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

[ngunn]

It's all too easy to picture the sun's stellar environment as a stable, uneventful sort of place with the nearest neighbours that are big enough to be visible at a comfortable few light years' distance. But in fact it changes very fast on a geological timescale. The constellations are by no means as old as the hills! Almost certainly in its 20 or so circuits of the galaxy the solar system has passed through some very different environments, some more lonely, some more crowded than today. Furthermore we have simply no idea how many bodies of substellar mass our galaxy contains or how they are distributed spatially, dynamically or in terms of size distribution. I am not arguing for the existence of any particular class of object or any particular scenario for what has shaped the outer solar system, just for keeping an open mind. I think there is plenty of room out there for quite a lot more interesting discoveries, and plenty of time since the formation of the solar system for subsequent events to modify it in complex ways. I doubt if that's ended for good, even now.

[The Messenger]

It's all too easy to picture the sun's stellar environment as a stable...we have simply no idea how many bodies of substellar mass our galaxy contains or how they are distributed spatially, dynamically or in terms of size distribution. I am not arguing for the existence of any particular class of object or any particular scenario for what has shaped the outer solar system, just for keeping an open mind. I think there is plenty of room out there for quite a lot more interesting discoveries, and plenty of time since the formation of the solar system for subsequent events to modify it in complex ways. I doubt if that's ended for good, even now.

http://planetary.org/blog/article/00000574/

"The major things that are still unknown: inside the classical Kuiper belt, there are two entirely distinct populations. One is a low-inclination population, and one is a more extended-inclination population. These are in exactly the same place in space. It's very difficult to do that mechanically; it's like trying to heat up only half of a cup of coffee. The other big one is the radial distribution in the Kuiper belt. You get a big peak right around 43 AU, then there is a big dropoff right around 50 AU...
We really know that the Kuiper belt doesn't extend out from 50 to 80 AU. But you can't see anything out beyond 100, because most surveys don't look for anything moving that slowly.

"One other population that I like to talk about, are objects that are really out beyond the Kuiper belt. Sedna -- when we first found it we thought it would be circular or scattered. We were really hoping it would be circular. We were shocked when we figured out what it was, and it's THAT." His initial graph was a plot of the current locations of objects in the Kuiper belt, projected on the plane of the solar system; Sedna sat just beyond the belt, but not far from it. Then he dropped in Sedna's orbit. The Kuiper belt shrank to cover less than a tenth of the slide, and the orbit of Sedna swept way out in a gigantic ellipse that always remained far outside the Kuiper belt, as far or farther than its current position beyond the Kuiper belt. "It never comes close to an outer planet; there has to be something out there beyond the Kuiper belt. This thing is probably ½ or ¾ the size of Pluto. If you have the same size distribution of objects out there as you have in the Kuiper belt, then you have a substantially larger population." There was some quibbling about this; it's kind of poor practice to create statitstical arguments from very small numbers.