In Brief
Any given mission to Mars is going to allow for new crops of images to be scrutinized. Images of Martian terrain are allowing a glimpse into the past of the planet to see how it was formed. Planet Four: Ridges is a project that is enlisting the public to examine photos to better help scientists identify new features of the Red Planet.

Mars has some impressive geological features across its cold, desiccated surface, many of which are similar to featured found here on Earth. By studying them, scientists are able to learn more about the natural history of the Red Planet, what kinds of meteorological phenomena are responsible for shaping it, and how similar our two planets are. A perfect of example of this are the polygon-ridge networks that have been observed on its surface.

One such network was recently discovered by the Mars Reconnaissance Orbiter (MRO) in the Medusae Fossae region, which straddles the planet’s equator. Measuring some 16 story’s high, this ridge network is similar to others that have been spotted on Mars. But according to a survey produced by researchers from NASA’s Jet Propulsion Laboratory, these ridges likely have different origins.

This survey, which was recently published in the journal Icarus, examined both the network found in the Medusae Fossae region and similar-looking networks in other regions of the Red Planet. These ridges (sometimes called boxwork rides), are essentially blade-like walls that look like multiple adjoining polygons (i.e. rectangles, pentagons, triangles, and similar shapes).

Shiprock, a ridge-feature in northwestern New Mexico that is 10 meters (30 feet) tall, which formed from lava filling an underground fracture that resisted erosion better than the material around it did. Credit: NASA

While similar-looking ridges can be found in many places on Mars, they do not appear to be formed by any single process. As Laura Kerber, of NASA’s Jet Propulsion Laboratory and the lead author of the survey report, explained in a NASA press release:

“Finding these ridges in the Medusae Fossae region set me on a quest to find all the types of polygonal ridges on Mars… Polygonal ridges can be formed in several different ways, and some of them are really key to understanding the history of early Mars. Many of these ridges are mineral veins, and mineral veins tell us that water was circulating underground.”

Such ridges have also been found on Earth, and appear to be the result of various processes as well. One of the most common involves lava flowing into preexisting fractures in the ground, which then survived when erosion stripped the surrounding material away. A good example of this is the Shiprock (shown above), a monadrock located in San Juan County, New Mexico.

Examples of polygon ridges on Mars include the feature known as “Garden City“, which was discovered by the Curiosity rover mission. Measuring just a few centimeters in height, these ridges appeared to be the result of mineral-laden groundwater moving through underground fissures, which led to standing mineral veins once the surrounding soil eroded away.

Mineral veins at the “Garden City” site, examined by NASA’s Curiosity Mars rover. Credit: NASA/JPL
Mineral veins at the “Garden City” site, examined by NASA’s Curiosity Mars rover. Credit: NASA/JPL

At the other end of the scale, ridges that measure around 2 kilometers (over a mile) high have also been found. A good example of this is “Inca City“, a feature observed by the Mars Global Surveyor near Mars’ south pole. In this case, the feature is believed to be the result of underground faults (which were formed from impacts) filling with lava over time. Here too, erosion gradually stripped away the surrounding rock, exposing the standing lava rock.

In short, these features are evidence of underground water and volcanic activity on Mars. And by finding more examples of these polygon-ridges, scientists will be able to study the geological record of Mars more closely. Hence why Kerber is seeking help from the public through a citizen-science project called Planet Four: Ridges.

Established earlier this month on Zooniverse – a volunteer-powered research platform – this project has made images obtained by the MRO’s Context Camera (CTX) available to the public. Currently, this and other projects using data from CTX and HiRISE have drawn the participation of more than 150,000 volunteers from around the world.

By getting volunteers to sort through the CTX images for ridge formations, Kerber and her team hopes that previously-unidentified ones will be identified and that their relationship with other Martian features will be better understood.