Re: YASID

On Mar 3, 3:28 pm, "Keith F. Lynch" <k...@xxxxxxxxxxxxxx> wrote:
Otto York <gophe...@xxxxxxxxxxxxx> wrote:
djhe...@xxxxxxxxxxx (Dorothy J Heydt) wrote:
As I recall, the orbit is eccentric, and the colonists find it hot
at perihelion, cold at aphelion, but not unbearably so.
In positing that "the orbit is eccentric," AWC's authors making but
a token gesture towards reality. Even an orbit that ranges from
Venus-distance to the sun to Mars-distance would kill life on planet
Beta well before Beta reached either orbital extreme, especially at
the Venus end.

How do you figure? It takes time to heat up or cool down. Anyhow, a
planet where Mars is would be warm enough to support a life if it had
Earth's mass, hence more air pressure. And a planet where Venus is
would be cool enough to support life if not for the runaway greenhouse
effect. It's not obvious whether that runaway greenhouse effect was
inevitable, if, say, Venus was less massive. Even if it was, it would
probably take many centuries.

Let's oversimplify just a bit by assuming that when the orbiting new
planet touches the former Venus orbit on the inward leg of its
journey (Venus has been removed by the gas giant that left the new
planet behind), the new planet follows the Venus orbit for about 150
degrees before moving out to Mars distance. We have already assumed
that the new planet has miraculously slowed down enough to go into a
not-very-elliptical orbit, averaging earth-distance from the sun, and
that the planet is roughly earth size. This means that it will
probably take roughly a little more than an earth year to complete an
orbit, say, 400 days. (By comparison, a Venus year is 225 earth days,
and a Mars year is 687 earth days. The new planet has more miles in
its orbit than Mars, so any error in the 365-day assumption should be
in the direction of a 500-700 day year, which means a longer spell at
Venus distance form the sun.) About one-fourth of the orbital trip
will be at close to Venus distance. So the new planet has roughly 100
days per orbit to get cooked. I can't see human beings surviving
under such intense heat AND solar radiation.

The issue is not whether an earth-mass planet in a Mars or Venus orbit
could support life. Life is adaptable and evolves to make itself
compatible with its environment. The real issue is whether colonists
from earth, homo sapiens, could survive, not having had a multitude of
generations to evolve into a Mars species or a Venus species.

But a merely eccentric orbit is out of the question.

I agree that the orbital capture is extremely impausible, unless it
ends up in an orbit as eccentric as [that of] a typical comet.

Now you have hit the nail on the head. For the new earth-sized planet
to be captured by the sun while the gas giant it has been orbiting
escapes, both planets must be moving at near marginal escape velocity
when they start moving past the sun. (I refer to forward motion alone
the gas giant's path, not to orbital motion.) The gas giant would
have to be moving at slightly faster than escape velocity; this would
permit it to escape to outer space. The smaller planet, whose orbital
direction might be backwards relative to the forward motion of the gas
giant, could be moving a little slower along the gas giant's path.
Adding the planet's negative orbital velocity to the gas giant's
positive path velocity could give the smaller, solid planet
submarginal escape velocity.

If the smaller planet were also between the sun and the gas giant, the
sun's stronger gravitational pull on it would pull it into a tighter
curve around the sun, facilitating capture. The gravity formula, G =
(M1 x M2)/D-squared, confirms that the sun's gravitational pull would
be stronger on the smaller planet. In the formula M1 is the sun's
mass, M2 is the planet's mass, and D is the distance between the two
centers of gravity.

The crucial point is that the captured planet would have a forward
velocity (not to be confused with orbital velocity) barely below
escape velocity; otherwise it could not be captured while the gas
giant escaped. That high, barely submarginal forward velocity would
send the planet way out to and beyond the Oort Cloud before it's
outward speed along the semi-major axis fell to zero and the planet
started falling back towards the sun.

Why do I say the orbit would reach out to or beyond the Oort Cloud?
Orbiting comets that originate in the Oort Cloud start falling back to
the sun when they reach the distance at which they originally started,
Oort Cloud distance. Those comets start falling at zero velocity
along the semi-major axis (not to be confused with the orbital path,
where velocity does not fall to zero at the turnaround point).
But the new planet and its companion gas giant were already streaking
toward the sun at high velocity when they reached Oort Cloud
distance. They will accelerate just as rapidly as the comet that
starts inbound at zero velocity. Therefore, when the planet starts
turning around the sun, it will be going faster than the comet. The
planet will therefore rebound farther than the comet, farther than
Oort Cloud distance. (Wikipedia says the Oort Cloud is about 2,000
times as far from the sun as Pluto is, which is why it takes most
comets so many years to complete one orbit.)

This orbital phenomenon is analogous to what happens to two equally
elastic balls dropped from different heights in a vacuum. The ball
dropped from a higher point will be moving faster when it strikes the
ground, so it will bounce back higher than the ball that started
closest to the ground.


--
Keith F. Lynch -http://keithlynch.net/
Please seehttp://keithlynch.net/email.htmlbefore emailing me.


.

Relevant Pages

  • Re: "Pluto Now Called a Plutoid"
    ... Sun, has sufficient mass for its self-gravity to overcome rigid body ... approximately as capable of clearing its orbit as Mars is. ... would likely be called a planet, ... cleared out its region in the Kuiper belt. ...
    (rec.arts.sf.science)
  • Re: Goddamn fscking ZFFDY ZFQR
    ... >> the same 1-year orbit around the Sun and you need one hefty deorbit burn. ... If the object achieves exactly escape velocity from Earth in any ... Sun similar to the Earth's, since as it gets farther away from the Earth ...
    (alt.sysadmin.recovery)
  • Re: OT Poll: Does our solar system have 8 or 9 or 10 known planets?
    ... defintion of planet, I would suggest any body that has sufficient mass ... to force itself to be spherical and orbits the sun as its primary orbit ... the Moon was orbiting Earth. ... primary orbit is around the Sun. ...
    (talk.origins)
  • Re: Two suns
    ... To shift the position of the orbit, ... zero, after all, because that would mean the sun would stand still. ... would orbit faster than Jupiter does (by a factor of the square root ... I assume you don't mean a planet year of 400 days, ...
    (rec.arts.sf.composition)
  • Re: YASID
    ... eccentric orbit spends more time near ... So a planet with ... between Venus distance and Mars distance from the sun). ...
    (rec.arts.sf.written)