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Re: Space Geography

From: Roger Burton West <roger@f...>
Date: Thu, 22 Sep 2011 21:21:14 +0100
Subject: Re: Space Geography

On Thu, Sep 22, 2011 at 03:15:48PM -0400, Tom B wrote:

>2) Similarly, within systems, most orbits follow some sort of plane. Is
>there data that lists how far on/off the plane of those orbits are that
>known planets are? (I'm thinking something that identifies how many
>off that plane the orbital plane of a system world is)

"Orbital inclination" is the term you're after here.

>Mostly I'm curious if
>a) most systems are flat with eccentric planets being unusual (and what
% of
>planets are thus slightly or highly unusual/eccentric)

Inclination of orbital plane relative to the ecliptic, which is what you
described in 2), isn't the same thing as eccentricity. (The ecliptic is
arbitrarily defined as the plane of Earth's mean orbit about the sun. If
you do it as a momentum sum, it's closer to Jupiter's orbit, for obvious

But all the planets' planes are within 7 degrees of Earth's orbit, and
all except Mercury within about 3.5 degrees. To a first approximation,
the smaller the body, the more inclined its orbit is likely to be -
Pluto's at 17 degrees, Pallas at 34, Eris at 44.

>b) same sort of question with systems relative to the plane of a galaxy
>(obviously highly galaxy shape dependent)
>Would that sort of approach help? Does background clutter matter?

With realistic sensors, yes, but to a limited extent - remembering how
sparse real-life asteroid fields are, unless you're willing to bury your
ship in a comet and wait for several years, it _is_ going to be spotted.


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