You can have your bumpy headed aliens that you’re likely to see on shows like Star Trek, but if you’re serious about your science fiction, you want to have alien aliens.
With that in mind, the aliens in Jump Temp are not humans with bumpy heads. Not only do they look weird, they’re darn hard to communicate with. Considering an alien is likely to have very different thinking than humans, it would seem unlikely that they would speak languages that we’d easily translate. The closest thing we have to an alien language on earth is whale song. So if it’s hard to talk to a creature that breaths air like we do, imagine how hard it would be to understand a creature that breaths ammonia at pressures that would crush our lungs.
There are three races established in the Jump Temp book. Two were discovered before they achieved space flight (no prime directive here!). One, the Neamasta, have their own starships and maybe a different FTL technology. They’re being very secretive and although humans have allowed them into our space, they have not returned the favor. What are they up to? What are they hiding? The book leaves that up to you. I know what I’m going to have happen in our gaming group, but the idea is to establish the world and then let the players find their own way.