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Comment by Santosh83 | Hacker News Reader

Since the observed composition of the comet is mentioned as being "remarkably" similar to solar system comets isn't there any possibility at all that it could indeed be from within our system? Can no combination of freak gravitational nudges/slingshots, however unlikely, result in the observed orbit?

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That’s a great question, and it’s (relatively) feasible to answer. The object is coming in towards the center the solar system, so its past trajectory lies outwards. If it has been disturbed into this path from a hypothetical sun-centered orbit, it would have to have happened very recently: otherwise it would be long gone, never to return. So it would be necessary for the back-projected trajectory to pass very close to a compact, massive object. Dare I say that the vast majority of all such massive objects in the solar system are well known; so if the trajectory doesn’t indicate a close encounter with a planet within the past decade or so, then this possibility is essentially eliminated.

That, or a spare comet prop accidentally dropped from the Oort catwalk that surrounds our solar-system-scale Truman Show /s

There was a recent paper that showed it is possible planet 9 is a primordial black hole - would that work?

https://phys.org/news/2019-09-planet-primodial-black-hole.ht...

No, that paper says "What if Planet 9 is a Primordial Black Hole?" and then works out some consequences and finds them to be not ruled out. It doesn't start from observations and arrive at the PBH in any natural way.

To judge for yourself hour serious the authors are in proposing a primordial black hole to explain the anomalies in the outer asteroid belt, I refer you to figure 1 in their paper: https://arxiv.org/pdf/1909.11090.pdf

Would you pass an opportunity to include illustration of an astronomical object at a scale of 1:1?

I stared at that figure for about a minute and wondered at how friggin' satisfied they have to have been about it.

It was and is really neat, even if the likelihood of its reality is low.

Right - that's why I worded my sentence "it is possible planet 9 is a primordial black hole"

If the aphelion (furthest point of its orbit) is significantly farther out than the Oort Cloud, then it fundamentally can’t be from anywhere inside our solar system per orbital mechanics. And in this case, its “orbit” is hyperbolic. Meaning it’s going faster than the escape velocity, so will never return.

It’s also a dead giveaway if the eccentricity or direction of its orbit are significantly different than those of the rest of the solar system

Edit: For objects as far out as the Oort Cloud, a few relatively small changes in velocity can actually result in hyperbolic orbits. The real distinction is a big difference in velocity.

Unless it interacted with other bodies in the ort cloud. If we consider three-body interactions, slingshots, most any trajectory/orbit might be possible.

It depends on interobject density and single object mass, I'd reckon.

Having it redirect the orbit at velocity might be astronomically (!) low

Also, I don't know it's trajectory relative to the solar plane; it might be ruled out by that alone

From Wikipedia:

"2I/Borisov also has a hyperbolic excess velocity of 32 km/s, much higher than what could be explained by perturbations, which could produce velocities when approaching an infinite distance from the Sun of less than a few km/s"

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