Humanity has often wondered about others. From another dimension. From the depths of time. From Heaven. We have gazed up in awe at the potential before us in the vastness of the dark. We have gazed up and asked "Do they have three green boobs?"
The answer is "Highly unlikely you weird perverted human."
Will we cry when they don't have breasts?
When it comes to fiction as long as it's not a horror movie almost all aliens have two things in common. The women are proportional (roughly) to human beauty standards, and those same vaguely proportional women have breasts.
It's pretty silly, considering that the odds of any other being we encounter being a mammal or mammal like creature is insanely small. The fact that we have weird fat holes to squirt milk out of on our chests is pretty bizarre, and disgusting already. Even more than that, if by some miracle they ARE mammal like, complete with milk utters, I dunno if you've taken a look at most mammals on this planet from a sexual perspective, but I gotta say...
They are not the most attractive creatures. The bear? The house cat? The Rat? The Gorilla?
And those CLOSELY related to us! Oh sure there's a odd person here or there in love with the cow, and people can say cats are 'sexy' or foxes are 'sexy', but almost all artistic and fictional depictions of said creatures being sexy anthropomorphize them to fit our own standards of proportional breast heavy beauty.
Poor humanity, green busty women of the stars shall never be. A tear is shed for every would be Kirk. But not all is lost, if aliens exist one can still bang them all animal planet style. Just you're going to have to put up with some weird mandible twisty death jaw that bites chunks out of your solar plexus.
Prepare yourselves now space sex artists and fetishists. For the abominations of the skydepths await!
SuperGenX
Spock: Captine, we have recevied word that there are no alien women with boobs.
Kirk: Oh. Well head back to earth. Our mission is a failure.
SuperGenX: I TOLD YOU!!
Emptygoddess
Why are you on the enterprise? How come I don't get to be on the enterprise?! WAAAH! I am jealous and angry!