Up near the north pole of Mars Nasa has come across structures that look remarkably like trees, but don't be fooled - it's just an optical illusion.
Nasa scientist Candy Hansen, a member of the Mars Reconnaissance Orbiter (MRO) team, told Space.com the Martian "trees" are dark basaltic sand pushed to the surface of sand dunes by sun-heated solid carbon dioxide ice, or dry ice. When this sublimates directly into vapour at the surface it leaves the dark sand to slide down the bright frosted portion of the dune.
The sand dunes form a ring around Mars' north pole and are covered by a thin layer of reddish Martian dust and patches of dry ice.
The image was taken as part of a series by MRO's High Resolution Imaging Science Experiment (HiRISE) camera.