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: http://www.cannonade.net/mars.php#map
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……
Thanks to your help, we’ve finished search area two for Planet Four: Ridges. We’re working on analyzing the results and hopefully starting work on a paper based on those results. Laura has come up with a new region and slightly different type of polygonal ridge to search for. We’re working on getting that dataset processed and uploaded to the site. We hope to have this completed by the end of September with updated tutorials. We’ll keep you posted. In the meantime, Planet Four and Planet Four: Terrains could use some help if you can spare the time to classify an image or two.
Perusing Planet Four: Ridges Talk I came across the image below. I thought I’d say more about it in case you encounter similar types of images. What drew my eye was the large diffuse lighter streaker on the one side of the crater.
That’s called a wind streak. Wind streaks have been found not only on Mars but also on Venus and Earth. As their name implies, they are formed directly by the interactions of the surface wind with the soil. The wind is impacted by obstacles in its path on the surface like crater rims. As the wind moves around the crater rim either picks up dust particles pushing them together collecting them to create bright streaks visible from orbit or the wind excavates material exposing a darker material than the surrounding top surface layer. Wind streaks extend into into the direction the wind is moving towards, so they are also good indicators of past wind direction.
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
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.
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?
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
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
I wanted to point out some features you might have noticed in the Planet Four: Ridges images. Dark wiggly blobs as shown in the images below are actually sand dunes on Mars.
We’re showing images from orbit, but to give you a sense of what some of these might look like from the ground, here’s a selfie of Mars Curiosity at “Namib Dune”, part of the informally named Bagnold Dune Field located in Gale Crater. I learned recently that on Mars, sand dunes are black because they are made of ground up basaltic lava rocks, just like black sand beaches of Hawaii are.