Another joked: "The coronal ridge shows ample structure to support the musculature of antennae, although none are visible in this view.
"The nose area is broad and blunted as you would expect to see in a cold and windy landscape. Is he decapitated or is he buried up to his neck?"
Previous images of a skull spotted on Mars in 2006 were believed to have been the result of tampering.
The famous Face on Mars, snapped by the Viking 1 spacecraft in 1976, which showed the shadowy likeness of a human face was late, was found to be a trick of the light when the area was re-photographed in 1998.