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. 

One Step Closer to Launching Planet Four 2.0

In May of last year, Planet Four project was paused. Since then we have been working on a new version of the project on the Zooniverse’s Project Builder Platform.  In October, we gave you a sneak peek of two potential versions of Planet Four 2.0.  Based on the feedback we received, we have made some tweaks and finalized the website design.

Before we officially launch the new website, we want your feedback.  Please go try our our latest version of Planet Four 2.0 and let us know what you think. You can take part here.

New data on Planet Four: Terrains

Planet Four: Terrains is back from hiatus. We’ve come up with a new set of images to search on the site. These CTX images will continue our trend of searching further northward and covering gaps in our coverage.


The figure above shows the newly uploaded CTX images on the geologic map of the Martian south polar region. The blue is the south polar layered deposits (SPLD). This is where most of the spiders are located, but we’ve already learned through Planet Four: Terrains that there are spiders also outside the SPLD, so that’s why the search region expands well beyond the SPD. The red rectangles show you the CTX images that we’ve currently uploaded to the site. The bright green rectangles are the second half of the dataset.

Our current plan is to write a summary science paper with a final catalog from the spider search over the past several years, after we get through both sets of CTX images. We’ll look at the soil thermal inertia and other properties and see if we find a links or correlations to where spiders are visible. We think this we’ll wrap up this phase of Planet Four: Terrains, but we already have some ideas where we might take the project next.

Thanks for your help! Dive in today at!

Help beta test the new Planet Four

In May, the original Planet Four project was paused. Since then the team has been working on a new version of the project utilizing the Zooniverse’s latest web tools. Great news! We’re nearly ready to launch the new and improved Planet Four on the Zooniverse’s Project Builder Platform.

Before we launch the site live, we need your help! We’re ready for you to take a sneak peek at the site and let us know what you think. We have developed two different styles for the classification interface, and the team is having trouble deciding between the two. We’d like you to try them out and let us know what you think. The team will be looking at performance of the two different classification interfaces and your feedback to figure out which design is the right one for the new Planet Four.

If you can spare a few minutes, please map fans and blotches in one or both of the workflow styles and let us know what you think. Try it out at

Research Experience for Undergraduates

There is a nice program for undergraduates here in the US that is called REU: Research Experience for Undergraduates.

Within this framework the Planet Four team here in Boulder, CO was fortunate to receive funding support by the United Arabic Emirates for one of these undergraduate positions for this summer.

Working with us was Shahad Badri, and the project we came up with for her was to look at blotch data from Planet Four. Our hypothesis was that it should be relatively straight forward and provide us with insights on jet eruption physics alone, because no wind was involved in depositing the jet deposits.

As usual, the reality turned out to be more complicated than our naive thinking, so we are still digesting the results of plotting blotch area and blotch eccentricities over the time of the Martian year (= Ls = Solar Longitude), but we wanted to show you the nice poster that Shahad came up with at the end of the summer project.

As in any exciting science project, the analysis created more questions than we had before. We will need to juxtapose these results with geometrical parameters of the fans, to see where we maybe have transitions between fans and blotches due to ground winds, shifting deposits around, making blotches look more fan-like.

Thanks to Shahad for her diligent work over this summer!

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Full res PDF

Building the NASA Citizen Science Community Meeting

Greeting from Tucson Arizona. I’m here with Planet Four PI Candy Hansen at the Building the NASA Citizen Science Community Meeting. The aim of the workshop is to bring together researchers engaged in successful citizen science projects, citizen science experts and platforms supporting citizen science projects (including representatives from Zooniverse), the NASA Science Mission Directorate, and researchers interested in applying citizen science to their research problems.

I gave an invited talk (my slides are included below) highlighting science results and the success of Planet Four and advertising Planet Four: Terrains and Planet Four: Ridges. It’s exciting that people in the planetary and astronomical community see Planet Four as a successful project. That is in large part due to the contributions of the Planet Four volunteer community.  It was great to talk about Planet Four’s first paper and also mention the science team is working on three other publications right now based on the first fan and blotch catalog.



Can I Lend a Hand? Co-operation between AI and Martian Scientists

Today we have a guest post from Dr Eriita Jones and Professor Mark McDonnell. Eriita is a Planetary and Space Scientist, Research Fellow at the School of IT and Mathematical Sciences, University of South Australia, and an ECR member of the National Committee for Space and Radio Science. Her primary research areas are (i) the remote detection and characterisation of subsurface water environments on Mars and Earth, and (ii) quantifying the habitability of other planetary bodies. She is particularly interested in new computational data analysis techniques and in assessing the benefits of machine learning for space science. Mark McDonnell leads the Computational Learning Systems Laboratory at University of South Australia. He has published over 100 research articles in the fields of machine learning, computational neuroscience, and statistical physics. Mark has worked extensively with industry partners to deliver applied machine learning solutions in areas such as precision agriculture, recycling, and sports analytics. His research interests lie at the intersection of machine learning and neurobiological learning.

Artificial intelligence may get some bad press, but there are of course many tasks with which AI can provide tremendous benefit to human beings. One of the tasks that AI can be utilised for is called ‘image segmentation’, which is the process of automatically dividing an image into objects or categories so that every pixel in the image receives an associated label (e.g. car, dog, tree). This is essentially what the Planet Four citizen scientists are doing when they manually outline the boundaries to fans and blotches in polar springtime imagery from Mars. Just like a human being, in order to learn a new skill a machine needs to be taught (or ‘trained’) in the task it is being asked to perform. For state-of-the-art automated image segmentation, this training requires large amounts of data in the form of images with the categories of interest clearly labelled. In 2018, researchers at the Computational Learning Systems Laboratory at the University of South Australia in Adelaide, Australia, realised that large amounts of labelled imagery was exactly what the citizen scientists on the Planet Four project were generating. That was the start of a collaboration with the Planet Four Science Team. We wondered – could we teach an algorithm to automatically detect fans and blotches in Martian imagery? How well could a machine learn these complex features? And could the algorithm provide information which would assist the scientists in their study of these Martian phenomena?

The machine learning algorithms used here are examples of deep Convolutional Neural Networks (CNN’s) which generally perform very strongly on image segmentation problems. The algorithms are fed thousands of labelled fan and blotch images produced by the Planet 4 citizen scientists. After lots of exposure to what fans and blotches look like at different locations, years, solar longitudes, and resolutions, the algorithms become able to generalize from their experiences and apply their learning to new situations – in this case, unlabelled images that they have never seen before. In order to assess how well the machine learning techniques are performing, the algorithms are given a test. They are asked to predict where the boundaries of the fans and blotches are in some labelled images – but the algorithms are not shown the labels and have never seen those images before. We can then compare the machine’s predictions with the ‘correct answers’ – the manual labels drawn by citizen scientists. We compare with another method as well– a more traditional and less complex image classifier that does not employ machine learning. The figures below shows the output on a subset of one HiRISE image.



We are busily working on validating the output of the machine learning algorithms on a large number of images, but we can already see ways in which they can be very useful. Although the algorithms might not always find every fan or blotch in an image, they are very good at deciding whether there is at least one feature present. In other words, they do a good job at sorting out the images which have a fan or blotch, from those that have no fans or blotches at all. This is a very useful way of streamlining the presentation of images to the Planet Four Zooniverse platform – for example, instead of having to click through ‘featureless’ images the Planet FourTeam in future may wish to make sure that every image that appears will have a fan or blotch in it for labelling. Additionally, by automatically predicting the presence of fans and blotches in new images the algorithms provide early information on feature number and density that can allow the Planet Four team to be more selective in which images have the highest priority for manual labelling.

Could machine learning one day put citizen scientists out of a job? We don’t think this is very likely. The algorithms may eventually learn to perform very well on new images if those images are similar enough to ones they have seen before. But if they are shown an image that is very different (e.g with unusual lighting conditions, strange background terrain, or uncharacteristic fans and blotches), it is likely that the machine won’t be quite as good at segmentation as a well-trained human eye. So don’t worry citizen scientists, AI is just here to lend a hand – thanks for all the fabulous data, and stay turned for an exciting update in a few months!

Not a Goodbye But A See You Soon

If you check out the Planet Four website now, you will now see that the site is on hiatus with the retirement of their older platform. A huge thank to you everyone who has contributed to Planet Four over these past six years and especially in the past few weeks. We completed the sets of HiRISE images we needed to complete before the site was shutdown. Mission accomplished. Thank you so much!

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This isn’t goodbye, it’s a see you soon. We’re learning so much from the Planet Four classifications/assessments that we’ll be back with more seasonal fans and blotches to map. We’re working on a new version of Planet Four with the Zooniverse’s new project builder platform, but it will take us time to build and test the new version of the project. In the meantime we have lots of classifications to analyze from the original site. The science team is currently working on four papers (!!!) based on your classifications, and this work will continue even if the website is paused. In addition,  Planet Four: Terrains and Planet Four: Ridges are on the Zooniverse’s newer platform and will continue to be active.


Final Push on Planet Four and Planet Four’s Future

We were formally informed this week by the Zooniverse, that the platform that Planet Four is hosted on will be retired and shutdown very soon. On April 30th, the platform will be shutdown. This means that the site will be on hiatus as the science team continues to work towards building a new version of the project on the Zooniverse’s project builder platform.  This is going to take several months to complete, but in the meantime we are also analyzing your classifications and the Season 2 and 3 fan and blotch catalog. The science team has papers in the works and have been exploring possibilities/synergies with machine learning as well.

Planet Four’s future is bright.  April 30th  won’t be the end of Planet Four. We’ll be back. For at least the time being Planet Four Talk will be accessible and you can login and continue to make posts. Some point in the future, Planet Four Talk will become read only. Rest assured, your comments, hastags, and collections are stored in the Planet Four Talk database, so that information is saved and accessible to the science team for further investigation.  We’ll keep you updated here on the blog.

Before we pause Planet Four, we need your help! We still have data on the site left to be classified. We believe we have found a connection between regional dust storms on Mars and the number of seasonal fans and blotches visible in a given spring season. To check whether or not these storms are playing a significant role, new images are live on the Planet Four website. We are hoping we can get as many images classified as possible before the site goes on hiatus.

Time is running out, and we need your help to get as many of these images classified before the old Zooniverse platform is retired on April 30th. If everyone classified 10 images, we’d be over the finish line. If you can spare a minute or two, please review images at 


A Sneak Peek at the Future of Planet Four

The science team is working on migrating Planet Four to the Zooniverse’s more modern project builder (or panoptes) platform. This is a slow process because things are different in how the newer Zooniverse platform displays images and also we want to take the lessons we’ve learned over the past 6 years and use it to make the web interface even better.  We thought we’d share some screen shots from our work-in-progress prototype.

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The next stage will be getting some images on the site and beta testing the changes we want to make and seeing how well these tweaks do compared to the current Planet Four website/classification interface. This might take a few months, but we’re working hard to have this ready before the end of the year.

In the meantime, we have new images on the original Planet Four website that we are hoping to get classified before the older Zooniverse platform that runs the current Planet Four site is officially retired. We’re trying to make the push in April to get these new images classified. If you can spare a few minutes to classify an image or two on the main Planet Four site, we’d appreciate it.