You have got to be kidding!
This is a silly question and deserves a silly answer.
However, let us stand back a moment from all the silliness, and think who the aliens are. Of course, they are the Other of our imagination. But just like Kant’s Copernican turn where we realize that objects must conform to the limits of our possibilities of experience, so also the Other must conform to our limits of comprehending Otherness, and thus actually the Other is always Us. So for instance the Barbarians of the Greeks, i.e. the Scythians, were just seen as inverting Greek values, and the Celts similarly were an invention of the Barbarian other by the Romans. So too today we are continually inventing the Alien, to horrify ourselves, and really merely exploring the limits of our own sensibilities. The truly Alien would be incomprehensible, might not even be experienceable.
So why is the question silly. We because it assumes that Aliens would have spacecraft, i.e. would need to travel in space as we do. It assumes that they would end up as part of what we fantasize as “objective reality”. And it assumes just as we have speed for our spacecraft, they have speed for their spacecraft. So this Alien is really just like us. And therefore is not really Alien. What is truly Alien is the unknown unknown. This question is silly because it assumes it can know about the unknown before it becomes known.
Now the corollary of this view is the fact that the true Alien is Us. We are the most Alien of all things in the known world, because we can Alienate ourselves from nature, to such an extent that we are destroying our own planet, when it is the only refuge in a hostile universe, and given the knowledge that we are probably trapped in our solar system. Just going to the nearest star would take a very long time given the speed of light as a speedlimit. If Aliens did exist in “Objective Reality” like us they would have the same problem, and so chances of meeting them are slim. Only if they had started broadcasting TV like we did announcing our presence to the universe, long ago would we have any idea that they ever existed. And in fact we find that there are no television signals flooding our skies from some alien civilization, and so we are feeling very alone in our universe right now. We are the only reasoning animal left on this planet and it is starting to look like we might be the only ones in the universe unless SETI comes up with something. Producing electromagnetic waves and broadcasting them is a very basic thing for another Alien civilization to do, or so we think based on our own behavior, so if there were others out there we would expect to find something. But then maybe other intelligent races on other planets realized that broadcasting their presence was probably a mistake, because they might come to our notice. And if they did come to our notice given our colonial past that might not be a healthy thing to do, and so in fear of the same thing happening to them, as happened to the many worlds that were destroyed by colonialism, they decided that it was better not to broadcast, and they instead put their effort into living at one with their planet and surviving, rather that producing global climate change and destroying themselves along with all the other species in their ecosystem. Any recent science fiction plots of movies come to mind? Those people who lived in trees and for whom trees were sacred, were us, the Indo-Europeans. That is how we started out before we started rapaciously destroying everything in site and had the bright idea of turning Earth into something like Venus.
So it is us who are the Aliens, because we are Alienated from ourselves and the planet’s ecology that supports us and allows us to live one brief moment as a so called civilization before we snuff ourselves out along with the rest of the species on the planet. All images of aliens are images of ourselves. We are the monsters, we are the source of horror and what is truly terrifying in the universe. We are that which is so cut off from itself that it does not know itself for the horror of what it is to everything else in the universe.
And what is so strange about this is that we think of ourselves as Dasein, i.e. that which projects spacetime and the categories within it and thus gives rise to its own world and to itself, bootstrapping itself into being from existence. This is the great Trinitarian project. God became human, so we can become gods ourselves and lord over creation. God the Father gave rise to the world, but God the Father is just God the son who is a human being in the world that he has created. This metaleptic move, of creating the world and oneself in the world, and thus seeing oneself as the source of the world in which one is in, means that we as autonomous and free beings are cut off from our own roots in nature, we live in the illusory world of Being cut off from Existence, i.,e. the nature that gave rise to us. And it is this that makes us a horror to everything in existence which we seem to be bent on exploiting until it is all used up. We are proving our groudlessness every day be eating up ground ourselves that we depend on, i.e. earthly resources. We believe that we can make our own resources, i.e. have the illusion that we can just keep printing money and it will continue to have value. Where ever you turn in our society there is this same motif being played out, i.e. the motif called Nihilism by Nietzsche and Heidegger that is at the core of the Western worldview. And it is this motif of our alienation not just from nature, but from our own human nature, that is truly Alien and terrifying.
We looked at the truly Alien and found out it was Us.
Given this all we need to know what our own spacecraft speed may be at any given time and we suddenly know the answer to this very silly question.