Nathalie Cabrol: “Bio-astronomy is going through a golden age”

Nathalie Cabrol searches for signs of life in the universe. Elementary or intelligent life, near or far, similar to ours or so different as to be unrecognizable. In short, she is a bioastronomer, or astrobiologist, depending on whether you want to emphasize life or the celestial bodies that could host it. It is a profession that did not exist twenty years ago.

Tormented story
For a long time, astrobiologists were not recognized as fully engaged researchers in their work. Officially, they were planetologists, radio astronomers, biologists, geologists, biochemists, perhaps psychologists… They dedicated part of their time to the study of extraterrestrial life and

marginal funding, they carried out an activity between volunteering and amateurism that some colleagues considered an extravagant hobby. The events of this scientific specialization are troubled. At the beginning we talked about exobiology. In 1981 the International Astronomical Union (IAU) created Commission 51 Astrobiology to search for extraterrestrial life. In 2006 he renamed it Bioastronomy with a focus on intelligent life. After the 2015 reform, it is now the F3 Astrobiology Commission.

Fatal encounter
Born in France 51 years ago, graduated from the Sorbonne, American citizen, Nathalie Cabrol tells us how scientists are trying to discover alien creatures in the book “The Dawn of New Worlds”, promptly translated by Chetro De Carolis for the publisher Castelvecchi ( 283 pages, 20 euros). It is a compelling read because it interweaves the author’s biography with parallel developments in bioastronomy. Nathalie had the fateful meeting for her destiny as a researcher in 1998 when she met Frank Drake, the radio astronomer who founded her, with the planetary scientist Carlo Sagan, of modern astrobiology. She happened in Mountain View, California, at the SETI Institute, Search for Extra-Terrestrial Intelligence. Drake was famous for being the first to look for artificial signals coming from space and to estimate the number of hypothetical extraterrestrial civilizations (the so-called “Drake equation”). With him Nathalie Cabrol, trembling, had an interview, and Drake assigned her a research position. Today you direct the Carl Sagan Center of the SETI Institute.

Fundamental problem
Cabrol believes she lives in the golden age of bioastronomy. «The dawn of new horizons» she reviews the stages. In the 1960s, the vision of the Earth suspended in space spread by the astronauts of the Apollo 8 mission – says Nathalie – made us aware that “thinking of being alone in this cosmic ocean is simply a statistical absurdity”. However, a fundamental problem remains: we still don’t know how life appeared on Earth, we can only make crude conjectures and experiments to reproduce the original environment: the first was done by Stanley Miller in 1953 in California, the latest is in 2022 all University of Tokyo. No such experiment has been conclusive.

A series of discoveries
But space exploration has already provided interesting results. Phosphine, a potential biological “signature”, has been discovered in the upper atmosphere of Venus. Now we know that there was water on Mars and that there is still some in the form of ice: perhaps elementary life forms developed, Cabrol herself looked for them in the Gusev crater with the Spirit rover. The Pioneer, Voyager, Galileo and Juno probes found a lot of ice on the Galilean satellites of Jupiter and on Enceladus, a small moon of Saturn. The European Huygens spacecraft landed on Titan, Saturn’s largest satellite, and revealed an unprecedented methane meteorology in three states, gaseous, liquid and solid. Pluto is partly covered in ice. Since 1995, evidence has accumulated that planetary systems like ours are not an exception, indeed, they are the rule: almost all stars have one, and runaway planets have been discovered, drifting in the interstellar darkness.

«Connect the dots»
The discovery of exoplanets and other research have led to an update of the “Drake equation”. Now the SETI program, says Cabrol, wants to “connect the dots”, put together all the observations made to actually discover extraterrestrial life forms. But here a problem arises again: how to define life? In 2011 the molecular biologist Edward Trifonov tried it starting from 123 definitions coming from science, history and philosophy. Reduced to the essential key words, the definition arrives at two antithetical concepts: self-reproduction and change, that is, the eternal copy of the identical and its evolution. Trifonov reconciled them like this: «Life is an almost exact self-reproduction, with some variations». La Palisse. Already in 1924 Oparin had said “Every system capable of replicating and changing is living”.

When Drake came to Turin
I was lucky enough to interview Frank Drake in 1998 when he passed through Turin. He told me that he had accidentally picked up a radio signal that seemed artificial in 1956, when he was 26 years old and preparing his doctoral thesis. «I felt a mixture of enthusiasm, joy and disbelief. I was breathing heavily with excitement, from that moment my hair began to whiten. Maybe it feels like this when faced with a miracle. You realize that in that moment another story began for the world, and you are still the only one who knows it. My hands were shaking thinking that somehow I had “touched” an alien mind.”

OZMA project
History repeated itself in 1960, when Drake organized Project Ozma (from the story «The Wizard of Oz» by Frank Baum). «For a few weeks we pointed the 25-meter radio telescope in Green Bank, Virginia, towards the stars Tau Ceti and Epsilon Eridani. From Tau Ceti, silence. But a strong, very clear signal came from Epsilon Eridani. Even too much. I did a series of checks. Eventually we discovered that we had picked up the radio of a U2, the spy plane that the United States then flew into the stratosphere to monitor the Soviets. It was a great disappointment, but it didn’t affect my desire to ferret out ET.”

By 2100?
After directing the Lunar and Planetary Section of JPL (Nasa) and the Center for Radiophysics at Cornell University, in his free time he was a passionate sailor and great swimmer, Drake continued his ET research in Mountain View, presiding over the SETI Institute. How likely – I asked him – do you think there is of actually picking up an alien signal by 2100? «It’s very unlikely but it can’t be ruled out. In any case, if it happened it would be such a revolutionary event that it would still be worth trying.” And if contact occurred, what do you imagine the content of the message would be: a simple “We are here” or something more? Again: what could our response be? “It depends,” Drake explained. “It doesn’t mean that the message has to be intentional. For at least thirty years we have been emitting radio waves that could be picked up by intelligent creatures living around nearby stars, but they are not intentional messages: they are television news, shows, advertisements. Of course, if the message was intentional, it would be necessary to evaluate it very carefully before reacting. A SETI conference in 1990 established a protocol to be respected in this case: the message belongs to all of humanity, and it is up to the United Nations to manage the response, while the announcement to the public, after very rigorous checks, would be up to the discoverer”.

The time is ripe
Drake, who died in 2022 at the age of 92, believed that humanity was ripe for such an experience: «52 percent of Americans believe in the possibility of contact, science fiction films themselves have contributed to creating a strong expectation. If, as is probable, the alien civilization were technologically much more advanced than ours, we could have suggestions for the solution to humanity’s most serious problems: how to have abundant energy at negligible prices, how to avoid conflicts, how to overcome diseases and perhaps death itself, how to ensure the happy survival of our species…”.

Ten thousand civilizations in the Milky Way?
Michel Mayor had recently discovered the first exoplanet. «Today – said Drake in 1998 – in our galaxy there should be at least ten thousand planets inhabited by intelligent creatures. But even if that were the case, statistically these planets would have to be on average more than a thousand light years away from each other: the time that would elapse between a message and its arrival, and then between the response and the second message, it would be several thousand years. Now, in my formula the most uncertain parameter is precisely the one that concerns the duration of a technological civilization. How long does a technologically advanced civilization survive? Here the estimate cannot be scientific. We are faced with a sociological parameter. It is possible for an advanced civilization to quickly self-destruct, as we risked happening to us with nuclear weapons… If civilizations capable of communicating live for a few decades, then the probability of coming into contact approaches zero. Instead the other parameters, with the accumulation of new discoveries, become increasingly optimistic: in recent years we have observed dozens of planets around other stars, we have discovered that there is water on Europa, Jupiter’s large satellite, and that perhaps on On Mars, life took at least its first steps, originating primordial microorganisms two billion years ago…”

The needle in the haystack
The first receiver used by Drake to listen to radio-universe analyzed one channel at a time. Current receivers analyze over one hundred million channels simultaneously. Yet finding an artificial signal in the cosmic buzz is more unlikely than finding the classic needle in the haystack. «We believe that the wavelength on which an alien civilization would most likely transmit is around 21 centimeters, i.e. 1420 megaherz. The hydrogen atom, the most widespread element in the universe, emits on this frequency. Furthermore, in this microwave region there are fewer disturbances… However, terrestrial electromagnetic pollution worsens. Satellite phones are a ruin. For now we defend ourselves by observing simultaneously with two or more radio telescopes, in order to eliminate spurious signals. But we will have to place the next radio telescopes on the hidden side of the Moon, or in interplanetary space, perhaps even in interstellar space, where the gravitational lens of the Sun concentrates the signals. Over there, a one-square-meter dish would be equivalent to a signal collection surface of one square kilometer!

The hands of the Universe
Let’s stay on the ET theme and point out other interesting readings. Francesco Rosario Ferraro, professor of astronomy at the University of Bologna, has just published «Children of the stars. A journey between space and time to discover our origins and our future” (Bietti, 217 pages, 18 euros). Giulia Fabriani deals evocatively with stellar and cosmic evolution in «History of light» (ilSaggiatore, 260 pages, 24 euros). The dating of great cosmic and biological events is the common thread followed by David Helfand in «The hands of the universe. Reconstructing history atom by atom” (Apogeo, 270 pages, 22 euros), a highly original text that takes us from the discovery of radioactivity to the nuclear processes used to date archaeological finds, climatic variations, dinosaur fossils, cyanobacteria, meteorites, formation of the Sun and the Earth, until the Big Bang, when the hands ticked the first seconds.

The dawn of life
A magnificent book on the origin of life was written by Raghuveer Parthasarathy, professor of biological physics at the University of Oregon (USA). The publisher Carocci is currently distributing the Italian translation, «A simple beginning» (350 pages, 32 euros). Given that physical laws and chemical elements are common to the entire universe, the author identifies four principles underlying the living world: “self-assembly”, which presides over the formation of DNA and proteins; the «regulation circuits», which control the stability of complex assemblies; «predictable randomness», which provides, on large numbers, valid results around the average values; “scalability”, i.e. the idea that the shape and structure of living organisms depend on physical forces and dimensions. In the light of these “simple” principles, Parthasarathy retraces the entire path of evolution, from pre-biotic molecules to man. And, incidentally, he also explains “why elephants can’t jump.”

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