It's not quite as dramatic of the famous Viking photo of the "Face on Mars" taken in 1976, but I really like the subtlety of the Happy Face crater. This image was released by the European Space Agency yesterday. (Photos with a more obvious Happy Face here.) From the ESA:
These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express spacecraft, show the Galle Crater, an impact crater located on the eastern rim of the Argyre Planitia impact basin on Mars…The 'face' was first pointed out in images taken during NASA's Viking Orbiter 1 mission.
Its interior shows a surface which is shaped by 'aeolian' (wind-caused) activity as seen in numerous dunes and dark dust devil tracks which removed the bright dusty surface coating.
Link
UPDATE: Thanks to the readers who point out that the smiley on Mars featured prominently in Alan Moore's 1980s comic book Watchmen.
