Ridges on Mars have variety of origins
This view from the HiRISE camera on NASA’s Mars Reconnaissance Orbiter shows part of an area on Mars where narrow rock ridges, some as tall as a 16-story building, intersect at angles forming corners of polygons. Image & Caption Credit: NASA / JPL-Caltech / Univ. of Arizona
Ridges of various sizes have been located in many regions of the Martian surface, and scientists surmise that they originated in a variety of processes and events.
Laura Kerber of NASA’s Jet Propulsion Laboratory conducted a detailed search for these ridges after discovering a network of polygon-shaped features in Medusae Fossae, a location close to Mars’ equator.
3-D view of blade-like ridges on Mars outlining polygons. (Click to enlarge) Image Credit: NASA / JPL-Caltech / Univ. of Arizona
The ridges of Medusae Fossae, which Kerber found in images captured by NASA’s Mars Reconnaissance Orbiter (MRO), are tall, stretching as high as 16 feet. Thin and shaped like blades, they intersect one another, dominating the region.
Similar networks of ridges cover other areas on the Red Planet.
Kerber, who published her findings in this month’s edition of the journal Icarus, said the ridges likely came about when lava flowed into fractures already present on the surface.
Over time, the lava within the fractures hardened and was less subject to erosion than surrounding material.
Many ridge networks on Mars are of a type known as “boxwork ridges”, in which raised lines intersect one another, forming shapes such as triangles, rectangles, and even more exotic polygons, such as pentagons.
While their sizes and shapes vary, even ridges of similar sizes and shapes can have very different origins.
MRO, which has been orbiting Mars since 2006, has six different science instruments, including the Context Camera (CTX) and the High Resolution Imaging Science Experiment (HiRISE).
Examples of Martian ridges
Smaller networks of ridges have been discovered by the various Martian rovers. Curiosity, which has been on Mars since August 2012, found several types, including small boxwork ridges that originally were mud cracks.
In one area known as “Garden City“, Curiosity located polygonal ridges that are actually veins, created long ago when groundwater filled with minerals flowed through underground cracks. Eventually, these veins were exposed by erosion.
Large ridges nearly a mile wide form several rectangles near Mars’ south pole in a region known as “Inca City“. These likely originated with faults created by impacting objects.
Subterranean fractures within the faults were subsequently filled with flowing lava that eventually hardened. Over time, erosion uncovered the hardened lava.
Ridge networks could potentially confirm Mars was once warm and wet. In the northern region of Nilosyrtis Mensae, ridge networks appear to be located in the same areas as other features that indicate water once flowed there.
Ridges at Shiprock in northwestern New Mexico. (Click to enlarge). Image Credit: NASA/JPL-Caltech
These features include the presence of minerals that form in hot springs, layers of clay minerals, and channels that appear to have been created by flowing water.
“Polygonal ridges can be formed in several ways, and some of them are really key to understanding the history of early Mars,” Kerber said. “Many of these ridges are mineral veins, and mineral veins tell us that water was circulating underground.”
Similar polygonal regions on Earth also have a variety of origins. Some were created by large walls of lava that later solidified underground, then were exposed due to erosion.
Smaller ridges inside limestone caves were created by a combination of physical and chemical erosion.
Citizen scientists wanted
Kerber is seeking help from citizen scientists who are interested in studying MRO images taken with CTX to find more Martian polygonal ridges that have yet to be discovered.
Working through Zooniverse, an online program that operates citizen science projects in a variety of fields, she started the project, titled “Planet Four: Ridges” on January 17.
Over 150,000 volunteers have worked on other Mars projects using CTX and HiRISE data. Anyone interested in the search for ridges should visit Planet Four: Ridges.
Laurel Kornfeld
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.
