Bill DunfordDec 09, 2013

The Mists of Mars

Late last month, visitors to Grand Canyon National Park in Arizona witnessed a rare and spectacular sight. A temperature inversion (where a layer of cold air is trapped beneath warm air) led to a canyon filled to the brim with clouds.

Grand Canyon Inversion
Grand Canyon Inversion A temperature inversion in November, 2013 created a rare sight for visitors to the Grand Canyon as the chasm filled with clouds.Image: NPS / Erin Whittaker

On the very same day, a robotic spacecraft at the planet Mars captured a similar scene. This one was a much more common event, but one that still makes for incredible imagery. Valles Marineris is a network of canyons that in many ways looks similar to the Grand Canyon--except that at more than 4,000 kilometers in length, if it were on Earth it would stretch across most of the United States.

This canyon, too, sometimes fills with clouds, made of tiny particles of water ice, though it's not caused by an inversion. Despite the Red Planet's well-earned reputation as a dry desert, there are hints of water on its surface and in its atmosphere. The Mars Color Imager (MARCI) on board the Mars Reconnaissance Orbiter makes daily observations of the entire planet. On November 29 and 30, MARCI returned pictures of wispy clouds clinging to the summits of Olympus Mons and the other towering volcanoes. It also showed Valles Marineris, a long horizontal scar probably formed in part by the tectonic effects of all those volcanoes. As happens seasonally, the canyon was clearly filled with clouds.

The Clouds of Mars
The Clouds of Mars A composite of global images of Mars taken on November 29-30, 2013 by the Mars Reconnaissance Orbiter. Water ice clouds cling to the summits of the major volcanoes, and fill the giant canyon of Valles Marineris (the long, horizontal feature in the south).Image: NASA / JPL / Malin Space Science Systems / Bill Dunford

Some of the first detailed pictures of this phenomenon came from the Viking orbiters back in the 70s. This still-stunning capture shows the maze of canyons at the west end of Valles Marineris called Noctis Labyrinthus, "the labyrinth of the night," as the morning sun vaporizes water that condensed in the shadows the previous night.

Water Ice Fog in Noctis Labyrinthus
Water Ice Fog in Noctis Labyrinthus The canyons of Noctis Labyrinthus, on the west side of Valles Marineris, filled with water ice clouds in the morning sun. Captured by the Viking 1 orbiter.Image: NASA / JPL

More recent missions bring us the same kinds of scenes in even more detail. Here, the Mars Express spacecraft's high-res camera reveals a portion of the immense canyon haunted by haze.

Mist in the Canyon
Mist in the Canyon A mist of water ice crystals hangs in the "Grand Canyon of Mars," Valles Marineris, as seen by ESA's Mars Express orbiter.Image: ESA / G. Neukum (Freie Universität, Berlin, Germany) / Bill Dunford

It's enticing to imagine the view from the edge of a Martian cliff on such a day. Thanks to an unusual gift from the Grand Canyon, now it's a little easier to do so. (Another temptation: picturing past eons when the skies on Mars might have been a little more blue.)

Morning Mist
Morning Mist A cloud inversion in the Grand Canyon in November, 2013.Image: NPS / Erin Whittaker

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