Wikipedia

Louth (crater)

Louth (/laʊð/) is an impact crater on Mars located at 70°11′N 103°14′E / 70.19°N 103.24°E / 70.19; 103.24 in the Mare Boreum quadrangle. Located within Vastitas Borealis, the crater has a diameter of 36.29 kilometres (22.55 miles) and is named after Louth, a town in Ireland.

Louth
Color photograph of Louth by the HRSC on ESA's Mars Express
PlanetMars
Coordinates70°11′N 103°14′E / 70.19°N 103.24°E / 70.19; 103.24[1][2]
QuadrangleMare Boreum
Diameter36.29 km (22.55 mi)[1]
EponymLouth, Ireland[1]

Louth's characteristic feature is the persistent ice mound at the center of the crater. The central ice mound is the closest to the equator of all analogous features on the Martian surface, and of particular relevance to researchers studying climatic variability on the planet's surface. Many theories exist for the creation and persisting nature of the ice mound, with the predominant explanation being that of advected water vapor being deposited over the crater's surface by southwesterly winds. Due to its particular interest to scientists, two mission drafts have been proposed to explore the crater's makeup.

Discovery

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First known from Viking images featuring an anomalous albedo feature at the center of a crater in the northern plains of Mars,[3] the deposit of ice was identified as being made of water ice by Xie et al. in 2006 through analysis of Thermal Emission Imaging System (THEMIS) data.[4][5][6] The researchers, who used similar techniques to their predecessors who had similarly determined the existence of water ice in the Martian polar ice caps, additionally noted the seasonal fluctuation of the central ice mound between the Martian fall and summer.[4]

Ice mound

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A simulated surface-level view of Louth's ice mound using HiRISE data

Louth contains the lowest-latitude permanent deposit of water ice on the Martian surface, in a mound situated at the crater's center.[7][8] The mound is quasi-circular and has an approximate diameter of 10 kilometres (6.2 miles).[9] The steady-state value for the albedo of the central ice mound is 0.431.[8] The mound consists of smaller ice grains interspersed with more palagonite contaminant at its edge, compared to the center.[4][3] Large grains of ice suggest that the central portion is the oldest in age, and brought to the surface either through the sublimation of ice or aeolian processes.[4] The water ice at the center of the crater as analyzed through spectral modelling determined that the water ice at the center of the mound was 99-percent pure at the optical surface.[4] The ice mound was determined to be similar in texture and composition to the northern polar ice cap.[10][11] Studies of the crater's interior, knowing their similar makeup, can yield insight on the interaction between the north polar region and the atmosphere.[12] Additionally, craters with ice mounds such as Louth can serve as records of the Amazonian era of Martian geology.[13] Craters like Louth have been used as potential analogues for understanding similar processes occurring on Pluto.[14][15]

 
Detail of the frost patch and dunes in Louth (Mars Reconnaissance Orbiter HiRISE)

The ice mound is divided into four feature types: smooth interior ice, irregular "trough-bearing" ice, sand dunes, and "stucco" rough ice.[4] One feature of the central mound are elongate features interpreted to be sastrugi, that being windswept ice mound and groove features. Unlike sand dunes, whose ridges are perpendicular to the direction of the wind, the ridges of sastrugi are parallel.[4][11] The variation in albedo featured by the aforementioned sastrugi that was observed by Brown et al. was not understood at this point.[4] Another feature of the central mound is that of a cluster of dark sand dunes at the edge of the deposit, water ice was found to have deposited likely after the formation of the dunes. The formation of the dune system is not fully understood, and multiple theories exist for their formation. This includes their formation prior to the ice mound's creation,[5] their formation after the ice mound and the ice found on the dunes is simply frost, or the dunes are a product of material left behind after another material sublimated.[4] It was later found that ice mound exchanges water ice from the surrounding regolith.[11] Ice that was described as resembling stucco was thought to be the youngest portion of the water ice mound. Arcuate features within the stucco ice is thought to represent the growth of the ice mound, similar to other features known as north polar layered deposits (NPLD) found in other Martian craters.[4] The northern border of the ice mound is abrupt in its transition to the regolith, the southern border in comparison, is diffuse.[8] Anomalous "defrosting spots" that persist into the summer are present in Louth, akin to features in other Martian polar regions, the features, which resemble dark smudges, are not fully explained.[16]

 
Color photograph of Louth from ESA's Mars Express (February 2, 2005)

Its low latitude compared to other Martian craters with similar features make Louth and its ice mound the warmest perennial surface of ice on the Martian surface.[9] Ice deposits on Mars serve as unique indicators for the climate variability on the Martian surface, due to their status as reservoirs for chemical compounds like carbon dioxide and water.[17][6][4][8] Louth's southerly position of 70 degrees north latitude gives it a unique potential for sensitivity to climatic changes on Mars.[9] The processes behind its long-term stability, especially at its southerly latitude is poorly understood.[4] Following a study by Brown et al., Louth's inner ice mound was determined to be currently in retreat, and the remnants of a once much larger ice mound at the center of the crater.[18][4] Observations of Louth over four years failed to find any growth or retreat of the ice mound.[8] The mound at the center changes seasonally, with non-uniform changes occurring dependent on the season. Water that has sublimated from the regolith of Mars recondenses on a crescent-shaped periphery of the mound, which is colder than its surroundings. Southwesterly winds, through the process of advection, deposit water vapor over the mound.[11] During the Martian summer, it is thought the mound undergoes the process of ablation[19] until Solar longitude (Ls) 150.[11] The rate is thought, for an angle of around 7 degrees and on the equatorial-facing side, to be around 2 millimetres (0.079 in) yearly.[8]

Formation

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The processes of how the crater came to have the water ice mound in the first place is thought to be a result of atmospheric deposition of water vapor at the crater's surface.[18][4][20][21] Seasonally, a polar hood with atmospheric water is incorporated into the frost cap of the northern Martian pole, water comes loose as the cap retreats. A ring of water frost forms as the cap retreats, and sweeps over craters in the process.[11] This process was thought to be more likely than the idea of Louth being an outlier from a larger polar cap,[20] or water deposited by aeolian processes from a feature dubbed "Mrs. Chippy's Ring", which was too far from Louth to likely be the source.[4] Follow up studies in 2021 suggested a similar conclusion, with additional findings that the ice mound casts a shadow in a process dubbed "self-shadowing", which either prevented further ablation or promoted the precipitation of water ice.[21] Other theories proposed for the formation of the central mound include: upwelling from an underground Martian aquifer, akin to the formation of pingos on Earth,[22] and melting of surface ice due to impact-induced hydrothermal activity.[20][11][13]

Exploration

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There is no active or currently developed mission that explicitly cites Louth as a potential target. Due to its unique features, however, there have been several mission proposals to explore the crater. HEMERA (Human Exploration of Martian Environment, Regolith, and Atmosphere) is a proposal to land humans on the northern polar region of Mars, with Louth as the landing site.[23] Astronauts would then be tasked with determining the purity of the water ice mound as per the mission objectives through collection of regolith.[23] Another proposal, dubbed MICKEY (Mars Ice Core Key Exploration Yacht), is a proposed sample-return mission that would obtain an ice core from the mound at the crater's center. Along with a lander, MICKEY would deploy a rover inside the crater to search for ice.[24]

Louth has been photographed by Mars-orbiting satellites, including Viking,[3] Mars Express,[6] and the Mars Reconnaissance Orbiter (MRO).[25] Both Mars Express and the MRO contributed data that was significant to understanding the surface dynamics of the crater.[26][5]

Etymology

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In accordance with the approved naming conventions, smaller Martian craters including Louth are named after towns and villages on Earth with an approximate population of fewer than 100,000 people.[27] The crater is named after Louth, a town in County Louth, Ireland. Unofficially known by the name Louth before it was officially approved,[6][2] the crater was formally named by the International Astronomical Union's Working Group for Planetary System Nomenclature on February 7, 2007.[1]

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Enigmatic Sinuous Features in Louth Crater Ice Mound, Mars Reconnaissance Orbiter HiRISE
(August 4, 2010).
 
East Louth Crater Ice and Dune Monitoring, Mars Reconnaissance Orbiter HiRISE
(September 4, 2021)
 
Changing Frost Patterns in Louth Crater, Mars Reconnaissance Orbiter HiRISE
(May 7, 2008).

See also

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References

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  1. ^ a b c d "Planetary Names: Crater, craters: Louth on Mars". IAU Working Group for Planetary System Nomenclature. United States Geological Survey. Archived from the original on 14 November 2021. Retrieved 14 November 2021.
  2. ^ a b Schmude, Richard (31 July 2016). "Variability of Mars' Seasonal North Polar Cap". Georgia Journal of Science. 74 (2). ISSN 0147-9369. Archived from the original on 24 January 2022. Retrieved 24 January 2022.
  3. ^ a b c Roush, T. L.; Brown, A. J.; Byrne, S.; Tornabene, L.; Seelos, K. D. (1 July 2007). "Modeling Water Ice Surface Deposits at Louth Crater Using Mars Reconnaissance Orbiter (MRO) Observations" (PDF). Seventh International Conference on Mars. 1353: 3260. Bibcode:2007LPICo1353.3260R. Retrieved 24 January 2022.
  4. ^ a b c d e f g h i j k l m n o Brown, A; Byrne, S; Tornabene, L; Roush, T (August 2008). "Louth crater: Evolution of a layered water ice mound". Icarus. 196 (2): 433–445. arXiv:1401.8024. Bibcode:2008Icar..196..433B. doi:10.1016/j.icarus.2007.11.023. S2CID 53385237. Archived from the original on 27 February 2022. Retrieved 23 January 2022.
  5. ^ a b c Xie, H.; Ackley, S. F.; Zeng, Z.; Qiu, F. (1 July 2007). "Permafrost and Its Implication in 'Louth' Crater (70.5N, 103.2E) of Mars" (PDF). Seventh International Conference on Mars. 1353: 3200. Bibcode:2007LPICo1353.3200X. Archived (PDF) from the original on 27 February 2022. Retrieved 24 January 2022.
  6. ^ a b c d Xie, H.; Guan, H.; Zhu, M.; Thueson, M.; Ackley, S. F.; Yue, Z. (1 May 2008). "A conceptual model for explanation of Albedo changes in Martian craters". Planetary and Space Science. 56 (7): 887–894. Bibcode:2008P&SS...56..887X. doi:10.1016/j.pss.2008.01.012. Archived from the original on 27 February 2022. Retrieved 23 January 2022.
  7. ^ "Enigmatic Sinuous Features in Louth Crater Ice Mound (ESP_018301_2505)". UA HiRISE. The University of Arizona. Archived from the original on 14 November 2021. Retrieved 14 November 2021.
  8. ^ a b c d e f Bapst, Jonathan; Byrne, Shane; Brown, Adrian J. (July 2018). "On the icy edge at Louth and Korolev craters". Icarus. 308: 15–26. Bibcode:2018Icar..308...15B. doi:10.1016/j.icarus.2017.10.004. S2CID 126009781. Archived from the original on 27 February 2022. Retrieved 23 January 2022.
  9. ^ a b c Bapst, Jonathan; Byrne, Brendan (2016). "LOUTH CRATER WATER ICE AS A MARTIAN CLIMATE PROXY" (PDF). Lunar and Planetary Science Conference. 47. Retrieved 14 November 2021.
  10. ^ Jian, J.-J.; Ip, W.-H.; Hsu, H.-J. (1 April 2009). "A Survey of The Ice-Bottomed Craters on Mars". EGU General Assembly Conference Abstracts: 12609. Bibcode:2009EGUGA..1112609J.
  11. ^ a b c d e f g Brown, Adrian J.; Bapst, Jonathan; Byrne, Shane (16 November 2017). "Observations of a new stabilizing effect for polar water ice on Mars". arXiv:1711.06372 [astro-ph.EP].
  12. ^ Melchiorri, Riccardo; Haberle, Robert H.; Roush, Ted L.; Brown, Adrian J.; Encrenaz, Therese (1 January 2008). "High Spatial Water Vapor Variability as Seen by CRISM/MRO in Louth Crater". 37th Cospar Scientific Assembly. 37: 1995. Bibcode:2008cosp...37.1995M.
  13. ^ a b Conway, Susan J.; Hovius, Niels; Barnie, Talfan; Besserer, Jonathan; Le Mouélic, Stéphane; Orosei, Roberto; Read, Natalie Anne (July 2012). "Climate-driven deposition of water ice and the formation of mounds in craters in Mars' north polar region". Icarus. 220 (1): 174–193. Bibcode:2012Icar..220..174C. doi:10.1016/j.icarus.2012.04.021. S2CID 121435046. Archived from the original on 2 May 2018. Retrieved 24 January 2022.
  14. ^ Sori, Michael M.; Bapst, Jonathan; Becerra, Patricio; Byrne, Shane (October 2019). "Islands of ice on Mars and Pluto". Journal of Geophysical Research: Planets. 124 (10): 2522–2542. Bibcode:2019JGRE..124.2522S. doi:10.1029/2018JE005861. hdl:10150/636169. S2CID 202921068. Archived from the original on 24 January 2022. Retrieved 24 January 2022.
  15. ^ Sori, M.; Bapst, J.; Byrne, S. (1 December 2017). "Icy Islands reveal similar volatile behavior on Pluto and Mars". AGU Fall Meeting Abstracts. 2017: P11C–2524. Bibcode:2017AGUFM.P11C2524S.
  16. ^ Howell, Elizabeth (21 October 2014). "Martian Permafrost And Dust-Sculpted Surface Captured By NASA Spacecraft". Universe Today. Archived from the original on 23 January 2022. Retrieved 23 January 2022.
  17. ^ Brown, A. J.; Bapst, J.; Byrne, S. (1 March 2017). "Louth Crater and Depositional Mode Flips" (PDF). 48th Annual Lunar and Planetary Science Conference (1964): 2672. Bibcode:2017LPI....48.2672B. Archived (PDF) from the original on 27 February 2022. Retrieved 24 January 2022.
  18. ^ a b Weitz, N.; Zanetti, M.; Osinski, G.R.; Fastook, J.L. (July 2018). "Modeling concentric crater fill in Utopia Planitia, Mars, with an ice flow line model". Icarus. 308: 209–220. Bibcode:2018Icar..308..209W. doi:10.1016/j.icarus.2017.08.023. S2CID 125438665. Archived from the original on 27 February 2022. Retrieved 24 January 2022.
  19. ^ Bapst, J.; Byrne, S. (1 September 2016). "Mass Balance Estimates of Louth Crater Water Ice and Climatic Implications". Sixth International Conference on Mars Polar Science and Exploration. 1926: 6097. Bibcode:2016LPICo1926.6097B.
  20. ^ a b c McDonald, G. D.; Ojha, L.; McConnochie, T. H.; Smith, M. D.; Wray, J. J. (1 December 2016). "Constraining the Sublimation Rate of the Louth Crater Ice Mound with Observations of Atmospheric Water Vapor in the Thermal Infrared". AGU Fall Meeting Abstracts: P21B–2090. Bibcode:2016AGUFM.P21B2090M.
  21. ^ a b Mantegazza, M.; Spagnuolo, M. G. (1 March 2021). "Illumination Analysis of Louth Crater and Its Relation with Ice Deposits" (PDF). 52nd Lunar and Planetary Science Conference (2548): 1492. Bibcode:2021LPI....52.1492M. Archived (PDF) from the original on 27 February 2022. Retrieved 24 January 2022.
  22. ^ Hovius, Niels; Conway, Susan; Barnie, T.; Besserer, J.; Lemouelic, S.; Read, N. (1 May 2010). "Exploring the origin of ice-filled craters in the north polar region of Mars". EGU General Assembly Conference Abstracts: 15299. Bibcode:2010EGUGA..1215299H.
  23. ^ a b Quiroga, Jason (August 2015). Human Exploration of Martian Environment, Regolith, and Atmosphere Humanity's Greatest Journey NCAS Mars Mission Proposal (Thesis). NASA Community College Aerospace Scholars Program. Archived from the original on 27 February 2022. Retrieved 24 January 2022.
  24. ^ Castaneda, Daniel; Benson, Matthew; Li, Jaren; Gonzalez, Cheyenne; Le, Khanh; Harbuck, Jarbuck; Finney, Kevin; Torres, Adrian; Di, Jingfeng; Nakhjiri, Navid; Edberg, Donald L.; Chai, Patrick (15 November 2021). "2020-2021 AIAA Undergraduate Space Design Competition: Mars Ice Core Sample Return - 2nd Place Team: MICKEY" (PDF). Ascend 2021. doi:10.2514/6.2021-4130. ISBN 978-1-62410-612-5. S2CID 243777002. Archived (PDF) from the original on 24 January 2022. Retrieved 24 January 2022.
  25. ^ Brown, Adrian J.; Storrie-Lombardi, Michael (13 September 2007). "MR PRISM: a software suite for CRISM analysis". In Hoover, Richard B; Levin, Gilbert V; Rozanov, Alexei Y; Davies, Paul C. W (eds.). Instruments, Methods, and Missions for Astrobiology X. Vol. 6694. pp. 354–361. doi:10.1117/12.732260. S2CID 120241477.
  26. ^ Brown, Adrian J.; Calvin, Wendy M.; Murchie, Scott L. (December 2012). "Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) north polar springtime recession mapping: First 3 Mars years of observations: CRISM NORTH POLAR MAPPING". Journal of Geophysical Research: Planets. 117 (E12): n/a. arXiv:1403.3273. doi:10.1029/2012JE004113. S2CID 118532576.
  27. ^ "Planetary Names: Categories (Themes) for Naming Features on Planets and Satellites". Planetary Names. International Astronomical Union - United States Geological Survey. Archived from the original on 25 May 2012. Retrieved 23 January 2022. Small craters (approximately 50 km and smaller) Small towns and villages of the world with populations of approximately 100,000 or less. This category is simply a large source of crater names. No commemoration of specific towns or villages is intended.
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