Why would an HE attempt to invade the planet Earth? More to the point, what reason would an HE have to make itself an HE? This question may seem overly philosophical and speculative, but it is important for the focus of Project Heimdall. Would it be for access to natural resources, either biological or mineral? Would they come to take us all as slaves? Would they just like to displace us and move in? For the reasons that will be brought up in this report, the answer to all of these is a resounding "No."
First, we will discuss a few basics of biochemistry as it pertains to exobiology. It is generally agreed upon that life as we know it tends to adapt to its own unique environment and, in turn, modifies its environment to suit its own needs. The most noteworthy example of this principle is oxygen. This chemical is absolutely necessary for life as we know it, not only being present in our proteins and cell membranes and DNA, but in life's universal solvent, water. Without oxygen, it's clear that life simply could not exist. But one form of oxygen used to be highly toxic to all life on Earth. This form consists of two oxygen atoms linked together by two covalent bonds. Inside a living system, this chemical oxidized its life-sustaining mechanisms to the point that they could not function at all.
During the Precambrian Period, a mass extinction event occurred that we now call the Oxygen Catastrophe. At that time, some bacteria managed to develop a way to use solar radiation to transform water and carbon dioxide into metabolizable sugars and oxygen molecules. This was a very effective strategy which gave them plenty of food and a deadly byproduct that kept predatory bacteria from eating them. As these photosynthetic bacteria became more plentiful, they transformed even more water and carbon dioxide into oxygen until the chemical was present in most of the oceans and atmosphere. Many living things died. But a few, including our direct ancestors, survived by developing biochemical strategies to fight the destructive effects of free oxygen and even managed to find a way to use those effects to generate energy. Because of this, almost all life now present on Earth is able to withstand and thrive in an oxygenated environment.
Let us now look at another pair of chemicals that are ubiquitous to life as we know it: Carbon and nitrogen. Once again, these chemicals are present everywhere and interact with one another to make life possible. But one interaction of carbon and nitrogen is highly toxic in the vast majority of cases. This is a simple negatively charged ion consisting of a carbon atom and a nitrogen atom linked by three covalent bonds, commonly known as cyanide. Ironically, cyanide ions are mostly hazardous to life forms that thrive on oxygen, by interfering with the biochemical pathways that transform the energy locked up in oxygen atoms into usable energy. It is easy to imagine a hypothetical alien planet saturated with cyanide where life learned to thrive on this, just like our distant ancestors learned to thrive in the presence of oxygen molecules.
And this brings us to the point: That life that developed on two separate planets with no interaction at all would end up biochemically incompatible, even at the most basic level, even if they were built from exactly the same chemical building blocks in exactly the same proportions.
This means that an HE would not choose to invade Earth to eat either us or any other life on the planet. In all likelihood, terrestrial life would simply be too toxic to ingest. We can at least rest assured, now that we will not be on the menu if something chooses to invade. Nor should we concern ourselves with the possibility that the HE might choose to take our place on a planet that would be far too poisonous to even touch. It would be the equivalent of murdering a group of innocents for the privilege of living inside of a tank of cyanide.
But should we worry about being enslaved by the HE? Once again, biochemistry provides part of the answer to this question. There would be no purpose to transport humans back to the HE's equivalent of home. These slaves would require a specialized environment and a unique diet that is incompatible with anything that exists on their homeworld. Land would have to be extensively terraformed in order to support our sources of food, thereby removing land that could otherwise be applied to other purposes by the HE.
The practicality of such an endeavour is brought further into question when looking at the resources required to do such a thing. Besides those needed to sustain the slave race after the invasion, the HE would have to accumulate resources sufficient, not only to subdue Earth's military forces, but to transport such military might to Earth in the first place. Let us set aside the force needed to conquer Earth and simply consider transportation:
The laws of physics allow low-energy methods of transportation between planets and stars. These methods, however, are slow, potentially taking hundreds or even thousands of years. Much can happen during this intervening time. The target might advance scientifically to the point where they can easily fight back against the force sent by the HE. Or they might become so populous that they can quickly collect the resources needed to defeat the invading force with minimal effort on the part of each member of the target species. Or they might simply go extinct, either through their own actions, or by some other event, thereby nullifying the intended purpose of the invasion.
Theoretical physics does provide certain loopholes that can allow much quicker travel to a target location. So far, though, all of these theoretical methods of transportation require vast amounts of energy in order to become feasible. The minimal energy requirements would be equivalent to converting the mass of an entire star into energy. A civilization capable of doing such a thing would have no use for a slave race. It is clear that there would be no reason to use such incomprehensible energies to obtain slaves or servants who, because of their biological requirements, would be more trouble than they are worth.
What of mineral or other chemical resources? When we look at our own solar system, we see numerous planets and moons and countless smaller astronomical bodies which have the exact same resources that we can find on the Earth, sometimes in quantities that put what we have here to shame. There are even some resources that can not even be found on Earth in any usable proportions, such as iridium. To put things bluntly, there are enough resources close-by that there would be no point to traveling farther for them. Were it more practical to travel to another star for your resources, for whatever strange reason, it would be easier to mine an uninhabited moon rather than invade a populated world and subdue its population in order to take their resources. Recent findings in mainstream exoplanet research have shown that at least half of all stars have planets orbiting them. When combined with the most liberal possible result of Drake's Equation, wherein the nearest likely alien civilization would be located hundreds or thousands of light years away, it is evident that there are enough resources between us and them that we are likely to be spared an invasion for this reason.
What purpose, then, would the HE have to invade Earth? With all of these other scenarios being unfeasible, there is only one reason that an HE would attack: Complete extermination. The human race would be considered a potential threat by the HE, either in its current state, or as extrapolated by our current paths of development.
If this is the case, it would stand to reason that the HE would use methods that have a high chance of success, with little consideration for collateral damage. Such methods may include a universal pathogen that is able to infect and destroy any and all humans, application of the Grey Goo scenario, or even the outright destruction of the Earth. Therefore, it is this researcher's opinion that there is little reason to focus on military, sociological, or economic attacks, as these all have varying degrees of risk inherent in their very natures and furthermore would do little to aid in the goal of extermination. Instead, the attack would be more covert and may not even be recognized as extraterrestrial in origin, rather being assumed to be a natural event or the result of an SCP's anomalous effects.
This means that the best thing that we can do is what we are doing right now. Secure, Contain, and Protect. It may very well be that some items currently in our custody may be the tool that the HE had intended for our destruction and that we have already foiled their plans without even realizing.
Another prudent course of action may be to invest in research into interplanetary and eventually interstellar travel. If we should go forth and multiply, a single attack on a single world, no matter how large-scale the attack may be, would not cause our outright extinction. In effect, we would have a backup or multiple backups. And, should we be successful in such an endeavour, we may even have a chance at becoming the HE ourselves.