Originally posted by SecretKnowledge
the first picture they look raised
the second picture they look like grooves
They are grooves. The sun is in different positions in each image, so the shadows could be confusing you.
Look at the bottom grayscale image. You can see by the horseshoe-shaped feature at the bottom that the sun is shining from the direction of the
bottom of that image. That would make them groves.
EDIT TO ADD:
And I agree that they look something like the rilles on the moon. Rilles can be formed by the collapse of lava tubes:
edit on 1/20/2013 by Soylent Green Is People because: (no reason given)