Mars is the planet in our solar system most like Earth, so it's no wonder people have long gazed at its faint red light in the sky and imagined Martians looking back. But since technology has made it possible to view Mars up close, life there — if it exists — has been elusive.
Though the red planet may have been fertile at one time, today it is a harsh, windswept sphere with an unbreathable atmosphere. Mars contains no civilizations, no forests or oceans, no multicellular organisms with complex nervous systems. Even so, that doesn't keep people from dreaming — and from seeing things.
In that spirit, here's our list of mysterious features on Mars that have been mistaken for signs of alien life. (Text: Bryan Nelson)