Gullies

The picture below left is one of the first pictures taken of Mars with a NASA spacecraft.  It was taken in July 1965.  The large crater with the two smaller craters on its floor was named Mariner Crater. 

Everyone was delighted with the quality of the image.  One experimenter called it, "one of the most remarkable scientific photograghs of this age." The picture below it is part of an image made with the MGS wide angle camera.  Next is an image by Mars Global Surveyor, is an  area of craters and hills that are directly below the Mariner crater on the Viking map.

Try to follow this picture sequence to gain an appreciation of how far NASA has come with Mars exploration.

The black box in the map above indicates where the MGS picture on the left is from. 

Martian Gullies

Discovered in Mars Global Surveyor images in 2000, gullies excited scientists because their formation probably involved the action of recent, liquid water. 

Gullies are found on steep slopes and have a broad alcove at the top, deep V-shaped channels, and an apron at the base.  The lack of many craters on and around them reveal their youth.  The older a surface, the more craters it contains.  On Mars everything gets quickly covered in bright dust.  Since the gullies are often dark and dust-free, they could be just weeks old.

When first described, scientists believed they were due to aquifers--water bearing layers of rock.  As more images poured in, other theories for their formation arose.  One of the first alternative ideas was that gullies resulted from melting under a snow pack.  The melting could occur from the pressure from the wieght of the snow and/or from heat flow from the planet.  Some areas of Mars have what appear to be snowfields--they seem to cover the terrain, making it appear to be smooth.

Some researchers noticed the similarity between Martian gullies and debris flows in Greenland.  The theory goes that when frozen soil on a steep slope melts, it will tend to move downhill and produce features that look identical to the gullies.

There are other ideas to explain these strange features, but at present , the cause or causes remain a tantalizing mystery.  Because many of the explanations involve recent, liquid water, the gullies hold the focus of scientists.

For more images click here.

Revised January 2007