It seems that humanity is surprised about the alien creatures in the solar system so it seems that they come from irregular means. Looking at the names of the DLC packs in the contract document (Comet 1, Comet 2) it made me wonder, what if the alien species arrived on small sub-planetoid objects such as asteroids or comets? It would seem to fit also with the theory that Traveler is a moon. Just a random thought.

Could be the other way around, we go out a bit farther than normal on ships called comets. Your way probably would fit a bit better though.

It seems that humanity is surprised about the alien creatures in the solar system so it seems that they come from irregular means. Looking at the names of the DLC packs in the contract document (Comet 1, Comet 2) it made me wonder, what if the alien species arrived on small sub-planetoid objects such as asteroids or comets?

Could be. If it's a universe where FTL doesn't exist, it might be that visitors from other places arrive here not because they came here on purpose, but because the rock they happen to live on passed by us.

It would seem to fit also with the theory that Traveler is a moon. Just a random thought.

"That's no moon" amirite?