How to prove there is life on Earth – PIEUVRE.CA

Thirty years ago, a scientific article showed that there was life on Earth thanks to a space probe heading to Jupiter.

The idea came from astronomer and popularizer Carl Sagan. Like many others over the years, he had wondered aloud how it would be possible to find evidence of life on other planets. No intelligent life: just life. What would be “recognizable” from a great distance?

An opportunity presented itself with the Galileo probe: it was launched in October 1989 on a long trajectory towards Jupiter, which resulted in it using the gravitational effects of Venus and then Earth to accelerate to its final destination while using less fuel .

And so in December 1990, when Galileo was 600 miles from Earth, it sent its instruments back to our planet. The result of his “discoveries” was an article published in Nature on October 21, 1993, entitled “A Search for Life on Earth from the Galileo Spacecraft.”

At the time, many suspected that one of Jupiter’s moons, called Europa, hid an ocean of liquid water beneath its thick layer of ice – a hypothesis that would strengthen Galileo. The most optimistic even said that this ocean might harbor life – something that is still being debated today. Could a possible life form be discovered there by Galileo? One way to test this was to see if Galileo could “detect” indirect traces of life on Earth.

And indeed, Galileo measured oxygen and methane in Earth’s atmosphere, the latter in quantities high enough to suggest a biological origin. He discovered a signature in the infrared light of the sun reflected from our planet that suggested the presence of vegetation.

By the way, radio signals were also detected: We can hypothesize, wrote Carl Sagan’s team ironically, “that these signals were generated by a form of intelligent life on Earth.”

If this “research” is still cited—a “brave” experiment, as this week’s Nature editorial puts it—it is because it had a profound impact on astrobiology or biology “elsewhere.” This science is clearly unable to study life forms anywhere other than on Earth. But she’s thinking hard about methods by which we might prove that life exists elsewhere – and perhaps even more difficult, proving that the “trace” or “signature” we’ve discovered is actually from living things and not from a chemical or geological phenomenon is caused.

When Galileo passed near Earth, astronomers had never discovered planets orbiting stars other than our Sun. Today there are more than 5,500 of them and some of these planets are in the so-called “habitable zone” around their star. The new James Webb Telescope has begun analyzing the atmospheres of some of them.

Science fiction had created the habit of easily identifying aliens. But reality in the not-too-distant future is more likely to take the form of questions about unusual methane levels, abnormal infrared fluctuations, or water vapor in the atmosphere.

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