If Aliens do in fact feature in some way in Indy IV,
I'd just like to back it up by saying this:
The concept of aliens or visitors from the sky is not a new one. It is not something purely of the 20th century but from thousands of years ago. Myth and folkore account, such as the Bible and other ancient texts tell of creatures descending from the sky, and of flying machines and creatures within them. The Book of Ezekiel (circa 593 B.C.), and in particular the passage (1:16) describing "Ezekiel's wheel," is believed by some to depict a UFO encounter. In Central Asia in 329 B.C., Alexander the Great is reported to have seen "two great silver shields" flying in the sky. On April 14, 1561, a woodcut by Hans Glaser records what some believe was a UFO battle over Nuremberg, Germany. As reported by The Nuremberg Gazette, there was a "dreadful apparition" with "cylindrical shapes from which emerged black, red, orange and blue-white spheres that darted about." Five years later, another woodcut, this time from Basel, Switzerland, shows the town's sky covered with dark flying orbs. Even Christopher Columbus is said to have recorded a UFO sighting in his diaries on his voyage to the New World.
Another event occurred in Basel, Switzerland, in 1566. At sunrise on August the 7th, 'many large black globes were seen in the air, moving before the sun with great speed, and turning against one another as though fighting. Some of them turned red and fiery and afterwards faded and disappeared'.