Considering the scale of the universe, I wonder why they bothered to demote it. Maybe they wanted to before it reached it's centennial anniversary as a discovered planet. I wonder what the criteria is now for the various classes.
Pluto, a planet since 1930, got the boot because it didn't meet the new rules, which say a planet not only must orbit the sun and be large enough to assume a nearly round shape, but must "clear the neighborhood around its orbit." That disqualifies Pluto, whose oblong orbit overlaps Neptune's, downsizing the solar system to eight planets from the traditional nine.
As scientists, the astronomers did not have much choice, IMO. There is at least one "trans-Neptunian object", 2003 UB313, that is larger than Pluto. If Pluto stayed a planet, then what to do with this new one.
The same announcement that downgraded Pluto upgraded 4 other objects based on the new definition so apparently we now have 12 planets.
I find it interesting that a group of several hundred of the smartest people on the planet have nothing better to do than to spend thousands (millions?) of man hours developing the first technical definition of a "planet". If Newton et al had bothered to write down a bad definition a few centuries back then just think what these big-brains could have done with the last couple of years.
Stupid question. If Pluto was demoted because it does not clear neptune out of it's path then why was neptune not demoted for not clearing pluto out of it's path?
Pluto’s demotion was a long time coming. Even my old astronomy textbook put Pluto into a class outside of the major planets and into Plutonian objects and other ‘space debris’. There was a theory at one time that Pluto is an ejected moon of Neptune. That theory fell out of favor with the discovery of Charon, Pluto’s moon that is nearly the size of Pluto itself.
The most popular working theory now is that Pluto used to be larger and that its moon was created by a large impact that broke the small planet into two nearly equal-sized chunks. Another theory is that it never re-coalesced into a planet due to the gravitational influence of Neptune.
The concept of a planet is not so much a scientific one, but a cultural one. It started out as something to describe celestial objects that did not behave as the stars. The planets appeared to wander and engage in odd behavior like retrograde motion. I think Pluto was kept in as a planet because so much effort was used to find it, and it’s the only planet to be discovered by an American. Only later with additional knowledge did the mistake become more apparent.
I think now that Pluto is out, the IAU will come up with a scientific definition of a planet instead of the culturally-based definition that has been used for so long.
"If you are going to walk on thin ice, you might as well dance!"
M 7 0
V 3 24
E 0 0
M 1 51
J 1 18
S 2 30
U 0 46
N 1 47
P 17 09
The plane of the Earth's orbit is called the plane of the ecliptic, it is a fairly arbitrary datum, but at least we know where it is.
The accepted wisdom is that all the home-grown planets were all formed out of the same spinning disc of pre-stellar material. So all the gas in that cloud had the same angular momentum vector, so their spin vectors were aligned, even after they clumped.
Even odder is the phenomenon of orbital resonance, which is one of the reasons why Pluto and Neptune have never said hello.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
There are at least 70,000 "trans-Neptunians" with diameters larger than 100 km in the radial zone extending outwards from the orbit of Neptune. There is a vast population of small bodies orbiting the sun beyond Neptune. This kind of ring is called the kuiper belt. Pluto is not a planet. Pluto is more a system of moons composed by Pluto, Charon (Pluto's satellite) and 2003 UB313.These moons, with complex orbits between them, are called KBO (kuiper belt objects), asteroids or comets composed of rock ice.
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