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An Update on Planet Four: Ridges

Today we have a guest post by Adi Khuller. Adi is a 3rd-year PhD student at the School Of Earth and Space Exploration at Arizona State University.

Woohoo!! Our project’s first research paper was finally published! We could not have done any of this work without all your help. As Laura mentioned in her last post, we went through the research paper review process and addressed the feedback we received from two anonymous referees. After two rounds of iterations and revisions, the journal editor (who makes the final decision on publication) decided that the paper was ready to be published. You can read it for free here.

Here’s a quick summary of the overall findings we describe in the paper:

(1)   With your help, we mapped the distribution of 952 polygonal ridge networks over an area of 2.8 × 107 km2. This large area is about a hundred times the area that previous studies had mapped looking for similar ridges!

(2)   Interestingly, we found that 864 out of 952 (91%) of these ridge networks were found in very old, eroded terrain (~4 billion years ago). Many scientists believe that this time period in martian history was warmer and wetter, which might be related to how these ridges form (more on that later).

(3)   We also studied some of these ridges using thermal infrared data (like Superman’s infrared vision) using NASA/ASU’s THEMIS camera. The ridges appear less consolidated than their neighboring material in the infrared data, but the resolution of the thermal camera is only ~100 meters per pixel. So, the thermal camera is probably not able to resolve the fine details of the ridges.

(4)   As you know, the formation mechanism of the ridge networks has remained a mystery ever since they were found from orbit. Three possibly separate processes/stages were involved: (1) polygonal fracture formation, (2) fracture filling and (3) erosion to reveal the ridge networks.

(5)   For the first stage, the polygonal fractures seem to have formed by impact cratering or the drying out of the sediment in which the ridges form.

(6)   For the second stage, the fractures were filled up. It seems like they were either filled by rocks or minerals precipitating out of groundwater.

(7)   Then, erosion by wind led to the ridges lying above their surrounding terrain.

(8)   It is hard to narrow down which of these processes were directly involved in the formation of these ridge networks from the data we have so far, but if the Perseverance rover on Mars can get to them one day (in the far future, because it is quite far away), then we will be able to figure out how they really form.

(9)   Our best, educated guess right now is that they form by minerals precipitating into polygonal fractures, which would mean that because these ridges are so widespread across Mars, that there was a lot of groundwater activity happening in this time period close to 4 billion years ago.

Thank you for all your help, and we hope to continue working with you on Planet Four: Ridges and future Planet Four projects!! 

Planet Four Roulette

With three projects under the Planet Four Organization, it might not be an easy task to decide which project to dive into today. You’re in luck. We’ve got you covered. Fancy a spin of the wheel?

An Update on Planet Four: Ridges

It’s been a busy summer for the Planet Four: Ridges science team. The project’s first research paper was submitted to the journal Icarus. A big thank you to all the volunteers and our active volunteers on Talk who have contributed lots of great polygonal ridge locations that went into the paper’s analysis. Below you’ll find a map showing the CTX images that were searched by Planet Four: Ridges volunteers using the main classification interface as part of the study.

Map of the locations of the CTX images searched on the Planet Four: Ridges website that was used in the analysis of the project’s first paper.

The first step in this process is getting the referee reports back. The referees are researchers studying Mars who give independent feedback on the paper. Normally the identities of the referees are anonymous, and the author does not know who they are. The referees read the paper and give the editor their opinion on whether the paper is of sufficient quality to be published in the journal and give feedback on how the manuscript/work could be improved. The job of the referee is to point out areas that should be clarified in the paper and where more analysis needs to be done if needed before the paper can be accepted for publication in the journal.

We’ve recently received the feedback from the two anonymous referees. The referees see that there is merit in the Planet Four: Ridges catalog. Thye also gave a lot of great feedback on where we can improve the analysis and manuscript. We’re working on addressing the referee’s comments and taking on board their feedback. We’ll keep you posted as we move through the paper revision process. We’ll do some further analysis, reworking of the paper draft, and add some additional text. Once we’ve done that, we’ll write a response to the referee’s report outlining what was changed/added to the paper to address the points raised by the referees. Then we’ll resubmit the paper and send the response to the referees to the journal. The referees will read everything and send back further questions, concerns, and points that need clarification. We will post more details about the key results of the paper once the paper is accepted and published by the journal.

New Planet Four: Ridges Search

Today we have a guest blog by JPL research scientist Laura Kerber,  our lead researcher on Planet Four: Ridges. Laura studies  physical volcanology, aeolian geomorphology, wind over complex surfaces, and the ancient Martian climate.

Greetings to you in these apocalyptic times! I hope that you and your families are doing well in isolation, or wherever you find yourselves to be.

 Over the last few years, Planet Four: Ridges has ranged far and wide across the Arabia Terra, from Nili Fossae near the future landing site of the Mars 2020 Perseverance rover, all the way to the plains of Meridiani Planum, near where little Opportunity lost its life in a 2018 global dust storm after 15 beautiful years of adventure. Along the way, you all have discovered many other treasures, including polygonal fracture networks, networks of dark lines, patches of desiccation polygons (mud-cracks) and many other fascinating features, each of which could seed a study of its own.

Your polygonal ridge discoveries are now being incorporated into a journal article, which has been undergoing many iterations as we prepare it for submission.

In the meantime, thanks to hard work by Meg Schwamb and Michael Aye, a new part of Meridiani has been opened up to us to search, just to the east of where we had been looking:

Figure 1. The broad region of study. The aquamarine dots are where you found Meridiani ridges in the last campaign. The turquoise squares are the footprints of the images that we’ll be looking through this time. The orange line is the fictional traverse of Mark Watney in the novel “The Martian” by Andy Weir. The yellow star is the location of the Opportunity rover. The background is from the Mars Orbiting Laser Altimeter, which gives us topography (blue is low and red is high).

On our last foray into ridge hunting, we learned that Meridiani has two distinct kind of polygonal ridges. There are regular polygonal ridges, which have straight connectors and enclose polygonal shapes (commonly found in northern Arabia Terra near Nili Fossae), and Meridiani ridges, which are often arcuate, enclosing circles or fractions of circles, and intersecting each other like tattered lace. While individual polygonal ridges are thin, Meridiani ridges can have wide, flat tops, or can appear splintered. There is a new tutorial to explain these two ridge types.

Your mission (should you choose to accept it) is to range around our new region of Meridiani, looking at images and classifying them into those that have regular polygonal ridges, those that have Meridiani ridges, and those which have neither (of which there are many!) I encourage you to use the “Done and Chat” button, hashtags, and collections to point out strange or mysterious things that you encounter on your way. There is a link on each image at the bottom (click the tiny “i” after clicking “Done and Talk”) that can take you to the source CTX image if you are curious about the area. Also don’t be afraid to zoom around on the Mars version of Google Earth (with the CTX global image layer on) and tell us what you find that way.

During this pandemic, many of us are cooped up in our homes with nowhere to go. Luckily, despite not being able to travel the Earth as we are used to, we are all free to fly over the vast empty deserts of planet Mars.

Whether you are a long-time Planet Four Ridge Hunter or you’re just joining us now, have fun exploring Mars and happy ridge-hunting!

Ideas on the Formation of Resistive Polygonal Ridges on Planet Mars

Today we have a guest post from Planet Four: Ridges volunteer, Bill Hood (geocanuck). Bill Hood is a semi-retired Canadian geologist who has spent 40+ years in the mineral exploration business as a contractor, consultant and prospector. When not wandering around in the mosquito-infested swamps of northern Ontario or the grizzly-prone mountains of the Yukon, he can be found residing in a small town near the city of Winnipeg. A self-confessed Star Trek fan, Bill occasionally argues that it is mineral exploration that will drive human exploration of space, and is rumoured to have already started Mars Palladium Corp. Bill spotted the NASA P4R news release in early 2017, and has been addicted to Mars images/geology ever since.

It appears customary on Planet Four, that after one does a talk or presentation involving Planet Four: Ridges material, a blog is in order. On January 8, 2020, I did a talk titled “Ideas on the Formation of Resistive Polygonal Ridges on Planet Mars” at a meeting of the Manitoba Mineral Society here in Canada. The Society meets monthly in the city of Winnipeg in the local planetarium building, so there’s a slight crossover with the astronomy crowd.

My presentation comprised three main parts: 1) fun facts about Mars, 2) Planet Four: Ridges and the science arising from it, and 3) my ideas on the formation of polygonal ridges. After a brief run-through of the basic geography of Mars, locations of all the landers, and some fun images of faces, structures and items that look like they could only have been constructed by beings with opposing digits or sharp teeth, I outlined how the Zooniverse Planet Four websites functioned to generate Mars data. Next, I outlined some of the science interpretations coming from this data, including the abstract for the talk by Aditya Khuller, Laura Kerber et al, at the 2018 American Geophysical Union convention, as well as a proposed paper titled “Polygonal Ridge Networks in Arabia Terra, Nili Fossae and Nilosyrtis: Evidence for Groundwater Influence”, presently in preparation by the same authors. I then summarized the basic hypothesis of this work to date, which suggests that “Nili” type polygonal ridges on Mars have resulted from burial, compaction and faulting of shallow-basin, clastic sediments, with subsequent groundwater flow and mineral deposition along these polygonal-oriented fault/fracture systems. Subsequent erosion exposed these hard, resistive ridges on Mars. Terrestrial models from the North Sea basin and resistive ridges exposed across the Middle East seemed to be an entirely plausible analogy.

But being a person of contrary character and residing in the frozen environs of rural Canada, I explained to the members of the society that I had difficulty being convinced by the proposed ridges formation argument. When I looked at Mars images, I saw glaciers and pingos and permafrost patterned ground that looked like something out of Arctic Canada, while my on-line Zooniverse friends, most residents of warmer climates, saw a world of palm trees and torrid deserts. As I told my friends in the local Mineral Society on that cold January night, it was clear that I had not just a responsibility, but a Canadian national duty, to advocate a “permafrost hypothesis” for polygonal ridges on Mars.

From my observation, it appears that the “Nili” type polygonal ridges, named for a future type locality in the Nili Fossae region of northeast Arabia Terra on Mars, comprise a range of polygonal oriented resistive ridges, as well as irregular or semi-circular ridges which enclose the margins of ridge areas. It appears that these polygonal ridges are forming in the subsurface, within the basal clastic sediments in local craters, valleys and basins, just above the unconformity at the top of the older Noachian cratered basement rocks on Mars. The similarities to ice fracture patterns and permafrost patterned ground were fairly obvious. So I presented a couple dozen slides, both from Mars and Earth, pointing out fracture pattern similarities, with the caution that there were scale differences and the obvious sub-sediment vs. sub-aerial disparities.

I concluded my talk showing a series of hypothetical cross-sections illustrating a possible process for forming these unusual polygonal ridges in the sub-surface on Mars. The basic idea I am presenting is that a sub-surface permafrost cap may have formed a confined groundwater aquifer. Evidence of sub-surface artesian flow is rather obvious in many Mars images, but the question of what triggered this flow is important. I’m suggesting that the accumulation of aeolian sediment may have formed a thermal blanket which allowed remnant geothermal heat to erode the permafrost cap, triggering artesian flow from the aquifer into basal clastic sediments above the unconformity and into overlying ice-wedge fractures in the permafrost. Having a long residence time, these groundwaters would be at maximum total dissolved solids, so mineral deposition would be significant on evaporation/sublimation. 

So that’s my Planet Four blog. I’ll conclude with one takeaway, which is that if this ridge process consumed all the subsurface ice, the Nili ridge areas may not be the best places to send future Mars colonists. I can also advise that the members of the Mineral Society asked that Mars be added to the summer field trip schedule. 

Early Warm Wet Mars
Cooling Mars. Permafrost.
Confined Aquifer. Aeolian Deposition.
Thinning Permafrost. Artesian Flow.
Open Aquifer. Evaporation/Sublimation.
Induration/Lithification of Basal Sediments/Fractures.
Erosion. Variable Exposure. 

New Meridiani Images on Planet Four: Ridges

After a hiatus, Planet Four: Ridges is back! We’ve get the second batch of Meridiani ridges search images live on the site. We’re finding from the analysis of the previous search classifications for regular polygonal ridges, that Planet Four: Ridges volunteers can identify polygonal ridges smaller than contained in previous catalogs. We expect the project can do the same for Meridiani ridges. Dive in today at https;// and classify an image or two.


One (Earth) Year of Planet Four: Ridges

Today we have a guest blog by JPL research scientist Laura Kerber,  our lead researcher on Planet Four: Ridges. Laura studies  physical volcanology, aeolian geomorphology, wind over complex surfaces, and the ancient Martian climate.

Dear Ridge Hunters,

Can you believe that it has been a year since we started to hunt for ridges??? We have accomplished a great deal in the space of a year! With 7,784 volunteers, we have made 135,976 classifications! We finished our first region (parts of Deuteronilus Mensae), second region (Protonilus Mensae) and third region (Nili Fossae)! We are now working on our fourth batch of images—from a new region in Meridiani Planum, closer to the currently operating Opportunity rover. Mapping our first three regions allowed us to understand the distribution of Nili-like ridges close to two of the Mars2020 rover candidate landing sites, and allowed us to see what sorts of geologic units were associated with the ridges. We found out that the ridge-bearing units are often buried units, and that polygonal ridges were almost never found in glacial terrain. There also wasn’t a strong correlation between craters and ridge networks. There was a strong correlation, however, between ridge units and ancient terrain from Mars’ oldest geological period, the Noachian. As its name suggests, the Noachian was a time when water was abundant on the surface of Mars. Our ridge discoveries suggest that the subsurface was also the site of extensive water-related processes. Since the subsurface would have also been protected from harmful UV rays, this watery environment could have been an interesting place to foster life.

Here is a map showing the ridges that were known before this project (green) and the enormous number of ridges in fine detail that we mapped throughout Nili Fossae (red):


But wait! There’s more! Intrepid ridge-hunter @bluemagi ventured outside of the Zooniverse-defined regions and is currently conducting a planet-wide search for more ridge-bearing regions. Here’s a map of the simply astonishing findings of @bluemagi across the rest of the planet (added in blue), which were transformed into an amazing .kmz file for Google Earth by @frognal! Check out their handiwork here and see if you agree with @bluemagi’s interpretations!


Thanks everyone, for a year full of amazing surprises in Planet Four: Ridges. Here’s to another year of exploring the planet Mars together!

More on Merdiani-type Polygonal Ridges

Today we have a guest blog by JPL research scientist Laura Kerber, one of  our lead researchers on Planet Four: Ridges .  Laura studies  physical volcanology, aeolian geomorphology, wind over complex surfaces, and the ancient Martian climate.

Merdiani-type Polygonal Ridges


Merdiani-type Polygonal Ridges

Hello Ridge Hunters!

We are nearing the end of the year on Earth, but we’re only in Martian month 4 on Mars (Solar Longitude = 99.2; Sol number = 214). But what a year on Earth it has been for Planet Four: Ridges. Since our launch on January 17th, thanks to 7,453 registered volunteers, we have retired 11,999 images! We have mapped ridges the length and breadth of the dichotomy boundary near Protonilus Mensae, Nilosyrtis Mensae, and Nili Fossae.

We are now moving into the strange and wondrous land of Sinus Meridiani, not too far from where the Opportunity Rover has been roving along at what might be the shore of a vast, ancient inland sea. The ridges in this new area are different—they are flat on top and splintered, and they can be dark or light compared to the background terrain. Instead of true polygons, they make broken circles. Take a look at the update tutorial to see examples of this new and strange type of ridge. By mapping ridges in Sinus Meridiani, we can compare and contrast them with their more northerly brothers, and determine why their morphologies are so different and what this meant for their environment and process of formation.

Happy Ridge Hunting, and if you find anything strange, let us know in the comments!

Planet Four: Ridges is Back

We’re thrilled to announce that Planet Four: Ridges is back. We’ve completed the Arabia Terra search for now, and today we’ve launched a new workflow to search for a different type of polygonal ridge that we’ve searched for previously. This new type of polygonal ridge is found in Sinus Meridiani,  a darker area of Mars located in the northern midlatitudes of  just south of the equator. You can see it’s located below Arabia Terra, the previous region we’ve been searching.


Hubble Space Telescope Image of Mars. Arabia Terra is the large triangular shaped region in the center. Sinus Meridiani can be seen as the darker region below Arabia Terra. Image Credit: NASA, ESA, and L. Frattare (STScI)

Meridiani-type polygonal ridges often look like broken spider webs or tattered lace. These ridges do not usually form neat boxy shapes, but they can be interconnected, looping, or branching. We need your help to identify these features, so that we can see if the Meridiani-type polygonal ridges follow the same trends we’re in seeing in the Arabia Terra polygonal ridges.

Meridiani-type Ridges in CTX subframes

We are continuing to work on analyzing and reducing the classifications from the Arabia Terra search. You can learn more about that in this previous blog post from Laura.

Dive back into Planet Four: Ridges today at

An Update on Planet Four: Ridges

Today we have a guest blog by JPL research scientist Laura Kerber, one of  our lead researchers on Planet Four: Ridges .  Laura studies  physical volcanology, aeolian geomorphology, wind over complex surfaces, and the ancient Martian climate.

Hello Ridge Hunters!

Thanks to you, we have mapped ridges all over Nili Fossae and Nilosyrtis Mensae!!

As you might remember, our ultimate goal was to determine the distribution of ridges so that we could see if they were correlated with any other types of interesting features, like valley networks, clay or chlorite detections, or even just with the dichotomy boundary itself, which could have aligned with the edge of an ancient ocean. Since I have found polygonal ridge networks in other places near the dichotomy boundary, I was thinking that there might be a relationship between the hypothetical ancient ocean and the ridge networks. Indeed, there are many polygonal networks in shallow marine environments on the Earth, thought to be due to shrinking that happens when water is forced out of clay layers as they are pressed. Thanks to your efforts, we discovered that the Nili ridges are very localized along the dichotomy boundary, crowded into Nilosyrtis Mensae, Nili Fossae, and Antoniadi crater, but missing in Protonilus Mensae and further west along the dichotomy boundary. These means that something special must have been going on close to Nili Fossae. It could be that the ridges were only forming in this region, or perhaps we see a deeper exposure of the subsurface here, which allows the ridges to be exposed. One intriguing possibility is that the presence of the ridges is related to the availability of carbonate, which is a common ridge-forming substance in some terrestrial deserts (in the form of the mineral calcite). The Nili Fossae region is one of the only regions on Mars where lots of evidence for carbonate minerals has been found. Perhaps ground water circulation through fractures was happening all across Mars, but only in the area where there was CaCO3 in the water could the mineralization of these fractures take place. WE DON’T KNOW!

The next step for us to take is to study all of the great examples that you have found and to tie them to their geological context, both in terms of where they are with respect to the dichotomy boundary, but also how they relate to #darklines, glaciers, and other interesting things in the area. (I think I’ve seen enough of the area by now to say that they don’t seem to be related to glaciers).

I have been working with Meg over the last couple of weeks to get all of the data that you have collected into a usable format so that we can start to write the paper. The actual writing process will take a number of months.

Meanwhile, we decided to expand our search to a slightly different part of the Arabia region—Meridiani Planum.


Here is a map showing roughly where we have been looking (jagged gray area with a black background) in the context of the broader Arabia area. Arabia is an interesting place because it is very dusty (making it hard to see what minerals are there) and it has an unusual chemical signature (it has elevated hydrogen compared to other nearby places). The white area is where I have previously found ridges in Meridiani Planum (and the center of where we will be looking next).

If you think you spy a crater whose name sounds familiar, it could be because we’re getting closer to the territory that Mark Watney traversed in Andy Weir’s The Martian.

[Spoiler Alert]: In the book, Mark Watney has to traverse from the northern plains through Mawrth Valles (another popular landing site candidate!) to get to Schiaparelli Crater. You can chart his course here on this cool fan-made website:

In 2004, the Opportunity Rover landed in Meridiani Planum. Its landing site was a wide, flat plain. In the 13 years since its landing, Opportunity has made some amazing discoveries, including the discovery of sedimentary rocks emplaced and modified by water, evidence that Opportunity’s landing site was close to the shoreline of an ancient, salty, shallow body of water. To the north of Opportunity’s landing site, Meridiani Planum becomes much less “plain-like”. Instead, it devolves into a tangle of arcuate, intersecting ridges.  While it would be a nightmare for a small rover (or Mark Watney) to traverse, this kind of bizarre geomorphology is fascinating from a geological point of view. In particular, these ridge patterns are similar in shape and morphology to some of those shallow marine polygonal networks that I was looking for along the dichotomy boundary. On Earth, one such polygonal network can be seen an ancient shallow marine environment now exposed in Egypt’s white desert. The desert is white because of the expose chalk formations, and the entire area is criss-crossed with veins full of calcite and hematite.


The Meridiani ridges are similar to the ridges that we have been finding so far in that they are intersecting, but those of you who have been with the project for a while will see immediately how different they look.

While the Nili ridges were rather narrow, discrete, angular, and polygonal, the Merdiani ridges are feathered, arcuate, varying in width, and flat-topped. They also seem to merge together in multiple areas, like in this image, where there seems to discrete ridges but also amalgamations of ridges that form a kind of mesa.


The other strange thing about the Meridiani ridges is that they are not always the same color. For the most part, the ridge-forming unit is white and the background plain is dark, but sometimes it looks like the opposite, as in the above image.

We will keep you updated as work progresses on the first paper. Meanwhile, we will work on getting you some images of Meridiani Planum to map!

If you are bored while you are waiting, try looking along the dichotomy boundary the other direction… around the Isidis Basin and into Nepenthes Mensae. Maybe the ridges appear on either side of the Isidis Basin, and represent circulation of groundwater caused by the remnant heat of the Isidis impact……