Planet Densities

Joel \ (
Tue, 12 Nov 1996 10:57:44 -0500 (EST)

On Mon, 11 Nov 1996, Michael Lorrey wrote:

> Thanks Twisty. BTW I like your pages. Do you think that there is a
> possibility that we would find the most dense planets of any solar
> system in the so called "zone of life" that Earth occupies? If so, this
> would greatly help locate extrasolar planets.
> Mike

My theory about the relationship of different densities in our own system
sorta springboards into other theories. Seems to me there is also a
relationship between planetary rings and low planet density, as well as a
relationship between Life and high planet densities.

Low planetary density can amass large total gravity while amassing lower
local gravity. This should be why Saturn, the solar system's least dense
planet, has the most splendid ring system. Low local gravity allows more
stable particle orbits around the rings.

Earth is the most dense planet in our system. It stands to reason that
its greater density and lower total gravity allow for some mighty-complex
systems to form. Perhaps Earth is the model of Extropian "Spontaneous
Order." Newton's Second Law of TD says that 'in a closed system, it can
only degenerate into a state of lower complexity.' With Earth open to
the sun's energy, and its great density and moderate temperature
facilitating the most fluid of systems, Life has the best chance of
forming and/or continuing. (By "most fluid," I mean the "triple point"
between boiling point and freezing point provides more range for liquids
to exist due to higher pressure.)

I'm only an amateur, (can't afford Institutionalized Ed without mortgaging
my future,) so I can only offer speculation about locating extrasolar
planets. The four known discoveries of such planets have been due to
sheer mass pulling their suns in rapid cycles. We need to improve our
perception, collect more discerning data, to find small-but-dense planets
like Earth. Gravity alone doesn't cut it, because Jupiter is so much
more massive (despite being less dense) that the sun get eleven to twelve
times the pull from Jupiter than it does from Earth, regardless that
Jupiter is four times as distant.

Density of planets today are estimated by visibly measuring speed,
distance, and diameter, in order to take a stab at the mass, and thus
mass per volume. One has to be in visual range to make good
measurements. It doesn't look as if this method will change in the near
future. Even if it did, we'd still likely have to move pretty close to
these bodies to determine density... There just aren't enough indicators
that can be read from an interstellar distance (at present).

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