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Thin, blade-like walls, some as tall as a 16-story building, dominate a previously undocumented network of intersecting ridges on Mars, found in images from NASA's Mars Reconnaissance Orbiter.
The simplest explanation for these impressive ridges is that lava flowed into pre-existing fractures in the ground and later resisted erosion better than material around them.
Survey - Ridges - Mars - Network - Medusae
A new survey of polygon-forming ridges on Mars examines this network in the Medusae Fossae region straddling the planet's equator and similar-looking networks in other regions of the Red Planet.
"Finding these ridges in the Medusae Fossae region set me on a quest to find all the types of polygonal ridges on Mars," said Laura Kerber of NASA's Jet Propulsion Laboratory, Pasadena, California, lead author of the survey report published this month in the journal Icarus.
Pattern - Boxwork - Ridges - Lines - Outlines
The pattern is sometimes called boxwork ridges. Raised lines intersect as the outlines of multiple adjoining rectangles, pentagons, triangles or other polygons. Despite the similarity in shape, these networks differ in origin and vary in scale from inches to miles.
Mars rover missions have found small versions they have been able to inspect up close. Some of these polygonal ridges, such as at "Garden City" seen by Curiosity, are veins deposited by mineral-laden groundwater moving through underground fissures, long before erosion exposed the veins. Curiosity recently also imaged small boxwork ridges that likely originated as mud cracks.
End - Size - Scale - Rectangles - Mile
At the other end of the size scale, ridges outline several rectangles each more than a mile (more than 2 kilometers) wide at a location called "Inca City" near Mars' south pole. These may have resulted from impact-related faults underground, with fractures filled by rising lava that hardened and was later exposed by erosion.
"Polygonal ridges can be formed in several different ways, and some of them are really key to understanding the history...
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