Questioning the existence of aliens is something that scientists and average Joes alike have done for decades. Everything from Spielberg's E.T. the Extra-Terrestrial to NASA's latest press releases shows just how large the discussion is and always has been. In fact, most people do believe that aliens exist in some fashion.
The main necessities for life are water and some form of energy source. Not surprisingly, there are some planets, exoplanets, and moons that fit the bill. Although we probably won't find little green men with bug eyes, that doesn't make the prospect any less exciting. Here are our 10 best chances at finding life in the universe.
TRAPPIST-1 is a planetary system a few dozen light-years away whose discovery was announced in early 2017. This system consists of seven Earthlike exoplanets orbiting an "ultra-cool" star, and it is one of our best shots at finding life beyond our own solar system.
For one thing, studying these exoplanets will be relatively easy because of how they rotate around their star. We can use a telescope to observe their transits, which is when they eclipse their star by passing directly in front of it from our perspective. We see the temporary dimming of the star's light as an exoplanet passes between the star and Earth.
These exoplanets also have reasonable temperatures due to the nature of their star. So they are cool enough for liquid water to have a chance to form.
Although all the exoplanets in this system are legitimate candidates to host alien life, three in particular are soundly in what is called the habitable zone. This is the area around a host star where an Earthlike exoplanet is capable of forming liquid water, assuming that all life-forms, like those on Earth, do in fact need water to survive.
Titan is the largest moon of Saturn, the sixth planet from our Sun. This moon could potentially harbor life but possibly not in the sense that we think. Titan does not exactly fit the description of being in a typical habitable zone.
Titan has water, and it has liquid. It just doesn't have liquid water. The water on this moon is completely solid because of the extremely cold temperature.
However, the liquid that fills the lakes and streams is not water but rather hydrocarbons. A hydrocarbon is a chemical compound of hydrogen and carbon in varying proportions. On Earth, we often think of these as gases like methane or propane.
This is the key factor that would make potential life on Titan so different. Essentially, these life-forms would not survive on liquid water like we do but rather on these liquid hydrocarbons.
Although there are still some technicalities and unanswered questions about science (like if life can live off something other than water), the possibility that Titan has alien life is certainly there.
Europa is one of Jupiter's moons here in our own solar system. It is another candidate due to its potential to hold liquid water. Europa is thought to have all the necessities for life including water, energy sources, and the right chemical buildup. The water is thought to be stored in oceans underneath Europa's surface.
It wasn't until recently that scientists made it possible to begin the exploration for life on this moon. It was announced in early 2017 that a mission called Europa Clipper would take place over the next several years. This mission is sending a spacecraft to Jupiter's moon to take pictures of the surface. This flyby would happen repeatedly, offering multiple opportunities to analyze the moon and search for life.
The Red Planet, the fourth from the Sun, is probably one of the most talked-about potential candidates for extraterrestrial life and even for human colonization. Despite the naysayers, finding extraterrestrial life on Mars really is a serious possibility.
We know by now that we won't find little green men or any intelligent form of life that we understand. However, there is evidence that there was and may still be microscopic life on the small red planet.
NASA's data suggests a past presence of floods and streams throughout the dry surface. So there is a chance that liquid water was once on the surface and life could have survived. With further exploration, scientists might find liquid water on Mars presently, instead of just the ice caps that they see today.
Enceladus, another of Saturn's many moons, has the astronomy world abuzz with its potential to hold water, unlike its hydrocarbon-rich sister. The water is supposedly underneath the crust of the moon, similar to Europa.
Once again, this would mean that microbes of some kind live there. At first, the presence of water was simply a hypothesis after some evidence found in 2015 gave scientists hope.
But in early 2017, a mission involving the Cassini spacecraft detected hydrogen molecules that point to a chemical reaction occurring under the surface. This chemical reaction, in which the ocean water reacts with surrounding rock to produce energy, could be useful to life-forms because an energy source is crucial to life as we know it.