Text 202, 193 rader
Skriven 2004-09-28 13:34:00 av Tomhendricks474 (1:278/230)
Ärende: Re: Different Forms of Li
=================================


>At http://www.ozi.com/ourplanet/lovelock2.html Lovelock queries "What is
>Gaia?" but his response doesn't even mention "atmosphere". 

Keep looking - its a main component of his ideas.


 Be that as it
>may, my point stands... the jury's still out.  And Lovelock (by your post)
>said his reason was because Mars didn't have a life atmosphere, and not
>because the mass was too low to support life.  Will you give me at least
>a
>possibility that a Mars-sized planet *could* support life under ideal
>conditions?  Say, in an ideal orbit, an appropriate amount of water, a
>"good" (Earth-like?) axial inclination and rotation period, etc., etc.?
> Or
>do you rule it out absolutely?


Well remember the gravity issue. The moon for ex. has no atmosphere to speak of
- and no life.
Whether Mars sized planet in earth orbi is large enough to contain the
necessary ingredients? I don't know.
Then IF life is a heat cycle, and the time for that heat cycle is caused by the
Moon spinning the earth (with the sun gravity pull too) then Mars-like planet
in earth orbit might need a Moon sized moon too - or it would lock into too low
a spin. So all that is something to consider.
I can't say for sure if that prohibits life, but its conditions that we should
consider.
>
>> > So what I'm saying is there's a reasonable range of
>> >masses that might well support life and the closer the mass
>> >(and other attributes) is to Earth's, the more likely that life
>> >will be similar. Conversely, the more divergent the attributes
>> >(while remaining in whatever range where life *can* begin),
>> >the more likely that life will be of a "different form".
>> TH
>> I agree with the first statement.
>
>Well, good.  Now I'll try to quantify a bit.  Let's say Earth is fairly
>ideal (for argument's sake, I'll agree with you here) and Mars is on the
>low
>end for mass.  Might you agree that, therefore, the range is roughly an
>order of magnitude either way from earth's mass?  That would give a pretty
>wide range, IMO, and *well* outside what anyone would consider "same sized".

OK.
>
>> I would say, 'the more divergent the attributes',
>> the less likely that life will be at all.
>
>Well, of course this is what you would say.  Would you care to try
>quantifying it?  Are you, for example, saying that life's impossible on
>any
>rocky planet outside +/-5% of earth's mass?  +/-10%?  +/-20%?  What is your
>boundaries for "same sized" planet?

I could only guess. But it can't be too far different I would think.

>> (snipped)
>> >> So to have a rocky planet - size of earth, it has to be in the
>> >> same life zone.  Also if all this is a sun too hot - it'll burn up
>> >> in a billion years before inteligent (?) life has time to form.
>> >Intelligent life is irrelevant to the topic.  And since we went from
>solely
>> >single-cells to intelligence in (arguabley) 800MY with "diversions"
>> >such as ~163MY of dinosaurs, I won't concede your point anyway
>> >(just because it took 3.xBY here doesn't mean it absolutely can't
>> >happen faster).  And there's all sorts of star sizes that won't burn
>> >up for 2BY, 3BY, 4BY, etc., right up to and beyond our sun's
>> >~9BY.  You're frequently taking extremes for your examples
>> >and not discussing all sorts of other intermeadiate possibilities.
>> TH
>> But a hotter sun means the planet has to be farther out to
>> be in the life zone. Farther out means a less circular orbit
>> and a greater variation in temps - perhaps the hot summer
>> would be too hot and cold winter too cold to keep water
>> liquid form (switch from Mars like to Venus like and back)
>> What I'm saying is not the extremes but pretty close to the norm.
>
>You're going into areas of unfamiliarity for me, but I thought Neptune's
>orbit, for example, was closer to circular than Earth's and Mercury's was
>less so.  

No its more like the outline of an egg. A study was done
on earth if it had a more uneven orbit. Life was possible but there was
problems. All the water may turn to ice at the fartherst point from the sun,
and be too hot at the closest. What ever life began would have to survive these
extremes. One advantage of life in water is that there is nothing that stays at
a stable temperature more than water. So life may be somewhat delicate when it
comes to temp extremes - even today it can survive only a few degrees on either
end of liquid water - and these are definiteyly extremophiles.

And I see from:
>http://cannon.sfsu.edu/~gmarcy/planetsearch/bd/ecc.html ...
>
> "The circular orbit of Jupiter in our Solar System promotes
>  the stability of circular orbits among the other 8 planets.
>  If our Jupiter were in an eccentric orbit, the Earth and
>  Mars would likely be gravitationally scattered out of the
>  Solar System. Thus our existence, and the existence of
>  life in the habitable zone, depends on both Jupiter and
>  Earth being in mutually stable, circular orbits."


You've brought up another point of how constricted life
may be if it also depends on a Jupiter sized planet farther out. And I will add
this. Jupiter may have swept up a lot of the planetary meteors and debris
before they could damage earth - so it is a sort of planetary sentry in that
way.

>If I understand these more or less correctly, then there's nothing stating
>that further out *absolutely* means more varied.  And even if I'm wrong
>here, how much would it vary?  (You say "perhaps the hot summer...";  well,
>"perhaps *not*", I'll shoot back.)

I think the study I read was in a pop science mag
like Discover (the one about - what if earth had a less
circular orbit)
>
>We can surely have some "variation in temps" over an annual period
>(especially in polar regions) while, for example, maintaing an equatorial
>(or other) region at an appropriate temperature for life to begin.  And
>I
>don't think you can justify saying you're "pretty close to the norm" at
>all,
>since we really don't know a norm for other planets.
>
>But you still didn't realistically (IMHO) respond to my comment of all sorts
>of sun sizes from, say "4BY, etc., right up to and beyond our sun's ~9BY".
>This implies, of course, cooler suns than ours as well as all sorts of stars
>a bit to significantly hotter.  Again, I take your comments as dealing with
>the extreme of a (much, much) hotter sun (based on your "one billion year"
>scenario), even if you're right about the eccentricity of orbits.  Your
>other extreme, AFAIC,  was gas giants- what about rocky planets 2x Earth's
>size?  3x? 5x? etc. 


I don't know the limits of size. 
But look at both Mars
and Venus - one is too cold and icy, the other (virtually the same exact size
as earth, is now a high pressure hell hole. So even a little distance (in
planetary terms , makes a big difference in the possibility of life). Lovelock
again suggests that all 3 probably began with similar atmopsheres.

 Maybe you have data I don't have, but the gas giants
>in
>our system are 14x to 317x Earth's mass - in the absense of information
>to
>the contrary, I'll assume that rocky planets of several times Earth's mass
>are at least possible.

I don't know. But that would make them hold in gases
that may not be advantagous to earth or hold in some
gases in too high a quantity. That has to be considered in a larger size planet
in the life zone.


>> (snipped)


>> Archae may be very old and may be closer
>> to the earliest common ancestor - but my point
>> was that the farther you go back the more alike
>> life would be. Today we have life that can live
>> in a temp range below 0C to above 100C. I
>> don't think you had any range like that when
>> life began.
>
>Well, I'll agree, of course.  What I question is your statement that "The
>extremophiles on planet earth took 4 billion years to evolve that ability."

Probably be more exact to say that it took millions
and perhaps billions of years to adjust to extreme
environments on the planet at that time.

(snipped)
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