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
Here’s a high resolution view of the SPLD from the HiRISE camera:
Where Do the Images Shown on the Planet Four Projects Come From?
The images you review on the Planet Four projects (Planet Four, Planet Four: Terrains, and Planet Four: Ridges) come from two different cameras onboard NASA’s Mars Reconnaissance Orbiter (MRO). MRO has been in orbit around Mars since March 2006. Science operations commenced in November 2006. Nearly 14 years later and MRO has continued to observe and monitor the Red Planet.
MRO is equipped with several instruments :
- HiRISE (High Resolution Imaging Science Experiment) – a high-resolution color imager
- CTX (Context Camera) – grayscale mid-resolution imager
- MARCI (Mars Color Imager) – color weather imager used to monitor clouds and Martian dust storms
- CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) – spectrometer that can take composition images of the surface – 2-dimensional maps of the different compositions of the surface
- MCS (Mars Climate Sounder) – probing the conditions within the Martian atmosphere: temperature, dust, and water vapor concentrations
- SHARAD (Shallow Radar) – ground-penetrating radar to explore the structure of the Martian subsurface
As MRO orbits Mars, it performs a complex ballet where the different images are taking observations at different times throughout the orbit. The observations are requested by the instrument science teams who are doing a wide variety of science with MRO.
On Planet Four, we use the high resolution color images from HiRISE which can see from orbit surface features down to about the size of your average. HiRISE has a resolution of about 30 cm/pixel. HiRISE is the highest resolution imager sent to another planet in Solar System. In Planet Four: Terrains and Planet Four: Ridges we’re using the grayscale CTX images which covers a wide area but at a lower resolution (6-8 m/pixel) compared to HiRISE. CTX actually provides context for where HiRISE and CRISM are observing and every time these two instrument takes an observaiton, CTX snaps an image as well. HIRISE is so high-resolution that CTX provides the context to tell researchers about what the topography and area around the HiRISE image. If you’ve ever checked out Google Mars visible imagery, you’ve seen some of CTX’s handywork. CTX has image nearly all of the Martian surface several times over.
MRO has now completed over 60,000 orbits around Mars and sent back a whopping 388 terabits of data to Earth. It’s still going strong and HiRISE and CTX are continuing to function. As long as they do, we hope to be able to put those images onto the project sites to continue exploring the current and past climate of Mars.To mark 15 year since the launch of MRO, NASA has put together a great collection of images taken by the spacecraft and its imagers and this video below to mark a decade of MRO science shows some of the striking images the cameras onboard have taken of the Red Planet.
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 http://terrains.planetfour.org!
Planet Four: Terrains at the Division for Planetary Sciences Conferences
Greetings from Provo, Utah. I’m here to present science results on Planet Four: Terrains among other things. The DPS is now trying out a new set of poster presentations using large touch screens, which they are calling iPosters. My abstract was selected for an iPoster. This means you can currently explore view and my iPoster online here. Enjoy!
Sagan Medal Public Talk at the Division for Planetary Sciences Meeting
This week I’m receiving the American Astronomical Society’s Division for Planetary Society’s Carl Sagan Medal for Excellence in Public Communication in Planetary Science in part for my activities with Planet Four. You can read the citation here.
I want to thank the Planet Four team and the Zooniverse team for all that they do. The Planet Four projects really are a team effort. I also want to take a moment to recognize the nearly 200,000 volunteers who have contributed their time and energy to the Planet Four projects. A little slice of this medal belongs to each and every one of you. I’ve been truly amazed what your combined effort has achieved, and I can’t wait to see what comes next. Thank you for time and your contributions. We couldn’t do this without you.
It’s traditional for the Sagan Medal recipients to give a public talk one evening of the meeting. I just got back a little while ago from giving the public talk on Brigham Young University’s campus. This year there are two Sagan Medal recipients: myself and Henry Throop, so we each gave a half hour public talk. I decided to talk about Planet Four and Planet Four: Terrains.
Last night, I recorded my practice run through of the talk so that I could share the talk with all of you. This very close to the version I gave tonight in Provo, Utah.
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: http://p4tauthors.planetfour.org
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:
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
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:
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 http://terrains.planetfour.org
New Images on Planet Four: Ridges
Thanks for everyone’s patience while we worked on getting new images on the Planet Four: Ridges website. The data is now live on the site. This set of images is the 2nd third of the new search region we’ve been focusing on. This search region includes two of the three remaining potential landing sites for the NASA’s next Mars rover, called Mars 2020. You can learn more about the region in this blog post. Dive in and search for polygonal ridges today on http://ridges.planetfour.org
New Images on Planet Four: Ridges
We’ve got some good news for your weekend. We’ve got brand new images on Planet Four: Ridges, expanding further south and east of our original area. More area covered, gives more opportunities to find unknown polygonal ridges. The more ridges we find, the better statistics we will have when we compare to other orbiter data sets to see if ground water is the main source for how these ridges form. You can see where the search area is in comparison to our first data set below. The cyan show the footprints of the new CTX images on the site, the magenta are the footprints of the CTX images we had uploaded at launch. We thought the magenta area would take a year to search, so we’re thrilled that we can expand the search radius. Thanks for your time and your contributions. We really appreciated.
We’ll have some more blog posts in the coming days and weeks to talk more about this new search region.
Dive in and search for polygonal ridges today at http://ridges.planetfour.org
Spiders are now in Planetary Database
Citizen scientists are helping us to find new targets for HiRISE on Planet Four: Terrains. They are looking at CTX images.
I once did a very similar search with Mars Orbital Camera (MOC) images. The camera worked on Mars Global Surveyor from 1997 to 2006. It had 2 sub-systems: a wide-angle camera and a narrow angle camera. The narrow angle camera obtained grayscale images with resolution from 1.5 to 12 m per pixel. It was just good enough to resolve larger spiders and fans.
In 2004 I looked through all MOC images that existed at the time and were located south of latitude -75º. I was hunting for spiders. The result is a list of MOC images that feature spiders and it is now being added to Integrated Database of Planetary Features. It will be available as a layer in JMARS system in a couple of months.
You can see Spiders map on Database of Planetary Features.
When we have a catalog of CTX images with spiders created by you, we will also integrate it into this database! Then everyone can easily navigate around different locations of spider terrains.
We started Planet Four: Terrains with the main goal of finding new regions to study during the upcoming seasonal processes HiRISE campaign. The idea was to have people scour low resolution Context Camera (CTX) images for terrains indicative of sculpting during the seasonal processes produced by never-ending cycle of carbon dioxide ice being deposited on the surface in the winter and that ice sublimating in the spring and summer. We would then select a portion of those areas for further study with high-resolution imaging with HIRISE. With the varied textures of the Martian surface it would be difficult for a machine to do this task, but the human brain is well suited to this task.
We launched Planet Four: Terrains at the end of June as part of the launch of the Zooniverse’s new citizen science platform and project builder portal. Planet Four: Terrains had little less than a year to review 90 full frame CTX images divided into 20,122 subimages or subjects as their known on the website. With your help, the project was able to get through all 20,122 subjects in time, and even put in more images. Thanks to your classifications and Talk discussions, the science team was able to come up with a list of images and locations for further study. We aim to have the HiRSE camera point at these locations and snap images. Some of these locations will be monitored throughout the Southern spring and summer. Right now these locations have been entered in the HiRISE target database. This means that Planet Four: Terrains has successfully achieved one of its prime goals!
Now, Candy Hansen, PI of the project and head of the seasonal processes campaign with HiRISE, will prioritize our targets with the rest of the regions that the HiRISE team wants to study. The first of these should with any luck get images in the next few months. We’ll keep you updated here on the blog.The final list of targets from Planet Four: Terrains is a mix of locations found on Talk and through the classification interface. We’ll have more details as we get closer to the start of Southern spring (July 5th), but we wanted to share one of the new locales,spotted thanks to the volunteer contributions on Planet Four: Terrains, that will be imaged by HiRISE. This specific region shown above was highlighted on Talk. It was noticed by the science team, and we agree it is an interesting area to look at how spiders develop. We’re interested to see how the seasonal fans and blotches over the coming Martian Southern spring and summer. We’re currently planning a sequence of images at this location. CTX has a resolution of 6-8 meters per pixel. HiRISE has a resolution of 30 centimeters per pixel, so we’ll get to see a lot more detail particularly in the structure of the spider channels than what’s current visible in the CTX image above.
This isn’t the end of the project, we’re really just getting stared. Because of your classifications, we’ve found spiders in interesting and potentially unexpected regions so we’ve decided to keep the project going with new locations to review. Help today at http://terrains.planetfour.org