What Jungle said. I have seen a LOT of airborne hardware and munitions in the military and it often looks pretty strange.

Like Jungle said, it's a BIG universe out there...the technical challenges of interstellar space travel are almost beyond human comprehension. If somebody had the ability to actually GET here and the desire to do so, they would be so smart and so advanced that they would either:

A. Land on the white house lawn and announce they are taking over.

B. Remain covert. If they choose to remain hidden, their technology will allow them to do so without difficulty, mistakes, or accidents. A starship is not going to suddenly develop engine trouble and crash in Roswell...after travelling 40 light years at god-only-knows what relativistic velocity

Get real folks...