The three places in the solar system where we should look for life

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Decades ago the great popularizer Carl Sagan masterfully imagined different environments for life in a solar system that we were discovering little by little. In recent times, speculation has given way to strong evidence that some of these environments have the potential to host strange but suspiciously familiar habitats. The latest scientific data allows us to focus the search towards the places that seem most likely.

In recent weeks, various news items have drawn three very different situations. Phosphane on Venus invites us to think of life forms suspended high up, in a completely aerial habitat. Just a few days later new results were announced on Enceladus, one of Saturn’s icy moons, emphasizing the idea of ​​an encapsulated ocean. Finally, Mars again presented its candidacy for habitability with the confirmation of lakes of liquid and salty water under its surface.

Life in the clouds, in an ocean trapped by ice, or in underground lakes? They are not as strange places as they might seem.

The possibilities of Venus have been much talked about recently. The authors of the phosphane discovery have also shown a possible life cycle that would allow the maintenance of microbes in an aerial biosphere. This hypothesis had already been discussed previously and allows opening various lines of research in the terrestrial environment. The hypotheses that are handled for Venus imply the life contained within the cloud droplets to compensate for both the acidity and the enormous lack of water in our neighbor.

Enceladus is a moon made up basically of water, covered with ice on the outside. Inside, the friction generated by Saturn’s tides would provide the energy source necessary to create a gigantic encapsulated ocean. This situation would be similar to that of other satellites, such as Europa, on Jupiter.

In 2005, the Cassini probe detected the presence of a water geyser. Since then, attempts have been made to determine by different methods what is the proportion of ingredients such as salt, urea, or ammonia both to favor and to harm the possible presence of living beings.

A deep reanalysis of the data accumulated over 13 years by Cassini has detected finer and younger regions around the “tiger stripes” shown by Enceladus. These zones could be related to hot spots in the deep ocean, perhaps, as on Earth, volcanoes, or fumaroles.

The underwater volcanic environment has been pointed out as the possible origin of life on Earth and is the dream of any astrobiologist since it allows us to search for life outside the Earth as well as study our own origin. The closest terrestrial analog would be Lake Vostok, in Antarctica. If we remember the enormous effort involved in accessing the lake itself under just a couple of kilometers of ice, it is clear the enormous complexity of accessing the possible habitat of Enceladus, under a crust perhaps ten times thicker.

Mars, the eternal candidate

Finally, Mars always appears in astrobiology, not only because of the more than firm evidence of the continued presence of liquid water on its surface but also because the exploration of its potential habitats, both present, and past, is perhaps one of the most simple.

Recently, the Mars Express mission has confirmed the previous detection of lakes buried a kilometer and a half below the surface. Although the interpretation of the observations continues to be debated, water with high salinity could remain liquid under these conditions, sheltered from some of the difficulties offered by the surface of the red planet, such as extreme changes in temperature and defenselessness against radiation. solar.

The Martian possibilities of halophilic organisms, addicted to salty environments, have been studied for their potential to generate methane, the biomarker gas that appears to have been detected on the red planet.

These three environments, so apparently different, have in common their analogies with the Earth and are therefore very suggestive scenarios where to look for simple life forms in our galactic neighborhood. All of them have their own limitations, but they also have great potential to increase our knowledge of how life could ignite and prosper on our own planet.

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