This Halloween eve, look upon in horror at the mark of a strange and terrible beast that roams the plains of the red planet. What horrible monster could leave such an eerie footprint? Also, it's over six miles long.
Of course, this isn't so much a gigantic footprint actually as it is a geological formation, albeit a fairly unusual one. This image, which was taken by the Mars Odyssey probe, was originally thought to depict an ancient, dried up lake bed, but the truth is a little more mundane: volcanic ash.
A NASA astronomer explains:
Studying the exact color of the formation indicated the possible volcanic origin. The light material appears to have eroded away from surrounding area, indicating a very low-density substance. The stark contrast between the rocks and the surrounding sand is compounded by the unusual darkness of the sand. The above picture was taken with the Thermal Emission Imaging System on the Mars Odyssey spacecraft currently orbiting Mars. The image spans about 10 kilometers inside a larger crater.
Whatever this really is - which, again, is probably volcanic ash - it's still a worthy complement to other great moments in Martian pareidolia such as the legendary Face of Mars...which, for the record, actually looks like this.