Natural Science Forum / Physics / Particle Physics / December 2005

"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
http://einsteinhoax.com/hoax.htm ("The Einstein Hoax" {1997});
http://einsteinhoax.com/gravity.htm; ("Gravity" {1987}); and
http://einsteinhoax.com/relcor.htm ("Corrections to Special Relativity"
{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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