The Scarcity of Life Bearing Planets

There is considerable interest in the possibility that there may be a
large number of planets in our galaxy that are suitable for life. In the hope
that there may be intelligent life on planets lying within a reasonable
distance, a project named SETI (Search for Extraterrestrial Intelligence) has
been set up to search for evidence of that life. The idea behind the project is
that intelligent life may be generating signals which can be received on Earth
that are either a by-product of their civilization (such as our own radio
broadcasts) or a deliberate attempt to communicate. Unfortunately, the
probability of success of those programs is far lower than currently believed.
If an Earth sized planet existed 93,000,000 miles from a star that was
virtually identical to the Sun, it is extremely unlikely that it would be
capable of supporting life. To see why this should be so, an examination of our
own Solar System is order.

With the exception of Mercury, the Earth, Mars, and Pluto, all of the
planets have enormous atmospheres (relative to the Earth). One can draw no
conclusions about the original conditions on Mercury or Pluto. Mercury is too
small and too close to the Sun to have prevented its atmosphere, regardless of
its original quantity, from boiling away to space. (There may be a remnant of
an atmosphere frozen at the poles.) At the other extreme, due to its distance
from the Sun, any atmosphere that Pluto may have had at its beginning and which
has not been lost by evaporation to space is of necessity frozen solid and is
therefore unobservable. Observations have shown that Mars once had a
significant atmosphere that supported running water (and, by implication,
oceans) but has lost both. Apparently, its low gravitational mass has made it
too easy for the Sun's radiation to cause Mar's atmosphere to evaporate to
space. Of all the planets, it is Earth that is the anomaly.

Due to its location, Venus receives about twice the heat input from the
Sun as does the Earth. Its gravitational mass is slightly less than that of the
Earth and yet it has an atmosphere about 70 times as dense as the Earth. In
addition, the atmosphere of Venus is alleged to consist of mostly carbon
dioxide. Since, under the evaporation process, the other normal atmospheric
gases, having a lower molecular weight, will evaporate before carbon dioxide
does, the initial Venusian atmosphere must have been significantly denser than
it is now.

The Earth, on the other hand, has an atmosphere that contains a negligible
quantity of carbon dioxide but is relatively rich in the lighter gases. In
addition, it is estimated that about 3 billion years ago the atmospheric
pressure on the Earth was about 20 PSI and has been reduced to its current
level of 14.7 psi. This means that, for the Earth, 25% of the atmosphere has
been lost in 3 billion years, probably by a net evaporation to space. (Any gas
or vapor subject to a vacuum will evaporate, an atmosphere is no exception.)

It seems reasonable to accept that the early history of the Solar System
approximated the following stages:

The planets were formed by the collision of smaller objects circling the
Sun in eccentric orbits. The collision process continued until the Solar System
was virtually cleared of objects in non-circular orbits.

During the planetary formation stage, the planets could not acquire
atmospheres because the bombardment that was forming them made their surfaces
extremely hot. Atmospheric gases which impacted the planet from interplanetary
space or from the accreting object might be expected to boil away quite
rapidly, particularly since they were being added to the surface of the
planets.

Once the rate of bombardment forming the planets reduced to the point
where the planets could cool sufficiently, they were capable of collecting
atmospheres from gases that remained in the Solar System. (There are arguments
that planetary atmospheres were formed by outgassing. The writer doubts this
was a major source of atmosphere, but whether it was or not does not affect the
conclusions.

For Venus and the gas giants to have their present atmospheric density,
all of the planets, including the Earth, must have initially acquired enormous
(by Earth standards) atmospheres. They gained their atmospheres by sweeping up
gases from the surrounding interplanetary space (and possibly by outgassing)
and lost some of that atmosphere by evaporation to that same space from the
uppermost layer of the atmosphere. In order for a molecule of gas to be lost to
the planet, it must acquire a thermal velocity greater than the planet's escape
velocity. This must occur at an altitude at which the atmosphere is
sufficiently thin so that it does not strike other molecules while escaping.
(This occurs above the altitude where the effects of diffusion are
significant.) The rate at which atmospheric gases are lost to space is
determined almost entirely by the rate of energy input from the Sun and by the
escape velocity of the planet at the top of its atmosphere The rate of
atmosphere loss is virtually independent of the amount of atmosphere the planet
owns at any instant of time.

The Earth-Moon system has two characteristics that are anomalous compared
to the other planets. The first is that it has far too much angular momentum
(orbital angular momentum, rotational angular momentum of the Earth and the
Moon, and orbital angular momentum of the Moon around the Earth). As pointed
out in a text by Dr. Urey, an exponential plot of angular momentum vs. total
mass for all of the other planets yields a straight line. The total angular
momentum of the Earth-Moon system lies far above that line. The second anomaly
is that it contains far too little atmosphere and, unlike Mars, the density of
that atmosphere has remained almost unchanged. A satisfactory explanation for
both of these anomalies seems to have been provided in the 80's by a computer
simulation of a glancing impact on the Earth by an object having a mass about
one sixth of its mass and which yields a conclusion for the formation of the
Earth-Moon system which seems to be currently accepted. The simulation
predicted the formation of a binary system with a Moon sized object orbiting
the Earth an altitude of about 12,000 miles, with the Earth having a 4 hour
day, and with the Earth having captured the iron cores of both objects. Since
the length of the Earth's day was, is, and will remain less than the Moon's
orbital period until the Sun enters its red giant stage, tidal effects on the
Earth will perpetually transfer angular momentum from the Earth to the Moon.
This transfer has lengthened the Earth's day to 24 hours and has caused the
Moon's orbit to increase to 238,000 miles. More important, such an impact would
have blasted away most if not all of the atmosphere the Earth had at the time
and, if the collision occurred late enough in the formation period of the Solar
System, most of the interplanetary gases would have already been absorbed by
the other planets and/or lost to interstellar space and not be available to
reform much of an atmosphere on the Earth. This scenario could easily allow the
Earth to have the comparatively puny but stable atmosphere required to support
the evolution of intelligent life
..
In order for a planet to support life, not only must it be in the "life
zone" about a suitable star, it must possess an atmosphere of a suitable
density for a sufficient period of time for life to evolve. On the Earth, life
does not seem to prosper above an altitude where the density is half an
atmosphere. At the other end of the scale, the atmosphere must not be too thick
or the wavelengths of radiation needed for photosynthesis not only will not
reach the atmosphere-water interface where life begins, that interface is
likely to be too hot due to the temperature rise of adiabatic compression.
(This temperature rise is the reason the surface of Venus is so hot). Making
the optimistic assumption that four and a half atmospheres is the highest
suitable atmospheric pressure requires that a life supporting planet not lose
more than four atmospheres of density in the period required for intelligent
life to evolve. For a planet starting with the atmospheric density of Venus to
lose 60 PSI of surface atmospheric pressure in 3 billion years (the time
required for intelligent life to have evolved on Earth), the existence of such
life would require an age of 50 billion years for the planetary system. Such a
conclusion presents problems. A star similar to our Sun will become a red giant
about 10 billion years after its formation and the apparent age of the Universe
is only 15 billion years. On the other hand, if a planet such as Mars lost its
atmosphere at a sufficient rate to reach compatibility with the requirements of
life before its star became a red giant, it would pass though the "life range"
so quickly that intelligent life would probably not have had time to evolve. It
is the author's belief that, without the addition of the 'wild card' implicit
in the postulated Earth-Moon collision, a planet capable of supporting life
cannot exist. (It is hoped that this question would be examined further.) It is
the author's belief that intelligent life is much rarer in the Universe than
Dr. Sagan suggested.

The asteroid belt exists as a ring of stony and iron rocks in orbit about
the Sun between the orbits of Mars and Jupiter. The radius of that orbit
coincides with the anticipated location of a planet under the conventional
theory of planetary formation. If one examines the objects in the asteroid
belt, the moons of Mars, and the meteorites that strike the Earth, one finds
that, unlike comets, many if not most of them composed of stone or of iron.
Unlike the flimsy comets, such objects cannot form by accretion, they can only
be formed within a planet-sized object that has already accreted. One must
conclude, therefore, that initially a planet did form at the radius of the
asteroid belt and was later shattered by a collision. Such a collision would
drive away most of the planetary material and leave a residue of rocks from the
planet's upper layers and iron objects from the planet's core. That collision
is a reasonable candidate as the source for the object that impacted the early
Earth to form the Earth-Moon system, the meteorites which strike the Earth, and
the moons of Mars.

The writer is of the strong opinion that, unless a planet that is located
around its star and sized to be suitable for the retention of an atmosphere,
undergoes such a history at the appropriate time in the planetary system
process a planet suitable for the evolution of intelligent life cannot evolve.
It would seem, therefore, that in addition to the probability factors now
considered for the existence of life bearing planets that yield the possibility
of perhaps 100 civilizations within our galaxy, an additional factor must be
considered for each candidate planetary system. This factor is the probability
of AN EVENT occurring at the right time in the planetary formation process to
drive off the excess atmosphere from a planet that is large enough to retain a
stable atmosphere. When added to the already tabulated probabilities assumed
for the SETI observations, it seems quite probable that instead of a
civilization occurring about 100 times in a galaxy as is currently hoped,
civilization would occur once in a hundred or a thousand galaxies. If this were
the case, the SETI project would seem to be doomed to failure.

The source material for this posting may be found in "Gravity" (1987),
"The Einstein Hoax" (1997), and "Corrections to Residual Errors in Special
Relativity (1999) located at http://www.members.aol.com/einsteinhoax/site.htm .
EVERYTHING WHICH WE ACCEPT AS TRUE MUST BE CONSISTENT WITH EVERYTHING ELSE WE
HAVE ACCEPTED AS TRUE, IT MUST BE CONSISTENT WITH ALL OBSERVATIONS, AND IT MUST
BE MATHEMATICALLY VIABLE. PRESENT TEACHINGS DO NOT ALWAYS MEET THIS
REQUIREMENT. THE WORLD IS ENTITLED TO A HIGHER STANDARD OF WORKMANSHIP FROM
THOSE IT HAS GRANTED WORLD CLASS STATUS.

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Subject: The Scarcity of Life Bearing Planets
From: (Dniheb29)
Date: 8/29/03 1:32 PM US Mountain Standard Time
Message-id:

If an Earth sized planet existed 93,000,000 miles from a star that was
virtually identical to the Sun, it is extremely unlikely that it would be
capable of supporting life. ....

Why use our solorsystem as a prototype when most solorsystems have Jup size
planets tending about the temperate region? Imagine what would have been if
Jupiter would have spiraled in within Earth's orbit durring the systems
developement. Europa which is covered with ice would be the solor system's
ocean bearing "planet". Earth would have been scattered out of the picture. I
find it far more likely that life will tend to occur on moons of Jup size
planets much more frequently than on earth size planets as they the Jups so
abundantly found and tend to be about this region. Life is probably very
abundant, we just got jipped with a little moon where in most life bearing
"planets" the inhabbitants probably get to look up at an enourmous gass giant
ruling their sky.

"WaiteDavid137" wrote in message
...
Subject: The Scarcity of Life Bearing Planets
From: (Dniheb29)
Date: 8/29/03 1:32 PM US Mountain Standard Time
Message-id:

If an Earth sized planet existed 93,000,000 miles from a star that was
virtually identical to the Sun, it is extremely unlikely that it would be
capable of supporting life. ....

Why use our solorsystem as a prototype when most solorsystems have Jup
size
planets tending about the temperate region? Imagine what would have been
if
Jupiter would have spiraled in within Earth's orbit durring the systems
developement. Europa which is covered with ice would be the solor system's
ocean bearing "planet". Earth would have been scattered out of the
picture. I
find it far more likely that life will tend to occur on moons of Jup size
planets much more frequently than on earth size planets as they the Jups
so
abundantly found and tend to be about this region. Life is probably very
abundant, we just got jipped with a little moon where in most life bearing
"planets" the inhabbitants probably get to look up at an enourmous gass
giant
ruling their sky.

What about intense radiation belts a gass giant would probably create? How
well would an extensive atmosphere on the moon protect the surface from a
constant shower of ionizing radiation? Granted, an orbit farther out from
the giant would reduce this, but this would narrow your choice of habitable
moons, wouldn't it?

--
The butler did it.

What about intense radiation belts a gass giant would probably create?

Why do you think radiation will prevent the occurance of life? You don't think
life must begin on a dry "exposed" surface do you? Removal of earths magnetic
field would flood the Earth with radiation from the Van Alan belts, but that is
only a problem for us surface dwellers who have evolved on a low radiation
surface.

"WaiteDavid137" wrote in message
...

What about intense radiation belts a gass giant would probably create?

Why do you think radiation will prevent the occurance of life? You don't
think
life must begin on a dry "exposed" surface do you? Removal of earths
magnetic
field would flood the Earth with radiation from the Van Alan belts, but
that is
only a problem for us surface dwellers who have evolved on a low radiation
surface.

I don't think life started on a dry surface, I'm just suggesting that a dry
surface would probably be more favorable for the development of an advanced
civilization. If the surface was flooded with radiation, (intelligent) life
could still exist in the oceans. I may be narrow-minded, but to to develop
an advanced civilization one would first expect the discovery of fire to
enable metallurgy and creation of various tools. That sounds rather unlikely
under water!

Just my thoughts, though!

--
The butler did it.

"WaiteDavid137" wrote in message
...
Subject: The Scarcity of Life Bearing Planets
From: "Ugo"
I don't think life started on a dry surface, I'm just suggesting that a
dry
surface would probably be more favorable for the development of an
advanced
civilization. If the surface was flooded with radiation, (intelligent)
life
could still exist in the oceans. I may be narrow-minded, but to to
develop
an advanced civilization one would first expect the discovery of fire to
enable metallurgy and creation of various tools. That sounds rather
unlikely
under water!

Maybe, but I doubt that too. Dolphins and octopus are fairly smart. Who
knows,

I never said they weren't intelligent!

maybe in a couple of million years and a few more ice ages an 8 tentacle
creature will be the dominant intellegence of Earth. Underwater, instead
of

Maybe, maybe not...

first discovering fire geothermal energy from volcanic vents may lead to
metallurgy and science.

I dunno, I find it hard to imagine melting and forging metals underwater,
water being such an efficient coolant... And imagine how long it would take
them to discover electricity - sea water isn't exactly a good isolator, you
know.
I'm sorry, I just don't see dolphins sending probes to space, not now, not
in a million years :-)

--
The butler did it.

Subject: The Scarcity of Life Bearing Planets
From: "Ugo"
Date: 8/30/2003 3:15 PM US Mountain Standard Time
Message-id:

"WaiteDavid137" wrote
geothermal energy from volcanic vents may lead to
metallurgy and science.
I dunno, I find it hard to imagine melting and forging metals underwater,...
And imagine how long it would take
them to discover electricity

It may take a long time, but whats a million years or so in the grand scheme of
things. Its probably more a matter of intellegence curiosity and need than
diffuculty in the long run.

I'm sorry, I just don't see dolphins sending probes to space, not now, not
in a million years

Not as long as they have flippers instead of digits, but I can see a tenticled
creature becoming proficient at manipulating its environment.

"WaiteDavid137" wrote in message
...
Subject: The Scarcity of Life Bearing Planets
From: "Ugo"
Date: 8/30/2003 3:15 PM US Mountain Standard Time
Message-id:

"WaiteDavid137" wrote
geothermal energy from volcanic vents may lead to
metallurgy and science.
I dunno, I find it hard to imagine melting and forging metals
underwater,...
And imagine how long it would take
them to discover electricity

It may take a long time, but whats a million years or so in the grand
scheme of
things. Its probably more a matter of intellegence curiosity and need than
diffuculty in the long run.

I'm sorry, I just don't see dolphins sending probes to space, not now,
not
in a million years

Not as long as they have flippers instead of digits, but I can see a
tenticled
creature becoming proficient at manipulating its environment.

Well, we'll just have to wait and see who turns out to be right!
;-)

--
The butler did it.

Emanretic30, who still can't wrap a line properly:

The unfortunate thing about replies to newsposts is that they do not address
the issue raised but get humg up on trivialities.

No, the surprising thing is that there are people who post to usenet
who know enough about the details to prevent you from from dismissing
them as trivialities.


The issue raised in th original post is that of a modification to th
accepted probability tree for the liklihood of a life bearing planet
If we accept that all planets are formed with atmospheres consistent
of Venus and the gas giants in our system, and lose their atmosphere

In other words, consistent with atmosphere's unlike earth, since
the atmosphere of venus is certainly nothing like the atmosphere of
jupiter. It's not much of a surprise that you would conclude that
there is little if any life elsewhere, if you assume that life must
resemble life on earth and you assume that few, if any planets have
earth like conditions. Your conclusion is contained in your assumption.
You've simply attempted to hide that fact with under verbosely written
garbage.


"evaporation from the top" as has been suggested in astronomical tex
planets which would have atmospheres in the "life zone", which appar
and Venus do not, would either pass though the "life zone" very rapi
would not achieve that state for a period of time greater than the l
Sun. The premise of the post is that the presence of the Moon and th
accepted "fact" of the Earth-Moon system being formed by a collisio

after the formation of the Solar System would allow the Earth to maintain a
stable and low atmospheric pressure for billions of years. It would appear
that, in the overall view, we are lucky.

So what? There are at least a trillion trillion stars out there.

In article ,
Emanretic30 wrote:
after the formation of the Solar System would allow the Earth to maintain a
stable and low atmospheric pressure for billions of years. It would appear
that, in the overall view, we are lucky.

no.

the thermal Archaea were the first creatures on earth (we know this
from genetic analysis) that is those creatures that live on thermal
energy deep inside the earth were the first to evolve. Which actually
makes sense, as they are less likely to be vaporized every time the
early earth got smashed. Afterwards, bacteria, and eukarya evolved.
Photosynthetic, or any other kind of life that depended on the Sun for
energy evolved long after the original Archaea.

So it seems more likely than not that there is life on Europa because
there is plenty of thermal energy, but we gotta drill through 10
miles of ice to find it.

Or maybe we just have to wait for them to drill out? However, they
would all be fishes, so it seems doubtful they would evolve hands and
tools, no matter how smart they became.

--- edt