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!! 


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