Real Engineering explains how solar sails work in the video below:
Real Engineering explains how solar sails work in the video below:
A few years ago I found an interesting article by Gregory Lee Matloff: The Reenchantment of the Solar System: A Proposed Search for Local ET’s. In this very speculative article Matloff argues for the possibility that intelligent extraterrestrials may have colonised our Solar System already. This hypothesis may have serious consequences for the humanization of Space. First we will discuss how plausible Matloff’s hypothesis really is, then we will discuss the possible consequences.
Dr. Matloff argues that extraterrestrial space ships may have crossed interstellar space and may have arrived in our Solar System in a distant past. These local ET’s might live in artificial worlds that masquerade as natural objects like comets. Subsequently he describes two types of civilisations that might be interested in migrating to other star systems than their. This might be a nice subject of a science fiction novel, however his description is nothing but speculation (I would say mostly garbage).
Whether Matloff’s typology makes any sense, is quite irrelevant as long as we can imagine any group of intelligent extraterrestrials with whatsoever motivation to leave their own star system and to cross interstellar space for a few thousand years. The main question is whether such migration is feasible from a technological perspective. Therefore Matloff discusses several suggested propulsion systems. Some of them are simply impossible, such as hyperdrive. Others are not feasible (yet), such as the Bussard ramjet or antimatter rockets. Since we do not know whether any of these system will work in practice we cannot assume that extraterrestrials has developed them.
However, there proposed propulsion systems which are feasible now. Matloff mentions fusion pulse propulsion and Solar sails. They are feasible because they can be build with present day technology, so we can reasonably sure that more advanced extraterrestrials would be able to handle these systems. So if there is civilisation with at least our level technology, they would be able to leave their stellar system and to cross interstellar space.
The next variable we have to consider is whether they can sustain themselves during the voyage, which will take several thousands of years. In theory a civilisation slightly more advanced than ours should be able to build a generation ship. The main problem on such ship would be an adequate energy supply, all other stuff could be recycled if enough energy is available. Nuclear fusion seems to me as the most likely source of energy for such ship, since a relatively small amount of hydrogen will be required annually and could be collected en route.
Another possibility would be sleeper ships, in which the crew is in suspended animation. Or our ET’s could live for several centuries. And if they can travel at near light speed, time dilatation will enormously reduce travel time for the crew. From our perspective their trip would take several thousands of year, but for the immigrants only a few decades.
Therefore it would be possible for a group of extraterrestrial nomads to cross interstellar space. And there so no reason why it couldn’t have happened. As yet we have no evidence for the presence of any extraterrestrial intelligence in our Solar System. But the absence is no evidence of absence, after all it is easier to proof something does exists than to proof that something does not exist (the best way to prove a negative, is to prove something cannot exist).
Detecting ETs in our Solar System
So if ET’s are in our own Solar System, where do we have to look? Matloff’s answer: in the Oort cloud and the Kuiper belt, because these are the outer layers of the Solar System. Any “invader” has to pass them, and since these outer regions contains millions of minor Solar System objects, it would be a nice place to settle down.
If intelligent extraterrestrials has settled the Kuiper belt or Oort cloud, how can we detect them? Especially if they, as has been suggested by Matloff, have disguised their habitat as natural objects. If this would be the case, then it would be a hard job to find them with optical telescopes. However, Matloff has pointed out that these habitats should have an internal temperature several hundred degrees centigrade higher than their environment. (The temperature in the Outskirts of the Solar System is in order of -200 degrees centigrade.) Therefore these world should emit more infrared radiation than we should expect from a natural object in that part of the Solar System.
By scanning the skies for objects with unusual high infrared emissions, we might detect potential alien hide outs. But if intelligent ET’s has already colonised our Solar System, we might wonder why they have not visited us already? This is the so-called Fermi-paradox. One of the traditional replies to this questions, is that aliens would have to travel several light years just to visit us, which would take several hundreds of years for them to complete. Such investment for satisfying a curious interest would not justifiable.
But the Fermi paradox becomes much more relevant, if we assume that intelligent ET’s might live in our Solar System. However, there a few simply explanations. The first one is the most simple one: the simply do not know about our existence. This might seem quite strange to most people, but it is a very reasonable option. Many people would be tempted to think that aliens living in our Solar System cannot possibly miss our planet. However, this would be a kind of what I would call psychological geocentrism. The planet Uranus is larger than our planet and it is much closer to us than Pluto, one of the innermost Kuiper belt objects, and we were not able to discover this particular planet until the invention of the telescope.
For this reason, we cannot assume that intelligent beings who have immigrated from other stellar systems might have discovered Earth. It is quite reasonable that they have never been in the inner Solar System. Why? That is because it cost more energy to through something to the Sun, than out of the Solar System. So unless they have a strong reason to explore the inner Solar System, they would stay in the outskirts.
If they should have discovered Earth, some thousands of years ago if not longer, then they might have visited our planet in a distant past. However if it was some fifty thousand years ago, they might have concluded that our planet contained our planet contained some primitive life. Recall that fifty thousand years ago, there were only a few ten thousand humans on Earth, and their effect on the biosphere was negligible. In this case the aliens might have concluded that our planet was not quite interesting and they have ignored us since.
If either of both scenarios would be true, this might solve another problem. Reported sightings of UFOs have only been made since the 1940s. So if Earth would regularly be visited by aliens, why are there no reports of those visits from before the twentieth century? If you live at more than a few astronomical units away from our planet, it is a hard job to detect whether there is intelligent life. At least that was the case until the early 1900s, when started to use Radio waves for communication.
Since man-made Radio waves leave our planet in all directions. Some of these waves might have been detected by intelligent ETs living in Outskirts of our Solar system. Unlike aliens living at distant star systems, these aliens might travel to Earth within a few years. Before we started to emit artificial radio waves, those aliens had simply no reason to visit us.
However, when the learned that there was a sudden outburst in radio waves from the center of the Solar System, this might have caused some worry among them. Whether it would be a natural phenomenon or the sign of intelligent life, this is a potential danger for their existence. So these aliens might have decided to start a mission to check out this sudden spectral emission.
Of course, this hypothesis is no prove that UFOs are indeed alien spacecraft. Most reported sightings of UFOs are misidentified natural phenomena such as birds, planets, aircraft etcetera or outright lies. There are only a very few genuine reports of unidentified flying objects. The idea that intelligent life might live in the outskirts of the Solar system, is only a possible explanation for some UFO sightings.
Consequences for Space colonies
If there are intelligent extraterrestrials in our own Solar System, this would have serious consequences for any Space settlement. These aliens might be hostile, and they might have the means to destroy space habitats. It’s impossible to know their attitude to us, until we have discovered them, which might be too late. Therefore Space colonists should be prepared to deal with this possibility.
If these aliens exist, they are likely technologically more advanced than us. Therefore governments of Space communities should develop adequate strategies for dealing with potential hostile intelligent ETs. Although we hear from time to time, that governments are designing plans to deal with the threat of an alien invasion, we seriously doubt the soundness of such plans. The problem is that such plan might be based on false assumptions, and we cannot be sure whether their developers know what they are dealing with. Our impression is that all talk of such plans is just propaganda for the general public, in order to prevent panic.
However it’s also possible, that those aliens will choose to be as quiet as possible in order to prevent their discovery. They might choose to leave the inner Solar System to us, just for keeping the peace. This would depend on the state of their military and their moral dispositions.