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The South Polar Layered Deposits

If you might have seen images like the ones above on Planet Four: Terrains and wondered what’s going on with these banded features in these images. That’s the South Polar Layered Deposits (SPLD). The SPLD are alternating layers of ice and dust, giving it that banded look. The are thousands of layers contained in this ~3km geologic unit. The SPLD has a counterpart in the North, unshockingly known as the Northern Polar Layered Deposits (NPLD). The SPLD (like it’s northern sibling) are mostly composed of frozen water ice in between the dust layers.

It is thought that the alternating layers are telling us that these formed from a cyclic climate process. Mar’s obliquity (axial tilt) has changed dramatically over time. The Moon prevents the tilt of Earth from changing significantly from 23.5 degrees, but Mars does not have a large moon. Instead for Mars, the axial tilt can change up to about 60 degrees. Like on Earth, the reason for seasons on Mars is the axial tilt. The more extreme the axial tilt, the more extreme the season are. Climate scientists think that the SPLD formation is related to the changing axial tilt of Mars.

Researchers are still learning about the properties of the SPLD and what it tells us about Mars’ climate history. In 2011, the ground penetrating radar measurements from Shallow Radar (SHARAD) instrument on Mars Reconnaissance Orbiter (MRO), the same orbiter that provides the images we show on the Planet Four projects, uncovered a large carbon dioxide ice reservoirs hidden, lurking below the surface of the SPLD

Extent of the SPLD and thickness of the SPLD (Image credit: NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team/USGS)

Here’s a high resolution view of the SPLD from the HiRISE camera:

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?

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!

Planet Four: Terrains Tutorial

You might have noticed that in July we added a tutorial to Planet Four: Terrains. After some changes to the front-end part of the Zooniverse platform, the team decided to add  the tutorial.  You’ll find it on the tab next to ‘Task’. There should be some new examples to help guide you while classifying. If you were a fan of the original help button and Spotter’s guide, don’t worry those are still available as well.

Screen Shot 2018-09-03 at 4.56.10 PM

We’re in the middle of going through a new suite of images on the site. Dive in and check out the new tutorial and classify a few images today at

New Images on Planet Four: Terrains

We’ve uploaded new images to Planet Four: Terrains this week. This dataset continues to fill in areal coverage to look for spiders outside of the south polar layered deposits and also examining the overall distribution of spiders and other features.

You’ll notice some changes to the look of the classification interface. Over the past several months, the Zooniverse development team has made updates and changes to the classification pages.  This  Zooniverse Talk thread is where you can share your thoughts and feedback on the new look.

Dive in today a

(Southern) Spring is Coming!

Southern Spring is coming to Mars very soon. May 22nd marks the official start of Spring at the Martian South Pole. We’ve been busy reducing the most recent sets of classifications from Planet Four: Terrains looking for new spider locales to target when the HiRISE and CaSSIS seasonal campaign starts. The CaSSIS camera is a recent addition to Mars, aboard the European ExoMars Trace Gas Orbiter (TGO). It takes slightly higher resolution images than the CTX, whose images we show on the Planet Four: Terrains website. CaSSIS is designed for  stereo imaging which is key for measuring depths and heights of features. Also unlike CTX, CaSSIS is equipped with several filters so color images can be made. Even with the addition of CaSSIS,  the decade old HiRISE remains the highest resolution imager  (~30 cm/pixel) in action around the Red Planet.

The PI of Planet Four: Terrains, Candy Hansen is a member of the HiRISE and CaSSIS science teams , and can ask for images to be potentially taken of the Solar Polar region if we find something interesting worthy of followup observations. We’ve asked for a few additional candidate spider locations (plotted below between -70 and -75 degrees latitude) outside of the South Polar Layered Deposits to be imaged if the observations can be squeezed into these cameras’ packed schedules. If confirmed in the higher resolution images, these will be the furthest spider identifications from the South Pole. Fingers crossed we’ll get some more detailed images of these places over the coming months.



Green boxes denote candidate spider/araneiform locations found by Planet Four: Terrains

Thanks for all your help. We plan to have new images on the Planet Four: Terrains site by the start of Southern Spring, so stay tuned!




Planet Four: Terrain’s First Science Paper Accepted for Publication

I’m pleased to announce that our first scientific paper for Planet Four: Terrains  was accepted to the journal Icarus.  Below is a snapshot from the top of the paper manuscript, and the paper is publicly available via the free preprint we’ve put online here.

A big thank you to all the volunteers who contributed to the publication. We acknowledge everyone who contributed to the project on the results page of the Planet Four at:

The paper presents the first spider and swiss cheese terrain catalog derived from your classifications. 90 CTX images comprising ~11% of the Martian South Polar region southward of -75 N latitude were searched by Planet Four: Terrains volunteers. This comprised approximately 20,000 subject images reviewed on the Planet Four: Terrains website with 20 independent reviews. The P4: Terrains search coverage is shown below:

Footprint of CTX image searched by Planet Four: Terrains for the first paper

Applying a weighting scheme, we combine classifications together to identify spiders and swiss cheese terrain. The weighting scheme isn’t testing anyone, but it helps us find more spiders by allowing us to pay slightly more attention to those that are better at identifying spiders and help increase the overall detection efficiency of the project. Details can be found in the paper.

Using the weighting scheme each Planet Four: Terrains subject has a spider score which is the sum of the  weights of the volunteers who identified spiders in the image divided by the sum of the weights of the volunteers who reviewed the subject image. Using classifications from Anya and I for a very small subset of the subject images, we found a spider scores above which we’re highly confident the identifications have few false positives.

To our surprise when we compared to the map of the secure spider locations to the geologic map of the South Polar region, we found araneiforms or spiders where we didn’t expect them to be. In previous surveys of the South Polar region, araneiforms were found to be located only on the South Polar Layered deposits (SPLD). The SPLD has been measured to have a height of ~4 km and covering a surface area of ~90,000 square kilometers mainly comprised of  varying dust and water ice layers as well as some buried carbon dioxide and water ice deposits. Previous works have theorized that something about the unconglomerated nature of the SPLD, might make it easier for spiders to form there than other areas of the South Polar region

CTX side view of the SPLD

Magenta points show the Planet Four: Terrains spider identifications on top of the geologic map. The dark blue represents the South Polar Layered Deposits (SPLD).

To confirm these identifications were real, we needed HiRISE imaging.  CTX has a resolution of 6-8 m/pixel. HiRISE can resolve up to a coffee table on Mars with a resolving power of 30 cm/pixel. With HiRISE we could see the wiggly dendritic nature of the channels and as well see seasonal fans to confirm that these form via the carbon dioxide jet process.  8 areas outside of the SPLD were targeted last Summer and Fall by HiRISE.

Below are just a few examples of the HiRISE subframes of these regions off the SPLD:

Image credit: NASA/JPL/University of Arizona

Image credit: NASA/JPL/University of Arizona – Schwamb et al. (in press)

Image credit: NASA/JPL/University of Arizona – Schwamb et al. (in press)

Image credit: NASA/JPL/University of Arizona – Schwamb et al. (in press)

Image credit: NASA/JPL/University of Arizona – Schwamb et al. (in press)

There be spiders! Araneiform channels can clearly be seen in the images above. The HiRiSE images confirm the spider/araneiform identification. We also see seasonal fan activity as well. For the first time we have found spiders/araneiforms outside of the SPLD!

This result is exciting. For some of these areas we have sequences with HiRISE taken over time which we hope we can put it into Planet Four to measure how the fans sizes and appearance are different from their counterparts on the SPLD. Now we get a chance to study how these locales off the SPLD are similar or differ from the SPLD and try to learn why these areas and not others have spider channels.

We’ve only searched a small fraction of the Martian South Polar region. We have more images on the site to expand the search area to see where else spiders/araneiforms may be. Help us today by classifying an image or two at


Happy 2nd Birthday Planet Four: Terrains

Happy Birthday Planet Four: Terrains! Last Thursday marked the second anniversary of the launch of Planet Four: Terrains. Thank you for all of your help over the past two years. We couldn’t do this without you. To celebrate here’s a recipe for a Martian South Polar Trifle for you to make for your own Mars party. It’s inspired by this recipe:

  • 1 package (20 ounce) chocolate cream filled cookies like Oreos or Hydrox
  • 16 ounces of cream cheese
  • 1/4 cup of unsalted butter
  • 2 cups of  powdered sugar
  • 2 small packages of instant vanilla pudding mix
  • 3.5  cups milk (recommend dairy milk  – skim to whole works fine)
  • 1 tub (20 ounce) of whipped topping (not canned whipped topping but the kind you find in the freezer section). ( You can also make your own from scratch using whipping cream if you like. Just add a little bit of powdered sugar mixed in to taste)

Making the ground layer: Place chocolate cream filled cookie in a bowl or plastic bag, saving 4-6 cookies for the top later. Use a rolling pin, bottom of a glass, etc to crush the cookies. Place 3/4 of the crushed cookies on the bottom of a nine-inch glass pie plate or any glass container so you can see through the sides if possible.

Making the seasonal ice sheet mixed with seasonal ice and boulder: Soften the butter., then mix together cream cheese, butter, and powdered sugar until smooth (electric mixer or whisk is fine). With whisk combine the pudding mix with the milk until smooth and slightly thickened. Fold together cream cheese mixture, whip topping, and pudding mixture.  Add 2-3 drops of  red food coloring to get a light red color (the red food color and the power sugar represent the atmospheric dust trapped in the ice sheet). Then mix in the remaining 1/4 of the crushed cookies to represent boulders trapped in the ice sheet. Pour the mixture over the ground layer of cookies.

Topping of seasonal fans: Crush the remaining few cookies very finely, sprinkle on the top to create seasonal fan shapes

Refrigerate the trifle for 3 hours or more before serving.




The inspiration – seasonal fans in the South Polar region as imaged by HiRISE in the Southern spring or summer.

Update on the Planet Four: Terrains Paper

A quick update on the Planet Four: Terrains paper. For the past month or so the team has been working on making changes to the manuscript and creating new figures to address the concerns of the two independent referees who reviewed the paper. The referees are experts in the field who assess and critique the paper. Having an independent set of eyes give feedback is useful and makes the paper better. We’ve submitted the revised draft on May 16th with a list of each of the changes we made to address the points raised by the referees. We’re waiting to hear back from the journal.  We hope that after this first round of review/edits that there will be only minor changes requested going forward. We’ll have to wait for the referees’ to read the revised manuscript and our report and send their assessment to the editor.  Fingers crossed for a speedy review.

As a teaser, below is a new figure we made for the paper.  The image is a subframe from a HiRISE observation of one of the regions targeted based on your classifications on Planet Four: Terrains. You can see that this area is like Inca City where we see fans emanating from a top the ice sheet where boulders are embedded/below the ice sheet. Not all the boulders exhibit seasonal fan/carbon dioxide jet activity when this image was taken

Screen Shot 2017-05-28 at 12.42.27 PM

Image credit: HiRISE/University of Arizona/JPL

An Update on All Things Mars

A quick update on all things Mars or at least all things Planet Four.

We got the referees’ reports back from the Planet Four: Terrains paper. The journal set it to two experts in the field. The read the paper and provided a critique of the paper. The reviewers gave positive feedback and have questions and concerns for us to address as well as other more minor requested changes to the manuscript. These additions and changes will improve the paper. So over the coming weeks, the science team will make modifications  additions to the paper draft over the coming weeks and we hope to have it back in to the journal as soon as possible. Then our written response to the referees’ report and the updated manuscript will go back to the referees for their second look. We’ll keep you posted as we make more progress.  In the meantime, there are new images we have uploaed on the Planet Four: Terrains website in need of review.

In regards to Planet Four: Ridges, thank to your help we’re completed 100 CTX images of our second search area. We’re currently working on getting new images onto the site. The CTX images are being processed as we speak and cut up into the subimages we need for the website. The images should hopefully be uploaded over the next week or so. Stay tuned to this space for more updates.

For Planet Four, we’re really at the stage of making the last changes and tweaks to the data analysis pipeline and switching gears to working on finishing the paper draft. We’ll have a separate blog post on that in the coming weeks.