J’atorg struggled along on his motile pods, wheezing badly as his air sacs fought with the new air. He cursed the humans, invoking the gods of his people. Reflecting, he cursed the humans by invoking their gods. The gods of his people had proven weak: the bipeds had come and were transforming his world into an environment more suitable for themselves, showing their gods were stronger. The humans said it would take a long time for the world to fully change, but J’atorg could already see, taste and smell the differences. He did not know who he hated more: the hard-eyed humans who were destroying his world or the soft-eyed humans who poured forth words about “rights”, “morality” and “lawsuits” while urging patience. He knew that his people would die, aside from those the humans kept as curiosities or preserved to assuage their conscience with cruel pity.
Terraforming has long been a staple in science fiction, though there has been some practical research in more recent years. In general terms, terraforming is transforming a planet to make it more earthlike. Typically, the main goal of terraforming is to make an alien world suitable for human habitation by altering its ecosystem. Since this process would tend to radically change a world, terraforming does raise ethical concerns.
The morally easiest scenario is one in which a lifeless, uninhabited (including non-living creatures) planet (or moon) is to be terraformed. If Mars is lifeless and uninhabited, it would fall into this category. The reason why this sort of scenario is the morally easiest is that there would be no beings on the world to be impacted by the terraforming. As such, there would be no rights violated, no harms inflicted, etc. As such, terraforming of such a planet would seem to be morally acceptable.
One obvious counter is to argue that a planet has moral status of its own, distinct from that of the sort of beings that might inhabit a world. Intuitively, the burden of proof for this status would rest on those who make this claim since inanimate objects do not seem to be the sort of entities that can be wronged.
A second obvious counter is to argue that an uninhabited world might someday produce inhabitants. After all, the scientific account of life on earth involves life arising from non-life by natural processes. If an uninhabited world is terraformed, the possible inhabitants that might have arisen from the world would never be.
While arguments from potentiality tend to be weak, they are not without their appeal. Naturally, the concern for the world in question would be proportional to how likely it is that it would someday produce inhabitants of its own. If this is unlikely, then the terraforming would be of less moral concern. However, if the world has considerable potential, then the matter is clearly more serious. To reverse the situation, we certainly would not have wanted earth to be transformed by aliens to fit themselves if doing so would have prevented our eventual evolution. As such, to act morally, we would need to treat other worlds as we would have wanted our world to be treated.
The stock counter to such potentiality arguments is that the merely potential does not morally outweigh the actual. This is the sort of view that is used to justify the use of resources now even when doing so will make them unavailable to future generations. This view does, of course, have its own problems and there can be rather serious arguments regarding the status of the potential versus that of the actual.
If a world has life or is otherwise inhabited (I do not want to assume that all inhabitants must be life in our sense of the term), then the morality of terraforming becomes more complicated. After all, the inhabitants of a world would seem likely to have some moral status. Not surprisingly, the ethics of terraforming an inhabited world are very similar to those of altering an environment on earth through development or some other means. Naturally enough, the stock arguments about making species extinct would come into play here as well. As on earth, the more complex the inhabitants, the greater the moral concern—assuming that moral status is linked to complexity. After all, we do not balk at eliminating viruses or bacteria, but are sometimes concerned when higher forms of life are at stake.
If the inhabitants are people (albeit non-human), then the matter is even more complicated and would bring into play the stock arguments about how people should be treated. Despite the ethical similarities, there are some important differences when it comes to terraforming ethics.
One main difference is one of scale: bulldozing a forest to build condos versus changing an entire planet for colonizing. The fact that the entire world is involved would seem to be morally significant—assuming that size matters.
There is also another important difference, namely the fact that the world is a different world. On earth, we can at least present some plausible ownership claim. Asserting ownership over and alien world is rather more problematic, especially if it is already inhabited.
Of course, it can be countered that we are inhabitants of this universe and hence have as good a claim to alien worlds as our own—after all, it is our universe. Also, there are all sorts of clever moral justifications for ownership that people have developed over the centuries and these can be applied to ownership of alien worlds. After all, the moral justifications for taking land from other humans can surely be made to apply to aliens. To be consistent we would have to accept that the same arguments would morally justify aliens doing the same to us, which we might not want to do. Or we could simply go with a galactic state of nature where profit is the measure of right and matters are decided by the space sword. In that case, we must hope that we have the biggest sword or that the aliens have better ethics than we do.