Adventure ideas might include: first contact or random contacts with humans, interactions and battles with other species, contact and intrigue with various earthly governments, and home planet internecine conflict.
I haven't bothered to look to see if there already is such a game, being the (aforementioned) slacker.
One of the first sci-fi RPGs I played was Star Frontiers. I remember getting it (for Christmas I believe) as a kid, and really being freaked by the notion of what amounted to intelligent extraterrestrial monkeys (Yazirians). Even at that age I recognized this as a totally ridiculous element. Star Frontiers is actually still available, now for free, via download. I don't remember if I'd bought the original (multi-booklet) Traveller by this time or not. Either way, shortly thereafter it was readily apparent that the two were about as similar as an episode of Lost in Space and the movie Blade Runner. Which isn't to say it couldn't be fun or that I don't appreciate the effort to keep it alive and on the net, but simulationist, it is not. In some ways, Traveller was the game that took me away from the joyful roots of old school D&D, towards ever increasing complexity and supplementation (even with its beautiful d6 system). Down that road were computer programming manuals, Chilton's guides to auto repair, and senior high school textbooks. Again, nothing wrong with those in and of themselves, but, well, what about the fantasy role playing dammit? :-)