I am a genius of the highest order, so I declare that aliens look like the included illustration! Also, I have included a picture of Jesus, for comparison.
Note how Jesus has more of a beard, and is considerably more gifted in the arms & legs department! Fascinating!
I have also concluded, after lengthy Halo 2 CTF games, that there is a great war, between these aliens, and the mysterious and benevolent Space Hamsters! The hamsters were genetically engineered by Trotsky, working with the surviving Beatles, to defend earth from the threat of inter-galactic pork!