Skip to comments.Astronomers say Pluto is not a planet (Eight Planets)
Posted on 08/24/2006 7:18:05 AM PDT by Lunatic Fringe
PRAGUE, Czech Republic - Leading astronomers declared Thursday that Pluto is no longer a planet under historic new guidelines that downsize the solar system from nine planets to eight.
After a tumultuous week of clashing over the essence of the cosmos, the International Astronomical Union stripped Pluto of the planetary status it has held since its discovery in 1930. The new definition of what is and isn't a planet fills a centuries-old black hole for scientists who have labored since Copernicus without one.
Although astronomers applauded after the vote, Jocelyn Bell Burnell a specialist in neutron stars from Northern Ireland who oversaw the proceedings urged those who might be "quite disappointed" to look on the bright side.
"It could be argued that we are creating an umbrella called 'planet' under which the dwarf planets exist," she said, drawing laughter by waving a stuffed Pluto of Walt Disney fame beneath a real umbrella.
The decision by the prestigious international group spells out the basic tests that celestial objects will have to meet before they can be considered for admission to the elite cosmic club.
For now, membership will be restricted to the eight "classical" planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Much-maligned Pluto doesn't make the grade under the new rules for a planet: "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit."
Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's.
Instead, it will be reclassified in a new category of "dwarf planets," similar to what long have been termed "minor planets." The definition also lays out a third class of lesser objects that orbit the sun "small solar system bodies," a term that will apply to numerous asteroids, comets and other natural satellites.
It was unclear how Pluto's demotion might affect the mission of NASA's New Horizons spacecraft, which earlier this year began a 9 1/2-year journey to the oddball object to unearth more of its secrets.
The decision at a conference of 2,500 astronomers from 75 countries was a dramatic shift from just a week ago, when the group's leaders floated a proposal that would have reaffirmed Pluto's planetary status and made planets of its largest moon and two other objects.
That plan proved highly unpopular, splitting astronomers into factions and triggering days of sometimes combative debate that led to Pluto's undoing.
Now, two of the objects that at one point were cruising toward possible full-fledged planethood will join Pluto as dwarfs: the asteroid Ceres, which was a planet in the 1800s before it got demoted, and 2003 UB313, an icy object slightly larger than Pluto whose discoverer, Michael Brown of the California Institute of Technology in Pasadena has nicknamed Xena.
Charon, the largest of Pluto's three moons, is no longer under consideration for any special designation.
The New Horizons mission statement needs rewritten. It is no longer headed to the outermost planet.
Somebody needs to go get these scientists a date.
If they had just one they would so not care about this.
To get an idea of comparative dimensions:
That being the case, I can see some arguing Pluto hardly deserves to be a planet, but the fact is that Pluto is now going to be classified as a planet...just a "Dwarf Planet". I am a bit surprised, as I expected it be re-classified as a "Binary Planet." I.e.,:
Under proposed International Astronomical Union definitions, two planets that orbit each other around a barycenter (or center of mass) between them are a binary planet. Those same definitions would expand the "family" of planets to include Charon, promoting Pluto's large companion from moon to planet and securing the pair's status as the first and (so far) only binary planet in the solar system.
"Binary planet" is a term often used to describe any pair of worlds that are similar in mass. Each orbits the other around a gravitational balance point that is between the two - a location called the center of mass. When one object has a much bigger mass and the objects are far apart then the center of mass is close to the center of the bigger object and the bigger object hardly moves. This is the case of the Earth orbiting the Sun - the Sun's moves only 0.0003 of its diameter due to the gravity of the Earth in its yearly orbit. In the case of Pluto and Charon, separated by 17 Pluto radii, the ratio of their masses is 8:1 so that the center of mass is outside Pluto.
Mercury isn't very big either, although it is very bright as seen from earth.
Instead of "My very excellent mother just served us nine pizzas" it will now be "My very excellent mother just served us nachos."
Mercury is even smaller than Ganymede and Titan.
Still, if I'd had a vote (which I don't) I would have voted for Pluto too, for historical reasons and so the public won't think science is too malleable a concept. Besides, it seems cheesy to do this so close to Clyde's death.
What is the name of the spacecraft headed to Mercury now? Hermes? Mercury is heavy, mostly iron core.
Poor Neptune!!! ;)
When I have great-grand kids and I tell them Pluto use to be a planet, I wonder what they'll say?
Yeah, and diamonmds are a girl's best friend.
So let's see...compare...dogs vs diamonds....
Care to speculate as to which sex contrived those rules?
Shhhhh! Are you crazy? Talk like that on an Evo thread and you'll be burned at the stake as a heretic!
No, Moderator, this was not an attempt to hijack this thread. It was just a piquant piece of cross-threaded humor.
Well Dagobah might not be a planet... but Uranus sure is!
LOL ....... your comment makes FR worthwhile.
But it's always been a planet. I don't think these guys have much respect for stare decisis! (Pun intended - actually it was the only reason for the post.)
What NASA will discover upon arrival:
It make sense. If Pluto got to be a planet, then why not Goofy? And once Goofy's a planet, where does it stop?!
Now my horoscope is all messed up.
My Very Educated Mother Just Served Us Nachos.
Sigh. Scientists are so subjective.
I strongly disagree. I think the most reasonable decision would have been to accept the first proposal and the idea of terrestrial, gas giants, and dwarf planets (didn't like the name pluton, but dwarf planet would have been fine). This new definition is entirely unacceptable in my book.
It doesn't matter. What counts is what they are called at the UN. Celestial bodies. Things we cannot mine or otherwise disturb.
Also, under this new system of categorization, a "dwarf planet" isn't considered a planet at all. It's bizarre. Only a very small fraction of the world's astronomers voted at all. Hopefully, this awful decision will be overturned soon and we can get something like terrestrial, gas giants, and plutons/dwarf planets, ALL of which should be considered planets. Thank God an intelligent astronomer is leading the charge to overturn this farce.
It's interesting to read my old Abell astronomy text, Exploration of the Universe ( 1964 ). It cites the discrepancy between the large estimated mass ( 0.9 Earth-mass ) and its "small" estimated diameter ( by Kuiper! ) of 3600 miles ( Now determined to be 1400 miles.)
Abell takes the mass very seriously as this was the whole basis for its discovery, even though he notes that it was determined to be too small to cause the perturbative effects that Lowell thought he had determined. He notes that Lowell "has justly earned the honor for its discovery," but this did not hold up, of course.
Pluto's stature has clearly been diminished with time, so its demotion can be seen as acknowledgment of a mistake. OTOH, it was discovered optically, and even if it represents a class of outer objects, it was the only one known for many years, and I don't see anything wrong with a "freeze" in the nomenclature extant for the last seventy years.
Planethood is, after all, a rhetorical and even a poetical designation. Pluto stands as the outpost of the solar system, and its name is perfect.
I wonder if this change will not suffer the fate of "New Coke". Perhaps popular usage will ignore the authority of this commision, or whatever it is, and adhere to the "Classic Planets".
It's not going to unEARTH anything! It will have to "... unpluto more of its secrets"! :-)
Pluto will always be the ninth planet.
Michael Brown had a page on his university website saying (a few years ago) that the then-recent discovery of a large (but not as large as Pluto) body should not be considered the discovery of a planet. But when UB313 was announced (and after all the controversy over who actually discovered it died down), he changed his mind. He seemed to change it again when the seven-member panel unveiled its recommendations. Soooo, I guess being a turncoat has cost him a planet, and FWIW, a fan (me).
Pluto isn't a planet, its a KBO, and it joins thousands of others.
If Pluto is a planet, then so is Ceres and Xena and perhaps Sedna and Quaror.
LOL! This group of astronomers can go be fruitful and multiply, but not in those words. [adapted from Woody Allen]
No, Neptune is on the eplictic plane that all the other planets are on, Pluto overlaps Netpunes orbit, not the other way around.
All the planets orbit in essentially the same allignment relative to the sun, pluto's orbit is several degrees off of that which all the other planet's orbit.
Layman here checking in. Intuitively, I agree with the decision, though "planetary status" will become less and less important the better technology does in identifying KBOs and even big stuff in the Oort Cloud.
Pluto will remain in its eccentric orbit, and as a nice relic of history and, perhaps, a catalyst in the art of astronomy. This sounds more and more like a scientific GroupThink dynamic. In the big scheme of things, there's still a google of research to be done out there, and every solar system discovery, no matter how seemingly mundane, still is exciting in the context of how hard scientists are working on these things.
I'd only heard recently of Ceres - that asteroid thingy that's spherical and has a regular orbit. Anyone have an orbit graphic for it? Absolute Magnitude?
"The Ecliptic is the plane of the Earth's orbit. Most of the planetary orbits are close to this plane. Pluto's orbit is inclined at an angle of 17.14 degrees to the ecliptic plane - the largest deviation of any planet." -- http://pluto.jhuapl.edu/science/glossary.html
Mercury -- "Its orbit is inclined to the plane of the ecliptic by 7 degrees (The plane of the ecliptic is the plane of the Earth's orbit. All planets orbit in planes that are nearly the same as that of the Earth.)."
Venus -- "Its orbit is inclined at an angle of 3.4 degrees."
Mars -- "The orbit's eccentricity is 0.093 at an inclination of 1.9 degrees."
Jupiter -- "The orbit has an eccentricity of 0.048 at an inclination of 1.3 degrees."
Saturn -- "Its orbit has an eccentricity of 0.056 with an inclination of 2.5 degrees."
Uranus -- "The orbit has an eccentricity of 0.047 and an inclination of 0.8 degrees."
Neptune -- "It has an eccentricity of 0.009 and an inclination of 1.8 degrees."
Please forgive my ignorance, but would the relative lack of eccentricity WRT Neptune and Terra Firma on the Ecliptic indicate something like Neptune being a dying star of sorts, perhaps central to the formation of Earth - sort of like us all exploding outward from somewhere else and settling around nice ol' Sol? What also confuses is the retrograde rotation of Uranus (or is it Neptune?).
Great thread, thank you so much for keeping this beancounter on your ping list.
OK - Back in the day, planets orbited stars/suns... moons orbited planets...
Now, moons orbit stars/suns while being orbited by moons and being continually billed by Orbitz.
Man. This was much easier in grade school.
We were just born too damned soon.
Neptune is smaller in diameter than Uranus, but a bit more massive; neither Neptune nor the other planets should be considered stars (dying or otherwise); Uranus is the planet with the axis tipped nearly into the ecliptic, IOW, one or the other of its polar regions faces the Sun during part of its orbit. Which is pretty wild.
Uranus should be excluded, its origin is obviously different from the other planets, and its axis is too freaky. :')
Now that Pluto is removed, Mercury is the smallest, and is too small, and its orbit is in precession, making it too weird to be considered one of the planets. :')
With the removal of Mercury, Venus is the only one left without a moon, which makes it too strange to remain. Out it goes. :')
Mars is also too small, and is less dense than the Earth. Also, it doesn't have proper moons (just oddly shaped space debris). Out it goes. :')
There are therefore only four planets -- Earth, Jupiter, Saturn, and Neptune.
Point very well-taken. I almost thought you were being facetious... ;-) FOUR! NO MORE!
So is the plane of an axial rotation due to solar magnetism or is magnetism the result of the axis? My guess would be the latter, because ions going 30-odd AU into the frozen void shouldn't have caused dramatic rotational tilting unless, as is possible in my pet barstool paradigmatic cosmology tonight, that Sol is merely where the Solar System settled, rather than being proximal to its origin.
Off to bed. Give it some thought (and put me on your GGG list, if you don't mind).
So is the plane of an axial rotation due to solar magnetism or is magnetism the result of the axis? My guess would be the latter, because ions going 30-odd AU into the frozen void shouldn't have caused dramatic rotational tilting unless, as is possible in my pet barstool paradigmatic cosmology tonight, that Sol is merely where the Solar System settled, rather than being proximal to its origin.Uranus is a puzzle from a uniformitarian perspective, although a number of ideas have been put forward. Since the Uranian moon system appears to be pretty conventional (unlike that of Neptune) it seems likely that the tipped axis of the planet was caused by something after the moons entered orbit (regardless of their origin). If it was caused by an impact, then it must have been one doozy of an impact.
Uranus: Magnetic Field And MagnetosphereIf the intrinsic magnetic field of Uranus had been nearly aligned with the rotational axis, as the planets previously visited were, the polar axis of the magnetosphere, or the polar cusp as it is called, would have been aligned with the solar wind flow as Voyager flew by the planet. Ironically, the magnetic axis of the intrinsic magnetic field of Uranus was far from spin axis-aligned, so that the solar wind blew nearly perpendicular to the magnetic axis, as it does at Mercury, Earth, Jupiter and Saturn. Thus, while Uranus has an unusual intrinsic magnetic field, the resulting magnetosphere was found to be very Earth-like.
by C. T. Russell and J. G. Luhmann
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