For many years, humankind has looked up at the night sky and asked one question: Are we alone in the universe? The existence of extraterrestrial life has been doubted by many, but with the sheer number of planets and stars in the universe, there's bound to be another "Earth" somewhere. But even with the question of being alone in the universe, many more subsequent questions arise. Are there other intelligent civilizations in the universe? What do they look like? Are there civilizations more advanced than Earth? How long have they been around?
In order to answer this question, it is crucial to understand how life began and evolved on our own planet. However, scientists are still unsure about the true origins of life on Earth. From our understanding, we know that life must have water in order to survive. This is because it can dissolve substances and enable key reactions in animal, plant, and microbial cells (Natural History Museum). Earth was able to develop liquid water on its surface because it is the right distance away from the Sun in order for water to exist in a liquid form. This is known as the habitable or "Goldilocks" zone. If Earth was farther away, the water would freeze, and if it was closer, the water would evaporate. We can all thank asteroids for bringing the "ingredients" that gave Earth water in the first place.
Enough about water on Earth, though. We're trying to figure out if this scenario could happen anywhere else in the Universe. It doesn't seem highly unlikely, right? As mentioned earlier, the amount of planets and stars alone means that there has to be another planet with liquid water on its surface, right? Well, Artist's impression of K2-18 b [Image credit: ESA/Hubble, M. Kornmesser]
astronomers have already found exoplanets with water on them! One highly potential candidate for life is exoplanet K2-18 b. Water was discovered in its atmosphere, and the planet orbits in the habitable zone of its star. This is a very crucial discovery, since this is one of the only planets we've discovered so far that is just the right temperature to support water, and that contains water in its atmosphere (Scientific American). This discovery even took place before the development of very advanced telescopes (such as the James Webb Space Telescope), which makes it even more groundbreaking.
Although water was found in the atmosphere of K2-18 b, scientists are currently unsure about the amount of water, saying that it could range from a hundredth of a percent up to half of the planet's atmosphere (Scientific American). Such an observation will require the use of more advanced telescopes which are currently under development (although there are a number of exoplanets where we can observe how much water they have on them). However, one of the biggest takeaways from this discovery is that water can exist on other planets. There may even be subsurface oceans existing on the icy moons in the outer Solar System, but that's not the focus of this.
Since we've discovered water on another planet, that means that life has to exist beyond Earth, right? Problem solved! Well, not quite... In order to sustain life, there has to be an adequate amount of water on the surface of the planet because of its importance to life. About 70 percent of Earth's surface is covered in water, which could be used as a rough estimate for how much water other planets would need, but then again, this is just me speculating. Something interesting to note is that water shouldn't be such a rare thing in the universe. It is just made of hydrogen and oxygen, which are some of the abundant elements out there. However, even though water may be "abundant" in the universe, it tends to come in small quantities. Scientists studying a group of exoplanets found that the ones with water in their atmospheres only had a small amount of it (Forbes). This means that "Earths" are rare, which is sad to think about. But this study was done with a very small sample size. We've discovered thousands of exoplanets, while only about 19 or so were chosen to be observed. That means that we could find something totally different in the future, which would lead us to believe something different.
Since we've discussed a crucial factor that makes planets habitable, let's stop and think for a second about the possibility of us finding life elsewhere in the universe. If we were to find it sometime in the near future, how would humanity react? You've probably seen your fair share of sci-fi movies with alien invasions of Earth, but are invasions really possible? Are there highly advanced civilizations somewhere in the cosmos that are watching Earth as we speak? What if humanity makes contact with those aliens? How would we handle it?
Believe it or not, there has actually been research done on this topic! Michael Varnum, an assistant professor of psychology at Arizona State University conducted a study analyzing the language in past newspaper articles about potential extraterrestrial discoveries. The articles included the 1996 discovery of possibly fossilized Martian microbes, the 2015 discovery of the periodic dimming of Tabby's Star, which was thought the indicate the presence of a Dyson sphere, and the 2017 discovery of Earth-like exoplanets orbiting in the habitable zones of their stars (Science Daily). These are all promising discoveries in the realm of alien life. Varnum and his team aimed to address the nature of reactions to alien life by analyzing reactions through a software program that quantifies emotions, feelings, and other psychological states in written text (Science Daily). This study found that the articles used more positive language than negative language when covering these discoveries.
In another study, the team asked about 500 participants to write down their own (and humanity's) hypothetical reactions to the discovery of microbial extraterrestrial life, and the results showed that their reactions were significantly more positive than negative, both when stating their own reactions and humanity's reactions to such a discovery.
Currently, it is unclear whether or not advanced, intelligent civilizations are out there, since we haven't been able to come into contact with them, but what if we did? What implications would this have for humanity? Scientific literature and science fiction as a whole have put forth various scenarios in which humanity could come into contact with an extraterrestrial civilization (Wikipedia). In one instance, the contact could be physical, where humanity is visited by an advanced extraterrestrial civilization (as shown in science fiction movies). Another instance could be through radio signals, as scientists have currently been doing. However, there is something to note in the case of contacting aliens via radio signals. There would be large gaps between sending and receiving messages (which depends on various factors such as the distance between civilizations) and this would potentially impact the consequences of contact as well as the mutual comprehension of humanity and the other civilization (Wikipedia).
Another fundamental question to ask is: what kinds of civilizations could humanity possibly come into contact with? Well, in this scenario, there are really only two possible answers: friendly civilizations or hostile civilizations. Let's go further into the implications of coming into contact with either one of these civilizations.
One would originally think that a friendly civilization might teach humanity the secrets of the universe or show us some highly advanced technology that we have not yet developed. Many writers have had their own speculations, such as Albert Harrison, a psychology professor at UC Davis. He thought that a highly advanced civilization might teach humanity things such as a physical theory of everything, how to use zero-point energy, or even how to travel faster than light, which humanity has stated is impossible (Wikipedia). Futurist Allen Tough possesses the view that an advanced extraterrestrial civilization may look back on its own hostile past filled with war and destruction and want to help humanity rather than destroying it. He then goes to identify three approaches that a friendlier civilization might take to help humanity (Wikipedia):
Intervention only to avert catastrophe: This means that there would be limited "interventions" from this friendly civilization where they would try and prevent humanity from a global catastrophe, such as a nuclear war, or even an asteroid impact. This is very beneficial for humanity because we are very capable of "wiping ourselves out" due to how many nuclear weapons we have. If we had another civilization to try and stop us, it could prolong humanity's existence ad teach us how to resolve disputes without resorting to war.
Advice and action with consent: In this instance, the extraterrestrial civilization would be more closely involved in humanity's affairs, and even consulting with world leaders and acting with their consent in order to protect against danger. This would be very beneficial for humanity as well, but we would have to make sure that the other civilization does not take things "too far" and still let humanity be able to make crucial decisions for themselves.
Forcible corrective action: This means that the extraterrestrial civilization could require humanity to reduce major risks against its will, with the intent of helping humans advance to the next stage of civilization. This instance could also turn out negatively for humanity if the aliens go too far, but in the end it could still be very beneficial if humanity is advancing as a civilization.
"However, even if such a technologically advanced civilization were to help humanity, humans could suffer from a loss of identity and confidence due to the technological prowess of the extraterrestrial civilization" (Wikipedia). In order to prevent this, the aliens could limit their contact with humanity in order for the interactions to have a net positive effect. Michael A. G. Michaud suggests that a friendly and advanced civilization may even avoid all contact with an emerging species like humanity, so that we can develop at our own pace. This is known as the zoo hypothesis (Wikipedia).
Now that we've discussed what it may be like to come into contact with a friendly advanced civilization, it's time to discuss another possibility, which is coming into contact with a hostile civilization. This is akin to what is shown in sci-fi movies, with aliens invading Earth and taking humanity as their slaves. "Scientists have the view that an extraterrestrial civilization with sufficient power to reach the Earth would be able to destroy human civilization with minimal effort" (Wikipedia). It's absolutely terrifying to think about, but there may very well be civilizations out there with the intent of "colonizing" the universe, and if these civilizations were to ever come in contact with humanity, the impact would be catastrophically devastating. This could be achieved in a number of ways, such as destroying the major population centers of the planet or bombarding the planet with deadly radiation.
It is speculated that only a small number of advanced civilizations in the universe would be hostile, but their hostility would range on a spectrum, with all of them having different "goals" in mind. "According to Albert Harrison and Steven J. Dick, hostile extraterrestrial life may indeed be rare in the universe, just as the belligerent and autocratic nations on Earth were the ones that lasted the shortest periods of time, because humanity saw a shift away from these characteristics in its own sociopolitical systems" (Wikipedia). There are many reasons why a civilization would become hostile, perhaps the lack of resources, or the need to expand and become bigger, which would require traveling the cosmos and finding places to do so. However, for now, it seems that it is unlikely that humanity will encounter such a threat, although it is not impossible.
Plumes on Enceladus [Image credit: Cassini Spacecraft]
Although none of these things have happened at this moment, we can still look forward to the many future discoveries being made by astrobiologists that will get us closer to finding life beyond Earth. We've already made some groundbreaking discoveries that have completely changed the fields of astrobiology and planetary science. These discoveries include Cassini finding plumes on Enceladus, hinting at a subsurface ocean that could possibly sustain life, and ancient riverbeds on Mars, indicating that it must have contained liquid water on its surface in the past. As the technology progresses, we will be able to make better discoveries and answer some of the remaining questions that we have in this field. This includes things such as the Europa Clipper mission, which will travel to Jupiter's moon Europa and learn about its potentially habitable environments. Needless to say, there are around 10 trillion galaxies in the universe, each filled with billions of stars and planets. The possibilities for what's out there are virtually endless! It would be strange to think that we are alone in the universe, because the odds of that happening are very small, due to the true vastness of the cosmos. As Carl Sagan once said: "Somewhere, something incredible is waiting to be known."
Sources used (if you want to do more research on this topic):
Past blog post: Are We Alone?
This blog post covers a similar topic, but goes more in depth on HOW to find aliens and where they are