Has our planet ever been visited by aliens? Could we ever prove it if it had?
While many stories of alien visitations are, to put it bluntly, less than credible, you might be surprised to hear that, from a certain point of view, not all of these stories are unreliable. In fact, as you are about to find out, they may well be living among us.
Perhaps, just perhaps, we may even have our origins in outer space too.
Big claims for sure, let's see if they hold water. Hold on tight, this is going to get wild.
Do aliens exist?
In order to even begin to address this question, we first need to ascertain if alien life actually exists.
As far as we know, our planet is the only one in the entire universe with life, but can this really be the case? In fact, just asking the question might be asking for trouble.
Either way, the answer is likely to not be good news. If there were other lifeforms, especially if they are more technologically advanced than us, contact with them could prove pretty devastating for our species. That is assuming that advanced intergalactic species are even a possibility – there may actually be a cap on how advanced we could ever get.
While it is amusing to hypothesize about the existence of aliens or make films about contact with them, the reality of the situation would change everything about how we think about ourselves and our place in the universe.
The opposite would also be horrifying, and, quite frankly, very saddening. If we (all life on Earth) are truly the only living things in the universe, that would likely be equally shattering for our psyche.
However, many experts on the subject are fairly certain there is alien life out there. In fact, if you are a gambler, there are probably some very good odds.
According to a formula called the "Drake Equation," we have a pretty good idea of the factors necessary in order for life to form. By adding in a few variables like star formation, the fraction of the stars with planets, so on so forth, of all the trillions of star systems out there, the chances of there being life somewhere else, while very low, are almost guaranteed, at least according to the formula. However, we can never really be sure, as we will never be able to gather all the information needed.
As far as we know, the main ingredients for life are pretty common in the universe. Everywhere we train our scientific instruments, we tend to find components like water, the elements associated with life, and sources of energy. This is excellent news.
We've also found many exoplanets out there. Some of which appear to be in what is termed the "Goldilocks Zone" around their parent suns. However, that is the end of the good news.
To date, we have not, as yet, conclusively found another Earth-like planet out there. While the conditions on Earth might only be critical for Earth-life, the possibility exists that alien life is, well, completely alien to us. Would we know it if we saw it?
This should come as no surprise. Life on other planets will likely fall between two extremes - either not advanced enough yet for contact, or long extinct. After all, for most of Earth's long history, even our Mother Earth was inhospitable to life. A similar story is probably likely on alien worlds.
The reason for our inability to detect extraterrestrial life may well be a combination of our lack of sufficient technology and a lack of knowledge of how to actually recognize the signs of alien life. For advanced alien civilizations, there is some speculation that we should be able to detect advanced technology, such as a Dyson sphere.
We've had some close calls, but they have all turned out to be a completely natural phenomenon.
So, with the very slim chances that alien life even exists, and the even slimmer chance they might be technologically sophisticated enough to travel between worlds, is there any proof to the claims we've been visited?
Have we ever been visited by aliens?
From "E.T." to "Independence Day" popular culture is obsessed with storylines of aliens visiting our planet - as invaders, explorers, or otherwise. Partly borne out of our species' long history of pondering about the heavens, this notion is deeply ingrained in our cultural psyche.
But is there any truth to it?
Stories of Unidentified Flying Objects (UFOs) are a common feature in our media, and for good reason - they make for fascinating reading. In fact, the U.S. Government recently released documents that officially recognize their existence (but not necessarily the existence of alien craft). Though the military tends to refer to them as "Unidentified Aerial Phenomena" (UAP). Not quite as catchy.
But, if they are out there, how on Earth could we ever prove it? What kinds of evidence would we need?
Very generally speaking, and assuming aliens have visited Earth, discussion on alien visits falls roughly into two main camps: theories and claims.
We are all more than familiar with the second form of discussion, like the famous 1960s story from a New Hampshire couple who claimed they'd been abducted by aliens. The other camp (those of the theoretical kind) are equally as popular in the public eye. They also tend to be taken more seriously - especially if made by respected members of authority, like scientists.
Discussions about the nature of 'Oumuamua are prime examples of the latter. One notable voice at the time being one Avi Leob. Loeb was the chair of Havard University's astronomy department who, with a colleague, believed that the cigar-shaped interstellar object was likely an alien probe.
Needless to say, this stirred up a lot of heated debate in the scientific community.
While claims about 'Oumuamua are fun to speculate about, they do raise an interesting proposition. If aliens were to take an interest in our planet, it would probably be highly likely that they'd first send drones or robots rather than risk their own lives.
With regards to questions as to why aliens might take interest in us in the first place, if life, especially complex life, is actually very rare, then that is probably enough of a motive in and of itself. Think about how obsessed our species is with trying to find life on Mars or Europa.
Scientists at the Search for Extraterrestrial Intelligence (SETI) program certainly believe so. Seth Shostak, an astronomer at SETI, is one of those who suggest that first contact with aliens will likely be via probes or robots rather than living organisms.
Space travel would take a very long time, given the distances involved, and would require a huge investment in resources and energy. If you factor in the life support needed for a trip lasting many tens or even hundreds of years, assuming that faster-than-light travel is not actually possible, this would make such an undertaking something of a forlorn hope. Depending on the average lifespan of such adventuring aliens, it would likely take several generations to reach us. Unless, of course, they managed to create some form of stasis device.
So why would they bother to make such as trip? Such an investment would likely mean the visiting aliens are exiles, refugees, traders, explorers, or, rather worryingly, invaders. If we use human history as an analogy for these activities, pioneers were not shy at making themselves known to the native populations, to say the least - though admittedly they were the same species.
Logically, if aliens did make the investment to come all this way, they would be unlikely to ignore us. We would know openly that aliens have made "first contact." But it would also be far easier to send out probes. Just as we do today.
It would also be the safest option, as contact with an alien civilization might become hostile, very quickly. For this reason, most experts in the field think that our first contact with aliens would be through their technology, not their persons.
But, there is also the very real possibility that alien drones/robots could, in fact, be the aliens themselves.
Whatever the case, these probes would need to be space-worthy and be capable of sending back signals to their source civilization. Many of the reports of UFOs would certainly fit the bill as potential probes, but we can only speculate until one is actually physically studied.
Such probes, however, would also likely need some form of long-range interstellar communication that should, in theory, be detectable. Given the extremely long distances involved, this would likely be using some form of communication that could move at the speed of light, as radio signals would take many human lifetimes to reach another world.
But the technology used might be beyond our understanding of physics and technology. If so, it is highly unlikely we'd be able to detect such communications, let alone intercept and decipher them.
So what about the physical drones themselves? Until one actually lands and is seen by the general public, this will continue to be the reserve of speculation and theory.
There are countless reports of UFOs, both from official government sources and civilians, but most of these have been found to have a completely rational and natural source. However, there are some reports, footage, and stills that remain unexplained to this day.
For example, in 1954, a crowd of football fans in Florence witnessed a strange craft flying over the stadium. Described as either cigar or egg-shaped, the ship apparently left behind silvery-white threads. Samples of this material disintegrated on contact, but some were examined and were found to contain boron, silicon, calcium, and magnesium, and to not be radioactive. While some have speculated it may have been the sunlight glinting off a large-scale spider migration using silk "balloons," the incident was so long ago now that we can never really be sure.
A more recent example occurred in 1980 when U.S. Airmen stationed at RAD Woodbridge, Suffolk were tasked with investigating some strange lights in a nearby forest. The men later reported seeing a strange 3-meter high by 3-meter wide object land on fixed legs.
The craft, according to reports, was "smooth, opaque black glass" in appearance. Returning to the scene the next day, indentations were found on the ground and radiation levels were taken. Not believing the accounts of his colleagues, another airman ventured to the same spot with a tape recorder.
He reported seeing lights in the sky that appeared to "wink" and saw a beam coming down to the ground. The incident would later come to be called "Britain's Roswell."
While there are obviously many believers that this incident is clear evidence of alien visitation, others are more skeptical. One such disbeliever was psychologist Professor Chris French. He conducted his own investigation and discovered that the indentations were likely caused by rabbits. Radiation levels were also not uncommon for the area.
The lights may well have emanated from a nearby lighthouse. But, of course, we can never really be sure.
Another, more credible potential UFO sighting came from the USS Princeton in 2004. While on maneuvers with the USS Nimitz carrier strike group, an unknown craft was detected on her radar 100 miles (160km) off San Diego. For over two weeks the crew managed to collate data on objects that appeared high in the sky and then plummeted, to hover just above the Pacific Ocean.
Several FA-18F fighters were scrambled to investigate and noticed what appeared to be churning water with a shadow of an oval just below the water surface. Moments later, a white Tic Tac-shaped object appeared with no visible markings, propulsion system, wings, or windows. Infrared monitors on the aircraft detected no heat signatures.
Black Aces Commander David Fravor and Lt. Commander Jim Slaight of Strike Fighter Squadron 41 attempted to intercept the craft, but it accelerated away. It then reappeared on radar 60 miles (96.5km) away. The craft moved at three times the speed of sound and more than twice the speed of the fighter jets. To date, no one has been able to explain it.
And these are but some of the more credible sightings of UFOs on record. Sadly, without any real concrete evidence of such craft, the safest bet is to assume such sightings are either figment of human imagination, or as yet unexplained natural phenomena.
After all, extraordinary claims require extraordinary evidence.
So, the possibility that aliens have visited our home planet is not looking likely - at least for technologically advanced ones. But that is not the end of the story.
It turns out, there is another very plausible possibility that our planet has, and likely continues to be, "visited" by alien life. Let us introduce the concept of panspermia.
What is panspermia?
Panspermia, derived from the Ancient Greek "pan" (all) and "sperma" (seed) is a scientific hypothesis that life exists throughout the universe and is regularly distributed by phenomena like space dust, meteoroids, asteroids, comets, and planetoids. For any species that is capable of venturing into space, as humans, contamination of craft with microorganisms is also another potential vector.
Admittedly not a widely supported theory in science, it is, at least on the surface, a plausible idea. One of the main criticisms of the theory is that it does not actually answer the question of the origin of life (especially on Earth), as it must still have arisen somewhere at some time. It is also a particularly difficult theory to test experimentally.
It is important to note, however, that proponents of the panspermia hypothesis are not attempting to offer an explanation for the origins of life on Earth, but rather provide a potential framework for how life could be more common than we once thought. It would, for example, only require life to arise on a limited number of worlds yet provide a means of populating many more.
The theory proposes that microscopic life forms can become trapped in debris ejected from life-harboring planets during collisions with other bodies like asteroids. Once in space, so long as the microorganisms can survive the very hostile conditions (like extremophiles), they should, in theory, be able to be carried between worlds, solar systems, and even galaxies over time.
Another related theory, called pseudo-panspermia, argues that pre-biotic organic building blocks, rather than fully-fledged microorganisms, are distributed using much the same methods. These building blocks could then become captured by solar nebula and any subsequent planets that may form (or indeed by existing planets) and could provide a kickstart to the development of life on those planets.
Any life-bearing dust can then, in turn, contaminate new planets when life-bearing interstellar bodies pass by, or land on, a new habitable planet.
The theory actually has a fairly long history, with the first mention of something similar by the 5th-century BC philosopher Anaxagoras of Clazomenae (500 to 428 BCE), who mentioned "seeds" of life as being a part of the cosmos.
While largely forgotten thereafter, the theory was given a new lease of life, so to speak, through the works of various 19th-century scientists such as Jöns Jacob Berzelius and Hermann E. Richter.
The modern theory, however, is largely thanks to the work of Fred Hoyle and Chandra Wickramasinghe in the 1970s. In 1974, the pair proposed the hypothesis that some dust in interstellar space was largely organic (carbon-based). Hoyle and Wickramasinghe went further with the theory and even suggested that life forms constantly enter Earth's atmosphere and may be responsible for epidemic outbreaks, new diseases, and could even be the major driving force of macroevolution.
Is there any scientific support for panspermia?
The panspermia hypothesis is very intriguing on the surface, but is there actually any scientific support for it? You might be surprised to find out that there is.
To be feasible as a mechanism for transporting life naturally between planets several important things need to be met. The first, obviously, is for conditions on other planets, or space, for biological material to actually form.
While we can only speculate about the prospect of life evolving independently on alien worlds, there is, it seems, evidence that biological building blocks are fairly common in space. For example, in 2019 a study reported that they had actually detected sugar-like molecules, including ribose and other bio-essential sugars, in meteorites.
So long as the meteorite had not been contaminated prior to the study, this suggests that asteroids can carry at least some of the essential ingredients for the emergence of life through space. Complex hydrocarbons, like sugars, are an essential component of RNA, so, theoretically, if such material was introduced to a lifeless yet habitable world, this could kick-start the process of RNA formation.
Other studies have also detected other forms of organic molecules in the depths of space. For example, isopropyl cyanide, a structurally fairly complex hydrocarbon, has been detected in giant gas clouds tens of thousands of light-years away.
The branched carbon structure of isopropyl cyanide is a common feature in molecules that are needed for life – such as amino acids, which are the building blocks of proteins. The study which found the compound, conducted by researchers at Cornell University in 2014, highlighted the possibility that some critical components for life can, and do, form in gas clouds.
This is not only interesting in and of itself, but it does offer some support for the possibility of such molecules either being incorporated into early planet formation or as repositories which interstellar objects, like comets, could fly through and become contaminated with such materials.
The arrival of ʻOumuamua a couple of years ago, also adds weight to the possibility of insteller objects being a method of transporting such material between planets and solar systems, too. We also have abundant evidence of material being ejected and surviving entry between worlds.
Martian-derived rocks, for example, are fairly common finds on Earth.
So far so good for panspermia.
For the life that evolves on an alien world (or Earth for that matter) to actually get into space, it must be able to survive the mechanisms proposed for reaching space in the first place - i.e. ejection after asteroid impacts, etc.
Amazingly, it seems this is also theoretically possible. Various experiments in laboratories and low-Earth orbit seem to support the idea that ejection, entry, and impact are actually survivable for some organisms. In 2015, for example, biological remains were found in 4.1 billion-year-old rocks in Western Australia.
At that time, the Earth was a relative baby, at around 400 million years old, yet this suggests biological material was able to survive in the conditions that existed - setting the scene for the rise of life on the Earth as soon as conditions were right. The material in question was found in ancient zircon crystals and consisted of a mix of carbon isotopes that are usually only found in living things. Researchers theorized that the carbon is from a colony of tiny organisms of some unknown type.
The next consideration is to show that biological material (either fully-fledged life forms or building blocks), can actually survive and remain viable for long periods of time in the void. As it turns out, this part of the process might actually be possible.
Between 2008 and 2015, a series of astrobiology experiments were conducted on the outer surface of the International Space Station (ISS). Under the EXPOSE study, a wide variety of biomolecules, microorganisms, and spores were exposed to solar radiation and the vacuum of space for between one and two years at a time.
Some of these organisms actually survived, albeit in a dormant and inactive state. Other experiments have been conducted to simulate biological samples sheltered inside a meteorite-like material which provide some support, at least in theory, that biological material can survive the rigors of space for long periods of time.
So, things are actually looking up for the panspermia hypothesis. But, there is one last barrier to overcome before we can say with a little confidence that it is plausible.
That barrier is obviously the possibility of life surviving entry into a planet's atmosphere. Not to mention the actual impact.
Intense heat, and other forces, would be expected to effectively sterilize asteroids or other interstellar objects, and impact would also be expected to lead to biological contamination from contact with the surface. Amazingly, it appears this is not necessarily the case.
A 2004 study published in Nature actually supports the possibility that life could survive re-entry. Conducted by a British team of researchers, the study found that it should be possible for organisms to survive impacts at speeds of more than 11 km per second.
The team created a series of porous ceramics infiltrated with bacteria and used a gas-powered gun to fire bits of the ceramic into targets of gel or ice at high speed. At similar pressures to those that would be felt inside a meteorite as it crashed, about one in every hundred thousand bacteria actually survived the impact into the gel and remained viable.
While only a very small percentage of the original "population" of bacteria survived the impact, the survival of just a few individual cells is all you'd really need for the population to explode once in a habitable world. For icy targets, the survival rate was even higher.
This discovery, believe it not, is also partially supported by other non-related studies. For example, a 2019 study on an earlier meteorite impact in India showed that certain heat-tolerating bacteria, like Bacillus thermocopriae IR-1, can actually survive meteorite impact-like conditions.
The team found that around 30 percent of the subject bacteria could survive temperatures of 400 degrees Kelvin, and pressure of 300 kPA, traveling at Mach 1.47.
While all of this does suggest that biological material can in fact survive each isolated step in the hypothetical chain of events needed to travel from one world to the next, there is still a vanishingly small percentage that this could actually happen.
After all, the death rate from some of these events would likely exterminate most of the hitchhikers at any point in the process. There would be no possibility for the population to recover while in transit between planets, and any that did survive would need to run the gauntlet once again at the next stage in the chain, as well as when arriving on a new world.
However, a small percentage, even a fraction of a percent, is all you'd really need.
Who knows, the first life on Earth may even have been one of those alien microorganisms. We'll probably never know for sure, but it is fun to think about.
Until a UFO packed full of aliens lands in a public place, or giant robots from another world step onto the White House lawn, it is unlikely that we will ever be able to prove definitively that aliens have visited our world.
Of course, there is also the possibility that governments are covering up such an event (after all, the social implications would be potentially devastating), but given the series of very serious intelligence leaks over the years, and the inability of even a small group of people to keep a secret, this is probably not likely.
For now, we can take solace in the fact that there is a high probability other alien life forms likely exist somewhere out there. But where, and how advanced such aliens are, we can only speculate on — for now.