How special is the Solar System?

Andrew Nowicki ) wrote:
: "How special is the Solar System?" by M. E. Beer1.,
: A.R. King1, M. Livio2 and J. E. Pringle2 is posted
: at: http://arxiv.org/pdf/astro-ph/0407476

: MY COMMENT

: The high eccentricity of the extraterrestrial gas giants
: implies that all or nearly all extraterrestrial planets
: have eccentric orbits and that solar system is uncommon.

Could this be due to us having several gas giants and that Jupiter and
Saturn are both large? Or that the measurements from AU are much better
than from LY, and that if we were actually near these extraterrestial
planets would be much more like our own? Further, does our solar system
from a few LY appear to have a 20 year wobble that coincides with
Jupiter and Saturn's synodic period? Since Jupiter's period is 12 years
this 8 year anomaly might make the orbit seem more eccentric.

: In addition to the nearly circular orbits (except for
: Pluto), the solar planets are almost evenly distributed
: as predicted by the Titius-Bode Law. The Titius-Bode Law
: also works for moons orbiting solar planets, but does not
: work well for Neptune and Pluto:
: http://astrosun2.astro.cornell.edu/a.../bodes_law.htm

: Apparently the solar system accretion disk was not
: disturbed by interlopers when planets and moons
: formed 4.5 billion years ago, except for the most
: distant planets: Neptune and Pluto. We still do not
: know if planetary orbits are inherently unstable.

We know that they are stable and have predicted when the perhelion points
move as well. See: http://ssd.jpl.nasa.gov/elem_planets.html

: It seems that planetary systems having many planets
: should be less stable than planetary systems having
: few planets. The absence of massive bodies in the
: middle of the solar system (known as the main
: asteroid belt) may have stabilized the solar system.
: If planetary orbits are inherently unstable than solar
: system is uncommon and SETI is a waste of time. Simple
: forms of life may survive on a somewhat unstable planet,
: but they cannot create a technological civilization.

My guess is that our solar system is typical of others, at least
others that have only one star.

: We need better computer simulations of orbital
: stability -- these simulations are more important
: than all the microwave SETI research.

Right, you cannot infer AU-based data with other data like it at LY-based
data. There is simply too much room for error.

Eric

: PS. I wonder if the Moon (Luna) acts like a vacuum
: cleaner in a sense that it hurls deadly asteroids
: away from the Earth.

: __________________________________________________ ______________


: RELATED ARTICLES


: Computer simulations of orbital stability are difficult.
: For example, the following paper is based on simulations
: made on a supercomputer having 128 processors, and yet it
: neglects possible inclinations as well as planetary systems
: having more than 3 planets:
: Stability of Terrestrial Planets in the Habitable Zone of
: Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208
: http://arXiv:astro-ph/0403152


: Excerpt from "The Stability Of The Orbits Of Earth-Mass Planets
: In And Near The Habitable Zones Of Known Exoplanetary Systems"
: by Barrie W Jones, David R Underwood, P Nick Sleep,
: http://www.astrophys-assist.com/educate/cgino617.pdf:
: "We have shown that Earth-mass planets could survive in
: variously restricted regions of the habitable zones (HZs)
: of most of a sample of nine of the 93 main-sequence exoplanetary
: systems confirmed by May 2003. In a preliminary extrapolation
: of our results to the other systems, we estimate that roughly
: a third of the 93 systems might be able to have Earth-mass
: planets in stable, confined orbits somewhere in their HZs."
: This is a poor quality article. It does not explain
: how they calculated the orbital stability.


: Excerpt from "Dynamical Stability and Habitability of a
: Terrestrial Planet in HD74156" by M. Colleen Gino,
: http://www.astrophys-assist.com/educate/cgino617.pdf:
: "The dynamical stability of the system must be taken into
: account as well, particularly in light of the impact that
: large planets can have on the orbit of the terrestrial planet.
: For a terrestrial planet to remain habitable, there is a
: dynamical requirement that other planets in the system don’t
: gravitationally perturb the planet outside of its habitability
: zone. In a recent study involving 85 of the known extrasolar
: planetary systems, Menou and Tabachnik (2003) found that more
: than half of these systems, primarily those with distant
: eccentric giant planets, are not likely to support terrestrial
: planets and are therefore dynamically inhabitable. Marcy and
: Butler (2000) give similar evidence for the likelihood of
: terrestrial planets to be scattered gravitationally from the
: high eccentricity of Jupiter-like planets that exist between
: 2 – 3 AU. Under such circumstances the circular orbits and the
: long term survival of terrestrial planets is not guaranteed."