It seems we still want to believe. With the much anticipated X-Files miniseries reboot having premiered on Sunday, once again the theories of alien life will reach peak curiosity. Of course, there hasn't been any conclusive evidence of alien life — here, visiting Earth, or in space — but there are plenty of compelling scientific theories, backed by hard evidence, that suggest alien life could be out there, perhaps, even within our solar system.
1. There are chemical precursors to life on other planets — the same ones that could have kickstarted Earth.
While the origin of life on Earth can still be debated among the scientific community, new findings suggest that the first traces of life on the planet over 3 billion years ago could be attributed to organic chemical reactions, according to Live Science.
The study, presented in 2013 at a meeting of the American Astronomical Society, broadly concludes that life could originate from complex organic compounds formed within gas, dust, and plasma-filled interstellar clouds. As a result, these chemicals were then deposited onto Earth in the form of asteroids and meteors — which hit our planet much more frequently in Earth's infancy.
How does this relate to aliens? Well, the same events could have, and could still be, happening on other planets. Titan, Saturn's largest moon, has had similar chemical precursors on its surface, which means life — albeit, on a very small scale — could be present. "On this moon, clouds with convective movements are formed and, therefore, static electrical fields and stormy conditions can be produced," said Juan Antonio Morente, a professor in the University of Granada's department of applied physics, according to Daily Galaxy. "This also considerably increases the possibility of organic and prebiotic molecules being formed."
2. Oceans and lakes are already in our solar system.
Just as life on Earth originated in our oceans, life on other planets could have started in a similar fashion. After all, there is already hard evidence of water once flowing on Mars, while Titan also has evidence of water as well. However, Europa — one of Jupiter's moons — stands as the best present-day example of potential alien life.
Essentially, scientists believe Europa has a gigantic ocean, completely covered in a layer of ice. What we don't know is if there was ever life in the water — or if there could still be organisms within the planet right now. Oddly, Hollywood might have jumped the gun with the Europa alien theories. In the 2013 sci-fi horror film, Europa Report, a group of scientists traveled to the moon to find potential sources of life. As it turned out, the moon did have life, and it was not happy to be disturbed.
While it's highly unlikely that an alien of that magnitude is hiding in Europa's planet-wide ocean, something could be.
3. Some creatures on Earth can survive in space.
There are a lot of species on Earth, big and small, but the most unique organisms are extremophiles. Extremophiles are able to "thrive in extreme environments such as hydrothermal vents," according to the National Ocean Service. What this allows scientists to see is the extent to which these organisms can survive, and therefore, the extent to which the conditions for life are possible.
Among these creatures, the Tardigrade, also known as the "water bear," stands out for its indestructibility. It can withstand intense heat, cold and radioactive conditions but, most notably, can survive in the vacuum of space. With regard to alien life, this demonstrates the extent of an Earth-based organism's capacity to survive, and if it can withstand the conditions of space, similar creatures could be on other planets and moons. "The fact that they can exist in vacuum means that other organisms might have a tun-like state, drifting through space in search of new worlds to thrive on," Annalee Newitz wrote for io9.
4. Earth-like planets are popping up more frequently.
Being able to find an alien planet that shares similar characteristics to Earth is an important indicator of potential habitable planets — namely, a planet's size and its distance to an orbiting star, according to Space.com.
Thus far, the Kepler space telescope has been able to find several planets that have Earth-like qualities, though we still cannot be sure if any of them can support life. The other issue is the distance of the planets: Even the best candidates are light-years away, and we've yet to send an astronaut to Mars. However, the discoveries are instrumental to understanding the complexities of our universe, and just how much we've yet to explore. And, of course, what kind of alien life could be around the long, long corner.