View Full Version : Definition of the Solar System

2003-Nov-08, 04:31 PM
There is strong circumstantial evidence for the existence of the Oort cloud. It is defined to be a spherical shell of cometlike bodies from about 50,000 AU to 80,000 AU radial distance from the sun. The Oort cloud is gravitationally bound to the sun and is my choice (at its outer limits) for the boundary of the solar system until some solar gravationally bound body at a further distance is discovered (or hypothesized). ;)

Currently there seems to be a tendency to use the heliopause (at 90 to 100 AU) as the boundary. :o

Has anyone seen an "authorized" definition of the size of the solar system and do you know which organization has the appropriate credentials to so authorize? :ph34r:

2003-Nov-08, 09:34 PM
Gourdhead, I think you're correct in your inclusion of the Oort cloud as a component of the solar system. Most of the literature I've encountered regards a solar system (this or any other) as the totality of the dynamically bound components of the principal star. But whether or not there is some "authorized" definition of the size of our system I don't know. The I.A.U. may have some branch dealing with this issue. I rather suspect, however, that the question of the solar system's size is an ongoing one, subject to current observational evidence and advancing theoretical understanding.

Clear skies.

2003-Nov-08, 10:45 PM
Good question Gourdhead. I'm not entirely sure how to answer your question properly, but I would think that the solar system ends where we can nolonger observe objects acting under the influence of the sun's gravitational field to a significant degree (the last 4 words in that sentence being most ambiguous).


2003-Nov-09, 02:39 AM
Given your limiting factor for the boundary of the solar system ... It's a good one too given that the edge of the Oort cloud is thought to be the end of the Sun's influence (in gravitational and dynamic terms at least).

The oort cloud is REALLY BIG! from the books on my bookshelf the general concensus is that it's approximately 3 light years, about 30 trillion kilometers from the Sun. That's about 190 thousand AU!!!!!!!

2003-Nov-09, 02:43 PM
I think I would set the boundary at the Oort cloud as well, but it depends. I mean the bow shock is another good definition.

2003-Nov-10, 12:13 AM
Isn't the Alpha Centauri trio just 4 light years away? Does that mean that our Oort cloud interacts with Alpha Centauri's? Does every star system have an Oort cloud?

2003-Nov-10, 06:50 AM
Just to clear up some misunderstandings in the conversion of units - 1 light year = 63,239.7263497 astronomical units. The aphelia of most non-periodic or extremely long period comets fall in the 50,000 - 100,000 a.u. range, and very few estimates put the diameter of the Oort cloud at more than 150,000 a.u. While the absolute diameter of the Oort cloud is, at this stage, a highly speculative measurement, it is unlikely to be much larger than 150,000 a.u., largely due to the disruptive tidal influences of close encounters with stars having large proper motions and the very attenuated effect of the Sun's gravitational influence at that distance.

As for Oort clouds surrounding other stars, there is some evidence that this may be the case, and in the most recent issue of Sky & Telescope there is a brief article stating that the presence of planets (and thus the protoplanetary material found in the Oort cloud and Kuiper belt in our solar system) around other stars may approach 100%.

Clear skies.

2003-Nov-10, 07:33 AM
It seems to me that the Orrt Cloud extends a quarter of the way to the Alpha Centauri system. :o
To fully include it as part of the Solar System seems just a bit too large to me, but to not include it doesn't do the Orrt Cloud justice. Especially since part of it is made up of Kupier objects. :unsure:

Perhaps the Orrt Cloud could be defined as a transition between the Solar System and intersteller space, with the heliopause defined as the actual boundry, which in itself is contained withing the Orrt Cloud. :huh:

Just a thought.

2003-Dec-18, 11:26 AM
NO Planetwatcher, there's NO need to find new definitions. To know why look no further than http://www.universetoday.com/forum/index.p...st=0&#entry9196 (http://www.universetoday.com/forum/index.php?showtopic=1427&st=0&#entry9196)