Morning fog developing in the Memnonia region of Mars. This pair of color images was acquired by Viking Orbiter 1 about half an hour apart during a search for morning fogs. Contrary to initial expectations, where fog evaporated after sunrise, Viking 1 saw that fog *increased* after sunrise.
It was found that morning frost evaporated in the morning sunlight, then immediately recrystallized as tiny ice crystals in the colder atmosphere just above the surface. Unlike Earth, where fog forms overnight and is slowly burned off during morning, fog on Mars becomes denser after sunrise. The fog remains dense until the atmosphere warms above the freezing point of water ice, at which point it rapidly burns off.
This gif captures one of the first observations of this post-sunrise fog. This pair of color images was taken on July 24, 1976, about a month after Viking 1′s arrival at Mars.
Image Credit: NASA / JPL / Viking Project / Justin Cowart










