Aliens don't need wormholes or gravity to travel here.

Aliens can travel at the speed of light through signal. You don't need to transport mass, you need to transport information to a planet that can host intelligence spawned from information, like Saturn. This sort of travel is not out of the reach of our own science to understand, we are already doing much of the science required for this. We already manipulate the magnetosphere of our own planet with HAARP to guide weather patterns. Gas giants have oceans of metallic hydrogen, super conductive...