Are we alone in the universe? Every one of us has thought about this question at least once in his life. Looking at the infinite amount of stars in the sky and realizing that we are just one of the trillions of planets in the universe, it is almost impossible to think that life just started on Earth.
Although we still do not have a definite answer, we made incredible advances in the last 50 years, from the first step of human kind on the Moon onward, and came to the conclusion that life could not be a prerogative of Earth.
What are we looking for?
The expeditions that NASA and other worldwide organizations are launching to look for life outside of our planet, are mainly trying to find two things: water and oxygen. Water is an amazing solvent, with perfect properties to allow the formation of organic molecules at the base of life. With its high boiling and low melting points, it can be found liquid at the right temperatures for life and used to transport nutrients and waste inside and outside of living organisms. Moreover, no matter how extreme the conditions are (very high pressure, extreme temperatures or pH) – life can be found on Earth only if there is water.
The second possible sign of life would be oxygen, and in particular oxygen present in the atmosphere together with methane. In fact, these two gases cannot coexist, because with time they would react with each other resulting in carbon dioxide and water. Therefore, if oxygen and methane are present, this can only mean that there are some living beings replacing them in the atmosphere, as it happens on Earth.
Places that could host life in our Solar System
In our system, there are other seven planets that orbit the Sun and take energy from it, and many of them have also a large number of moons. Although there are still no signs of oxygen anywhere else except from Earth, water has been found in different forms. There are 23 places in our Solar System that have water and two of those places are of special interest: the planet Mars and Jupiter’s moon Europa. While on Mars the water is evident at the two poles in the form of ice and rivers of salty water appear in summer on the surface of the planet, on Europa a big ocean is trapped under the superficial layer of ice. Scientists think that alien microorganisms could be living in this water: it would be incredible to be able to really find them, study their biology and understand how different they are from their terrestrial counterpart!
In additon to Mars and Europa, the Cassini expedition funded by NASA, ESA (European Space Agency) and ASI (Italian Space Agency) discovered water on one of the moons of Saturn: Enceladus. Also in this satellite, an ocean is hidden under the surface, thus increasing the number of places in our Solar System with the right conditions for life. During the ten years of Cassini’s expedition, Enceladus was not the only surprise. The scientists managed to observe that Titan could also have the right conditions to host life. But not life as we usually think of it. Titan has oceans and rivers on the surface, very similar to those on Earth. The difference is that instead of being formed by water, which cannot be liquid due to the very low temperatures, they are made of methane and ethane. More surprisingly, on this moon methane may cycle as water does on Earth, forming clouds in the sky and falling down on the surface as rain. Here life could have evolved with a completely different biochemistry in comparison of what we expect, a biochemistry that employs methane instead of water!
To learn more about this and other incredible discoveries made by the Cassini expedition, you can watch the extraordinary TEDx talk by the NASA scientist Carolin Porco.
Looking for an Earth-like planet.
Another project funded by NASA looks for Earth-like planets outside of our Solar System. In fact, it is very likely that there would be another planet among the trillions out there with the right size, the right distance from its own sun and the right composition not only to host life, but to be just like Earth. To do that, they are building the biggest microscope that ever existed and they think that they will be able to get the first answers already 20 years from now. See how they will do it by looking at the inspirational TEDx talk from Shawn Domagal-Goldman.
Now, next time that you look up at the sky, you will be able to imagine that there is something else alive out there and that our first encounter with alien organisms might not be so far away.