My Math Forum Gravity of Oort cloud on planets

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 June 26th, 2018, 10:55 PM #1 Senior Member   Joined: May 2015 From: Arlington, VA Posts: 394 Thanks: 27 Math Focus: Number theory Gravity of Oort cloud on planets Does the Oort cloud (2% of the mass of the Sun at > 2000 AU) and its comets have as substantial a gravitational effect on the Solar System as any of the individual planets?
 June 26th, 2018, 11:05 PM #2 Senior Member     Joined: Sep 2015 From: USA Posts: 2,299 Thanks: 1220 I'm going to guess no simply because of $\dfrac {1}{r^2}$ of course you don't define substantial...
 June 27th, 2018, 01:56 AM #3 Senior Member   Joined: May 2015 From: Arlington, VA Posts: 394 Thanks: 27 Math Focus: Number theory Still, comets are drawn to the Sun over that distance. "Substantial" must mean at least the magnitude of attraction between Mercury and Neptune at their greatest separation.
June 27th, 2018, 02:18 AM   #4
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 Originally Posted by Loren Does the Oort cloud (2% of the mass of the Sun at > 2000 AU) and its comets have as substantial a gravitational effect on the Solar System as any of the individual planets?
Try a quick calculation: what is the gravitational force of a comet in the Oort cloud compared to the gravitational force of a nearby star or the galactic centre?

June 27th, 2018, 11:42 AM   #5
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 Originally Posted by Benit13 Try a quick calculation: what is the gravitational force of a comet in the Oort cloud compared to the gravitational force of a nearby star or the galactic centre?
Enough for a nearby star to put the nascent comet in an elliptical orbit around the Sun. But what about the gravitation of trillions of comets comprising the Oort cloud (weighing ~2% of the Sun's mass), on planets in our Solar System?

Comets are freed from the Oort cloud by the gravitation of nearby stars. My question now compares the gravitation of nearby stars on a comet to the entire Oort cloud on any of our planets. I believe the comparison is small, but not negligible.

 June 27th, 2018, 03:19 PM #6 Senior Member     Joined: Sep 2015 From: USA Posts: 2,299 Thanks: 1220 Sounds like you've got the mathematical and physics skills to answer the question yourself. One thing to consider w/regard to the overall effect on the solar system is the symmetry of the Oort Cloud. Obviously it's not perfectly symmetric but I bet it's pretty close and thus every gravitational affect one bit of it will have is going to be countered by another bit. This doesn't negate every bit of influence but on average it does tend to mitigate them.
 June 27th, 2018, 09:56 PM #7 Senior Member   Joined: May 2015 From: Arlington, VA Posts: 394 Thanks: 27 Math Focus: Number theory I agree, the weakness of my argument has mostly to do with the spherical symmetry of the dominant, outer Oort cloud. The inner Oort cloud is disk-like, though, which coincides with the planetary plane. So instead of a wide spherical shell canceling its own gravity, the inner Oort cloud also would act to dilute forces on the planets due to its own cancellation -- a two-dimensional version of the effects from the outer Oort cloud. Aside: maybe the Oort cloud represents a low-energy state compared to the original planetary accretion disk, migrating outward both as a disk and a sphere. Indeed, one would expect the inner Oort cloud to have some residual angular momentum. Has the Oort cloud ever interfered with telescopy?

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