Spiders in the South Polar Layered Terrain
Previously I talked about the South Polar Layered Deposits (SPLD) that you’ve probably seen in some of the images you’re reviewing on Planet Four: Terrains. Last week on Talk, I learned something new. Volunteer Ray noticed this image:
I thought it was pretty neat to see spiders directly carved into into some of the bands of the SPLD. According to the rest of the science team, this can be a frequent experience, and they’ve seen it before. This was my first time encountering that, so I thought I’d share.Thanks Ray for spotting this.
Spider formation is caused by carbon dioxide gas trapped underneath a sublimated ice sheet during the Spring and Summer on the south pole of Mars. Eventually the gas breaks escapes through the ice sheet creating geysers but in the process it also exploits weaknesses in the surface regolith creating spiders. For some reason it appears those sections of the SPLD are weaker.
You can find more finds like this by classifying CTX (Context Camera) images of Mars’ south pole at http://terrains.planetfour.org
Some More Example Terrains
Over the past couple of days, I’ve started looking at the Planet Four: Terrains classifications data. I’ll be looking at how best to combine the assessments to identify the different terrains, but for now I’m taking a preliminary look at the raw data. I tallied up the votes for each of the images we’ve shown on the site that have been completed (have had at least 20 independent reviews). Perusing the results I have found some nice examples that I thought I’d share below.
Swiss Cheese Terrain
Image Credit:NASA/JPL-Caltech/Malin Space Science System
Image Credit:NASA/JPL-Caltech/Malin Space Science System
Image Credit:NASA/JPL-Caltech/Malin Space Science System
Craters
Image Credit:NASA/JPL-Caltech/Malin Space Science System
Image Credit:NASA/JPL-Caltech/Malin Space Science System
Image Credit:NASA/JPL-Caltech/Malin Space Science System
Channel Network
Image Credit:NASA/JPL-Caltech/Malin Space Science System
Image Credit:NASA/JPL-Caltech/Malin Space Science System
Image Credit:NASA/JPL-Caltech/Malin Space Science System
You can also find more examples on our Site Guide.
The South Polar Layered Deposits
While classifying on Planet Four: Terrains images you might have seen images like these:
These banded layers are part of what is known as the South Polar Layered Deposits (SPLD) (an equivalent version exists on the North Pole of Mars as well). There is dust and water ice composing these layers. The SPLD has been measured to have a height of ~4 km and covering a surface area of ~90,000 square kilometers. Unlike the temporary seasonal ice cap which is comprised of carbon dioxide, the 1.6 million cubic kilometer SPLD is mainly water ice mixed with dust comprising on the order of 10% volume of the entire structure. Above this SPLD sits the very thin temporary (1-10 m) cap of amount of carbon dioxide ice/frost that snows out in the winter and sublimates over the spring and summer seasons. In 2011, it was discovered by radar sounding that although the structure is mainly water ice and dust there is a buried reservoir of carbon dioxide ice within a section of the SPLD, with a volume of 9500 to 12,500 cubic kilometers. If this frozen gas was exposed and released in contact with the current Martian atmosphere, the atmosphere would almost double in its inventory of carbon dioxide by mass.
How the SPLD layers are exactly deposited and whether there are new layers actively forming are open questions. The exact age of the SPLD is unknown. We know there is a heavily cratered terrain that covers much of the Southern hemisphere, but there are relatively few craters on the actual surface of the SPLD. This suggests that the top of the SPLD is about 10 million years in age, relatively a youngster in terms of geological time scales. The fact there is banding indicates the existence of a repetitive cycle that built up the SPLD and its northern equivalent over time. The darkness and thickness of the banding is thought to be controlled by the amount of dust present in Mars’ atmosphere (and likely by the past frequency of global Martian dust storms). The SPLD then likely represents a locked away record of the Martian atmosphere at the time of deposition, showing how dusty the atmosphere was compared to the water vapor present. If we can understand the formation mechanism, then we would be able to read this natural historical record.
One other important thing about Mars is that without a large moon like the Earth has, Mars’ axial tilt swings significantly over time up to ~60 degree obliquity, which can put the poles in significant light and darkness. This giant swings in axial tilt (as well as other orbital properties occur in cycles known as Milankovitch cycles). The increased summer and longer winters likely impact dust storms and the formation of the SPLD, but what role it plays is still an active area of study.
The extent of the SPLD has been mapped both with ice penetrating radar and a laser altimeter aboard orbiting spacecraft , so that is why it is not list as of one of the categories to select on Planet Four: Terrains. While we’re not asking you to identify the Solar Polar Layered Deposits in the classification interface, if you’re interested in identifying them in the CTX images you can add a hashtag in Planet Four Terrains: Talk (we recommend #spld ) or you can make a collection of those images.
A Planet Four Science Poster
ASIAA, my institute in Taiwan had its 5 year external review where a panel of experts in the field from outside the institute come in and give a critique and highlight both the positive things that are going well and also the potential areas to be strengthened. At this review there was a poster session for postdocs and other researchers to present their projects. Last week was the poster session. I gave an update on Planet Four and presented Planet Four: Terrains. I thought I’d share (typos and all) the poster with you. You might find that some of the figures are familiar and that you’ve seen them on this very blog in one form or another.
Click on the image to get a higher resolution version
Where Exactly on Mars are the Terrains You’re Looking At?
With our new addition Planet Four: Terrains, we need your help to review CTX (Context Camera) images and identify ‘spiders’ (radially organized channels carved in the surface), craters, pitted sheets of carbon dioxide ice nicknamed Swiss Cheese Terrain, and channel networks carved by carbon dioxide gas trapped below the thawing ice sheet and also by the freezing and thawing of water ice permafrost.
The CTX images are of the South Pole, but you might be wondering where exactly we’re looking. One of the main aims of Planet Four: Terrains is to identify new areas of interest to point HiRISE, the higher resolution camera on Mars Reconnaissance Orbiter. CTX is named the Context Camera because it provides the larger picture or context for HiRISE’s detailed but narrow image swaths. Anya’s gone in to more detail about this, so check out her blog to learn more.
To find new areas of interest, for Planet Four: Terrains we wanted to extend beyond the regions we know have spiders because they’ve been imaged by HiRISE during the seasonal processes campaign. To give you some sense, here are the regions targeted by HiRISE that are currently uploaded in the Planet Four database. This compromises all imaged locations from Seasons 1,2,3 and Manhattan Season 4 and Inca City Season 4 and a small part of 5.
For picking the first set of CTX images, I went through and found what we think are ice free images from the end of Summer and early Fall, and selected as much of a random uniformly distributed sample south of -75 degree latitude. The reason we didn’t want ice if possible is that if there’s ice, there’s a chance for carbon dioxide geysers and fans (the ones we ask you to mark on the original Planet Four). The fans would block you from seeing surface features in the ground below them.
Above are plotted the locations of the full frame CTX images used to make the subframes that you see on Planet Four: Terrains (Note: we cut up the CTX images into 800 x 600, width x height, pixel images). We currently have a random third of this set live on the site. We’ll be add the remaining subimages to the site over the next month or so.
For comparison, here again the previous HiRISE seasonal monitoring images locations uploaded on the original Planet Four, plotted on the same scale as the CTX plot above.
As you can see most of the HiRISE images from the seasonal monitoring campaign are focused south of -80 degrees. As you can see , we’re looking at much more of the Martian South Pole with Planet Four: Terrains. Soon the South pole will be in darkness again, and the temporary carbon dioxide cap will start growing again. Our hope is that we can have these images reviewed before the start of the Spring on the South Pole to add new locations to the target list for Season 6 of the HiRISE monitoring campaign that starts around July 2016.
Check out Planet Four: Terrains, and classify an image or two today at http://terrains.planetfour.org
Why we need Planet Four: Terrains?
Hi there!
I want to talk why we created the new project Planet Four: Terrains if we have Planet Four already.
The very high resolution images of HiRISE camera are really impressive and one might think that there is no reason to use a camera with lower resolution anymore. Wrong!
First, high resolution of HiRISE image means large data volume. To store on-board and to download large data from MRO spacecraft to Earth is slow (and expensive) and this means we are always limited in the number of images HiRISE can take. We will never cover the whole surface of Mars with the best HiRISE images. Sadly. so we use different cameras for it. Some – with very rough resolution and some – intermediate, like context camera (CTX). We can use CTX, for example, to gain statistics on how often one or the other terrain type appears in the polar areas. This is one point why Planet Four: Terrains is important.
Second, because HiRISE is used for targeted observations, we need to know where to point it! And we better find interesting locations to study. We can not say “let’s just image every location in the polar regions!” not only for the reason 1 above, but also because we work in a team of scientists and each of them has own interests and surely would like his/her targets to be imaged as well. We should be able to prove to our colleagues that the locations we choose are truly interesting. To show a low-resolution image and point to an unresolved interesting terrain is one of the best ways to do that. And then, when we get to see more details we will see if it is an active area and if we need to monitor it during different seasons.
Help us classify terrains visible in CTX images with Planet Four: Terrains at http://terrains.planetfour.org
The Mars Polar Lander Spider Encounter
Today we have a post by Dr. Candice (Candy) Hansen, principal investigator (PI) of Planet Four and Planet Four: Terrains. Dr. Hansen also serves as the Deputy Principal Investigator for HiRISE (the camera providing the images of spiders, fans, and blotches seen on the site). She is also a Co-Investigator on the Ultraviolet Imaging Spectrograph on the Cassini spacecraft in orbit around Saturn. Additionally she is a member of the science team for the Juno mission to Jupiter. Dr. Hansen is responsible for the development and operation of JunoCam, an outreach camera that will involve the public in planning images of Jupiter.
My first glimpse of a “spider” on Mars was in 1998. The Mars Global Surveyor (MGS) had gone into orbit around Mars, and winter was turning to spring in the southern hemisphere. The Mars Polar Lander was en route to Mars, and we were anxiously waiting for polar night to lift so that we could see our landing site.
The Mars Observer Camera (MOC) onboard MGS started returning images just a few weeks before Mars Polar Lander (MPL) was due to arrive. We would scrutinize long rolls of film, and that was when we realized that the terrain was not exactly what we expected. Dark spidery forms and cracks that resembled caterpillars fascinated us. I was hooked on trying to understand these exotic features.
We now know that if the MPL made it safely as far as the surface it landed in very inhospitable terrain. We use the colloquial term “spiders” to describe an array of interconnected channels on the surface. The branching channels, now formally referred to as “araneiform” terrain, cover the surface where MPL was predicted to land. They occur in a wide variety of morphologies, from isolated to connected to starburst to lace, with channels that are typically 0.5 – 2 m deep, and ~5m wide.
High resolution image of Spiders at Mars’ south pole taken by the HiRISE camera – Image credit NASA/JPL/University of Arizona
We never heard from MPL after it entered Mars’ atmosphere. Any number of things could have gone wrong. Or everything might have gone perfectly and it landed with one leg in a channel and simply tipped over.
Help identify spiders and other araneiform terrain with Planet Four: Terrains at http://terrains.planetfour.org
Introducing Planet Four: Terrains
Dear Martian Citizen Scientists!
We are excited to introduce to you a new companion citizen science project to Planet Four called “Planet Four: Terrains” built on the Zooniverse’s new platform. You have explored with us here in Planet Four some of the most detailed surface observations ever made in our solar system and many of you have acknowledged and wondered about all the other amazing features visible in these images that we did not ask to be studied, like spiders, networks of channels and weirdly looking craters. (some of you will remember that one of these even led to a re-observation of the same crater with the HiRISE camera).
HiRISE imaged spiders Image Credit: NASA/JPL/University of Arizona
It is an interesting fact that when one decides to make a camera that can resolve a lot of small details, that it will not be able to scan a lot of area. One has to decide, as long as we don’t have infinite data transport capabilities and infinite mission time at other planets and moons in the solar system. That’s why the Mars Reconnaissance Orbiter (MRO), the spacecraft that houses the HiRISE camera that produced all the images in the Planet Four project has a complementary camera system onboard to provide context, appropriately called CTX for ConTeXt camera. It has a lower resolution than HiRISE (approx 5-6 m compared to HiRISE’s 25 to 50 cm) but takes images from a far larger region than HiRISE.
CTX image – Image Credit:NASA/JPL-Caltech/Malin Space Science System
So here is our idea: We confirmed that many of the features you were asking about are still recognizable with the lower resolution images of CTX. Therefore we would like your help in gathering spatial statistics in where around the south pole we can find which kind of patterns on the ground that are related to CO2 ice activities. Your help in classifying CTX data into a set of ground patterns will serve to decide where the HiRISE camera will be pointed next during 2016’s south polar spring season observation campaign. This way your contributions directly improve the scientific output of both CTX and the HiRISE camera and we are very excited to provide to you a way to point the highest resolution camera in the solar system to the most interesting areas of the Martian south pole!
You can find the new project, a more detailed science case description and an awesome spotter’s guide at this address: http://terrains.planetfour.org
Thanks as always for your time and your enthusiasm!
Michael
Planet Four Blog 