It is about a mysterious eleiptic shadow over Mars which it seems throwing a giant object that is in orbit around Mars .. The photo was taken by the spacecraft (Fear) and the Russians for years and caused a sensation caused by the research community.
Some suggest that this is the shadow of the moon Phobos, but this option is excluded because it is the same in any case the shape of the satellite and in addition we have seen the shadow of Fear pictures of the Mariner of Americans and does not seem to appear there and also to be related to this photo.
