Text 229, 242 rader
Skriven 2004-09-29 06:06:00 av Brett Aubrey (1:278/230)
Ärende: Re: Different Forms of Li
=================================


"TomHendricks474" <tomhendricks474@cs.com> wrote in message
news:cja9kt$g2a$1@darwin.ediacara.org...
<snip>
>  >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.

That's why I didn't include something as small as the moon.

> Whether Mars sized planet in earth orbi is large enough to contain the
> necessary ingredients? I don't know.

But you've ruled it out in the rest of this thread.  Why (if you don't
know)?  And by implication, you've ruled out planetary object 2x, 4x and 6
times Mars' size, as well as 2x and 4x Earth's size.  You're arguing for too
many limitations given the unknowns, IMO.

> 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.

Planets spin regardless of moon(s).  Mars, for example, spins almost the
same as Earth (40 minutes longer for a Martian day.) You're arguing for too
many limitations given the unknowns, IMO.

> >> > 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.

This was one of *the* major components of your argument, by my reading.  The
other one was star size.

> >> 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.

But you just said "OK" for planets with a range of 1/10 Earth's mass to 10x
Earth's mass (which seems reaonable to me without facts against it).  Which
is it?

> >> (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.

Where are you getting this? At
http://brahms.phy.vanderbilt.edu/~rknop/classes/a250/fall2002/pellish/table_of_distances.pdf

it gives the following eccentricity values (other sites roughly agree):
  Planet      Eccentricity
  Mercury      .21
  Earth           .02
  Neptune      .01

The way I read this (although I may be reading it wrong) is "Neptune's
orbit, for example, is closer to circular than Earth's and Mercury's is less
so."  And except for Pluto, the other planets are all .09 (Mars) or
significantly less (.00 to .05).  These (I believe) are far closer to
circular that egg-shaped.  Methinks your facts or your interpretation are
wrong here.

> 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.

But there must have been parameters with this study.  Obviously I'm not
saying that you can't get this with a less even orbit, but there must be
boundaries where it's less even and all the water doesn't turn to ice and
it's not too hot.  And besides, you're still saying "Life was possible."
That's what this whole thread is about.

> 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.

Tell that to the musk-ox.

> >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.

Why am I not surprised that you took it another limitation?  Try taking it
that in 100% of the solar systems we know about in detail, life abounds in
all habitats and niches on one planet.  Of all the billions of other
probable solar systems, there's a chance that life might abound there too
(maybe even different forms).  BTW, what do *you* mean by "different form"?

> >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)

Again, what were the parameters (we've got 6 planets with eccentricity of
..05 or less).  And note that Mars, at .09, is the other planet most likely
to contain life.

> >We can surely have some "variation in temps" over an annual
> >period (especially in polar regions) while, for example, maintaing
> >an equatoria l(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.

Then why the limitation?

> 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.

Fair enough, but these don't really apply.  We were talking about planet
size and sun size at the start of this thread,  My contention is that both
can vary significantly in a hupothetical solar system and still permit life.
I've always agreed with you on the temerature issue (though by your talk, I
might allow for more latitude than you here, too, but let's not get into
that! :-) )

> >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)
> Tom Hendricks,  Musea zine ed.

Regards,  Brett.
---
ū RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info@bbsworld.com

---
 * RIMEGate(tm)V10.2á˙* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 9/29/04 6:06:08 AM
 * Origin: MoonDog BBS, Brooklyn,NY, 718 692-2498, 1:278/230 (1:278/230)