What are the most mysterious discoveries made by satellites?

 I don’t know about mysterious, but amazing? Try this:

NASA took this pic to look at the Nile delta, but look at the Sinai! We think of it as dry, deadly desert, but see those pale lines in the middle, joining together into one pointing north-ish toward Israel? That’s an ancient river system there’s no sign of on the ground.

They also found ancient riverbeds in Arabia, but I couldn’t find an image of those.