The other times we thought we found extraterrestrial life

It's hard to imagine a more exciting discovery than extraterrestrial life.

We know that the entire cosmos is made of the same bricks, hydrogen atoms that accumulated to form stars, which when exploded produced new elements that ended up filling the periodic table.

Despite the diversity of the worlds that populate the Solar System, its volcanoes, its plains or its oceans are composed of the same materials as Earth.

However, something happened on our planet, not long after its formation, that allowed some combinations of elements to come to life, and, after billions of years of evolution, made possible the appearance of primates capable of wondering if that phenomenon was a unique miracle or life, like mountains, is prevalent in the universe.

Scientists have never managed to explain well how living things can appear from inert elements, but there is some consensus that at least the simplest forms of life should not be a rarity in the cosmos.

It is believed that the first living things appeared on Earth a few hundred million years after its formation, 4.540 million years ago.

The first animals, however, took 3.5 billion more years to appear, and 500 million more years passed until human ascent.

Intelligent beings are much rarer than bacteria.

Mars and Venus had oceans shortly after their formation and they were much more habitable than today

Despite the fascinating discovery of life outside our planet, the process of discovering it may not be so exciting.

Intelligent aliens are a rarity and may be found in unreachable regions of the universe and microbes will be discovered little by little, through their signals, long before they can be seen under the microscope.

When they get there, decades or centuries of indirect study of their existence may have diluted the surprise.

This Monday, the journal

, announced the discovery in the atmosphere of Venus of phosphane, a gas that on Earth has fundamentally a biological origin.

The authors suggest that, once other possible origins for the substance have been ruled out, this could be a sign that living things could be found in the upper parts of the atmosphere, where the temperature and atmospheric pressure are somewhat more bearable than on the surface. .

There will be other groups that will seek to improve observations with ground or space telescopes, but only a mission to the planet to take samples would undoubtedly confirm the existence of extraterrestrial life.

It is not the first time that the discovery of microscopic aliens from indirect signals has been announced.

In 1976, Viking probes sampled the soil of Mars for such clues.

In an experiment led by Gilbert Levin, they mixed radioactive carbon-labeled nutrients with soil samples.

In this way, they observed the production of radioactive methane, a signal that was interpreted, at least momentarily, as an indication that microbes were metabolizing nutrients and generating the gas.

Decades later, the scientific consensus considers those results to be inconclusive, although Levin has continued to defend that they detected life.

Two decades later, in the summer of 1996, a group of NASA scientists claimed that they had found fossilized microbes in a rock that arrived 13,000 years ago from Mars and that it had been found in Antarctica in 1984. As in previous cases, the evidence they were indirect.

The meteorite contained particles of magnetite, a mineral sometimes found in terrestrial bacteria.

Over time, evidence has accumulated that magnetite was not like that found in bacteria and that the crystals they formed could be due to other chemical processes.

Like his colleague Gilbert Levin, David McKay, the leader of the NASA team that signed that announcement of extraterrestrial life, has defended his results for years.

Much farther away, on Jupiter's Europa satellite, traces of sulfur have also been found that some scientists have attributed to biological activity.

This element would suggest that the ocean discovered under the icy surface of this moon could be habitable, but as on previous occasions, explanations simpler than the existence of life have been found.

In the coming decades, there are plans to develop missions that search for life in Europa, but the experience of that search in much closer worlds like Venus and Mars gives an idea of ​​the difficulties of the hunters of extraterrestrials.

There are also hopes pinned on many of the exoplanets discovered in recent years, but there, once again, unequivocal signs of biological activity will have to be found and visiting those worlds, light years away, will require travel technologies not yet invented.

If life is finally found on Mars or Venus one day, it would be an indication of its ubiquity in the universe, but also of the fragility of the most complex forms when things get ugly.

Both Venus and Mars were originally more habitable, with oceans covering their surface.

In those first hundreds of millions of years of existence, as happened on Earth, life could appear.

Later, Venus turned into a hell caused by the greenhouse effect and Mars lost a protective atmosphere for life.

It is possible that in the former some bacteria took refuge in the upper layers of the atmosphere, where the pressure and heat are bearable for the most resistant.

On Mars, the microbes would have retreated underground.

For now, they are hypotheses as plausible as that life never arose in those worlds or that two extreme climatic changes devastated it completely.

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