"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:

A:- 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.

B:- 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.

C:- 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.

D:- 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
http://einsteinhoax.com/hoax.htm (1997); http://einsteinhoax.com/gravity.htm
(1987); and http://einsteinhoax.com/relcor.htm (1997). 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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