Digging Deeper into the Planet Four: Ridges Preliminary Results
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! We have been finding lots of ridges in Nilosyrtis Mensae, and I wanted to give you a bit of an update on our progress. Here is a map showing the images that we have looked through (blue), the places where I thought there might be ridges before the project started (circled in orange), and the spots where you have actually found ridges (purple dots).
As you can see, most of the ridges were found in the southeast portion of the search area. I took a look at the outliers, and they aren’t the kind of polygonal ridges we are looking for—meaning that all of the polygonal ridges we found have been in a pretty restricted area. Here is a close-up of that area:
There are a couple of important things that we have already learned from what we’ve found so far. First, we can see that the ridges aren’t correlated with craters. One of the early theories about these ridges was that they were breccia dikes—that is, dikes of broken-up material that was forced through surrounding terrain during a violent impact event. The presence of polygonal ridges both in craters and on the inter-crater plains makes this hypothesis seem less likely.
Here are some great ridges that you found on the intercrater plains:
And an even closer close-up:
We also want to know whether or not the ridges are correlated with valley features. At first glance, it looks like valleys and ridges aren’t correlated, because there are plenty of ridges in the inter-valley plains, and valleys like Auqakuh Vallis that don’t have a lot of ridges near them:
Upon closer inspection, we can see that the ridges are correlated with what we call an “etched” terrain—terrain that has been heavily eroded, leaving bits and pieces of the terrain that came before it. The southern part of Auqakuh Vallis is dominated by etched terrain, and we can even see that part of the valley has been inverted by erosion (what was once the valley floor is now standing higher than everything around it). We can also see that the western branch of Auqakuh Vallis has cut this positive feature, meaning that it was active long after the eastern branch stopped flowing. There were a lot of ridges identified both surrounding the river deposits that make up the top of the inverted Auqakuh Vallis channel and around it. This may suggest that ridges are preferentially forming in old river sediments:
But why aren’t there ridges further north along Auqakuh Vallis?
Actually… there are! Here is an image further north along the Vallis. We can see that northern Auqakuh Vallis cuts through a ridge-containing unit, but in most of the surrounding area, the ridge-containing unit is capped by a unit with glacial morphology that hides the ridge unit from view:
Our current hypothesis: The ridge unit formed before or at the same time as the valleys were being cut. Afterwards, glaciers and ice sheets covered the area and deepened and widened the valleys. The glaciers covered the northern Auqakuh Vallis region and most of the terrain north of it, including the western part of the study region.
The next group of CTX images extends our search area to the east. This is the area where this type of polygonal ridges were first mapped, before we had CTX images covering the entire area like we do now. The first mapping project (in 2006) identified ridge lattices inside mostly inside craters, leading to the hypothesis that they were impact-related breccia dikes. The second project (in 2013) mapped ridges along the Nili Fossae trough system, leading those scientists to hypothesize that the original fractures may be related to the trough system. Our study of the ridges to the west has been offering an expanded context for these hypotheses. The other special thing about this region is that we will be covering two of the three remaining potential landing sites for the next NASA Mars rover, called “Mars 2020”. Mars 2020 is carrying a suite of instruments that it will use to search for habitable places on Mars as well as organic material. The new rover will also carry a drill that it will use to take samples of many different rocks and cache them in tubes for a future mission to bring back to Earth. Wouldn’t it be great if they could bring a bit of ridge back for us?
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
Planet Four Clustering investigations
We want to share a quick update on the depth and details we are investigating to close out the last issues for our analysis pipeline for identifying the fans and blotches from the classifications from the original Planet Four.
We recently realized that it might be a good idea to allow different limits for clustering depending on the general marking size. Intuitively this seems to make sense as one automatically takes a bit more care the smaller an object is to mark.
However, more clustering versatility also means more parameters to set which need to be tested for their efficacy.
Below you can see two plots, one for “fan” markings, the other for “blotch” markings, that show different parameter settings for a clustering run and their effects on the final result.
This planet four image tile with the ID ’17a’ is one of the more problematic ones due to its very large but diffusively defined blotch and the markings are, understandably, all over the place.
Each plot title has the values EPS and EPS_LARGE called out. These are the above mentioned distance limits for clustering to happen. Here I leave the EPS value, the one for smaller markings constant over several tests, while I step the one for larger markings, EPS_LARGE, between 50 and 90 in steps of 20.
As one can see the large blotch is “surviving” in all cases (which it wasn’t before we introduced the split-by-size clustering approach), while in the fan case it only survives when the “MS” parameter, the number of minimum markings that a surviving cluster needs to have, is at 5. When requesting 7, it’s just not enough markings to have it survive. But that’s okay, because I’m pretty sure that we will have this survive as a blotch rather than a fan, due to the higher number of markings that voted for that.
Working on Preliminary Planet Four: Ridges Results
I’ve been working on getting some preliminary locations of polygonal ridges in the completed Planet Four: Ridges subject images. I thought I’d share. Here’s locations where 7 or more volunteers who reviewed a subject image and said there were ridges present. We have 10 people review each of the subject images on Planet Four: Ridges.
I’ve made some figures to show the locations of these subject images. Below are MOLA shaded elevation maps with the CTX images we searched outline in blue. The red boxes are the prelminary locations of polygonal ridges, based on the criteria discussed above,
And zoomed in more
We’ll use take these locations and eventually compare to the maps of minerals to further explore the formation mechanism for poylgonal ridges in the area. Stay tuned. More to come as we finish the next set of images live on the site. Help classify an image or two on Planet Four: Ridges today at http://ridges.planetfour.org
Where Planet Four: Terrains Might Go Next
We’re now 60% through the third set of CTX images on Planet Four: Terrains. We’ve started to think about where we want to search next. We want to continue to fill in the area searched from -70 N latitude to the Martian South Pole. I’ve been coming up with the CTX image selection since the launch of Planet Four: Terrains. I wrote a code that goes through the list of publicly available CTX images and tries to pull out a well balanced distribution of ice-free CTX observations across specific latitude and longitude bins. I thought I’d share my proposed set of new CTX images to search. I’ve sent this list of images to the rest of the science team, and I’m awaiting their feedback. The new set if accepted by the team, will fill in gaps in our coverage and especially between -70 and -75 N latitude. When we have a final list of CTX image to search after dataset 3, we’ll update you here on the blog.
Color Code for figures below.
Red= first dataset at launched and used in our first paper
Green= second dataset
Magenta = third dataset that expanded out to -70 – currently being reviewed on the site
Gray = 4th proposed set of CTX observations to search
The CTX image outlines are overlaid on an elevation interpolated map. Latitude and longitude lines are in 10 degree intervals for above and below. The colors below represent geologic units, but for this comparison we’re focusing on spatial distribution and coverage. More details can be found here
First Planet Four: Terrains Science Paper Submitted
It is my great pleasure to announce that we have written up the first science results for Planet Four: Terrains in a science paper. After months of writing an analysis we have a final draft ready, and last night I submitted it to the journal Icarus to be considered for their Mars Polar Science special issue.
Right now the manuscript is in the hands of the editor. After some checks, the paper should be sent on to two anonymous reviewers. In what we call the peer review process, these reviewers are independent researchers in the field who read the paper, critique it, and provide feedback which the I will have a chance to respond to and make some or all the recommended revisions to the paper. This process can have a few rounds of iterations with the referee. Ultimately, the referees will recommend to editor of whether the paper merits being published, and the editor makes the final decision.
So now we wait. The manuscript is in the hands of the editor at Icarus who is likely selecting and contacting possible referees. In a month or so we should get back the first round of reviews. I’ll keep you posted here on the blog. So stay tuned! This paper focuses on the distribution of spiders and swiss cheese terrain from the data on the site at launch. We’ve also included analysis of some of the HiRISE observations taken of some of these new spider locations. I’ plan to write a fully summary of the paper results once the paper is hopefully accepted in a few months.
Thank you to all of you who have participated in Planet Four: Terrains. We could not have done this without you. We appreciate the time and effort you put into this project. Thank you for collaborating with us.
We also want to thank the Zooniverse team for giving the research team early access to their Project Builder platform to build and design Planet Four: Terrains.
Planet Four: Terrains is not finished. This is just the beginning. We’ve expanded out search more areas way from the South Pole. Many of those images are in need of review. So jump in and help explore Mars today at http://terrains.planetfour.org