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Interstellar Interlopers, Coming in from the great beyond
JRehling
post Apr 28 2020, 01:42 PM
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QUOTE (tanjent @ Apr 26 2020, 08:12 PM) *
I can't find the reference via Google so I am short on details, but I recall several years ago there was a proposal for a retrograde head-on flyby of multiple asteroids in the main belt. It could not have gotten very far, but maybe a trajectory of that sort could be adapted to closely inspect this object at aphelion. I guess the power requirements would be in Juno's class though, so it would not be cheap.


As far as I know, this proposal was mine and hasn't had any life beyond that (which is to say, just some energetic posting on a fanboy basis).

The MANTIS Discovery mission proposal would have flown by nine asteroids via a prograde solar orbit. A retrograde orbit might require a Jupiter gravity assist and more.
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stevesliva
post Apr 29 2020, 06:45 PM
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QUOTE (nprev @ Apr 26 2020, 01:47 AM) *
I was surprised to see this considering it's now a couple of years old. Looks like a small object in a retrograde 1:1 orbital resonance with Jupiter may be of extrasolar origin, and the same may be true of some Centaurs.


Phil Plait covers this in passing and some of the ensuing topics here:
https://www.syfy.com/syfywire/has-the-sun-c...her-star-wellll

The trigger is the same sort of work for the high-eccentricity Centaurs.
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Holder of the Tw...
post Mar 17 2021, 04:20 PM
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It looks like researchers at Arizona State University have come up with a very good explanation for all of Oumuamua's observed properties.

Origin Determined


Two good tags for this article would be "Nitrogen ice" and "Don't jump to conclusions".
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HSchirmer
post Mar 17 2021, 04:37 PM
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QUOTE ("Holder of the Two Leashes")
It looks like researchers at Arizona State University have come up with a very good explanation for all of Oumuamua's observed properties.Origin Determined

Grin- hmm, that looks familiar...
QUOTE ("Holder of the Two Leashes")
Two good tags for this article would be "Nitrogen ice" and "Don't jump to conclusions".
Perhaps a better tag is "Lando's cool wardrobe."
Lando Calrissian "Hey L3-37, my new cape is finished, plan a jump to the Earth system..."
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fredk
post Mar 17 2021, 05:05 PM
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I would replace the headline "ASU scientists determine origin of strange interstellar object" with "ASU scientists make new proposal for origin of strange interstellar object". But it is a really nice sounding proposal.
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HSchirmer
post Mar 18 2021, 07:34 PM
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QUOTE (JRehling @ Dec 20 2017, 10:08 PM) *
The velocity of 'Oumuamua is far beyond the escape velocity of the Sun. There is no circumstance of orbital mechanics in our solar system that could accelerate an object that was initially in solar orbit to this velocity.
I was re-reading this thread- I noticed a paradox: Isn't there a disconnect between
1-) "Oumuamua can't be a comet because natural objects in solar orbit can't achieve escape velocity."
and
2- "Oumuamua must be an object from a distant solar system that achieved escape velocity."

If there are "no circumstance of orbital mechanics in our solar system that could accelerate an object" then how do we get the Nice model and Steppenwolf planets?

Can we predict about solar systems that COULD have tossed out Oumuamua? Would a low escape velocity red dwarf be best, or does a bigger star like a blue giant work better at accelerating things to escape velocity?
So, anybody know of papers evaluating the "comet flinging" capacity of various combinations?
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john_s
post Mar 18 2021, 08:53 PM
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No paradox- objects in our solar system can be readily accelerated to hyperbolic trajectories, but then they leave immediately, never to return. The only way we would observe a hyperbolic object from our own solar system would be if we saw it immediately after the close planetary encounter that had accelerated it, and that would be easy to check.

John
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HSchirmer
post Mar 18 2021, 10:33 PM
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QUOTE (john_s @ Mar 18 2021, 09:53 PM) *
No paradox- objects in our solar system can be readily accelerated to hyperbolic trajectories, but then they leave immediately, never to return. The only way we would observe a hyperbolic object from our own solar system would be if we saw it immediately after the close planetary encounter that had accelerated it, and that would be easy to check.John

A question- since 99.9% of the mass in the solar system in the sun, how do the (decimal-round-off) planet accelerate something to over solar escape velocity Do we need a "grand tour" of multiple gravity assists to accomplish escape?
I (perhaps naively) figure that the only thing in our solar system that could impart solar-escape-velocity trajectories IS the sun with 99.9% of the mass and thus the ability to impart acceleration?
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Explorer1
post Mar 18 2021, 11:28 PM
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Jupiter alone does the job well enough. Especially if the orbits are already (as for incoming Oort cloud objects) just a tad below escape velocity, an encounter does not even need to be particularly close to give that extra little momentum to send them away forever.
For example: https://en.wikipedia.org/wiki/C/1980_E1_(Bowell)
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Holder of the Tw...
post Mar 18 2021, 11:39 PM
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The Solar system's planets orbit pretty far out from the depths of the Sun's gravity well. Escape velocity from the surface of the sun is 618 km/sec. Solar escape from the distance of earth's orbit is only 42.1 km/sec. An object in tandem with the earth will be going at an orbital speed around the Sun of 29.8 km/sec, so it would only need a gain of 12.3 km/sec in the direction it is already going in order to escape.

The situation with the outer planets is even more favorable since they are that much further out from the sun. Recall that Pioneer 10, which was launched near a minimal energy Hohmann transfer orbit from earth to Jupiter only needed that one flyby to get kicked out the solar system. Jupiter regularly kicks comets out of the Solar system, some of which are already pretty close to escape velocity anyway and don't need to get all that near to a planet.

I was going to leave it to JRehling to reply to your earlier quoting of him, but since I'm here anyway I should point out in your quote from him that he said that Oumuamua's velocity is "far beyond the escape velocity of the Sun". The key word there is "far". Most objects escaping from our system are barely above escape velocity, and Oumuamua probably started out that way leaving its system. Most end up with eccentricities below 1.01, with only a few getting as high as 1.05. Oumuamua came in with an eccentricity of 1.20 and comet Borisov was at (an astonishing) 3.36. There is no contradiction between an object barely escaping it own system and then plunging headlong into another system that is moving entirely differently through the galaxy, and therefore with much greater relative speed in regards to said object.
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Xcalibrator
post Mar 19 2021, 01:46 PM
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In all seriousness, this comic provides a helpful illustration of the gravitational potentials involved: xkcd681 Gravity Wells
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JRehling
post Mar 20 2021, 05:53 PM
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It would be nice to have a simple formula for the results of gravity assists, but there's nothing simple about them. However, to clear up one misconception implicit above, they are a dynamic that occurs with a pair of large bodies accelerating a third, and they are not in any way a dynamic that can exist with just one large body and one small one. That will give you Keplerian motion. A body from the outer solar system cannot get a gravity assist from the Sun and be accelerated beyond the Sun's escape velocity; it can only orbit the Sun. The Sun is not a body that can deliver gravity assists.

Oumuamua approached the Sun already far above escape velocity. This is probably a consequence, as others have noted, of Oumuamua escaping some other system at a more pedestrian velocity, but that system and ours having a high difference in relative velocity.

Both Voyager spacecraft were launched into elliptical orbits that could not have left the solar system. For each, the gravity assist at Jupiter was sufficient to allow them to escape the solar system, but Voyager 1 now has only about half the velocity with respect to the Sun that Oumuamua had at a comparable distance. However, if Voyager randomly wandered into some other sunlike star's planetary system, its velocity with respect to that star would in many cases be dominated by the proper motion of the star (= relative velocity of that star and the Sun with respect to one another). It's like someone in a car throwing something out their window and into the window of another passing car. How fast the object is tossed will be almost irrelevant to how fast the object is going with respect to the second car. There's no reason to suppose that the velocity of Oumuamua was exceptionally fast with regard to its star of origin.
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