TNOs: could some have formed elsewhere? Options

[elakdawalla]

I got a question today for Planetary Radio Q&A that I couldn't answer, being pretty ignorant about solar system formation research. Can anybody help?

We know from the metal composition of our solar system that the Sun is at least a second or third generation star. It made me wonder if it was possible that some of the comets or other KBOs that we witness might be from the Sun's predecessor star or stars. If not, could such bodies exist a bit further out? I should think it would be fantastic to be able to investigate such objects.

--Emily

[Guest_AlexBlackwell_*]

I got a question today for Planetary Radio Q&A that I couldn't answer, being pretty ignorant about solar system formation research. Can anybody help?

That's not your run-of-the-mill Q&A inquiry, Emily. Is this, by chance, a grad student asking?

I'm working off dim memory but I believe Jane Luu and David Jewitt did some work a few years ago on the survival of Kuiper belts over the main sequence lifetime of central stars. I believe they (or someone else) came up with estimates on the sizes of given belts and the amount of material that would survive the clearing phases of stellar evolution.

I'll try and track down a reference.

[Alan Stern]

Hi Emily,

I personally have worked on this problem and can help you out. First, comets in the KB cannot survive the red giant phase. This work was published in Nature (1990, by Stern, Shull, and Brandt). OC comets can survive this phase of stellar evolution because they are so far out.

As to the capture of interstellar comets, various dynamycists have looked at this and the capture efficiency is dismal-- <10^-12 per interloper comet. This indicates that no KB comets and only a handful of the OC comets could be captured. As to larger (KBO-sized) bodies-- forget it, the odds ar there isn't even one object that is from a passing star UNLESS the Sun was born as a double or in a cluster-- which is possible but controversial.

-Alan

[Guest_AlexBlackwell_*]

I personally have worked on this problem and can help you out. First, comets in the KB cannot survive the red giant phase. This work was published in Nature (1990, by Stern, Shull, and Brandt).OC comets can survive this phase of stellar evolution because they are so far out.

For the cognoscenti:

Evolution and detectability of comet clouds during post-main-sequence stellar evolution
S. Alan Stern, J. Michael Shull and John C. Brandt
Nature 345, 305-308 (1990).
doi:10.1038/345305a0
Abstract & References

I would also recommend:

Delayed Gratification Habitable Zones: When Deep Outer Solar System Regions Become Balmy During Post-Main Sequence Stellar Evolution
S. Alan Stern
Astrobiology 3, 317-321 (2003).
Abstract

[elakdawalla]

Thanks, Alan, Alex!

Emily

[SFJCody]

As to the capture of interstellar comets, various dynamycists have looked at this and the capture efficiency is dismal-- <10^-12 per interloper comet. This indicates that no KB comets and only a handful of the OC comets could be captured. As to larger (KBO-sized) bodies-- forget it, the odds ar there isn't even one object that is from a passing star UNLESS the Sun was born as a double or in a cluster-- which is possible but controversial.

Could cometary interlopers 'aerobrake' into orbit around a star with a proto-planetary disk and in doing so kick start planet formation or is the gas/dust density of such a disk too low?

[Alan Stern]

Could cometary interlopers 'aerobrake' into orbit around a star with a proto-planetary disk and in doing so kick start planet formation or is the gas/dust density of such a disk too low?

Perhaps, but I see three difficulties: First, the typical speed of interlopers is near 30 km/sec, so that's one heck of a lot of
braking. It's more like aerocapture. Second, comets are fragile, so you'd have to do it very slowly, over a great path lentgth
with only a small drag. There is also the problem that the disk is transient-- it's only in place for <1% the age of the solar
system.

My guess is that this won't work out.

-Alan

[Stephen]

For the cognoscenti:

Evolution and detectability of comet clouds during post-main-sequence stellar evolution
S. Alan Stern, J. Michael Shull and John C. Brandt
Nature 345, 305-308 (1990).
doi:10.1038/345305a0
Abstract & References

A very different (and more technical) abstract of this paper than the one in Nature is available via the "Bulletin of the American Astronomical Society" here.

======
Stephen

[ngunn]

Another angle on Emily's query. The recent paper on the capture of Triton begs the question: could the sun have captured objects in a similar way? If there is an interstellar population of planetary sized bodies then perhaps some of them are double or multiple systems. This would greatly enhance the probability of solar capture. The orbits of any such captured objects would presumably be arbitrarily distributed in size, inclination and eccentricity - in fact rather Sedna-like.

[ugordan]

The recent paper on the capture of Triton begs the question: could the sun have captured objects in a similar way?

Alan already dismissed this as highly improbable, see previous posts:

As to larger (KBO-sized) bodies-- forget it, the odds ar there isn't even one object that is from a passing star UNLESS the Sun was born as a double or in a cluster-- which is possible but controversial.

[ngunn]

I saw that, and I can see why the probability of a solitary object getting captured by the sun is virtually nil, but I'm not convinced that it's true if there is a significant population of dark, loosely-bound multiple systems floating about. Nobody knows whether or not there are, and if so how common, so I don't think we're in a position to calculate odds.

[ugordan]

I saw that, and I can see why the probability of a solitary object getting captured by the sun is virtually nil, but I'm not convinced that it's true if there is a significant population of dark, loosely-bound multiple systems floating about. Nobody knows whether or not there are, and if so how common, so I don't think we're in a position to calculate odds.

Somehow, I get the feeling that this binary capture scenario only works well when there's an appreciable gravity gradient across the binary object separation distance. Alternatively, you could state this as the two-body distance being not too small compared to the large 3rd body distance. How does this apply to the KBOs and OC? These are so far away from sun, that two components in a binary system would need to be very, very separated for this capture scenario to be feasible. At tens and hundreds of AU from the sun, both objects are likely to feel effectively the same amount of gravitational pull from the sun, with the net effect being virtually no disrupting force upon the binary pair.

I agree we can't know how many binary objects there are that wander around the interstellar space, but even if there are many (not likely), furthermore ones that are very loosely bound (even less likely), IMHO the Triton-like capture mechanism would be highly improbable. I'd be interested to hear if more knowledgeable people know more about this -- Alan et. al. ?

[ngunn]

I'd be interested to hear if more knowledgeable people know more about this -- Alan et. al. ?

Me too! I was only speculating, not calculating. Relative velocity's important too. I'm guessing that for maximum disruption you would want the dark binary to be in the vicinity of the sun for about half of it's own mutual revolution period. Experts please come in! Computer simulations??

[Bob Shaw]

What about a close (in interstellar terms) encounter with another star-mass (or large Jupiter) object? You'd only need a few such spread over billions of years to have strange Oort Cloud effects up to the present day. If the intruder isn't gravitationally bound to our Sun then it could be halfway across the galaxy by now. I suppose it's a statistical thing - and the sort of area where Hipparcos and similar astrometry craft might be able to give pretty good answers by identifying anomalous proper motions of stars.

Bob Shaw

[Guest_Richard Trigaux_*]

Well, such interstellar interactions and captures seem rare, if not impossible, even in assuming that there is a large interstellar population of small objects (Jupiter-size or smaller).


But there is a moment where it is much more possible: when the forming star already has its well individualized bok globule or accretion disk. At that stage, objects are not yet condensed (although they already exist individualy as gravitationally bound cloud structures) so they are much larger. In more, into star formating nebulae, the distances are much smaller, and relative velocities too.

The result of this is that interactions would mostly happen at this time, and be much easier at this time, to the point of having common and drastic effects.

For instance in the thread about the hypothetical Triton capture by Neptune, I imagined that it could result, not from an interaction between already formed moons, but between protoplanetary clouds. For instance the Pluto cloud would have passed through Neptune's disk. In doing so, it was captured by the Sun, but also it forbad any large satellite formation around Neptune, lefting only the two close satellites or the too far Nereïde. Of course in this hypothesis Triton would be a part of the Pluto cloud left around Neptune, but in a reverse orbit.

Recent thinkings came into a similar way, wondering if the chaotic outer KBO belt and its abrupt cutt-off would result simply from collisions between accretions disks, which would be relatively common in star formation zones. Many puzzling features could also result from a deeper interaction, for instance large planets into very excentric orbits, of very close from their star.

I think we should think of an accretion disk as something complex, formed of lumps of various materials and various speeds, with an history of interacting each other and with other disks, before being constrained to take the relatively regular position we see today.

Eventually it would not be astonishing if other planets of our sytem, or some KBO, would appear to come from different nebulae, with different composition. Pluto and KBOs are good candidates for this, as they may result from matter swaps between two colliding disks. For instance radioisotopic analysis show that Earth and common meteorites all formed from materials of a supernova some 20 millions years before accretion (I have not the exact figures in head). But similar radioisotopic analysis with comets or other far objetcs may show some with a different origin, perhaps another supernova, of another older source of matter.