# The Naked Scientists Forum

### Author Topic: Can a comet like Kohoutek use a planet's gravity to maintain its orbit?  (Read 2617 times)

#### Emc2

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##### Can a comet like Kohoutek use a planet's gravity to maintain its orbit?
« on: 17/08/2012 07:22:31 »
question.

the theory is that this comet and many others, use the gravity of the outer planets, and other objects in space to maintain its orbit around our sun.

My question is, assuming that all the bodies this comet uses for gravity are always moving, and odds are they are never in the same alignment each time comets such as these pass, yes they somehow maintain the same orbit around the sun.

how is this possible that it keeps the same orbit, yet the objects can not be in the exact position every time..

is there some "other; force keeping these types of long orbit comets in there orbits ?

http://en.wikipedia.org/wiki/Comet_Kohoutek
« Last Edit: 21/08/2012 23:00:28 by chris »

#### yor_on

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##### Re: Comet Kohoutek
« Reply #1 on: 20/08/2012 10:52:44 »
Are you thinking about the uncertanity of position and speed over prolonged time? I think it has a lot to do with HUP?

#### Emc2

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##### Re: Comet Kohoutek
« Reply #2 on: 21/08/2012 08:07:15 »
yes, how it is very improbable that the objects that the comet uses to make its orbit around our sun one time, are there the next time that it makes its orbit, there has to be some other forces letting it maintain such a far reaching orbit.

I can not see it "getting" lucky each time as to the position of the objects it uses to maintain its orbit around our sun.

Unless our Sun can have a gravitational pull that far out, though I doubt that.

"something", other then gravity,  I dont know what, has to be keeping it in the same orbit, time after time...

#### CliffordK

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##### Re: Comet Kohoutek
« Reply #3 on: 21/08/2012 09:19:37 »
I find it doubtful that comets would develop a resonance pattern on the order of thousands of years.

Consider Pluto (which has a highly eccentric orbit), has a 3:2 orbital resonance with Neptune and an orbital period of 248 years.  One might imagine somewhat longer resonance periods.  But, I would find it to be unlikely that a 75,000 year orbit would be in resonance with the much shorter orbital periods of the planets.

Comets, by definition have highly eccentric orbits.  If they had round orbits closer to the sun, they would likely loose most of their water and be merely considered asteroids.  Further out, and we might not ever see them.

Now, the planets, however, might still have a role.  Consider the two body problem.  If a comet is created by a distant supernova, and was wandering through the galaxy.  It would pass by our sun ONCE.  Perhaps doing a slingshot, to be sent off in another direction, and out of proximity of our sun.  To take up orbit around the sun, it would require at least one planet to alter its orbit...  the first time.

#### Emc2

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##### Re: Comet Kohoutek
« Reply #4 on: 21/08/2012 09:36:57 »
okay, I just found the result. it is the Sun that holds them..hmm. thats some gravity..

http://en.wikipedia.org/wiki/Long-period_comet

By definition long-period comets remain gravitationally bound to the Sun; those comets that are ejected from the Solar System due to close passes by major planets are no longer properly considered as having "periods". The orbits of long-period comets take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic. Long-period comets such as Comet West and C/1999 F1 can have barycentric apoapsis distances of nearly 70,000 AU with orbital periods estimated around 6 million years.

#### graham.d

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##### Re: Comet Kohoutek
« Reply #5 on: 21/08/2012 09:46:28 »
I think the mistake is in thinking that comets depend on interactions with planets to maintain their orbits. For most comets the interaction with planets is minimal and, should it occur, could change the orbit significantly or even send the comet out of orbit forever. It is all (to some extent) predictable if the comet's trajectory is known although a mathematical solution is hard with multi-body interactions.  The confusion may result from the theory that comets start their excursion from a more regular orbit from the Oort cloud or Kuiper belt because of interaction with planets.

#### Emc2

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##### Re: Comet Kohoutek
« Reply #6 on: 21/08/2012 09:54:04 »
might be...maybe the bodies affect its orbit from time to time, but I guess the Suns gravity is very far reaching it seems.

#### damocles

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##### Re: Comet Kohoutek
« Reply #7 on: 21/08/2012 21:44:52 »
I had thought that the short period comets, like Halley's comet (86 year cycle) originated from much further away, but were catapulted into an elliptical orbit of (relatively) lower eccentricity and period by a single close encounter with a planet -- usually Jupiter. Once in an orbit of this sort, a body will simply cycle (with minor perturbation) for the rest of its life.

The life of a comet could be determined either by solar wind destruction as its substance is torn away little by little on each visit to the inner solar system, or by another (improbable) close encounter with a planet.

#### yor_on

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##### Re: Can a comet like Kohoutek use a planet's gravity to maintain its orbit?
« Reply #8 on: 23/08/2012 06:28:23 »
As I remember it, it was NASA discussing the difficulties/uncertainty defining a position over a prolonged time, although having to do with chaos mathematics, not HUP. It's probably me mixing it up there, but I'm not sure? Do/can HUP add up over time for a massive body in relative motion?

And I think i wrote about it here too? But can't find it, as usual :)
http://ptrow.com/articles/ChaosandSolarSystem5.htm

#### damocles

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##### Re: Can a comet like Kohoutek use a planet's gravity to maintain its orbit?
« Reply #9 on: 23/08/2012 06:54:20 »
In a many-body system like the solar system there are many perturbations to orbital parameters very much greater than HUP. Even if we suppose that all motion within the system is accounted for (quite impractical with our present incomplete data-set and the many factors to be taken into account), there is also the question of occasional bombardments or encounters from bodies outside the system -- e.g. novae and supernovae, varying levels of cosmic rays, varying solar behaviour and solar wind, and we do not really even know if the nemesis star is a reality or not (I happen to believe not, but that is immaterial).

#### Emc2

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##### Re: Can a comet like Kohoutek use a planet's gravity to maintain its orbit?
« Reply #10 on: 23/08/2012 07:38:52 »

#### evan_au

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##### Re: Can a comet like Kohoutek use a planet's gravity to maintain its orbit?
« Reply #11 on: 24/08/2012 14:13:46 »
Quote
is there some "other" force keeping these types of long orbit comets in their orbits ?

Yes, it's called "Energy".

There are two kinds of Energy that are important to the orbit of comets:
• Kinetic Energy: The comet has it's highest velocity and maximum kinetic energy as it passes close to the Sun. This is where it's Gravitational Potential Energy is at a minimum. The Sun's gravity cannot hold the comet at this speed, and it then shoots far out into the Solar System.
• Gravitational Potential Energy: The comet has its maximum Gravitational Potential Energy when it is furthest from the Sun. The Kinetic Energy reaches a minimum at this point. The comet's low velocity cannot sustain its orbit, and the Sun's gravity then pulls the comet back in towards the sun
There is a continual exchange of Kinetic Energy and Gravitational Potential Energy as the comet passes around its elliptical orbit. The sum of the two types of Energy is constant at all points in the orbit. There is essentially no air and no friction in the vacuum of space which would slow down the cometary nucleus, so it does not need energy input from an external body like a planet to keep the comet in its orbit.

It is possible that this beautiful rhythmic Energy balance can be disrupted if the comet passes close to an external body like a planet, which can result in the comet's velocity being increased or decreased. This could modify the orbit slightly (Halley's comet is not exactly regular), or in extreme cases, throw it right out of the solar system, or even plunge it into the sun.
« Last Edit: 24/08/2012 21:53:30 by evan_au »

#### The Naked Scientists Forum

##### Re: Can a comet like Kohoutek use a planet's gravity to maintain its orbit?
« Reply #11 on: 24/08/2012 14:13:46 »