NASA/JPL/University of Arizona

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).

This vertically exaggerated view shows scalloped depressions in a part of Mars where such textures prompted researchers to check for buried ice, using ground-penetrating radar aboard NASA’s Mars Reconnaissance Orbiter. Image Credit: NASA/JPL-Caltech/Univ. of Arizona

My paper on the discovery of a widespread (~375 000 sq km) subsurface water ice deposit in southwestern Utopia Planitia, Mars, was published in Geophysical Research Letters (GRL) a few weeks back, along with a NASA press release today. The detailed version is offered in the journal article, but I thought I’d include a higher-level description of what’s up in here.

When you look at Utopia Planitia, there’s a lot of weird stuff going on. For those that aren’t intimately familiar with martian geography, Utopia Planitia is a huge, ~3300 km diameter basin that formed by impact early in Mars’ history. It makes up part of what’s known as the northern plains, the more-or-less flat terrain north of the martian dichotomy boundary. For as long as we’ve had good imagery from the region, we’ve noticed interesting features on the surface—features like polygonal cracked terrain and oddly-shaped, rimless pits called “scalloped depressions”. When we see features like this on Earth, they’re associated with subsurface ice or permafrost. These features led scientists to believe that this is an ice-rich region of Mars, and inspired my team to examine radar sounding data from the area.

Martian gullies were in the spotlight recently thanks to a NASA press release stating they were “likely not formed by liquid water.” The release concerns the publication of a new paper by Nuñez et al. in Geophysical Research Letters, which looked at spectral data of gullies from the Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars (CRISM).

In their study, Nuñez and his colleagues looked at over 100 gullied locations on Mars. They found no evidence of minerals that would be expected to form in the presence of water. Rather than water, they point to sublimation of seasonal carbon dioxide frost as the main culprit behind gully formation on Mars. Other people have proposed a similar model to explain present-day activity in gullies, which appears to happen during periods of active defrosting. But this process has been a topic of debate among the Mars gullies community, and was a big discussion point at the “Martian Gullies and Their Earth Analogues” workshop in London back in June. Can this dry process explain both the initial formation of gullies and gullies’ modern-day activity?