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_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.