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what (if anything) "defines" an orbit as being "cometary" vs "asteroidal"?



 
 
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  #1  
Old December 22nd 18, 09:22 PM posted to sci.astro.amateur
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Default what (if anything) "defines" an orbit as being "cometary" vs "asteroidal"?

Is there some combination of orbital element values that establishes the orbit of a minor solar system body as being "cometary" as opposed to "asteroidal"? Something akin to "eccentricity 0.6, inclination 30d (or retrograde)"? I understand that highly-inclined, highly-eccentric orbits are more likely to be those of a comet than are those orbits with low such values, but are these parameters actually "defined"? (My question is about the orbit itself, not the body - I understand that comets can have "asteroidal orbits" (e.g. 29P) and that asteroids can have "cometary orbits" (e.g. 2006 EX52))
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  #2  
Old December 23rd 18, 03:13 AM posted to sci.astro.amateur
Quadibloc
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Default what (if anything) "defines" an orbit as being "cometary" vs "asteroidal"?

On Saturday, December 22, 2018 at 2:22:36 PM UTC-7, wrote:
Is there some combination of orbital element values that establishes the orbit
of a minor solar system body as being "cometary" as opposed to "asteroidal"?
Something akin to "eccentricity 0.6, inclination 30d (or retrograde)"? I
understand that highly-inclined, highly-eccentric orbits are more likely to be
those of a comet than are those orbits with low such values, but are these
parameters actually "defined"? (My question is about the orbit itself, not the
body - I understand that comets can have "asteroidal orbits" (e.g. 29P) and that
asteroids can have "cometary orbits" (e.g. 2006 EX52))


Yes, there is, and I believe cometary orbits are ones with such a high
eccentricity that it's hard to tell that they're not parabolic. I can't find the
definition online, I suspect it's something like an eccentricity 0.9 .

John Savard
  #3  
Old December 23rd 18, 03:54 AM posted to sci.astro.amateur
palsing[_2_]
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Default what (if anything) "defines" an orbit as being "cometary" vs "asteroidal"?

On Saturday, December 22, 2018 at 7:13:56 PM UTC-8, Quadibloc wrote:

Yes, there is, and I believe cometary orbits are ones with such a high
eccentricity that it's hard to tell that they're not parabolic. I can't find the
definition online, I suspect it's something like an eccentricity 0.9 .


Well, I don't know the answer, but a quick search turned up this NASA page...

https://nssdc.gsfc.nasa.gov/planetar...cometfact.html

.... where there is a list of 20 "selected" comets, and if I counted correctly, 5 have eccentricities greater than 0.9 and 15 have eccentricities less than 0.9... so perhaps your suspicions are incorrect... but then, this is just one reference...

In general, it looks like the comets with long periods are 0.9 and those with much shorter periods are 0.9. Also, in general for the comets on that list, the high eccentricity comets have much higher orbital inclinations.

\Paul A
  #4  
Old February 16th 19, 07:13 PM posted to sci.astro.amateur
corvastro
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Default what (if anything) "defines" an orbit as being "cometary" vs "asteroidal"?

On Saturday, December 22, 2018 at 1:22:36 PM UTC-8, wrote:
Is there some combination of orbital element values that establishes the orbit of a minor solar system body as being "cometary" as opposed to "asteroidal"? Something akin to "eccentricity 0.6, inclination 30d (or retrograde)"? I understand that highly-inclined, highly-eccentric orbits are more likely to be those of a comet than are those orbits with low such values, but are these parameters actually "defined"? (My question is about the orbit itself, not the body - I understand that comets can have "asteroidal orbits" (e.g. 29P) and that asteroids can have "cometary orbits" (e.g. 2006 EX52))


No, orbital elements do not matter, as both comets and asteroids can be perturbed out of their original orbits into greatly different ones. For example: it is possible, in theory, for an asteroid to be flung completely out of the solar system.

The common differentiation is where they formed and their composition. Asteroids formed in the inner solar system and are primarily composed of minerals and rocks. Comets formed far outside the orbit of Pluto and are composed primarily of dust, small rocks and ice.
 




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