Drake's equation

Frank Drake was convinced that the first contact with an extraterrestrial civilization would occur during his lifetime.

He was wrong — he died on Friday without having seen it — but the astronomical world that bids him farewell is surely very different from the one in which he was born, when the mere fact of mentioning the possibility of extraterrestrial life was a passport to scientific ostracism.

Today there is even the specialty of astrobiology in some prestigious universities.

It is true that astrobiologists tend to spend their days in Rio Tinto, Huelva, and other mundane places of extreme conditions, but their knowledge is useful in designing the

that search for life on Mars and the telescopes that will track it in the atmosphere of planets as far beyond even our imagination can reach.

Much of this change in attitude is due to the massive discovery of extrasolar planets in the last couple of decades.

And the other part is due to Frank Drake, the astronomer who founded the SETI (

) program and took the first look out there by tracking radio signals coming from a distant civilization.

The idea that advanced civilizations emit radio waves comes from our own experience, since we have inadvertently emitted them at least since the 1940s, when radio and television broadcasts began with a certain intercontinental power.

Drake and his closest colleagues, Jill Tarter and Carl Sagan, reversed the argument and began looking for signs of others.

Sixty years of failure later, the exploration continues.

But is there anyone there?

Why so much impertinent silence?

It's frustrating, don't you think?

The unofficial name for this metaphysical vertigo is "Fermi's paradox," which has this form: if there are so many stars in the galaxy, and such a fraction of stars have planets, and such a fraction of planets are at the proper distance from their sun, etc. … Where is everybody?

That is more or less the mental calculation that Enrico Fermi made during a meal in the laboratory, and the phrase that he pronounced when he returned to the mainland.

Because, according to Fermi's mental calculation, and given how long it should take to colonize the galaxy, the aliens would already have to be here.

Drake was a good astronomer, and his colleagues knew it perfectly well.

He made the first radiowave map of the center of the Milky Way, discovered the Van Allen belts on Jupiter, measured the density of the atmosphere of Venus, and directed the Arecibo Observatory in Puerto Rico when it was the largest radio telescope in the world.

He also made wine and grew orchids.

But his greatest contribution to science will, in all likelihood, end up being a correct, if somewhat truistic, formalization of the Fermi mental math I told you about earlier.

It's called the Drake equation, and it estimates the number of civilizations in the Milky Way as the product of the number of stars times the fraction of them that have planets times the fraction that are the right distance from their sun, and so on up to seven factors.

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