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A New Definition Would Add 102 Planets To Our Solar System -- Including Pluto (washingtonpost.com)
The Grim Reefer quotes a report from The Washington Post: Is Pluto a planet? It's not a question scientists ask in polite company. "It's like religion and politics," said Kirby Runyon, a planetary scientist at Johns Hopkins University. "People get worked up over it. I've gotten worked up over it." For years, astronomers, planetary scientists and other space researchers have fought about what to call the small, icy world at the edge of our solar system. Is it a planet, as scientists believed for nearly seven decades? Or must a planet be something bigger, something more dominant, as was decided by vote at the International Astronomical Union (IAU) in 2006? The issue can bring conversations to a screeching halt, or turn them into shouting matches. "Sometimes," Runyon said, "it's just easier not to bring it up." But Runyon will ignore his own advice this week when he attends the annual Lunar and Planetary Science Conference in Houston. In a giant exhibit hall crowded with his colleagues, he's attempting to reignite the debate about Pluto's status with an audacious new definition for planet -- one that includes not just Pluto, but several of its neighbors, objects in the asteroid belt, and a number of moons. By his count, 102 new planets could be added to our solar system under the new criteria. USA Today reports: "In the mind of the public, the word 'planet' carries a significance lacking in other words used to describe planetary bodies," the proposal states. "In the decade following the supposed 'demotion' of Pluto by the International Astronomical Union, many members of the public, in our experience, assume that alleged 'non-planets' cease to be interesting enough to warrant scientific exploration."
He's a dog!
-=This sig has nothing to do with my comment. Move along now=-
Nothing should be called a moon if it doesn't have the gravity to produce plasticity in the rock.
Actually, I think most planets exists in a vacuum.
640k planets ought to be enough for anybody.
And then Ptolemy's geocentric model put Sun and Moon in a special group, because differently than the other planets, they never change direction in the sky, which the others do. Thus, the trajectories of Sun and Moon were easy, while the other planets needed cycles and epicycles to describe. This was one of the reasons, Nicolaus Copernicus came up with the heliocentric model, because then it made sense why Sun and Moon were "circular" wanderers, while the other planets were "epicyclic" wanderers, So, Sun and Moon were no longer considered planets, a position already shaky in the Ptolemian model. But it added Earth as a new planet. Copernicus' system didn't come up with good predictions of the planetary positions though, thus it wasn't widely accepted and even considered heretic by the Catholic Church. Johannes Kepler improved on the predictive power of the Copernican system, but Ptolemy's model was so finely tuned by now that it still was preferred for practical reasons. Galileo Galilei's discovery of the Iovian Moons gave credibility to the Keplerian model, but for navigational and other purposes, Ptolemy was still more exact. And it created a new class of celestial bodies: Suddenly, there wasn't one Moon, there were several moons out there. From a classical point of view, all moons were planets too: no fixed positions within the stellar constellations. At the end of the 17th century, Isaac Newtons Theory of Gravity gave a better model, Ole Roemer's discovery of the Speed of Light added some clues, and finally, the heliocentric model was better at predicting planetary (and lunar) positions than Ptolemy. But then a flood of new discoveries of celestial bodies clouded the view again: Uranus, Ceres and finally Neptune were discovered, and then all the other asteroids circling the Sun between Mars and Jupiter. Somehow the size of the Earth moon was used as a cut-off: Everything larger than the Moon circling the Sun was considered a planet, everything else an asteroid (which literally means "star like"). It was as arbitrary as anything else, but the Moon was close by and well studied, so for practical purposes, it made sense.
When Pluto was discovered, it became planetary status, because at first, its size could not be determined from direct observation, only because of the brightness (15 mag), it was at first considered to be Earth sized. So it got the planetary status. Later there were better pictures with larger resolution, and the estimated size shrank down to ~2500 km in diameter, and in the same way, the estimated reflectiveness (albedo) increased, so in the 1980ies, Pluto was considered a "dirty snowball", consisting mainly of water ice mixed with planetary rock. Thus the cut-off point "Moon size" was crossed, and doubts about Pluto's nature as a planet arised. It was speculated that it was a former Neptune moon losing its orbit. And when the next transneptunian objects were discovered, like Eris, with about the same size than Pluto, the whole "what is a planet" question became virulent. Simple enumeration as in "The planets are those nine celestial objects we call Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune and Pluto" didn't work anymore, and a meaningful definition which included Pluto, but not too many other newly discovered objects, wasn't readily available.
All planets are within the heliosphere, the region where the solar wind is not countered by interstellar medium. It does cause a very slight amount of orbital decay, but it's much closer to a vacuum than can be easily obtained on Earth. It was very exciting for some of us when Voyager left the heliosphere in 2012 and was _still working_.
The last time this was discussed on slashdot there was a very interesting series of comment posted by Rei that shed a lot of light on what the issues surrounding this are and how the situation (and redefining what a planet is) came to be.
The proposed definition can be found at words 765-799 of the article.
A planet, he says, is anything massive enough that gravity pulls it into a sphere (a characteristic called “hydrostatic equilibrium"), but not so massive that it starts to undergo nuclear fusion and become a star.
The preceding 764 words are a useless regurgitation of how people feel about definitions in general and Pluto in particular. Spare me.
"We reject as false the choice between our safety and our ideals." --The American President (20.1.2009)
Just wait until you see all the Sailor Moon sequels this can start!
#naabhaprzrag, #sverubfr-000, #agi-fcbafberq, negvpyr[pynff*=' negvpyr-ary-'] { qvfcynl: abar !vzcbegnag; }
A planet is any object in orbit around a star, of sufficient mass to reach hydrostatic equilibrium, has not reached critical mass to achieve stellar fusion, and is the most prominent body in its orbit and neighborhood. That definition is going to add a few more planets but not many.
The suggested definition from TFA is just as terribly obtuse as the 2006 definition. Even worse is the suggestion to change the word 'planet' to become an all encompassing term that now also means most smaller bodies as well (but not all). It makes things unnecessarily confusing. This just seems tantamount to two-year-old logic where one word now means everything.
And look, my suggested definition expands.
A moon is any object in orbit around a planet, of sufficient mass to reach hydrostatic equilibrium, and is the most prominent body in its orbit and neighborhood.
A moonroid (haha maybe?) is any object in orbit around a planet, has not reached critical mass to achieve hydrostatic equilibrium, and is shares its orbit and neighborhood with other objects of similar mass.
An asteroid is any object in orbit around a star, has not reached critical mass to achieve hydrostatic equilibrium, and is shares its orbit and neighborhood with other objects of similar mass.
And so on. The hydrostatic equilibrium is critical to defining celestial bodies but it shouldn't be the only requirement to define a planet.
Well, then, it's time to start teaching that there's only 8 rivers in the world, and all others are dwarf rivers and don't count as rivers. And 8 bones in the human body, the rest being dwarf bones that aren't really bones. And 8 particles in physics, and all others dwarf particles and don't count as particles. And 8 galaxies in the universe.... you get the picture.
Since we're apparently going into shouting mode, Pluto IS FAR MORE LIKE THE TERRESTRIAL PLANETS THAN THE TERRESTRIAL PLANETS ARE LIKE THE GAS GIANTS. If anything should be kicked out of the planet club, it's the gas giants.
The issue isn't whether KBOs should have their own classification. They do: KBOs. The question is whether it makes sense to group dissimilar objects (terrestrial planets and gas giants) but artificially exclude other objects in hydrostatic equilibrium, objects with active geology, internal differentiation, fluids, and all of the other hallmarks we associate with planets. Nature has given us a very clear dividing line: objects in hydrostatic equilibrium are where you go to see tectonics, mineralization, fluids, search for life, etc, while objects not in hydrostatic equilibrium are where you go to learn about the formation of the solar system, find its building blocks, learn about what life was built from, etc. Nature rarely gives us such meaningful dividing lines, but in this case, it has, and we should respect it.
Aeris Died For Your Sins.