Re: How special is the Solar System?

From: Andrew Nowicki (andrew_at_nospam.com)
Date: 08/07/04 

Date: Sat, 07 Aug 2004 22:22:57 +0200

"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.
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/academics/courses/astro201/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.
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.

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

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."

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