A Brief Summary Of Carl Sagan's Tought And Activity
How many of you have seen the film Contact directed by Robert Zemekis, starring Jodie
Foster, or read the homonymous science fiction novel by Carl Sagan which inspired the movie?
Both the book and the novel describe a hypothetical first contact between humans and aliens and
the related ethical and religious implications, as well as in general dealing with of the
relationship between faith and science.
But who was Carl Sagan?
Carl Sagan was born on November 9th, 1934 in Brooklyn, New York.
At the age of 7 he went to the library to find out what the stars were, and this anecdote
testifies that from an early age he began to be very curious about everything related
to space and astronomy.
In 1956 he graduated in physics, and then specialized in astrophysics at the University
of Chicago, where he earned his PhD in 1960.
He was one of the founders of exobiology, a branch of astronomy that deals with the
search for life in space, from the identification of the prerequisites for its birth, to the
possible environments for its evolution and maintenance.
He was one of the greatest supporters and popularizers of SETI (Search for Extraterrestrial
Intelligence), the program aimed to search of extraterrestrial intelligence: in this
regard in 1966, together with the Soviet astronomer Iosif Školovskij, he published the first
book dedicated to this topic: Intelligent Life in the Universe.
Still in the SETI environment, in 1974 a symbolic attempt was made to send a message to other
worlds.
To celebrate a substantial expansion of Arecibo's 305 m radio telescope, a coded message of
1679 bits was transmitted to the globular cluster M13, about 25,000 light-years away
from us.
The sequence of 0s and 1s that made up the message was a 23 × 73 matrix that contained
some data on our position in the solar system, the stick figure of a human being, chemical
formulas and the outline of the radio telescope itself.
The 23 × 73 matrix was chosen because both 23 and 73 are prime numbers.
It was assumed that this fact would help a hypothetical alien listener recognize the
matrix structure.
Since the message has been sent at the speed of light, no eventual response can reach us
before 50,000 years; for this reason the whole experiment was dismissed as a sort of commercial.
Unfortunately, the glorious Arecibo radio telescope, due to severe damage resulting
from the Puerto Rico earthquake of January 1st, 2020, completely collapsed on December
1st, 2020.
Would you like to transmit a message like this?
With Louis Friedman and Bruce Murray, Carl Sagan founded the Planetary Society in 1980,
an organization that now brings together more than 100,000 members passionate about space
adventures and exploration of the Solar System.
He was the first to understand the origin of the very high temperatures recorded on
the surface of Venus (due to the greenhouse effect).
He helped solve the mystery of the profound changes that astronomers observed every year
on the surface of Mars.
Sagan had speculated that they were due to dust storms, hypotheses later confirmed.
In this lively context of space exploration, two of the initiatives for which Sagan is
remembered are inserted: the message on the Pioneer 10 and 11 probes aimed at a possible
extraterrestrial intelligence and Pale Blue Dot.
Let's see them in detail.
In 1972 Pioneer 10 was launched by an Atlas/Centaur rocket.
The launch saw the use of a three-stage launch vehicle for the first time.
The third stage was needed to launch Pioneer 10 at the speed of 51810 km/h required for
the flight to Jupiter.
This speed made it the fastest man-made object to leave Earth, enough to reach the Moon in
11 hours and cross the orbit of Mars, some 80 million km away, just 12 weeks later.
On July 15th, 1972, Pioneer 10 entered the Asteroid Belt.
Objects in the belt move at great speed and their size varies from speck of dust to rock
as large as Alaska.
After crossing the Asteroid Belt without problems, Pioneer 10 headed for Jupiter.
The acceleration due to the mass of Jupiter has increased its speed to over 11 km per
second.
He flew over the Jovian clouds on December 3rd, 1973.
During the passage near Jupiter, Pioneer 10 obtained the first close-up images of the
planet, discovered the presence of intense radiation belts, located its magnetic field
and discovered that Jupiter was a liquid planet.
After his encounter with Jupiter, Pioneer 10 explored the outer regions of the solar
system, studying the energetic particles from the Sun (the solar wind) and cosmic rays that
reach the branch of the Milky Way where we are.
It is the first man-made object to leave the Solar System on June 13, 1983, when it passed
the orbit of Neptune (which was the most distant planet from the Sun at that time, due to the
eccentricity of Pluto's orbit).
On March 31st, 1997, when the mission was formally over, Pioneer 10 was 10 billion km
from Earth.
At this distance, a radio signal traveling at the speed of light would take 9 hours and
43 minutes to reach us.
Originally designed for a 21-month mission, the probe has been active for more than 30
years.
"After 32 years of service - commented the head of the mission, Larry Lasher, in the
NASA center of Amer Research - it was a more than honorable performance for an instrument
initially designed to last just 21 months".
In 1973, the sister probe, the Pioneer 11, was launched.
Pioneer 10 is currently heading towards the star Aldebaran, in the constellation of Taurus.
It will take more than 2 million years to reach it.
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Both Pioneer 10 and Pioneer 11 carry a message aimed at any extraterrestrial civilizations,
actually an aluminum plate anodized with gold, on which a series of designs are engraved
that would allow a possible extraterrestrial civilization to know us, understand how we
are made and place us. in the space.
The original idea was not born directly from Sagan's mind, but was conceived by Eric Burgess,
a space science journalist, during a visit to the Jet Propulsion Laboratory in Pasadena.
But the proposal was immediately welcomed with enthusiasm by the astronomer and his
colleague Frank Drake (famous for the mathematical formula used to estimate the number of extraterrestrial
civilizations able to communicate in our galaxy) who, within three weeks, conceived the message.
and engraved the plaque.
But what do the figures engraved on the gold plate of the Pioneers mean?
The most immediate drawing for us to understand is that of the man and woman, positioned on
the right side of the plate and both naked: the woman with her arms at her sides and the
man with his right hand raised in greeting.
A gesture familiar to us, but not easily understandable for a completely different civilization from
ours.
The wave of greeting is more than anything else useful to show the joints of our limbs
and the opposable thumb.
Behind the two human figures, the outline of the probe itself is traced, drawn with
the same scale factor, with the intention of making it clear how big we are.
The meaning of the left side of the plate is more complex, where a series of lines - 15
to be precise - appear, radiating from a single point.
They represent 14 pulsars, whose distance from the Sun is indicated by the length of
the corresponding line, while the fifteenth line - the one that extends behind the human
figures - represents the distance of the Sun from the center of the Galaxy.
Each of the 14 lines is accompanied by a number in binary digits, which indicates the period
of the pulsars, an important information, because it allows to determine the epoch in
which the launch took place (the periods of the pulsars, in fact, change over time).
Once the time and place of origin of the plate have been identified, the hypothetical alien
could know in detail our planetary system and the exact position of the Earth through
the drawing located along the lower edge: here we see the Sun, the largest circle, followed
by nine smaller circles, the planets; attention, nine and not eight because in the seventies
Pluto was still considered a planet.
An arrow that starts from the Earth and goes towards Jupiter, and then passes the gas giant
towards the immensity of the cosmos, represents the trajectory of the probe, which is also
drawn in small format.
Finally, perhaps the most enigmatic representation is the one placed at the top and which represents
the transition of hydrogen due to spin inversion, that is, the passage of the hydrogen atom
from a spin-up state to a spin-down state.
This transition corresponds to a very precise wavelength (21 centimeters) and a very precise
frequency (1420 MHz).
All binary coded numbers that appear on the plaque use this length (or this frequency
in the case of time measurements) as the unit of measurement.
And what would you have written in this message?
Also famous is the Pale Blue Dot, a photograph of planet Earth taken in 1990 by the Voyager
1 probe, when it was six billion kilometers away, well beyond the orbit of Neptune.
The idea of turning the probe's camera and taking a picture of the Earth from the edge
of the Solar System came from Carl Sagan, who later also used the name of the photograph
for his 1994 book Pale Blue Dot: A Vision of the Human Future in Space, which describes
his vision of the human future in space.
In his book Sagan exposes his thoughts on deep meaning of that photography.
Here is a famous passage: “From this distant observation point, the Earth may not seem
of particular interest.
But for us, it's different.
Look at that dot again.
It's here.
It's home.
It’s us.
On it, everyone you love, everyone you know, everyone you've ever heard of, everyone who
has ever lived has lived their own life.
The whole of our joys and sorrows, thousands of religions, ideologies and economic doctrines,
so self-confident, every hunter and gatherer, every hero and coward, every creator and destroyer
of civilization, every king and plebeian, every young couple in love, every mother and
father, hopeful son, inventor and explorer, every preacher of morality, every corrupt
politician, every "superstar", every "supreme commander", every saint and sinner in the
history of our species has lived there, on a tiny speck of dust suspended in a ray of
sunshine.
Earth is a very small stage in a vast cosmic arena.
Think of the rivers of blood spilled by all those generals and emperors so that, in glory
and triumph, they could become masters of a fraction of a dot for a moment.
Think of the endless cruelties inflicted by the inhabitants of one corner of this pixel
on the scarcely distinguishable inhabitants of some other corner, how frequent the misunderstandings,
how eager to kill each other, how fervent their hatred.
Our ostentation, our imaginary self-esteem, the illusion that we have some privileged
position in the Universe, are challenged by this point of pale light.
Our planet is a lonely speck in the great, enveloping cosmic darkness.
In our darkness, in all this vastness, there is no indication that help will come from
somewhere else to save us from ourselves.
Earth is the only known world that can host life.
There is no other place, at least in the near future, for our species to migrate.
Visit, yes.
Colonize, not yet.
Like it or not, for the moment the Earth is where we play our cards.
It has been said that astronomy is a humble and character building experience.
There is perhaps no better demonstration of the folly of human vanities than this distant
image of our tiny world.
For me, it underscores our responsibility to look after each other more kindly, and
to preserve and protect the pale blue dot, the only home we've ever known."
Sagan was also director of the Laboratory for Planetary Studies at Cornell University
and professor: he held courses in critical thinking until his death.
Although the places available for each semester were only 20, these courses had hundreds of
students per year: Carl Sagan was also an illustrious exponent of the movement of scientific
skepticism, to the point that he was one of the promoters of the CSICOP (Committee for
the Scientific Investigation of Claims of the Paranormal), born to combat pseudoscience
and irrational beliefs.
The last book he published in his lifetime, The world haunted by demons, represents a
sort of spiritual testament in which Sagan warns humanity against the proliferation of
a new obscurantism.
He was also very active as a science communicator.
Carl Sagan died in Seattle on 20th December 1996, but he’s still alive in our memory:
a 95 km diameter impact crater located near the Martian equator bears his name as well
as the asteroid 2709 and the prestigious Carl Sagan Memorial Award.
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