What qualifies as “life” and when do we start looking for it throughout the universe?

What qualifies as “life” and when do we start looking for it throughout the universe?


Centuries ago we wanted to find living beings in space.

What is concretely what we look for when we look for alien life? And what do we hope to find?

These are two of the questions that listeners sent from various parts of the world to the BBC Radio 4 program “The Curious Cases of Rutherford and Fry”, which is dedicated to investigate mysteries of daily life.

Concerns led the presenters, scientists Hannah Fry and Adam Rutherford, to investigate the subject thoroughly.

The first thing they investigated was the origin of our fascination : when was our scientific love story with ET born?

“We can trace this idea that we are not alone to the invention of the telescope, in the 1600s, ” said Seth Shostak, an  alien seeker” who works at the Seti Institute, the Carl Sagan research organization. of extraterrestrial intelligence.

“When Galileo pointed this small telescope at the sky and saw little balls, he looked at Jupiter and saw that it was a round ball and not a light, as it had been seen up to that moment,” Shostak recalled.

And from that moment it was assumed that those little balls in the sky were similar to our Earth and it was assumed that they would be full of life .

Alien theories

Different scientists and intellectuals wove their own theories of how these extraterrestrial beings would be.

For example, the Prussian philosopher Immanuel Kant, who lived in the eighteenth century, believed that the intelligence of extraterrestrial beings was inversely proportional to their distance from the Sun.

Painting of Galileo with his telescope
Copyright of the GETTY IMAGES image
Image caption The interest in extraterrestrial life arose after Galileo identified planets with his telescope.


Thus, the Mercurians were idiots and the Saturnians, ingenious. Meanwhile, Kant speculated that the Venusians would be passionate.

Another theory presented in 1848 speculated on how large the alien population was in space. It was estimated that if the density of that population coincided with that of England, the Solar System should contain 22,000 million inhabitants .

But the truth is that no one had concrete evidence … until the Italian astronomer Giovanni Schiaparelli turned his telescope to Mars in 1877, and noticed some traces of ocher and somewhat blurred crossing the surface.

He called them “canali,” which means channels, and some scientists believed that they were evidence of a network of channels dredged by a large number of Martians.

The emotion for the possibility of Martian life flourished in such a way that the French astronomer Camille Flammarion dared to declare: “It is almost certain that the inhabitants of Martet have a different form to us and fly in its atmosphere”.

A painting that shows Giovanni Schiaparelli with his telescope.
Copyright of the GETTY IMAGES image
Image caption Schiaparelli thought he saw traces on Mars that indicated the presence of life, but it was an error.


In the end, however, it turned out that everything was a mistake.

“Schiaparelli used a relatively primitive telescope and what he saw was a poorly focused image of Mars,” explained planetary scientist Monica Grady of the Open University (Open Univeristy) in the United Kingdom.

What are we looking for

Grady explained why so much of the search for extraterrestrial life centers on Mars.

“I think we’re obsessed because now we know what Mars looks like and we see that it must have been similar to Earth in the past,” he said.

Illustrations of Mars in the past with atmosphere and oceans like Earth and currently
Copyright of the NASA image
Image caption Mars in the past and now, according to an illustration from NASA. The red planet would have had an atmosphere and oceans in the past.


“The features seen there must have been rivers and lakes and there is some evidence – although not everyone accepts it – that there may have been an ocean on Mars,” he added.

“Now that we know all this, it really seems like the kind of place where you could imagine life .”

But what is that famous “life”? How could we define it? Asked Rutherford and Fry.

The answer was provided by the British biologist Matthew Cobb, from the University of Manchester.

” There is no generally accepted definition of what life is, as with art: we recognize it when we see it,” he said.

Astronauts with plant
Copyright of the ISTOCK image
Image caption There is no agreed definition of “life”.


However, Cobb clarified that there is a series of characteristics or basic attributes that are considered to be present in any living organism.

The list is known in the scientific and academic world under the acronym in English MRS GREN .

The letters represent the words: Movement, Breathing, Sensitivity, Growth, Reproduction, Excretion and Nutrition.

However, NASA does not use this definition.

“They have a Darwinian vision that maintains that life is a group of entities that is subject to natural selection,” says Cobb.

“Because all life must be able to reproduce and when reproducing errors occur and if those errors cause small differences they will eventually lead to evolution by natural selection,” explains the biologist.

Where to look

Despite our obsession with Mars, Monica Grady believes that our best chances of finding extraterrestrial life are neither there nor on another planet, but in distant moons that we know contain water .

An example is Europe , an icy moon of Jupiter. Another, Enceladus , Saturn’s sixth largest satellite.

Image caption Under the surface of Europe lies an immense ocean of liquid water.


And how could you see a way of life found there?

For now, experts believe it would be an aquatic lifestyle .

“According to physics, if there were large organisms living in the oceans (of these moons), within some bizarre ecosystem, some of those organisms would have to be able to move quickly either to be able to eat other organisms or avoid being eaten, therefore they would look like something like a dolphin or a squid or a shark, “predicts Cobb.

“If you want to move quickly in water, physics makes you look a certain way,” explains the biologist.

The idea of ​​an alien squid could disappoint more than one ET fan who hopes to find intelligent life off Earth.

But although today there is no evidence that exists, hope remains.

According to the Seti, each year at least one new planet suitable for life is created in our galaxy , so the odds are high that at least one of them will develop an intelligent species.

Of course, the next question will be whether they will have the means to communicate with us or us with them.

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