Pit or Crater Chains,
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<<<<<<<< Left image is an example of pits created by lava tubes. Below shows a variety of pit shapes found on Mars around the Tharsis Mons volcanic area. Lava tubes collapse to create type I, II and III pits. APC = Atypical Pit Chain |
Above images obtained from this
paper related to pits and craters on Mars >>>>>>>>>> |
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Pit Chains differ from what were once identified as crater chains. Crater chains were thought to be a string of craters created by an impactor that broke apart upon impact, in turn, splattering debris in a straight linear pencil like line. This concept is relatively ridiculous when anyone looks at a splatter pattern created by impactors. Impactors don't create linear craters one after the other often touching.
The pit chain's key features of tapered conical slopes (not impact bowls), missing raised rims and missing central peaks were explained away by calling them secondary breakup debris. This idea expanded to include Shoemaker-Levy 9 type breakups that occurred as the result of gravitational stress prior to impact. This concept, while more palatable still does not fit the observed scene as great distances separate each object and they still don't line up precisely, on top of that, impactors leave craters with raised rims and central peaks while pit chain depressions don't have either. The pit chains also start out as conically shaped holes not bowls. Eventually we got it right by identifying these features as internal thrust fault processes not external impacts. Conically shaped pits within Pit Chains are important time scale indicators as they are young recently occurring processes and they exist on multiple solar system bodies. |
This Bad Astronomy article incorrectly explains how these pit chain features are crater chains formed by an impactor.
The article uses this X marks the spot series of pit chains on Mercury as evidence of crater chains but in 2016 T. Watters et al., correctly identifies these features. These pit chain features on Mercury were errantly identified as crater chains that were said to form from an impactor that broke up and somehow created a string of dozens of straight lined craters (without lateral ejecta) touching each other none of which had raised rims, internal peaks, rings or ejecta. Mercury is now known to be geologically active and is constricting (puckering its surface like a raisin). Thrust fault scarps were identified by the Mariner 10 probe, these thrust faults create pit chains as seen in this image of Mercury. ![]()
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Following, is how many of these crater chains are described.
The irregular shape of the crater rims and tapered appearance suggests that these are not primary but rather secondary craters, formed from material ejected from a larger primary impact. Secondary material is invoked to explain the irregular shape of the crater rim and tapered appearance of these pits and reminders of Shoemaker-Levy 9 colliding with Jupiter are also invoked to support this errant interpretation of pit chains as impact crater chains. Crater chains do exist but often times thrust fault pit chains are misinterpreted as impact crater chains. The more accurate explanation for many these features is the one given by Ferrill et al., 2004. The irregular shape, lack of rim, lack of central peak, lack of ejecta and tapered conical appearance occur as thrust faults slip or slide past each other creating subsurface voids where loosely dispersed surface regolith/dirt debris sinks inward to form these "tapered appearance" sink holes. |
Mars Young Pit Chains
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D. Ferrill et al., 2004 produced a paper related to Pit Chains on Mars. Quote Based on these analyses, we conclude that pit chains form in response to dilational fault slip (expansion fractures). Pit craters lack a raised crater rim or ejecta deposits, form alignments (chains), and are likely the result of collapse of loose surface material into a subsurface void... The close association of pit crater chains with faulting on Mars indicates that some Martian faults produce considerable subsurface void space... We conclude that pit chains form in response to fault slip and dilation, consistent with the interpretation of active faulting on Mars.... |
We interpret these as being youthful pits where surface subsidence has not progressed so far as to have destroyed the original surface of in-falling material... Several large pits appear to have conical forms with no evidence of wall erosion or sediment accumulation. These observations suggest that the pit craters are among the youngest features on Mars. I added the red and blue text to their Figure 2B image. >>>> This is how I imagine some of the material on Pluto east of SP is layered forming its own version of pit chains from subsurface thrust fault slippage and dilation. |
Lower right section of panel D vs C developed pits in 8 years.
Iceland was created as two deep crustal continental plates pulled apart and magma spilled out. Iceland's land mass is the cooled frozen magma which arose from deep in the planet. Pit Chains have emerged on the surface where near surface fractures develop. The formation of Iceland is a deep older hot process the pit chains are a shallow younger colder crack slippage process . That's not to say Iceland isn't a volcanically hot zone, it is but its pit chains are not. The above pit chains are developing on Iceland along the northern portion of the Mid-Atlantic Ridge in response to very shallow dilation and/or fracture formation and possibly thrust fault slippage. This is a geologically young recent process. |
pit_chains_on_enceladus_signal_the_recent_tectonic_dissection_of_the_ancient_cratered_terrains_201737ce.pdf | |
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According to this above paper by E. Martin et al., pit chains exist on
I sent an email to E. Martin asking her opinion about these pit chain features on Pluto. Hopefully she will reply. |
Recently (page 100), I was studying Jason Cook's paper related to the various locations on Pluto where there are high concentrations of water ice.
My logic is that if the bedrock crust is water ice and there are concentrated clusters of water ice then those clusters should display signs of cryovolcanism or surface erosion. The Cook paper's image was blurry and I really wanted to see the terrain in detail at these crystalline water ice locations especially the very bright spot to the east of Sputnik Planitia (SP). I found some better quality images that were good but not quite good enough. The below image was just good enough to make out some land features which in turn allowed me to go to the next resolution level and finally see the detail at these specific locations to the east of SP. |
identification_and_distribution_of_pluto’s water ice | |
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I have a really high resolution image of Pluto (largest I've seen) 8,000 x 8,000 pixels. Please feel free to download it as it allows you see details otherwise missed. >>>>>>>>>>
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Much of the detail in the below HiRes image gets muddled when I upload it to this web page. Here's a clear HiRes downloadable version. >>>>>>>>>
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This pit chain shows obvious red color (tholin hydrocarbons) changes associated with its water ice signature. >>>>>>>
The single larger pit has deep steep smooth walls (young). This also indicates the surface material is loose and granular similar to sand. As the bedrock below dilates and slips, the surface sandy sediment sinks into the cavity creating a sink hole pit. The sink hole either exposes the surface water ice that is otherwise covered by methane and/or nitrogen or is actively expelling subsurface particles of water ice. If the material was getting expelled it would likely disperse more broadly around the pit's rim. In this particular case it appears as though the water ice is simply exposed as the grains of sand slide down the pit wall grinding away at the surface veneer. Other pits and surface water ice signatures are totally different than this. |
Sometimes erosion appears to describe the water signature while other times ejection seems to be a better description. But considering how small the water ice footprint is compared to the rest of this area east of SP, I think its safe to conclude that all water ice signatures are young by comparison. Most of the time there is also a red color associated with the water ice signature along with nearby smooth walled pits or pit chains but sometimes tholin appears to exist inside individual pits or even pit chains without a water ice signature and other times pits appear with no tholin (gray material) or water ice signature. |
This is one of the more difficult scenes to interpret. Everything in this area seems to want to defy definition.
There's a reddish raised mountain in a crater that could be an impact crater or a cryovolcano. The water signature around the mouth of this peak suggests volcano but the areas southward at 5 and 7 o-clock seem to tell a different story. The rim is raised and jagged indicating it's a young impact crater. The four pits off to the right are not colored red but display a strong water ice signature. They appear to be sink hole pits but have raised rims but are clearly not impact craters. There is an impact crater mostly colored whitish with a pinhole in the center but there is absolutely no water ice signature. This crater's rim is raised and smooth (eroded) indicating it is older than the red one above. There seems to be an area floating in SP that has red goose bumps, the central portion of which displays water ice. |
On the opposite shore of SP (western side) there are slip fault fractures but no pit chains. >>>>>>>>> This indicates the surface material on the western side of SP is solid, hard, rigid while the material on the eastern side is more granular in nature. This material on the eastern side of SP is more loosely compacted like sand. As subsurface fractures develop, the sandy material slips down creating smooth walled inverted cones.
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The area I outlined in blue is sorta like a bay but it is elevated with steps. So its not really a bay per se, its more like a lock with steps but the real point is that its all awash with soft gray nitrogen fluid ice material which has erased any surface topographic features as it migrates down into SP. This gray stuff is an ice not a liquid but it is in a far more fluid state than its surrounding land ice. In other words the pit chain thrust fault evidence is erased by this more fluid ice but, nevertheless, the faults are present in this area. Its similar to what takes place on Earth at fault lines where water back fills (in Pluto's case nitrogen) into the low elevation cracks creating lakes and rivers. These faults extend into SP and are the cause of its formation. These fractures migrate into SP and are deepest at the focal point where Charon's tidal bulge distorts Pluto as is noted by the lack of polygonal cells. |
pluto_pits_and_mantles_on_uplands_north_and_east_of_sputnik_planitia.pdf | |
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