Post n. 47 English
For thousands of years, humans have been observing the sky to understand
where we are and what our place is in the universe. In recent centuries, we
have discovered that we live on a planet within a system made up of a star,
other planets and a myriad of asteroids. We now know that, together with many
other stars and planets, we are part of a cluster of stars that we have called
the Galaxy and that there are a huge number of galaxies that make up the
universe. Since, as has already
happened, some asteroids could fall on us and annihilate us, astronomical
research also becomes a quest for survival. Understanding where we really are,
what our place in the universe is, and knowing how to survive, leads us to the
study of the formation of our solar system, the search for other solar systems
and solar systems in formation.
But how many galaxies are there in the universe, how many stars and how
many planets? We don't know, some scientists estimate the galaxies to be around
100 billion others at 500 billion, a huge number anyway. A more realistic
estimate made by several scientists considers the universe to consist of about
200 billion galaxies. Our galaxy would contain 200 billion stars and even if
not all of them are part of a solar system, these would be a huge number around
which an endless number of planets (exoplanets) revolve.
And how many planets could harbour life?
As Alan Boss reports in 'The Crowded Universe' 2009, in 1995 Michel
Mayor published the discovery of the first extrasolar planet around a solar-type
star 51 Pegasus. The planet, named 51 Pegasus b, had a mass half that of
Jupiter and an orbital cycle of 4.2 days compared to Jupiter's 12 years. In the
same year, George Wetherill, who had studied the problem of solar system
formation for a long time, had come to the conclusion, through computer
simulations, that planetary systems can also form on stars with either double
the mass or half the mass of the sun. Mayor's discovery and Wetherill's
conclusions triggered the worldwide hunt for exoplanets. Within a decade, 120
extrasolar planets were discovered, most of them revolving around red dwarfs,
all Jupiter-sized and gaseous planets, others rocky and about 2-10 times the
size of the earth and called super-terrestrial
Red Dwarfs are a type of star with a mass between 0.5 and 0.1 solar
masses and appear to make up 80% of the stars in the Milky Way. Most of these
stars, due to their low luminosity, are invisible to the naked eye.
When Dimitar Sasselov wrote the 2012 essay 'Another Earth', some 600
planets discovered within a 500-light-year circle of our galaxy were already
known, all exoplanets of the Jovian or Super Earth type. Sasselov estimated the
number of planets that could harbour life at 100 million, and this estimate
included Super-Earths. At the time, people were already aware that the
technology of the time made it easy to detect large planets, yet many
scientists were of the opinion that large planets predominated in solar
systems.
it.wikipedia.org/wiki/Super_Terra
Sasselov included super-Earths among the habitable planets because he
considers them better than Earth in terms of habitability. He noted that life
cannot exist in an equilibrium system and therefore needs materials and energy
continuously. All of this on Earth is provided by plate tectonics, which causes
continental drift that recycles all the material in the Earth's crust over four
hundred thousand years: the so-called carbonate-silicate cycle. The emission of
CO2 and the presence of water create a powerful thermostat on our planet that
keeps the temperature within a range favourable to life. But plate tectonics
makes the planet dynamic in continuous renewal and vital. This condition,
within our planet, is determined by the presence of a molten core. Mars is too
small to have a substantial molten core within it. Rocky super-Earths will
undoubtedly have a larger molten core than Earth and thus have more sustained
plate tectonics that could recycle more materials and better support life.
With the development of surveying techniques and in particular the use
of space telescopes, there are now about 5000 known planets and among them some
of Earth size.
Scientists' interest has therefore shifted to planets of terrestrial
mass, rekindling a question that mankind has long been asking:
Is there life in space? And if there is life in space, is it similar to
our own? And could there be life very different from ours, i.e. based on
different chemical elements?
Iris Fly addresses the first question in The Origin of Life on Earth,
(2005), when she reports on the ideas of Shapiro and Feinberg. These authors
suggest that a definition of life should be independent of the local
characteristics of life on earth. They argue that life is the activity of a
highly ordered system of matter and energy characterised by complex cycles that
gradually maintain or increase order. Life would therefore be innate in matter.
They therefore believe that life based on silicates is also possible. In
particular, since at 1000°C silicates become liquid, on a planet close to the
sun or within our own planet, life based on silicates could have evolved.
Of course, there are those who conjecture diametrically opposed
environments. Saturn's satellite Titan apparently has an ocean of liquid
hydrocarbons at a temperature of -180°C where islands of frozen water float.
According to Goldsmith, hydrocarbon-based life could have evolved on Titan.
However, scientific research has shown that there can be no life without
atmosphere, energy and liquid water.
To answer the second question, we start from the observation that all
the chemical elements, of which planets and the substances essential for life
are composed, were produced by the evolution and collapse of massive stars. The
final explosion of such stars dispersed the elements produced into space.
Subsequent aggregations and reactions of these elements gave rise to clouds of
gas and dust that gave rise to solar systems. So in general terms, we can say
that all the solar systems in the universe have the same chemical elements as
life in our solar system.
Well, even though 92 natural chemical elements are available, living
organisms use only 4 of them by 96% of their weight: H (hydrogen), O (oxygen),
N (nitrogen), C (carbon), to which small percentages of P (phosphorus) and S
(sulphur) must be added. Together these 6 elements are called 'biogenic
elements'. They give rise to all the fundamental molecules of living matter.
The synthesis of these molecules gives rise to all the polymers necessary for
the origin and evolution of life.
Now given the need for an atmosphere and energy and liquid water, is it
possible that some other element could replace carbon?
In the periodic table of elements, silicon (Si) is below carbon C and
contains, like carbon, four electrons in the last orbital that give rise to
four bonds. Furthermore, silicon is an abundant element in the universe and
especially on our planet.
The subject, from a chemical point of view, has been dealt with at
length in the article: "We, Aliens, Matter: Is Another Life
Possible?", label L, to which I refer you and whose conclusions I quote:
With reference to silicon, Mario Ageno (Lezioni di Biofisica 3 1984)
adds: "[...] silicon is completely unsuitable as a building material for
living organisms [...]"
We can therefore conclude that, due to the peculiarities of their atomic
structures, biogenic elements are the only ones that, through their compounds,
are suitable for performing the numerous biological functions in living
organisms. Matter provides us with no other solution: the transition was
obligatory.
Moreover, since the laws of physics and chemistry are universal if,
given certain conditions, life occurs in other solar systems, it uses the same
biogenic elements and macromolecules as terrestrial living organisms.
But what does a planet have to be like to give rise to life?
To answer this question, one would first have to know how life
originated on our planet. There are two views on the origin of life on our
planet: that of Jacques Monod, 'Chance and Necessity' 1979, according to which
the origin of life on earth was a random event, our number came up at roulette,
or in the words of Crick, almost a miracle, and that of Christian De Duve,
'Vital Dust' 1995, according to which life is the product of deterministic forces;
life could not but originate under the conditions prevailing at the time and
will similarly originate wherever and whenever the same conditions reappear.
Then there are theories that seem far removed from Monod but actually
fall under Monod's randomness. It is now an established fact shared by all
scientists that in order for life to originate, all the substances necessary
for it must be selected, accumulated and placed in a condition to react. The
most widely accepted theories at present are: the primordial soup theory, the
'RNA world' theory, which postulates the origin of self-replicating molecules
in reservoirs, and the theory of the origin of life in the ocean floor near
hydrothermal vents. All these theories are not supported by precise knowledge because
they do not explain how the substances necessary for the origin of life would
have selected, accumulated and interacted to give rise to the macromolecules
that constitute life, they are more ideas than theories and are related to
Monod's randomness. In an aqueous environment, only a miracle could have
originated life.
Well, these ideas, coupled with the fact that on Earth water is
necessary for life, led many astronomers and astrobiologists to believe that a
necessary condition, namely the presence of water, was also sufficient. So
where to look for life in space? Wherever there is water, thus believing that
life could have originated even under the solid blanket of Jupiter's satellite
Europa where there seems to be liquid water.
Now, it is unclear why some astronomers, astrobiologists and SETI
researchers continue to search for life beyond the earth while accepting the
ideas linked to Monod's theory. It is unclear why they would waste time, energy
and resources searching for an event whose probability, out of 100 million
planets, is practically zero.
If one wants to search for life on other planets, one must instead
appeal to the universality of the laws of physics and become aware of the fact
that life, in every part of the universe, is the result of deterministic
forces. De Duve's view relates directly to Bernal's theory, which postulates
how clay, in prebiotic times, was able to select, accumulate, protect and
interact with the substances necessary for life. This theory has been
extensively expounded in 'Prebiotic Chemistry and the Origin of Life' 2019.
Clay, however, forms in the presence of rocks, water and the atmosphere.
So, if life needs clay to emerge, one must look for planets that also contain a
rocky part.
In conclusion, planets on which life may have originated must receive
energy from a star, it must contain an atmosphere, it must have a landmass and
it must be far enough away from the star to allow water in a liquid state.
These conditions are what defines a habitable
zone. These are minimum conditions because, as astrobiologists suggest, the
planet must also possess a molten core to allow a magnetic field to deflect the
life-threatening solar wind and allow plate tectonics to recycle chemical
elements.
Given these conditions, is it possible that life could have originated
on these planets?
As we have said, the laws of physics are universal and according to De
Duve not only life but also intelligence emerges everywhere and whenever
circumstances permit.
So the laws of physics allow for the origin of life on other planets
with the characteristics already listed, but then could life on those planets
have really originated?
Peter Ward (a geologist and palaeontologist) and David Brownlee (an
astronomer and astrobiologist) have conducted extensive research on the subject
and believe that yes, life may have originated on other planets. In his essay
'Physics of the Impossible' M. Kaku, 2010, reports their thoughts "We
believe that life, in the form of microbes and other equivalent organisms, is
widespread in the universe. As we have said, if the laws of physics are
universal, then one cannot but agree with Ward and Brownlee's thoughts.
But can, as De Duve suggests, intelligence also emerge from the
evolution of these organisms? And here serious doubts begin to creep in.
According to some scientists, for life to evolve (in addition to the
conditions already listed: Energy, atmospheres, water, land and a molten
central core to generate a magnetic field and clod tectonics), the presence of
a giant planet like Jupiter is also necessary to make us avoid asteroid and
comet impacts, and the presence of a Moon to stabilise the earth's axis.
Finally, an adequate rotation of the planet and the right distance from the
centre of the galaxy were added.
Finding a planet in the Galaxy that satisfies these conditions is a
somewhat difficult problem. And M. Kaku again reports Ward and Bronwlee's
thoughts: 'It is probable, however, that complex forms, the higher animals and
plants, are much rarer than we used to think'. In fact, Kaku further writes,
Ward and Brownlee do not rule out the possibility that the earth is, in the
Galaxy, the only planet populated by animal life forms.
The famous biologist Ernst Mayr is of the same opinion, but looks at the
problem from a biological point of view.
He has listed a dozen evolutionary bottlenecks that intelligence has had
to overcome on our planet and it is not certain that this is possible on some
other planet.
According to De Duve, intelligence emerges everywhere and whenever circumstances
permit. The fact is that the stringent physical conditions associated with
evolutionary processes really reduce such circumstances and thus the
probability of the emergence of intelligence to almost zero.
Nevertheless, many scientists still think that given the huge number of
planets in our galaxy, it cannot be ruled out that in some of them life has not
attained some form of intelligence.
A problem arises, however. The universe in its early days consisted
mainly of Hydrogen. The nuclear fusion of this element within massive stars and
their explosion gave rise to all the other elements that were dispersed in
space. The massive stars took about 5-6 billion years to fertilise space. At
this early stage of the universe, the amount of carbon, nitrogen and oxygen was
low, and rocky planets could not exist because there was not enough silicon. So
the first solar systems with rocky planets formed about 7 billion years ago,
which is three billion years before the formation of the earth.
it.wikipedia.org/wiki/Formazione_ed_evoluzione_del_sistema_solare
The question then returns: where is everyone?
And here scientists have indulged in a variety of solutions. The most
popular solutions are
The aliens are not interested in leaving their worlds and wandering
around the galaxy.
All the aliens scattered around the various planets in the galaxy do not
want to leave their worlds?
Meteor showers or comets have destroyed their worlds.
All possible worlds destroyed by meteor showers?
Perhaps they self-destructed, causing climatic, pandemic and nuclear
disasters.
Surely, they were all as stupid as humans!
Perhaps the most credible solution is that of Ward and Brownlee. Life is
probably widespread in the universe but in the form of microbes while complex
forms are very rare. If we add the evolutionary bottlenecks that intelligence
has to overcome, one would like to conclude that we are the only ones.
Stephen Awking, in "My Answers to the Big Questions" 2018, has
not lost hope, however, and writes: "For my part, I prefer that there are
other intelligent life forms out there but that, so far, we have escaped their
notice. ...We should, however, be alert to any alien communication before we
have developed a little more. At our present stage, an encounter with a
civilisation more advanced than ours would be comparable to the encounter of
the indigenous Americans with Columbus: I really do not think that, in
hindsight, the indigenous people considered it a happy event.
I would like to close this article by summarising Stephen Webb's
conclusion in "If the universe is teeming with aliens... where are they
all?" 2018.
We are looking for a planet that has an energy source, an atmosphere,
water in a liquid state and a landmass.
We are looking for a planet that contains a molten core so that it can
generate a magnetic field and support plate tectonics.
We are looking for a planet in whose solar system there is a giant
planet like Jupiter to shield the meteor shower and possess a moon to stabilise
the planet's axis.
We are looking for a planet that has adequate planet rotation and the
right distance from the centre of the galaxy.
We are looking for a planet that has remained habitable for billions of
years.
"We are looking for intelligent life forms that have developed
conscious self-awareness. ... We are looking for conscious, tool-making,
communicative intelligent beings who live in social groups (so as to reap the
benefits of civilisation) and who develop the tools of science and mathematics.
We are looking for ourselves ...”
Giovanni Occhipinti
(*) When science does not accept criticism and becomes dogmatic.
In 2005, I wrote an article in the school newspaper Il Magistraccio, 'On
the origin of life', which concluded:
[...] And does life outside our solar system exist?
And why not, indeed it may be more widespread than we think.
The question is: how far has life outside our solar system evolved?
Our advanced technology can be traced back to the discovery of radium
and nuclear fusion; less than a century. And what is a century, l00 years compared
to over 3,000,000 years when life began on our planet. The probability of life
elsewhere being at our stage of evolution is virtually nil.
We send signals in all directions in the universe: but who is the
recipient?
If life on some other planet has not reached our stage of evolution and
technology:
they don't understand us!
If life has surpassed our level of evolution, imagine aliens a million
years more evolved than us:
let's hope they don't understand us!
Because the risk is to end up like the American Indians, with the
aggravating circumstance that we have shouted to the four winds: ... WE ARE
HERE.
For this conclusion, I have been reproached by some colleagues for
conveying the wrong message, because scientific research must be free, in all
directions and with no stakes.
Years later, I am glad to know that I am not alone.
Next article: Origin of life: first proteins or first self-replicating
molecules (RNA world)? The search for common ground to overcome a dichotomy that
blocks the solution to the problem for more than half a century.
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