11:00 〜 13:00
[PPS01-P03] Toward the identification of potential planetary-scale tidal-cryotectonic cycles in Europa
キーワード：Europa, Jupiter, ridged plains, linea, tidal-cryotectonic cycles
More and more attention has been raising toward the icy moons of the Solar System since the discovery of their potential liquid water [1], and the astrobiology potential below their surface ice [2]. In addition, the ongoing preparation of Europa Clipper and JUICE (JUpiter ICy moons Explorer) missions are boosting the research as well. Before the hopefully successful missions, the re-evaluation of the existing data from new viewpoints may help to understand some segment of the cryotectonic processes and its relation to the subsurface ocean of Europa.
One of the many research topics, connected to the study of Europa, the second Galilean satellites of Jupiter is the interpretation of the cryo-tectonic features on its surface and their relation to tidal processes triggered by Jupiter [3] and moon-moon interaction as well [4]. Following the detailed studies around the early 2000s, [5, 6] the goal of this research is to revisit Europa and re-investigate its surface by mapping one of its most characteristic surface patterns and test an approach toward an established “linea-stratigraphy” and the identification of planetary-scale tidal-cryotectonic cycles.
The base map of the studied area is used trough the “Planetary WMS service hosted by Astrogeology, USGS of Jupiter's moon Europa” [7]. The focus of the research is the complex lineage system in various locations, including the Awnn and Balgatan Regio and the neighborhood of the Belus – Phoenix - Rhadamanthys (BPR) Linea triangle [8]. Based on the recent geological map of the moon [9], the regions are defined by “ridged plains” with “bands”, “high albedo bands”, “undifferentiated lineas” and “chaos” terrains.
During the separation of the linea generations at the BPR triangle location (PDS Image Atlas, Galileo mission; image 1865r) , parameters, such as the i) physical-morphological appearance; ii) “linear feature stratigraphy”, i.e., the appearance of overlapping and transform faults; iii) impact crater density; and iv) unique morphological indicators were considered. Under- (“stratigraphically older”) and overlying (“stratigraphically younger”) lines were counted in the case of the sampled linear features from Awnn and Balgatan Regio (only lower resolution image was avaiable) and the ratio of the two parameters were calculated. To avoid the possible bias due to the length of the lines, the length parameter was used on the calculated over/underlying lines ratio as a normalizer to decrease its possible effect on the results. Furthermore the distribution of the normalized ratio was analyzed by histograms (Fig. 1a and b). Theoretically, the distribution peaks on the histogram indicates characteristic groups of linea, which belongs to the same linea-generation, i.e., formed at the same time and are overlaying and underlaid by similar amount of other linea. Based on the distribution peaks in the histograms seven and nine possible ratio-categories were separated. These categories may represent stratigraphical units, which indicates various linea-generations (Fig. 1a and b).
Various allocation and linea morphology were identified, such as the regional-scale “cycloidal ridges” [3] and smaller asymmetrical Y fault patterns, which may indicate quasi-circular shape dome forming-like processes [10]. The observed linea-generations at Awnn and Balgatan Regio may indicate regional(/palenetary)-size, repeating bulge of the ice-crust, possibly triggered by the allocation of water-mass in the subsurface hydrosphere below the ice shell of Europa, driven by “tidal-pumping” in daily basis [3], and, based on our results, in long-term tidal periods as well (Fig. 1c and d).
References: [1] Carr et al. 1998 Nature 391, 363–365 [2] Chyba & Phillips 2001 PNAS 98, 801-804 [3] Greenberg et al. 2002 Rev. Geophys. 40, 1004 [4] Hay et al. 2020 Geophys. Res. Lett 47, e2020GL088317. [5] Geissler et al. 1998 Icarus 135, 107-126 [6] Figueredo et al. 2004 LPSC XXXV Abstract #1118 [7] http://planetarymaps.usgs.gov/cgi-bin/mapserv?map=/maps/jupiter/europa_simp_cyl.map [8] map USGS. https://astrogeology.usgs.gov/search/map/Europa/Nomenclature/europa_comp. [9] Patthoff et al 2017 GSA 2017, 146-7 [10] Yin & Groshong Jr 2007 AAPG Bulletin 91, 343–363.
Figure 1. Separation of various linea-generations by a) the ratio of underlying and overlying lines (“Relative age”), and b) by the same ratio but normalized by the length of the studied linear features. Linea-generations in the studied locations (indicated by various colors) based on the linea generations from Fig. 1a and b. The color gradient toward lighter colors indicates younger and younger “relative age” defined by the under- and overlying line ratio.
One of the many research topics, connected to the study of Europa, the second Galilean satellites of Jupiter is the interpretation of the cryo-tectonic features on its surface and their relation to tidal processes triggered by Jupiter [3] and moon-moon interaction as well [4]. Following the detailed studies around the early 2000s, [5, 6] the goal of this research is to revisit Europa and re-investigate its surface by mapping one of its most characteristic surface patterns and test an approach toward an established “linea-stratigraphy” and the identification of planetary-scale tidal-cryotectonic cycles.
The base map of the studied area is used trough the “Planetary WMS service hosted by Astrogeology, USGS of Jupiter's moon Europa” [7]. The focus of the research is the complex lineage system in various locations, including the Awnn and Balgatan Regio and the neighborhood of the Belus – Phoenix - Rhadamanthys (BPR) Linea triangle [8]. Based on the recent geological map of the moon [9], the regions are defined by “ridged plains” with “bands”, “high albedo bands”, “undifferentiated lineas” and “chaos” terrains.
During the separation of the linea generations at the BPR triangle location (PDS Image Atlas, Galileo mission; image 1865r) , parameters, such as the i) physical-morphological appearance; ii) “linear feature stratigraphy”, i.e., the appearance of overlapping and transform faults; iii) impact crater density; and iv) unique morphological indicators were considered. Under- (“stratigraphically older”) and overlying (“stratigraphically younger”) lines were counted in the case of the sampled linear features from Awnn and Balgatan Regio (only lower resolution image was avaiable) and the ratio of the two parameters were calculated. To avoid the possible bias due to the length of the lines, the length parameter was used on the calculated over/underlying lines ratio as a normalizer to decrease its possible effect on the results. Furthermore the distribution of the normalized ratio was analyzed by histograms (Fig. 1a and b). Theoretically, the distribution peaks on the histogram indicates characteristic groups of linea, which belongs to the same linea-generation, i.e., formed at the same time and are overlaying and underlaid by similar amount of other linea. Based on the distribution peaks in the histograms seven and nine possible ratio-categories were separated. These categories may represent stratigraphical units, which indicates various linea-generations (Fig. 1a and b).
Various allocation and linea morphology were identified, such as the regional-scale “cycloidal ridges” [3] and smaller asymmetrical Y fault patterns, which may indicate quasi-circular shape dome forming-like processes [10]. The observed linea-generations at Awnn and Balgatan Regio may indicate regional(/palenetary)-size, repeating bulge of the ice-crust, possibly triggered by the allocation of water-mass in the subsurface hydrosphere below the ice shell of Europa, driven by “tidal-pumping” in daily basis [3], and, based on our results, in long-term tidal periods as well (Fig. 1c and d).
References: [1] Carr et al. 1998 Nature 391, 363–365 [2] Chyba & Phillips 2001 PNAS 98, 801-804 [3] Greenberg et al. 2002 Rev. Geophys. 40, 1004 [4] Hay et al. 2020 Geophys. Res. Lett 47, e2020GL088317. [5] Geissler et al. 1998 Icarus 135, 107-126 [6] Figueredo et al. 2004 LPSC XXXV Abstract #1118 [7] http://planetarymaps.usgs.gov/cgi-bin/mapserv?map=/maps/jupiter/europa_simp_cyl.map [8] map USGS. https://astrogeology.usgs.gov/search/map/Europa/Nomenclature/europa_comp. [9] Patthoff et al 2017 GSA 2017, 146-7 [10] Yin & Groshong Jr 2007 AAPG Bulletin 91, 343–363.
Figure 1. Separation of various linea-generations by a) the ratio of underlying and overlying lines (“Relative age”), and b) by the same ratio but normalized by the length of the studied linear features. Linea-generations in the studied locations (indicated by various colors) based on the linea generations from Fig. 1a and b. The color gradient toward lighter colors indicates younger and younger “relative age” defined by the under- and overlying line ratio.