What the Heck is This in the Sky Over O’Hare Airport?

Is it an alien invasion, is it a comet, may a glowing vapor trail. As one person said, "it looks like "a giant space sperm." What is this in the sky?

As you'll read in the comment section of this Facebook post, nobody seems to know what this is. But now we have your eyes looking at it, so what do you think it is?