Many scientists have spent many, many, many hours, rather, pondering whether we will ever stumble upon any life forms in some corner of the solar system. As the Fermi paradox says, how is it that no extraterrestrial civilization has visited us if the universe is such a big place with so many planets, stars and galaxies?
Precisely trying to answer this question, many scientists have presented justifications to support those places in the cosmos or, rather, in our solar system, that would have more possibilities to harbor life – perhaps as we know it .
In this regard, a team led by Dimitra Atri from New York University Abu Dhabi (United Arab Emirates) has created a methodology to classify the potential places where we should look for extraterrestrial life. We now know that life on Earth can thrive in even the harshest and most brutal environments, in super-cold and super-dry conditions, depths of unimaginable pressures, and without the need to use sunlight as an energy source.
The methodology, published on arXiv, focuses on a new variable: the microbial habitability index (MHI), which measures how habitable a specific environment is for the various types of extremophiles found in extreme places here on Earth. After defining several environmental variables that can affect habitability for life (temperature, pressure, ultraviolet radiation, ionizing radiation, pH, and salinity), they chose seven habitable worlds and collected as much data as they could about the environmental factors for each type of environment in each world potentially friendly to life.
The lucky ones?
It is one of the most likely candidates for finding bacterial life. Europe is literally awash in water. Beneath its outer layer of ice, there is a vast global ocean three times the volume of all the oceans on Earth. The intense tides caused by Europa’s interaction with Jupiter and its other moons create friction that generates heat, keeping the ocean warm. Furthermore, it is suspected that radiation hitting the icy surface could generate oxygen that could reach the subterranean oceans and be used by emerging life. We potentially have all the ingredients for life in Europe. The Clipper mission will help us discover the secrets of the moon Europa from 2024.
He is another of the ideal candidates (and also closer). Mars was habitable billions of years ago , when it had lakes and rivers of liquid water on its surface. If we find signs of ancient life, it is possible that life still exists on Mars. Maybe underground.
Covered in ice, it is not only one of the most reflective bodies in the solar system, but its plumes expel salty water, ammonia and organic molecules such as methane and propane. The moon is covered in ice 20 to 30 kilometers thick, and the surface temperature is about -201 degrees Celsius, but this water ejected in the form of jets of water vapor and ice crystals comes from a salty ocean. hidden under the ice of the satellite.
Saturn’s largest moon centers another of the places where we should be looking for life. It has one of the most robust atmospheres for a rocky world in the solar system outside of Earth and Venus. It is full of lakes, rivers and seas, although made of methane and other hydrocarbons. And there are many organic materials. NASA’s Dragonfly mission, which will send an unmanned helicopter to explore Titan’s atmosphere directly, will give us another closer look at this possibility of finding life.
The icy moon Ganymede, the largest natural satellite of Jupiter and the solar system in general, could contain a warm ocean under the ice and, perhaps, relatively complex life forms swimming in it. This hypothetical ocean would be ten times deeper than Earth’s ocean.
On Callisto, another moon of Jupiter (the third largest satellite in the solar system), it is also believed to have a vast subterranean ocean, underground. It retains a thin atmosphere of hydrogen, carbon dioxide and oxygen and could be habitable. Although, yes: it is quite cold. About -120ºC.
It is probably the one that surprises us the most of all. The dwarf planet Pluto is almost 5 billion kilometers from Earth, so it is not exactly a close destination since it is located in the confines of our solar system. However, studies indicate that it would have had the necessary conditions to harbor life . It could also harbor an ocean below its surface.
There is something about each of these floating orbs that could signify habitability. Astrobiologists are eagerly waiting for the Martian samples collected by Perseverance to return to Earth via the Mars Sample Return Mission and quell our curiosity about what might lie below the surface of Mars.
Reference: Dimitra Atri et al, Assessment of Microbial Habitability Across Solar System Targets. arXiv:2203.03171v2 [astro-ph.EP], doi.org/10.48550/arXiv.2203.03171