Le 25/02/12 19:19, Thomas Smid a écrit :
At 1000 AU, the orbital speed is of the order of 1 km/sec, and this is
about the speed an object must have for there to be any chance of
being captured. So 30 km/sec (which is what I assumed above for the
average peculiar speed of interstellar objects) is much too high for a
capture. And the density of objects with a speed of just 1 km (or
less) would be much smaller. If you assume a Maxwell-Boltzmann
distribution, then the density of particles is proportional to v^2 for
speeds small compared to the average speed, so in this case only
(1/30)^2 = 1/900 of the total density N. And because v would be
smaller by factor 1/30 as well, you would then still be at a time of
5*10^12 years, i.e. there would be just a 1/1000 chance that it has
occurred during the lifetime of the sun. And this is only the
probability for an object to get sufficiently close to the sun in the
first place. You then have to multiply this with the (conceivably even
much smaller) probability that it has a very close encounter with an
object of a comparable size in the solar system (because that is the
only way for it to lose kinetic energy and thus become captured by the
solar system).

The key parameter here is the density of the free floating planets.
A press release published yesterday by Stanford University says that
there should be 100 000 (one hundred thousand) planets for each star.
Please look in this URL, I may have misunderstood something:

http://groups.google.com/group/sci.s...0725bb1d?pli=1

That is a 5 orders of magnitude more than what you assumed in your
calculations.

The problem with astronomy now is that the fact that we have entered
space and we have now space telescopes opens such an avalanche of new
data that many theories just will not stand the test of time.


But anyway, as we know from previous discussions, Robert suggests the
capture theory as a general alternative to explain the formation of
planetary systems, so also at 1AU or even closer (because that is what
his principle of a fundamental similarity between planetary systems
and atomic systems would demand).


I wasn't arguing either for or against Robert's theory. The fact that
so many free floating planets are there is just mind boogling. That has
surely consequences but I am not competent to figure them out.

jacob