SETI again

On Jul 28, 2006, at 9:08 AM, Robert wrote:

> im not sure where you got the idea that the oort cloud spread out
> that far into interstellar space. when i was reading about the object
> they are calling the 10th planet, it was discussing the fact that
> that was very near the point where solar gravity would no longer keep
> the planets in orbit. there was some discussion on wheither or not it
> was really a rogue object that happen to be passing though the fringe
> of our solar system. orbits around the sun dont extend as far as one
> light year, let alone two.

There have been several planetoids called the 10th planet, most in
the Kuiper belt. Sometimes called TNO's (Trans-Neptune objects). The
Kuiper belt starts around 30 AU's out (just past Neptune) and drops
off pretty quickly at around 50 AU's (around 5 billion miles). The
Oort cloud doesn't begin until 50,000 AU's (5 Trillion miles). We
don't know where the Oort cloud ends. Probably different distances in
different directions thanks to new data from the Voyagers (yes,
they're still working hard out there). The Kuiper belt is a ring,
while the Oort cloud is a shell, completely surrounding the Sun. The
nearly 5 trillion miles of space in between is sometimes called an
"outer Kuiper belt" or an "inner Oort cloud". No Oort cloud object
has actually been seen at the Oort cloud distance. Its existence is
calculated by many different means. The small-moon sized object Sedna
is considered an Oort Cloud object even though it is in the empty
zone less than 1000 AU's out.

We don't know how many objects exist in this empty zone between the
Kuiper belt and Oort cloud, its simply too dark to see with a
telescope. Sedna could be an oddball planetoid adrift in the trans-
kuiper desert, or there could be many other objects floating around
out there waiting for us. Voyager is probably not sophisticated
enough to answer that, but within 50 years, we may know.

We have no visual sighting of any planetoid beyond 1000 AU's. The
Oort cloud goes out to at least 100,000 AU's, if not more, and Alpha
Centauri is just under 300,000 AU's away.

For those who don't know, 1 AU is the distance from the Earth to the
sun, about 93 million miles. The voyagers are still less than 100 AU
out I believe.

doug