Liquid water, energy sources and a very specific combination of chemical elements. Life as we know it – that is, life on Earth – basically needs these ingredients to exist. However, this is just “life as we know it” and, therefore, we cannot rule out the possibility that life flourished in other worlds from different combinations than what happened here. Except that even thinking only about the combination that we already know for life, there are still other worlds that have a great chance of providing us with a positive answer to the question: “Is there or has there been life outside Earth?”.
The recent discovery of phosphine on Venus may be an example of this. “It can”, because it is not yet known what is the source of phosphine in the Venusian atmosphere – if it really has biological origin, or if it would be the result of physical and chemical processes that we did not expect to happen on rocky planets. It is still too early to say that there is life on Venus, although that possibility has taken the spotlight when it comes to the search for life forms in other worlds.
But we claim that there are other worlds in the Solar System that look promising in the search for life – albeit microbial or ancient, which may no longer exist today, right? Meet some of them!
When it comes to looking for life in our surroundings, the Red Planet follows as the “darling” in that sense. This being one of the most Earth-like planets in our system, a day there lasts 24.5 hours and its polar caps expand and contract according to the seasons. In addition, in recent years we have found that many of the characteristics of its surface have been sculpted by liquid water that existed there for a long time – and, well, where there is water, there can be life, right? We have just learned that there are more reserves of liquid water below the ice at the Martian south pole.
Also in recent years, we have discovered organic molecules on Mars, which may indicate the existence of ancient microbial life there. Specifically, the organic compounds called thiophenes, found on the Red Planet, can be produced by living beings, since, here on Earth, they are produced through biological processes – that is, bacteria that would have existed on Mars more than three billion years ago. years could have produced the thiophene discovered in the Martian rocks.
In addition, we have also found strangely high levels of methane on Mars, another thing that may indicate the existence of life there. On our planet, most of the methane in the air is produced by living creatures, although methane is also emitted through geological processes, without the interference of living beings.
Discovering reservoirs of liquid water and methane in the Martian atmosphere makes the Red Planet one of the great candidates for the discovery of life beyond Earth – which is why space agencies such as NASA and the European ESA are so dedicated to sending in-person missions. there, with probes and rovers doing continuous work of analysis and studies in this direction. By the way, NASA’s new Perseverance rover will arrive in February 2021 precisely with the main mission of searching for bio signatures on Mars (that is, concrete evidence that life existed there at some point in its distant past).
Europa is one of the moons of the Solar System that are always involved when it comes to the search for life outside Earth. Discovered by Galileo Galilei with the other three large Jovian moons (which became known as “Galilean moons” because of this), Europa is slightly smaller than the Earth’s Moon and is quite affected by the tidal effect – that is, it it is constantly compressed and stretched by the gravitational pull of Jupiter, as well as the other larger moons that are there.
This allows the existence of its underground water oceans, which are below its frozen crust, since the tidal effect warms the rocky and metallic interior, allowing the existence of liquid water. Were it not for this, the distance that Europa is from the Sun would cause its water to always remain frozen – as with the outside of the surface. Therefore, as Europe is home to a global ocean (which can be more than 100 km deep), it is worth following the maxim that “where there is water, there can be life”.
But there can also be life on the surface, especially in the “gaps” on the surface, where geysers expel the inner water, which is poured into space. Recently, it has also been confirmed that water vapor exists on the surface of Europa. This vaporized water may contain microbes that can survive radiation for a short time. To find this out, both NASA and ESA have face-to-face missions planned here: the European Space Agency works on the JUICE mission, which will launch in 2022, while the US agency has the Europa Clipper mission, which is due to launch between 2023 and 2025 .
A similar process to that discovered on the Jovian moon Europa happens in Enceladus, one of Saturn’s moons that also has a frozen crust, also has a liquid underground ocean, and also expels this vaporized water as plumes through cracks in its surface.
In addition to water, we also discovered that there are complex organic molecules in Encélado, with this discovery being reaffirmed shortly afterwards when NASA discovered other types of organic compounds there.
Some of these compounds can only exist if groundwater is in physical contact with a rocky bottom at a specific temperature, which, for many scientists, is extremely strong evidence that there are hydrothermal vents at the bottom of this ocean, which may be providing all the energy and chemistry needed to have life there.
Another Saturn moon that also draws attention due to the possibility of harboring some kind of life is Titan – the largest around this gas giant. It is the only moon in the Solar System with a substantial atmosphere, and has very familiar geological features, similar to those on Earth. However, Titan has, instead of liquid water, rivers and lakes of liquid and methane and ethane, and its atmosphere consists mainly of nitrogen – an important chemical element that is part of the construction of proteins.
Titan also appears to have an underground reserve of liquid water, as there, it appears that there are cryovolcanoes – geological structures similar to our volcanoes, but which erupt water instead of lava. This moon also has plains covered with organic material and has maritime activity.
To study all this up close, NASA will send the Dragonfly mission there. It is a mix of drone and exploratory robot that will fly through Titan’s dense atmosphere and land in strategic places with the aim of, among other things, providing us with more information to find out if life may also have appeared there.
* With information from The Conversation
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