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If gravity is required, what are the planets in the SolarSystem?
http://www.spacedaily.com/news/outerplanets-04b.html
According to an article on SpaceDaily, planetary scientist S. Alan Stern suggests that the deciding factor in deciding whether or not a body is a planet should be gravity. If a body is rounded by its own gravity, then it should be considered a planet. If this were the rule that decides what is a planet, what would be the planets in the Solar System? Mr. Stern mentions Pluto, Sedna and Ceres along with several asteroids and large Kuiper Belt Objects. What would the planet count be in the Solar System and what would be the total list of planets? |
#3
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If gravity is required, what are the planets in the SolarSystem?
No body in the Solar System is round. I assume that
you'd have to go by some sort of percentage deviation from a iso-potential surface. Perhaps he meant "roundish"? Just off the top of my head, we'd add: Earth's Moon, Io, Europa, Ganymede, Callisto, Titan, Titania, Triton, and Charon. If we take it all the way down to Ceres' size / sphericity it'll be a mess. The big question is, where's the dividing line and WHY? Maybe I was just reading between the lines, but I got the impression that he was going on the principal that planets orbit a star and moons orbit a planet which orbits said star. That would leave out all of the moons that you listed. Since you seem violently against such criteria, what would you suggest as a criteria for determining whether an object is a planet? |
#4
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If gravity is required, what are the planets in the Solar System?
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#5
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If gravity is required, what are the planets in the Solar System?
"quilty" kirjoitti viestissä
om... No body in the Solar System is round. I assume that you'd have to go by some sort of percentage deviation from a iso-potential surface. Perhaps he meant "roundish"? Just off the top of my head, we'd add: Earth's Moon, Io, Europa, Ganymede, Callisto, Titan, Titania, Triton, and Charon. If we take it all the way down to Ceres' size / sphericity it'll be a mess. The big question is, where's the dividing line and WHY? Maybe I was just reading between the lines, but I got the impression that he was going on the principal that planets orbit a star and moons orbit a planet which orbits said star. That would leave out all of the moons that you listed. Since you seem violently against such criteria, what would you suggest as a criteria for determining whether an object is a planet? Gravity is proportial to mass. If all objects are put in a same list in the order of their mass we can see that there are some clear limits of different groups: 1.Sun is a star, it is a thousand times as massive as the biggest planet Jupiter. 2. The giant gas planets are clearly one group. 3.The terrestial planets could be considered another group as the smallest gas planet Uranus is 14.6 times more massive than Earth. However both these groups are clearly planets. Both groups have roughly as massive metal and stone cores. 4. The moons, asteroids, comets and kuiper belt objects(KBO) are clearly smaller in size. The smallest planet Mercury is 4,5 times more massive than biggest of them, our Moon. 5. Pluto is 18.4 times lighter than the smallest planet Mercury, so it is not a planet by weight. It is clearly a Kuiper belt object, the biggest, but only slightly bigger than the next 100 KBOs known today and belongs to that group. There are many moons bigger than Pluto. Pluto is called a planet only because it was found years before other KBOs |
#6
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If gravity is required, what are the planets in the Solar System?
In article ,
"Jarvi" wrote: 4. The moons, asteroids, comets and kuiper belt objects(KBO) are clearly smaller in size. The smallest planet Mercury is 4,5 times more massive than biggest of them, our Moon. Our Moon is not the biggest of these, by mass or by radius. Sorting by radius: Name Orbits Dist(km) Rad(km) Mass(kg) ---- ------ -------- ------- -------- Mars Sun 227940 3398 6.42e23 Ganymede Jupiter 1070 2631 1.48e23 Titan Saturn 1222 2575 1.35e23 Mercury Sun 57910 2439 3.30e23 Callisto Jupiter 1883 2400 1.08e23 Io Jupiter 422 1815 8.93e22 Moon Earth 384 1738 7.35e22 Europa Jupiter 671 1569 4.80e22 .....and sorting by mass, we have: Name Orbits Dist(km) Rad(km) Mass(kg) ---- ------ -------- ------- -------- Mars Sun 227940 3398 6.42e23 Mercury Sun 57910 2439 3.30e23 Ganymede Jupiter 1070 2631 1.48e23 Titan Saturn 1222 2575 1.35e23 Callisto Jupiter 1883 2400 1.08e23 Io Jupiter 422 1815 8.93e22 Moon Earth 384 1738 7.35e22 Europa Jupiter 671 1569 4.80e22 So, not to pick a nit, but our Moon is smaller than Ganymede, Titan, Callisto, and Io no matter how you look at them. Also, Mercury is smaller than Ganymede and Titan by radius, and only about a factor of 2 larger than Ganymede by mass -- about the same as the difference between Mercury and Mars. So I don't see a clear distinction between planets and moons here. ,------------------------------------------------------------------. | Joseph J. Strout Check out the Mac Web Directory: | | http://www.macwebdir.com | `------------------------------------------------------------------' |
#7
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If gravity is... Joe Strout is right
Joe Strout is right below. Thank you Joe, for correcting my error. I had
forgotten the biggest moons: Ganymede, Titan callisto and Io. The right conclusion is: All planets, moons, asteroids, Kuiper belt objects, comets (and other Oort cloud objects) orbiting our Sun form by mass a continuous serie where are no major gaps in relative mass between two following objects smaller than Earth untill microscopic dust particles. However There is major gap in mass 43:1 between the smallest terrestial planet Mars and Pluto. So we should not call Pluto a planet, if we do not call all Kuiper belt objects planets as they all form another continous series by mass with no major gaps by mass. Antti Järvi "Joe Strout" kirjoitti viestissä ... In article , "Jarvi" wrote: 4. The moons, asteroids, comets and kuiper belt objects(KBO) are clearly smaller in size. The smallest planet Mercury is 4,5 times more massive than biggest of them, our Moon. Our Moon is not the biggest of these, by mass or by radius. Sorting by radius: Name Orbits Dist(km) Rad(km) Mass(kg) ---- ------ -------- ------- -------- Mars Sun 227940 3398 6.42e23 Ganymede Jupiter 1070 2631 1.48e23 Titan Saturn 1222 2575 1.35e23 Mercury Sun 57910 2439 3.30e23 Callisto Jupiter 1883 2400 1.08e23 Io Jupiter 422 1815 8.93e22 Moon Earth 384 1738 7.35e22 Europa Jupiter 671 1569 4.80e22 ....and sorting by mass, we have: Name Orbits Dist(km) Rad(km) Mass(kg) ---- ------ -------- ------- -------- Mars Sun 227940 3398 6.42e23 Mercury Sun 57910 2439 3.30e23 Ganymede Jupiter 1070 2631 1.48e23 Titan Saturn 1222 2575 1.35e23 Callisto Jupiter 1883 2400 1.08e23 Io Jupiter 422 1815 8.93e22 Moon Earth 384 1738 7.35e22 Europa Jupiter 671 1569 4.80e22 So, not to pick a nit, but our Moon is smaller than Ganymede, Titan, Callisto, and Io no matter how you look at them. Also, Mercury is smaller than Ganymede and Titan by radius, and only about a factor of 2 larger than Ganymede by mass -- about the same as the difference between Mercury and Mars. So I don't see a clear distinction between planets and moons here. ,------------------------------------------------------------------. | Joseph J. Strout Check out the Mac Web Directory: | | http://www.macwebdir.com | `------------------------------------------------------------------' |
#8
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If gravity is required, what are the planets in the Solar System?
Jarvi wrote:
3.The terrestial planets could be considered another group as the smallest gas planet Uranus is 14.6 times more massive than Earth. However both these groups are clearly planets. Both groups have roughly as massive metal and stone cores. 4. The moons, asteroids, comets and kuiper belt objects(KBO) are clearly smaller in size. The smallest planet Mercury is 4,5 times more massive than biggest of them, our Moon. 5. Pluto is 18.4 times lighter than the smallest planet Mercury, so it is not a planet by weight. It is clearly a Kuiper belt object, the biggest, but only slightly bigger than the next 100 KBOs known today and belongs to that group. There are many moons bigger than Pluto. Pluto is called a planet only because it was found years before other KBOs This is not quite that straightworward - there are moons in this system that fit very well inbetween the mass of mars and mercury. -- Sander +++ Out of cheese error +++ |
#9
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If gravity is required, what are the planets in the Solar System?
quilty wrote:
No body in the Solar System is round. I assume that you'd have to go by some sort of percentage deviation from a iso-potential surface. Perhaps he meant "roundish"? Just off the top of my head, we'd add: Earth's Moon, Io, Europa, Ganymede, Callisto, Titan, Titania, Triton, and Charon. If we take it all the way down to Ceres' size / sphericity it'll be a mess. The big question is, where's the dividing line and WHY? Maybe I was just reading between the lines, but I got the impression that he was going on the principal that planets orbit a star and moons orbit a planet which orbits said star. That would leave out all of the moons that you listed. Since you seem violently against such criteria, what would you suggest as a criteria for determining whether an object is a planet? The Sun's gravitational pull on the Moon is greater than the Earth's. The moon is orbiting the Sun. --Jeff -- A man, a plan, a cat, a canal - Panama! Those who do not learn from history are doomed to repeat it. --George Santayana Unthinking respect for authority is the greatest enemy of truth. --Albert Einstein Freedom's just another word for nothing left to lose. --Kris Kristofferson |
#10
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If gravity is required, what are the planets in the Solar System?
I thought it had to do with orbit. If it orbits a sun, it's a planet. If it
orbits a planet it's a moon. Large elliptical orbits by tiny objects don't count as planets. Comets and asteroids can't have moons because of insufficient mass, therefore can't be planets. Another line of reasoning might be that what we call it is what it is. You could have a planet floating around in deep space that has escaped it's sun or the sun burnt out. A lost planet? A rogue moon? "quilty" wrote in message m... http://www.spacedaily.com/news/outerplanets-04b.html According to an article on SpaceDaily, planetary scientist S. Alan Stern suggests that the deciding factor in deciding whether or not a body is a planet should be gravity. If a body is rounded by its own gravity, then it should be considered a planet. If this were the rule that decides what is a planet, what would be the planets in the Solar System? Mr. Stern mentions Pluto, Sedna and Ceres along with several asteroids and large Kuiper Belt Objects. What would the planet count be in the Solar System and what would be the total list of planets? --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.658 / Virus Database: 421 - Release Date: 4/9/2004 |
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