By Harry Keller
Editor, Science Education
We live in a very large universe. By all accounts, it’s over 14 billion light-years to the edge from here. That’s nearly 10,000 billion billion miles. Our galaxy contains billions of stars. Our universe contains billions of galaxies. Somewhere out in those vast spaces, there must be, or have been, or will be another advanced civilization.
Unfortunately for those yearning to communicate with aliens and fortunately for those who fear alien contact, we are very unlikely — in the extreme — ever to communicate with an alien civilization. Our only real hope lies in violating Einstein’s laws of relativity, and so far they’re as solid as granite.
The vastness of space that makes the existence of aliens, at some time, likely also means that they will be too far away for any meaningful communication. If any are in our galactic neighborhood, they may have broadcast pictures of themselves just as we are doing every day with television, and we may intercept them if we can tease them out of the background noise of quasars, exploding stars, and so on.
Even an image of an intelligent, technologically advanced alien would add enormously to our knowledge of science. Speculation about what an alien would look like may seem like a waste of time, but it can help us if we ever do see one to recognize it.
The topic of what an alien, one with technology, with whom we could, in theory, someday communicate, will look like, act like, and so on has been in science fiction books and movies for many decades. Hollywood tends to reach for the extreme and depict aliens as very frightening. The movie, Alien, is a good example of that trend. Going back very far, there’s It Came from Outer Space.
The science suggests otherwise. Not that real aliens wouldn’t be, well, alien. The likelihood of them passing for one of us is rather remote. If you are teaching science, this concept can begin an excellent and engaging project investigating the possible parameters of alien beings capable of broadcasting images of the themselves. Before heading into the appearance of aliens, consider two separate issues that bear on this topic.
The first issue is evolution. The concept of evolution has become the bedrock of modern biology. It also helps enormously to pare down the range of possible alien appearance and internal biology. If you’re an evolution denier, then you should go off and read science fiction. We’re dealing with fact, not fiction, here, and non-evolution is definitely fiction.
The second issue relates to interstellar travel and probabilities of an appropriate planet being nearby. Our galaxy is about 100,000 light-years across. Current technology can support travel at only a small fraction of the speed of light. Even though we may eventually be able to send our astronauts on long voyages using hibernation technology, that will do us here on Earth little good. We have found only about 54 stellar systems within 16 light-years of Earth. With much more advanced propulsion systems, we may someday be able to visit them on journeys lasting less that today’s typical lifetime. Rest assured that traveling 16 light-years will take very much longer than 16 years. We may be able to do it in 80 years sometime in the future. Even then, the message from those who made the trip would take 16 more years to come back to us.
Unless those aliens are residing in one of those 50+ star systems nearby, we will not be traveling to meet them in the lifetime of anyone reading this. SETI has pretty much ruled out a technological civilization that close to us that is sending out radio-frequency radiation. We are alone on our “block” in our galactic neighborhood.
A particularly long-lived alien civilization with sufficiently advanced space travel technology could reach us from a larger radius, but certainly not more than 100 light-years. That radius may encompass 10,000 stellar systems. Although SETI has not definitively ruled out radio-frequency transmissions from anywhere within that radius, it has made it rather unlikely after roughly 50 years of searching.
Some science-fiction scenarios imagine a race of aliens who had to leave their native planet and now have become interstellar nomads who raid appropriate planets for raw materials and/or seek a new home planet. The vastness of space within our galaxy suggests that there would have to be thousands, if not tens of thousands, of such nomads for any likelihood of an encounter with one of them. Technological advances argue otherwise. A race on a doomed planet that had the capability to travel vast interstellar distances to seek out planets would be able to find them locally and adapt them to their needs. They’d hardly be likely to doom themselves to wander until chance brought them to a “good” planet.
We can rest assured that we are unlikely in the extreme to ever encounter aliens in our lifetimes. Only unheard-of technological advances could make that event even remotely likely.
Given the above, our best hope for seeing an alien is to have a picture transmitted to us from far away, really far away. Even that possibility is remote. Despite these reasons to ignore what aliens look like, it’s a great bit of speculation that touches on many different areas of science. Besides, it’s not completely impossible for us to see an alien.
Aliens Do Exist
All science indicates that life on Earth began nearly as soon as it could. As the Earth cooled down from the Hadean epoch and moved into the Archaen, our best calculations based on all evidence indicate that single-celled life started rather quickly, maybe in only a few million years or even a few hundred thousand years. We know that oceans worth of water rain down from space on planets every few million years, the product of stellar explosions, along with plenty of carbon, nitrogen, and other elements necessary for life more or less as we know it.
For these reasons, we can safely assume that finding a planet with the right stuff for life means that we have found a planet with life. However, when you realize that Earth’s life was single-celled for around four billion of its four-and-a-half billion years, you can expect that the life on those other planets will mostly be single celled too.
Given that evolution requires a kick in the teeth to do anything, you can further estimate that some planets could be operating with single-celled life for much longer than four billion years. Most planets with recognizable life will find that life existing as single cells in bodies of water.
We will find plenty of alien life once we can get out there with our spacecraft and look at planets first-hand, but we won’t be talking to those cells. The science of other-worldly life will be fascinating in its similarities to and differences from ours. Alien biology may provide the clues we are missing to fix whatever remains of our mortal ills here on Earth at the time we find it.
Before delving more deeply, you should take a moment to reflect on chemistry. I know, that was probably the worst class you took, but what you must consider involves only a tiny bit of it, mostly related to the Periodic Table of Elements. We refer to ourselves and all life on Earth as being carbon-based and for good reason. For example, all proteins consist of amino acids that have a carbon backbone. Carbohydrates have carbon backbones. Fats, aka fatty acids, also have carbon backbones. Carbon is a versatile element being the sole ingredient in both graphite and diamond.
Science fiction often has fun portraying aliens as having a chemistry that is not carbon-based. Unfortunately, that’s not at all likely. In fact, it’s nearly impossible. For example, silicon, the next quadrivalent element in the Table after carbon, also forms a dioxide, but silicon dioxide becomes solid silica and is not soluble in water — unlike carbon dioxide.
Despite silicon being one of the major ingredients of the Earth’s crust, it’s not as common as carbon. Dying stars make lots of carbon, nitrogen, and oxygen. The universe is mostly hydrogen. Those four elements make up most of the amino acids. A very few also use sulfur. To build up life in water, you must have lots of the necessary elements and compounds. Along with oceans of water that rain down on planets throughout the galaxy every several million years, they also receive massive amounts of other compounds such as simple amino acids, cyanogen, carbon monoxide, and so on. With seas full of these compounds, life is ready to go as a carbon-based biology.
Covering a planet with life requires incredible amounts of basic elements, amounts unavailable if you choose some weird elements like arsenic or selenium. Carbon, nitrogen, and oxygen, along with hydrogen, provide the necessary chemistry and are already present in space combined in the basic compounds of life. This fact is a simple fact of stellar life. Those stars make the elements, and the environment around the stars forms those elements into water, amino acids, and the rest.
Worms and Bugs
It took a long time for those single cells to have anything to do with each other. Initially, they just did their own thing. Like bacteria today, they must have been opportunistic. No nutrients would mean no growth. Bump into some nutrient, absorb it, and turn it into more of self. Eventually, make copies of self, which allows for variation, which allows for evolution if the change increases the efficiency of the organism enough to out-compete its forbears.
It must have been in this fashion that the first colonies of bacteria arrived. The first bacteria must have had no predilection for association. There weren’t enough of them in close proximity to make that concept worthwhile. Once colonies formed, there would be reasons for other bacteria to visit. It could be the products of that particular life were useful or that cells died and left debris that could be fed upon by others. We only know that bacteria must have associated with others not of their kind because some combined to form new and more powerful species. Today’s eukaryotes must have been one of the more successful because their pattern is repeated across so much of today’s life.
The second thing that eukaryotes did was to share. We don’t know how long that took, but it changed everything because it allowed the first multicellular organisms to evolve. A multicellular organism contains more than one sort of eukaryotic cell. It involves specialization. This cell does this, and that cell does that. They both survive by working together, and their specialization allows them to compete more effectively for resources. Without the evolutionary step of multicellular life, visits to alien planets would see nothing but microscopic life, perhaps some goo here and there.
Locomotion must have come along as some cells helped with movement while others digested food. Early on, that food would have been raw materials in the oceans. Eventually, lots of dead bacteria would have become food as some bacteria adapted to digest them. Some multicellular organisms could develop chemical sensors to help find this dead matter to feast upon.
Movement and senses — these started something very big. Here on Earth, they led to what we call the “Cambrian Explosion.” A vast number of new life forms popped up around 540 million years ago in the fossil record. They had to have hard body parts to do so. Those parts attest to an evolutionary arms race that must have been going on for a long time, perhaps millions of years.
Many of the new life forms disappeared as quickly as they appeared, unsuited for the new way of life on Earth. Some did well. Among those with greatest success were the segmented worms. The idea of body segments, a further expansion of specialization, did well. Another great success was bugs. They had hard shells and also were segmented. One lineage did particularly well, the trilobites. In essence, they ruled the Earth for 100 million years before they began their gradual decline and eventual extinction. Most were small, and you would call them bugs with their hard upper shells and many legs extending below. They could curl up too. They were sort of an aquatic pill bug or sow bug.
Without worms and bugs, we would not likely be here as the descendants of this early life. Neither would our aliens.
Piecing Together an Alien
Looking about at all of life on Earth, both present and past, we see some patterns of a very general nature. Foremost among these is bilateral symmetry.
Bilateral symmetry makes great evolutionary sense. It means that DNA only has to keep one copy of how to make, for example, a hand. It hasn’t stood in the way of success either. You can find some animals that are relatively undeveloped, the starfish being one example, without this symmetry, but no large animals are made without it, and certainly none on land.
We seek aliens with intelligence sufficient to communicate with us about life and the universe. We seek aliens able to put together equipment that can send out radio-frequency waves on which they can put their image. This requirement immediately rules out aquatic creatures because they will be missing two crucial ingredients.
The first of these ingredients is obvious: fire. Without fire, you cannot refine ore, form metallic tools, or melt glass. In fact, you cannot develop any technology at all. This all does not rule out intelligence. It merely means that the intelligence involved will not be applied to creating a technological society.
The second ingredient denied to aquatic creatures is manipulative appendages. Swimming in water means that you must be streamlined. Water is far too viscous to allow for hands and fingers dangling around. They would slow you down enough to guarantee that you’d become shark meat. There’s also the matter of what you’d manipulate. Whatever it is, it must assist materially in your survival.
The sea otter may be a counter-example, but it is a return to water and is not wholly aquatic like whales. It’s able to retain those hands because it spends much time out of water.
Our aliens will have been able to make and use fire. They also will have some way to perform fine manipulation.
You can also be sure that aliens have some sort of neurons, a nervous system. Without one, one part of the body cannot coordinate with another. At some point, a central coordinating organ will develop — a brain if you will. It turns out that brains are expensive from an energy point of view. They take an inordinate fraction of the energy produced by a creature compared to other organs on a mass basis. Large brains would generally be a big mistake from an evolutionary point of view.
The Cambrian creatures barely had started on the evolutionary journey for multicellular animals. You cannot expect them to have built much in the way of gray matter. Yet, they did do one thing that just kept on going forward. They protected their minuscule brains. Loss of a brain is much more serious than the loss of a leg.
Technology-using intelligence requires a substantial brain. That brain will be well protected because of inherited evolutionary events. The best protection against injury to this sensitive organ is a hard shell. While some dinosaurs had an extra brain due to their very large size, neither of those brains was very large.
Just consider that simple fact. Dinosaurs had well over 100 million years to develop intelligence. They didn’t even come close as judged by brain size. Yet, mammals managed it in just 66 million years. As best as scientists can piece together the evidence, intelligence as we know it came about through an unlikely sequence of events. Early hominids were forced out of trees by climate change. Some had sufficient intelligence to fashion very simple tools. Those tools allowed these otherwise hapless creatures to survive.
DNA evidence strongly suggests that there were very few of our hominid ancestors at one moment in time, possibly a small band that could have been wiped out by any of a number catastrophes — disease, flood, storm, or any fatal event. By chance, we deduce, they survived by using their wits and their primitive tools. The odds were against them. The odds were against them ever existing in the first place.
Once they made it and began to grow in numbers, they still could have been exterminated but with steadily declining likelihood. Their large brains allowed them to communicate complex ideas — for the time. Tool-making and communication were the backbone of their survival.
These ideas allow the beginning of a picture of an alien to emerge.
A Fuzzy View
The basics of the alien begin to take shape. It has bilateral symmetry. It has a brain encased in a hard shell. It has the means to perform fine manipulation. It must be able to move about just as all larger land animals can here on Earth.
Because a large brain requires lots of energy, the alien must be warm-blooded. Cold-blooded animals could not support a large enough brain.
It’s time to begin looking at each separate part of the alien. Each time, evolution will make the decisions. The first version of the alien had to survive in a primeval setting. The image of an alien with a tiny body and large head doesn’t make any sense. You might imagine that evolution will continue and so make these changes. However, evolution requires a small, isolated population. The vast genetic pool we have on Earth today along with fast travel, makes genetic mixing so common that isolating a genome that might confer evolutionary advantages won’t happen. It would be swamped in the normal mating and mixing that takes place every day. A new race just would not come forth. A new species would be impossible as things are, although nuclear cataclysm might just do it.
Moving on. What about eyes? Naturally, you cannot manipulate things, evade predators, etc. unless you can see. The exact nature of the eyes will depend on the light and atmosphere on the planet where the aliens evolved. We can be sure that they will bear at least a faint resemblance to eyes on Earth. Mammals have blind spots in their eyes, while squid do not. The structure is totally different, but they look superficially the same. In other words, eyes have developed independently many times over the course of evolution. Some trilobites even had crystalline eyes. They all have means to focus light and to sense that focused image. Expect alien eyes to look somewhat like Terran eyes. The whites may not be white. Eyelids may look very different.
How many eyes will an alien have? Again, evolution helps us out. Spiders and scallops notwithstanding, the evolutionary cost of extra eyes would not be carried forward without excellent justification. One eye is not sufficient to see things because it cannot perceive distance and/or does not view a wide field — necessary to detect that predator or find food. You can be rather certain that the alien has two eyes. While eye stalks are seen often enough in the ocean, they’re not at all common in larger land animals, not even in dinosaurs. The aliens are unlikely to be “bug-eyed.”
Eyes are so important that they are more often enclosed in sockets than set out on the surface of bodies. Eyes also require close communication with brains and certainly evolved near them for efficiency reasons. Expect your alien to have two eyes on a “head” that is solid and contains a brain.
Where will this “head” be on an alien body? For maximum visibility, eyes should be high on the body. You can expect aliens to match most land animals, especially the endotherms, and be the topmost element of each body.
What about a nose? Small ectotherms (cold-blooded) animals such as insects can get away without breathing. Their energy needs are small. Once you become large enough to house an intelligent brain, you have to be an endotherm (warm-blooded) and breathe quite a bit. You have to get oxygen to all of those cells and remove the carbon dioxide waste that will kill you if it builds up.
You must have air intake and exhaust removal. Animals ended up with lungs for this purpose. You have to have a way to exchange those dissolved gases with the air and to move the fresh air in and the used air out. Another planet might find a slightly different method such as passing air in one end and out the other like an internal combustion engine. Because of the extra parts necessary, this way is less likely than a single passage but not at all impossible. Aliens might have two noses, one for inhaling and the other for exhaling — both continuously.
Two noses side by side makes no sense because you save on energy and parts by combining them. It makes more sense to have the exhaling near other waste elimination portals. The intake or intake/exhaust (for a single-nosed system) nose could be anywhere. Because a planet with life must have bodies of water, the air intake should be high up to avoid drowning or even unnecessary intake of water.
Note that whale noses are not where you expect them to be so that whales can breathe as they breach. Living on land poses no such problem, and an alien nose is most likely to be somewhere on the head, probably up high. It could be above, below, or level with the eyes. It could be two holes or one merged hole. Two holes could be out near where our ears are. Ours is a hybrid with two external holes in one protuberance that merge internally. If two holes, then they’ll be bilaterally symmetrical.
Are you just starting to see the alien, albeit fuzzily, now?
A Bit Less Fuzzy
Move on to food ingestion. Somehow food (and maybe water) must be taken in and the remnants after digestion eliminated. Some of the simplest life forms on Earth use the same orifice for both. The non-bilateral starfish does it like that. The idea of a pass-through sort of conveyor belt system for food processing caught on early, however, and has stayed with myriad species since. It’s clearly efficient.
The issue of where the mouth should go is an interesting one. It’s easy enough to add it on to the head. However, you cannot build a creature however you like. Evolution must work with what’s already there. Early animals developed a mouth at the front so that forward motion would bring in floating debris, alive or dead, for digestion. Eyes formed nearby and also at the front so that animals could seek and eat in a coordinated fashion. (The nose doesn’t figure here because sea animals don’t breathe air.)
There would have to be a powerful reason to move the mouth away from the front of the animal — away from its head. You can expect a mouth on the head as a near certainty. There’s no reason to put the mouth above the nose or eyes, and those should be up high. Expect the mouth to be a low fixture on alien heads.
Lizards, birds, mammals, and many others here on Earth follow this pattern. It’s not an accident. Necks came later. You don’t see them in fish, who do have heads with eyes, mouth, and brain — and gills instead of noses. A neck is easy for evolution and has the competitive advantage of being able to survey the dry domain of the land with little energy by simply twisting the head about. You can imagine other ways to turn the head such as a supple waist. Necks don’t have to be a part of the alien body but probably are.
What about the inside of a mouth? Will the alien have teeth and a tongue? Because of the evolutionary arms race over millions of years, eating requires chopping up and grinding up food, whether plant or animal based. Birds manage without teeth because they have developed gizzards in which they have pebbles to grind up food. Some animals early in Earth’s history apparently used extensions of the jawbone to grind rather than separate teeth. Ruminants such as cows partially digest their food before grinding it in their mouths again — “chewing their cud.”
The point here is that a wide variety of food cropping and grinding strategies could be developed. Teeth had to be difficult for evolution. Gizzards are much easier. Yet, once developed, teeth have stayed with us and been adapted to a wide variety of eating patterns. The molars of lions slice off chunks of meat and have no grinding ability at all. Horses have broad molars adapted to grinding tough grasses and long incisors for cropping grass. Aliens could have teeth or no teeth at all.
Tongues, on the other hand, appear all over the place. Once food is in the mouth, animals must be able to move it to be ground and/or push it back into the digestive system. Our tongues have the very valuable secondary property of being an integral part of speech.
Complex communication could well have been the turning point in our species survival and eventual success. We can be reasonably sure that it all began with noise, gestures, and facial expressions. Somehow, humans began to use more refined sounds and put them together to make sounds with more precise meaning. Being able to communicate complex ideas allowed humans to cooperate to build shelter, to seek food, to avoid predators, and to make and use tools.
Among the major senses, smell, touch, and taste have not been important in communicating complex and abstract thoughts. Only sight and sound fill that role. After all, touch and taste require close contact. Smell does not provide for rapidly changing messages.
Some science fiction stories have had aliens that communicated through flashing body color patterns. This approach has the same problem that sign language has. You have to be looking at the person doing the signaling. It’s highly directional. Sound even goes around corners.
Sound turns out to be the ideal communication medium provided that your planetary environment is not excessively noisy. Even insects use it. You can be quite certain that aliens will use sound to communicate. Creating a complex and abstract language requires some sophistication in the sound generation apparatus. A mere membrane that vibrates like a drum head will not do. In our case, we generate sound by moving air vibrating a membrane (vocal chords) and then being shaped by our tongue, teeth, and lips. Some birds have very complex songs that could be shaped into more informative sounds if only they weren’t just “bird brains.”
Who knows what other sound creation options may have developed with different evolutionary paths? While the aliens may make sound in ways that we could understand, it’s just as likely that they make sounds in ways that don’t resemble ours at all and that would require mechanical interpretation because of information carried at wavelengths beyond our hearing or that involve aspects of sound that we aren’t readily able to distinguish.
While aliens must have ears to listen to each other and to have survived before developing technology, they could range from invisible, like seals or birds, to very large, like bats. There’s just no way to know ahead of time what they will look like or even where we’ll find them. Like other sensory organs, they will most likely be on the head so that sound location works along with sight location.
Will aliens have legs? How many? What sort of skin will cover them? Will they have arms or tentacles? How many? These sort of questions allow you to approach the overall appearance of an alien. For example, will aliens have an exoskeleton, like ants and crabs, or an endoskeleton like fish, snakes, and pigs? This question is easy to answer.
Exoskeletons on land are used only by smaller animals. None of these are endotherms. There are problems with breathing if you have an exoskeleton. The necessity of shedding that shell as you grow makes exoskeletons a big problem for larger animals. Finally, there’s just the matter of strength. That exoskeleton would have to be very thick indeed to support an animal of our size. Building up and tossing out so much material would doom such a creature to failure in evolutionary terms.
Intelligent aliens will not be insects or crabs or spiders.
Legs are another matter. People have imagined fanciful creatures for centuries. The centaur is one example of a four-legged creature with a pair of arms — six limbs altogether. Insects have six legs. Why not?
Moving from sea to land represents a severe challenge to evolution. The first forays onto land may have failed. We may never know. The advantages of land would have been the lack of predators and the availability of vegetation as food. Plants certainly preceded animals on land. Exoskeleton creatures that may have resembled crabs would come next. They would be small and light so that the loss buoyancy of water would not hinder them. As discussed above, they would not be the basis for intelligent alien life.
It’s the fish on our planet that made the heroic leap to land and became the first amphibians. Alien fish could have been different from ours but certainly would have been streamlined for swimming in water. Our amphibians, such as salamanders and frogs, have four legs that developed from fish fins.
Because of the pressure on fins to become legs and the difficulty in doing so, this evolutionary step would not happen more than necessary. It would happen symmetrically due to bilateral symmetry. Two legs would not do. Sure, they work today after millions of years of evolution to make animals with balance. The first fish out of water would not be able to balance on two legs. Once they progressed to four legs, then they could begin to move about with some speed, and more legs would be unnecessary.
For these reasons, evolution demands that endoskeleton-based land animals have exactly four legs. This is not an accident but rather a necessity. Think about all such animals that you have ever heard of. They all have four limbs — bats and birds, cows and dinosaurs, reptiles and frogs. Snakes have no legs, but you can find vestigial legs in them. Creatures can lose legs but have no evolutionary pressure to add them. Besides, where would they come from? Evolution must work with what’s on hand.
Given four limbs to begin with and the requirement of fine manipulation, it makes perfect sense to modify the front limbs into arms with hands and fingers. Birds and a number of primates have shifted to two legs. Even some dinosaurs were bipedal.
Using the same limbs for locomotion and for manipulation doesn’t work very well, not well enough to catapult a species into technology. It also doesn’t work for flight.
Expect aliens to stand upright on two legs and to have two arms that were once legs far back on the evolutionary tree.
Alien legs do not have to look like ours. They could look like ostrich legs, for example. Aliens standing on two legs must have feet and not hooves or paws. Balancing on two legs requires a broader base than hooves or paws provide. Our feet came from tree-dwellers. The aliens’ feet may have come from a very different source. We can assume that both legs and feet support fast movement because slow-moving animals would not have the evolutionary pressure to develop intelligence.
What would the arms and hands look like? Remember that the arms have come from legs. They will have the same joints as the legs but otherwise don’t have to resemble them. Hands will evolve from feet and so have similarities. For fine manipulation, hands will have to have at least two and probably three fingers, one being opposable like our thumb. Three or four fingers are the most likely numbers. Our five-fingered hands are a bit strange because there’s no real reason for the extra finger or two.
The number of joints per finger must be sufficient to provide grasping and manipulation abilities. Our three joints seems about right. Fewer would limit abilities. More is unnecessary. We have fingernails because of claws in our evolutionary background. Aliens might not have them because they could be lost in some evolutionary scenarios.
Where will digestive organs and others necessary to support life reside? The system of putting them in a central body out from which radiate the limbs and head makes sense. The earliest animals had a simple gut running their length. Organs formed around that gut and behind the “head.” There’s no reason for them to move somewhere else.
Moving air and nutrients around a body requires a circulatory system, something like our heart, arteries, and veins. Our circulatory system could be improved in details but would remain the same with a central pump and the arteries growing smaller until they reach the capillaries. Then, they join as they work their way back to the pump in the veins. One pump works for an ordinary lifetime when our species evolved. Just as our creatures here on Earth have different sorts of blood, so the alien’s blood could be quite different from ours. It could be blue or green,for example and result in that sort of cast to any bare skin.
Most animals have a skin covering. Depending on environmental factors and environmental heritage, aliens could have a covering of scales, feathers (more like chick than chicken feathers), hair, or fur — or something we haven’t imagined. As with us, much of that covering could be vestigial.
The size of the aliens could be anywhere in the range of humans. Gravity on their planet may increase or reduce that range.
The Alien Visualized
You can draw a picture of a potential alien based on this analysis. It might have a thin covering of pin feathers with a plume on the head, which has no apparent nose, just two eyes with slits and blue color surrounding them. The legs are slightly like that of an ostrich but not quite with broad, flat feet. Arms also follow the leg appearance but with four fingers extending from the flat palms and ending in slightly broadened pads. The mouth is beak-like but not quite a true bird beak. No teeth show. The lower part of the torso is quite round. Shoulders are so narrow that it looks like the arms sprout directly from the upper torso. It has no visible ears.
You can literally draw hundreds of images like this one based on the suggestions given. Details matter, and the alien could look cute and cuddly or very scary and even repulsive. Distortion of human features usually creates revulsion if distorted enough.
Draw your own alien image, but keep to the guidelines unless you have a good, scientific reason not to.
All of the above presumes that you see the aliens as they naturally are. If you assume that these aliens are “advanced,” then they may be a hundred years or more ahead of us in technology. Given what we’re just starting to do with bionics, the aliens may already be able to use very advanced bionics to mold their bodies into powerful, disease-free avatars that look like whatever they choose. In other words, they could look like just about anything you might draw.