Trick of the light
It's obviously a shadow or some weird rock formation. The funniest reaction has to be the Daily Mail's precis of the photo. The headlines next week will be something along the lines of "House prices soar as priority housing given to Martians".
And the Express will be "Madeleine McCann in Martian kidnapper / Princess Diana link"...
If I'm wrong then, of course, I welcome our Martian Overlords...