like titan will be habitable.
I thought this appropriate…
“I don’t think I’m alone when I say I’d like to see more and more planets fall under the ruthless domination of our solar system.” -Jack Handy
I use CELESTIA at home a LOT, and am hoping that when they get off their collective rear ends and decide something, then the software will reflect this, as it works real-time, but I’m still not sure if it updates its info by itself.
I have noticed some disturbing things happening in our neck of the woods, however. It would seem that our solar system is in imminent danger of being overrun by POTATOES! Yep, look at the graphic representations of Jupiter & Saturn’s newest “Moons”, and you’ll see what I mean.
The hell with defining a planet. These people need to get organized enough to define a ‘moon’!
There ARE a few bodies in the insystem asteroid belt that by ordinary convention could be described as ‘planetoid’, i.e., they are spherical, and seem to have an orbital path around the sun, whereas the other big rocks either have very little or NO orbital stability of their own. Wonder how this IAU group missed THOSE?
“Third, Xena (as the largest of these three objects) would get planet status–and probably a more serious name, though I’d love to see the TV name become official.”
I think it’d be a cool official name too. We could call it “Planet X” for short. Kinda has a nice 1950s Science-Fiction B-movie sound to it, no?
Great post, Jimmy. I learned a lot.
Wow. They do pick on the little ones, do they? (Pluto)
This is interesting, Now the number of planets has doubled. I wonder if other planets get discovered then probably we’ll have many planets that we’ll be a HUGE Solar System.
It is currently not yet known whether planet Xena is inhabited by beautiful scantily clad large bosomed Amazonian warriors whose insatiable lusts can only be fulfilled by nerdy earth-men.
Xena? We can come up with a better name than that. How about these:
Rayton
Metaluna
Dagobah
Hoth.
I vote for Magrathea.
Last night on the phone, a friend suggested that we should up the number of planets to, say, 153. The idea is that schoolkids would never be able to memorize that many, thus making grandparents look smarter when they say they memorized them all in school.
All this is, of course, in what we admit is revenge for being forced to take Earth Science, for the crime of scoring too high on the latest Standardized Test of Unknown Origin, thus making us unfit for General Science.
It sounded like a great idea, until I remembered that she has a grandson who is perfectly able to memorize a thousand & 53 planets.
Now I feel 😉 old again….
You know, if they want to define the stuff past Pluto as non-planets, they could always declare that planets have to be with X distance of their star. Maybe with a sliding X depending on the size of the star.
acronym anyone?
My Very Educated Mother CAN Just Serve Us Nine Pies – CHERRY & X.
Stuff past Pluto’s orbit is cool and everything, but what about Orcus or Ceres? Hell, even 2004 XR190 enters into the planet(oid) category! These are actual spheroids within the asteroid belt, and they orbit the sun on a fixed path, unlike the other rocks around them which wobble around randomly. Why not map these as ‘planets’ first?
Since when is an asteroid perfectly spherical? I certainly have never heard of one that was(see previous post remarks re: Potatoes invading the inner system). My vote goes for naming the bodies within the A-Belt as planets BEFORE moving on to the outer edge of our system.
+J.M.J+
Call the last planet Minerva. That was one contender for Uranus’s name way back when.
I imagine feminists will be happy to see a few more “goddess” names among the “gods”. Up to now there was just one – Venus {unless we call earth Terra or Gaia, but that would be cheating ;-)}. Now with Ceres they get another “girl” in there, and Xena is “female”, too – at least temporarily (who knows what the final name will be).
In Jesu et Maria,
Just a few thoughts:
Quick prediction on how the IAU vote will go – Yes on planetary status for Charon, because if we call Pluto a planet, we have to call Charon one for the same reasons. Yes on planetary status for 2003 UB313 (Xena) because, well, it’s a planet. No on planetary status for Ceres, because it’s just a big rock in the asteroid belt, but still much smaller than the Earth’s moon. Were would the IAU draw the line on what is a planet and what is an asteroid?
Also, I suggest we start pronouncing Charon “Karon” since it is a Greek name, and we wouldn’t stand for people calling our savior Jesus Shrist. 🙂
+J.M.J+
Another interesting question: What will astrologers do with these new planets?
For the longest time astrology just had seven “planets” to deal with: Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn. When scientists discovered Uranus, Neptune and Pluto, the astrologers had to scramble to assign various influences to them, so as to include them in their cosmic calculations.
Now with three more potential planets, what will the astrologers do? Especially since Ceres falls within the plane of the original “seven”; astrologers may have to deal with the question of how Ceres might have been “influencing” people and events over the centuries without the astrologers knowing about it.
(Not that I believe in astrology, I’m just looking at it from their POV).
In Jesu et Maria,
Back in my day, if you were a planet, you knew you deserved to be a planet! Now, we don’t want to offend anyone so soon everyone will be a planet!
Where are the standards?!?!
(tongue firmly in cheek)
I just find it amusing that we humans beings can put so much energy into debating something as silly as what is and isn’t a planet. Do these people know that there are better, more important ways to spend their time? The coporal and spiritual works of mercy, anyone? How about helping out your fellow man? It makes me sad to think that our tax dollars are being wasted on stuff like this.
In the end, however, I DO think that we need a good name for this “Xena” planet. Some thing along the lines of “Salusa Secundus”, or “Kythamil”, or something equally esoteric and creepy.
Quote: “No on planetary status for Ceres, because it’s just a big rock in the asteroid belt, but still much smaller than the Earth’s moon.”
That makes no sense when you consider the fact that there are a few other objects out there smaller than or roughly the same size as Ceres, and they have their own moon, or satellite, or whatever the hell you want to call it!
Case(s) in point: 2003 UB313, and it’s “moon”, 2005 (2003 UB313) 1, *OR* 2003 EL61, and it’s binary satellites, 2005 (2003 EL61) 1&2.
AAAAAND, guess what? They are ALL spherical. The fact that they spin fast enough to attain this shape and attract a satellite is proof enough of planethood, even if they are smaller than our moon.
So bang goes the theory of size being an indicator of planetary status…
I also like this quote: “Call the last planet Minerva. That was one contender for Uranus’s name way back when.
I imagine feminists will be happy to see a few more “goddess” names among the “gods”. Up to now there was just one – Venus {unless we call earth Terra or Gaia, but that would be cheating ;-)}.”
AMEN to that! We need EQUALITY in our male-dominated solar system! We have enough planets named after male deities, let’s give the ladies a shot for once! I agree that “Xena”, named for the Large-Breasted Amazon goddess of ass-kicking and lesbo deep-kissing, was a BAD idea thought up by those few geeks down at the lab who watch WAY too much BAD TV. As a placeholder name, it’s okay…. MARGINALLY. We need to find a better name for this new rock, and soon.
OOps! I goofed up there! Seems 2003 UB313 and its moon are actually Xena. Celestia gives no real frame of reference re: location sometimes, so I sometimes get stuck. Just wanted to point out the earlier gaffe.
My bad.
Xena’s moon is Gabrielle, IIRC.
ROTFLMAO. *sigh* When will these people EVER learn?
How about the saints? Are there enough of them for all of the KBOs and Centaur objects?
Ceres is spherical, so is Vesta (though a big chunk got taken out of it, Juno is pretty close, Pallas isn’t, but why I don’t think we know. They are quite unlike the fragments otherwise known as asteroids, aka planetismals.
Wonder why the IAU threw out Planet, planetoid, planetismal, and even Centaur and Plutino or KBO?
The Norse frost giants for the largest Plutinos, until we run out of names?
Whaddabout ‘Planet Lucas’? Is everyone forgetting the Tolkien pantheon?
I just figured that since George Lucas was eventually gonna get a planet named after him, why not do it now?
“Planet Gollum”, anyone? Or maybe even “Galadriel”?
Oh no, no, no! Nothing can be named after a CATHOLIC saint! What are you thinking? The ACLU would be all over that. And Tolkein (and LOTR characters)? No, he was Catholic, so forget that, too. How about Planet Carl Sagan? Now there is a good atheist who the ACLU would be more than happy to have a planet named for.
“Billyuns and Billyuns of aeons ago….” LOL….
I still think we should at least name one of them “Death Star”. Or Hell name the ball o’ rock after George Lucas or something.
Jimmy:
There are two television references… after all, don’t we have a lot of TV Ceres!
I know — groan! — but, being a baseball fan as well as an amateur astronomer, at least I didn’t make a crack about the World Ceres!
Pax
I heard that one of the planets was going to be named after an Eskimo Goddess. No way, they should all have Greco-Roman names to keep the current nomenclature.
Any chance of changing Charon and Xena to Goofy and Minnie?
No, let’s keep the evil that is DISNEYCORP LTD.(We own EVERYTHING)out of this. The only good movies they made were TRON and The Black Hole.
Obviously this is a chance to rename the planets after the Apostles.
Nah, we’d need 4 more after John, Paul, George and Ringo.