An Update on Planet Four: Ridges
Today we have a guest post by Adi Khuller. Adi is a 3rd-year PhD student at the School Of Earth and Space Exploration at Arizona State University.
Woohoo!! Our project’s first research paper was finally published! We could not have done any of this work without all your help. As Laura mentioned in her last post, we went through the research paper review process and addressed the feedback we received from two anonymous referees. After two rounds of iterations and revisions, the journal editor (who makes the final decision on publication) decided that the paper was ready to be published. You can read it for free here.
Here’s a quick summary of the overall findings we describe in the paper:
(1) With your help, we mapped the distribution of 952 polygonal ridge networks over an area of 2.8 × 107 km2. This large area is about a hundred times the area that previous studies had mapped looking for similar ridges!
(2) Interestingly, we found that 864 out of 952 (91%) of these ridge networks were found in very old, eroded terrain (~4 billion years ago). Many scientists believe that this time period in martian history was warmer and wetter, which might be related to how these ridges form (more on that later).
(3) We also studied some of these ridges using thermal infrared data (like Superman’s infrared vision) using NASA/ASU’s THEMIS camera. The ridges appear less consolidated than their neighboring material in the infrared data, but the resolution of the thermal camera is only ~100 meters per pixel. So, the thermal camera is probably not able to resolve the fine details of the ridges.
(4) As you know, the formation mechanism of the ridge networks has remained a mystery ever since they were found from orbit. Three possibly separate processes/stages were involved: (1) polygonal fracture formation, (2) fracture filling and (3) erosion to reveal the ridge networks.
(5) For the first stage, the polygonal fractures seem to have formed by impact cratering or the drying out of the sediment in which the ridges form.
(6) For the second stage, the fractures were filled up. It seems like they were either filled by rocks or minerals precipitating out of groundwater.
(7) Then, erosion by wind led to the ridges lying above their surrounding terrain.
(8) It is hard to narrow down which of these processes were directly involved in the formation of these ridge networks from the data we have so far, but if the Perseverance rover on Mars can get to them one day (in the far future, because it is quite far away), then we will be able to figure out how they really form.
(9) Our best, educated guess right now is that they form by minerals precipitating into polygonal fractures, which would mean that because these ridges are so widespread across Mars, that there was a lot of groundwater activity happening in this time period close to 4 billion years ago.
Thank you for all your help, and we hope to continue working with you on Planet Four: Ridges and future Planet Four projects!!
What have your fan markings told us about the conditions at “Potsdam”?
Today we have a guest post by Tim Michaels. Tim is a research scientist at the SETI Institute who studies how the weather and climate of other worlds affects their surface features.
Have you ever wondered what the Planet Four science team has been able to discover from the many fan measurements that you all provided at the Potsdam fan site? Read on! This is a small part of our new paper in press (Portyankina et al.) at the Planetary Science Journal.
As shown on the topographic map above, the Potsdam site (81.68 S, 66.3 E; the red dot) is located on a broad equator-facing slope at the edge of the South Polar Layered Deposits (or SPLD). The SPLD are a huge layered pile of dirty water ice, dust, sand, and carbon dioxide ice (or “dry ice”) near the south pole of Mars — the pile is kilometers high! They are thought to be the result of many thousands (perhaps even millions) of Mars-years of shifting climate cycles. See the 10 December 2020 blog post below for more info. The black arrows represent the overall fan directions marked by you at Potsdam (for Mars Years 29 and 30).
Based on the topography and some knowledge about how the Mars atmosphere behaves, we can come up with a hypothesis: The fans are pointed in the same directions as katabatic flows would probably be — that is, cold winds rushing down from the higher elevation portions of the SPLD to the south (that is, nearer the pole), twisting toward the left (in this case, toward the west) because of the Coriolis effect. Note that katabatic flows (on Mars and Earth) are often strongest at night.
So, does the state-of-the-art computer climate model (MRAMS; Mars Regional Atmospheric Modeling System) that we are using agree with our hypothesis above? How well does the model output match with the fan measurements that all of you provided?
In the plot below there 3 early-spring seasonal windows shown — the first, Ls 180, is at the beginning of southern hemisphere spring. For each season panel, downwind direction (the direction in degrees that the wind is blowing toward; 90 = E, 270 = west) is on the vertical axis and wind speed is on the other axis (in units of meters per second). Fan directions from your fan markings are shown as horizontal red lines, while the vertical red dashed lines indicate conservative estimates of wind speeds derived from your fan markings. MRAMS (computer model) winds at 5 m above ground level (AGL) are shown as black dots, and winds at 91 m AGL (about the height of the CO2 gas jets that probably create the dark fans) are shown as cyan dots. A single Mars-day (or sol) of MRAMS winds is shown for each season.
The plot shows that MRAMS wind directions at Potsdam agree with (or are quite close to) P4 wind directions when the MRAMS wind speed is highest. The MRAMS output also tells us that these winds blow at night, and that the winds that blow more toward the east (90) and south (180) are daytime winds. This *does* strongly support our hypothesis that the fans at Potsdam are directed by katabatic winds! An added bonus is that most MRAMS wind speeds matching the P4 directions also are stronger than the conservative wind speed estimates derived from P4 fan markings, as we would expect.
Is that all that is possible to understand about Potsdam using your fan markings? No! We would like to know at what season (Ls) the fans stop being active, which would help us better confirm how they form. There are also clearly big differences in fan directions from year to year that may give us clues to how Mars’ atmosphere works. Please help us answer these questions (and others) at Potsdam and at the other south polar fan sites by continuing to mark fans on actual high-resolution spacecraft imagery using this platform!
A Planet Four Update
Today we have a post by Candy Hansen, principal investigator (PI) of Planet Four and Planet Four: Terrains. Candy also serves as the Deputy Principal Investigator for HiRISE (the camera providing the images of spiders, fans, and blotches seen on the original Planet Four project). Additionally she is a member of the science team for the Juno mission to Jupiter. She is responsible for the development and operation of JunoCam, an outreach camera that involves the public in planning images of Jupiter.
Dear Planet Four Volunteers,
Years ago we enlisted your help to measure spring fans on the surface of Mars’ seasonal CO2 polar cap. Our small science team had a vision of what we could learn from those fans about the weather on Mars, but we did not have the resources to make the needed measurements.
With your investment of your time we now have an extensive catalog of fan measurements. The catalog crosses space (the Mars south polar region) and time (8 years of Mars southern spring images). The contents of the catalog and potential science use was documented in a paper by Michael Aye, published in Icarus in 2019. We have a new paper by Anya Portyankina, in press at the Planetary Science Journal, that compares wind direction and speed (from your measurements of fans’ orientation and length) to one of the standard Mars weather models. From this we can explore where the models do and do not do well to predict the weather. This very important goal that we envisioned from the beginning has now been achieved thanks to your generous donation of your time to make these measurements.
Over the years we have realized that seasonal activity is affected by Mars’ dust storms. Using the catalog we can quantify the differences in the number and size of fans after a dust storm. That work is now underway so we have posted more images and we hope you will help us again by making more measurements. We know your time is valuable and we sincerely appreciate your willingness to help with this analysis of the weather on Mars.
One final note – we have explored doing this task via machine learning. People still win!
Planet Four in French
The Planet Four website is now available in French. A big thank you to Louis who volunteered to lead the translation effort. We asked him to write a few words:
My name is Louis Verhaeghe, I am a French student, I am currently in BTS CRSA (Brevet de Technicien Supérieur – Design and Realization of Automated System), I intend to continue my studies via a License in Robotics Engineering.
Later I would like to work on planetary satellites and maybe if I’m lucky on intergalactic probes.
Although I have more than 12,000 classifications on Zooniverse, I think the translations of different projects is my most important contribution because it allows thousands and thousands of French speakers who do not speak English to be able to participate in the immense citizen science effort that is the Zooniverse platform.
I am also a fairly seasoned amateur astronomer, I like to believe that the Fermi Paradox will find an answer one day.
If you’re interested in translating one of the Planet Four projects do get in touch on Talk!
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:
Pocket Mars Reconnaissance Orbiter
The images we show on the Planet Four projects come from Mars Reconnaissance Orbiter. Although MRO won’t be coming back to Earth, you can have your very own pocket-sized MRO.
If you’ve got a 3-D printer, you can try your hand at printing out your own mini-MRO to keep you company while classifying images on Planet Four, Planet Four: Terrains, or Plant Four: Ridges.
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.
A View From Mars
Anya and Michael were recently interviewed about Planet Four for the Fiske Planetarium’s podcast, A View from Earth. Have a listen down below.
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?
You have a catalog of seasonal fans and blotches… Now what?
Today, I wanted to share a bit of the analysis we’re working on for Planet Four. Taking the Planet Four fan and blotch catalog from Season 1 and 2 of the HiRISE monitoring campaign, we’re now looking at what the average/dominant wind directions, derived for your classifications is telling us about the Martian south polar surface winds.
I wanted to show an example of what the science team is doing this. Tim Michaels has joined the science team and he’s an expert on climate modeling. We’re using the MRAMS (Mars Regional Atmospheric Modeling System) climate model/computer simulation to compare the fan directions to what direction is expected from the simulation. MRAMS is taking all the physics that we have about atmospheres and how we think these processes are working and computes what the atmosphere is doing and its conditions. We’re working on comparing the output of MRAMS to the wind directions we infer from the Planet Four fan directions.
Below is an example of one of the types of plots the team has been looking at. Here we show where the dominant fan direction is pointing in the full HiRISE frame from the Planet Four fan catalog. Think of this has telling you where the wind is headed. Each arrow represents a HiRISE observation image taken as part of the Spring/Summer monitoring season. The color of the arrows tell you which block of the Spring/Summer season the image was taken. For timekeeping on Mars, we use L_s, solar longitude, where Mars is located in in orbit around the Sun. L_s=180 is early Southern Spring. 220 is into early Southern Summer. We have 2 Mars Years as part of the current Planet Four catalog We plot the directions from each separately in the left and middle plot, and jointly all together in the right most plot. The left and middle plot show the topography that was used by the MRAMS model and the right most post shows the highest resolution topography measured by the Mars Global Surveyor’s Mars Orbiter Laser Altimeter.
Plots like this help the team look at the impact of topography and the structure of the local surface that might be contributing to how the wind blows. From this image we see that Giza is on the edge of an area where the elevation is dropping as we move more northward in latitude. Here we can see that the topography is likely playing a significant roll with the wind likely traveling from the highest elevations region (bottom of the plot) to the lower elevations. We’ll be able to compare with the detailed ouptut from the MRAMS simulation, but the topographic plots help us put the results from MRAMS in context. The simulation will tells us what direction it think the wind is blowing, but it won’t tell us necesarily why. These topographic plots help us add more explanation to the story.