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Optical Illusions 3
A Smile and a Valentine
 
Can you see the smile on the face of this crater on the left? It is in the Argyre Planitia, a massive crater basin in the southern hemisphere southeast of Tharsis. It is like the Hellas Planitia, but smaller and not so deep.
Other recent images from Mars Global Surveyor also show (right) a heart shaped feature in the region of Alba Patera. Does it bulge out towards you or does it look like a pit? It is in fact a graben, a depression in the ground that is associated with movement of the planet's crust. Nearby are lava flows that are cut into by the graben, which is one in a row of several depressions.
Most people will see this as a bulge, but in fact it is the opposite.
Now look at the same image in negative, and it looks correct. Or perhaps it is the other way round for you.
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EXPLORING MARS 
