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Mouza Al Amiri1, Rawdha Al Beshr1, Claus Gebhardt2, and Abdelgadir Abuelgasim2,3 1Department of Physics, College of Science, United Arab Emirates University, Al Ain 15551, United Arab Emirates, [email protected], [email protected] 2National Space Science and Technology Center, United Arab Emirates University, Al Ain 15551, United Arab Emirates, [email protected] 3Geography and Urban Planning Department, College of Humanities and Social Sciences, United Arab Emirates University, Al Ain 15551, United Arab Emirates Introduction Methods and Materials The Mars surface is heavily cratered. As to that, catalogues provide statistically complete descriptions of We performed a case study on a selection of 3 impact craters down to ca. 1 km in diameter [1]. This includes a detailed specification of crater craters Korolev crater characteristics such as position, geometry, morphology, and degradation. In total, a number of several - Korolev Crater, hundred thousand craters are cataloged to date. - Lowell Crater, and Impact craters are a key proxy used for age-dating the Mars surface in a global sense and hold crucial - Rabe Crater. implications for the geologic history of Mars regarding volcanism and erosion processes [10]. In addition, For this, we used satellite imagery from craters allow for the reconstruction of Mars orbital parameters such as obliquity [9]. - HRSC/Mars Express, Moreover, craters are promising for searching evidence of ancient life on Mars. That is because related - THEMIS/Mars Odyssey, impact-induced hydrothermal systems may have sustained habitable conditions for tens to hundreds of - HiRISE/Mars Reconnaissance Orbiter, and thousands of years. Compliant with that, Mars craters are a favorable field of study for Mars rovers. We explored each of these craters as a whole Rabe crater Lowell crater Craters are selected as landing sites for rovers, such as the Gale crater for the Curiosity rover and the and some region(s) of interest. For the Jezero crater for the upcoming Mars2020 rover. In addition, the Opportunity rover visited several craters geographic position of the 3 craters, see the such as the Eagle crater, Endurance crater, Victoria crater, and Endeavour crater. map on the right. The Korolev Crater The Korolev crater is located in the northern lowlands of Mars (latitude ca. 73°N). It is approximately 82 km in diameter and 2 km deep. Also, it is surrounded by a 2 km high crater rim. An outstanding feature is the crater interior filled with a 1.8 km high mound of water ice [Fig. 2A,B,C]. The air over the ice cools down and becomes heavier than the surrounding air. It thus increases thermal stability and acts as a “cold trap”, which shields the ice from disappearing [14]. The radar instrument SHARAD/MRO and HiRISE imagery at the edge of the ice mound indicate layered deposits of surface ice [Fig. 2C,D]. This layering indicates that the ice mound in Korolev Crater was formed by local deposition of surface ice rather than being part of a larger ice sheet in the past [13]. In total, more than 10 craters with water ice mounds are known at northern polar latitudes [20]. In Fig. 2C: Crater cross-section from SHARAD/MRO addition to Korolev Crater, there are the Dokka and Louth Crater. The Louth Crater is located at a Fig. 2B: Topographic Map latitude of ca 70°N and is thus the southernmost crater with an all year long body of ice. Fig. 2A: HRSC Image of Korolev Crater Fig. 2D: HiRISE image The Rabe Crater Rabe crater is in the Noachis Terra region (west of Hellas Basin) (43.9°S, 34.8°E), the diameter is ~108 km. There is a large sand sheet with surface dunes on Rabe Crater [Fig. 3A,B]. The dunes are colored dark and their height ranges are from 150 to 200 meters or more. They are mostly composed of transverse and barchanoid dunes [Fig. 3D,E]. Dunes of this type are expected to migrate downwind by saltation processes (if not frozen or indurated). At the downwind side of the dunes, streak patterns have been identified in Narrow Angle images of MOC/MGS. These streaks indicate grainflow events (i.e. sand avalanches). This points towards the sand dunes being at least seasonally and partially active. The estimated sand dune migration rate is 1-2 cm per Martian Year [15]. The Rabe Crater hosts an intracrater pit. At the pit walls, there is an exposed layer of dark basaltic material of volcanic origin. This indicates that the dark sand dunes in Rabe Crater have a local source rather than sand being blown from outside into the crater (this is likely similar for other FIGURE 3C craters with dark sand dunes) [18]. Fig. 3C: Map of Rabe Crater Another interesting field of study are the Bagnold Dunes in Gale Crater. They were investigated by a campaign of the Mars Rover Curiosity from November 2015 to April 2017 [19]. Fig. 3A: HRSC Image Fig. 3B: HRSC Image Fig. 3D: THEMIS VIS Image Fig. 3E: HiRISE Image The Lowell Crater Lowell Crater is roughly 200 km in diameter. In its interior, there is a ring of mountains with a diameter of ca. 90 km [Fig. 4A-C]. Similar peak-rings are known from craters on the Earth, Venus, Mercury, and Moon. They form because of gravitational collapse and uplift of the floor during the process of the formation [16]. The collapse of craters of a certain diameter can form a complex interior structure with a flat bottom, central peaks, mountain rings [Fig.4D] The Lowell crater has large dark interior deposits of sand. These are separated into two deposition areas by the mountain ring [Fig. 4A]. There is a compacted layer of sand in the inner deposition area. A sand dune is discernible in the outer deposition area. These are mainly Fig. 4C : THEMIS VIS Image crescent-shaped and barchanoid dunes [17]. Fig. 4A: HRSC Image Fig. 4B: Map of Lowell Crater Fig. 4D: Peak ring formation References 1. Robbins S. J. and Hynek B. M. (2012). J. Geophys. Res., 117, E05004, doi: 10.1029/2011JE003966 Summary 2. Lowell Crater. (2018, May 25). 3. Retrieved from https://www.geo.fu-berlin.de/en/geol/fachrichtungen/planet/press_rd/2019_lowell_crater/_content/faq_text/index.html 4. NASA/JPL/Malin Space Science Systems List of Figures 5. www.lpi.usra.edu, http://www.planetary.brown.edu/planetary/documents/Micro_36/Abstracts/031_Head_etal.pdf The selected craters for this study are the Korolev Crater, Rabe Crater, and Lowell Crater. These 6. Xie, Hongjie & Guana, H & Zhu, M & Thueson, M & Ackley, Stephen & Yue, Zongyu. (2019). Short communication A conceptual model for explanation of Albedo changes in Martian craters. 1. Mars Orbiter Laser Altimeter (MOLA), Goddard Space Flight Center, NASA. 7. Uahirise.org. (2019). HiRISE | Korolev Crater Layers (ESP_052267_2525). 2. a. PERSPECTIVE VIEW OF KOROLEV CRATER, ID 412947 , ESA/DLR/FU Berlin 8. European Space Agency. (2018). PerspeCtive view of Korolev crater. b. TOPOGRAPHIC VIEW OF KOROLEV CRATER, ID 412946, ESA/DLR/FU Berlin. craters were selected because of interesting morphological features like ice traps, sand dunes, 9. Holo, S. J., Kite, E. S., and Robbins, S. J. (2018). Mars obliquity history constrained by elliptic crater orientations. Earth and Planetary Science Letters, 496, 206-214, doi: 10.1016/j.epsl.2018.05.046 c. Brothers and Holt(2016), Geophys. Res. Lett. (see also References, 13.), their Figure 4 10. Barlow N. G.(2015). Constraining geologic properties and processes through the use of impact craters, Geomorphology, 240, 18-33, doi: 10.1016/j.geomorph.2014.08.027 d. Korolev Crater Layers, ESP_052280_2525, NASA/JPL/University of Arizona. 11. https://mars.nasa.gov/news/nasa-mars-weathercam-helps-find-big-new-crater/ 3. a. RABE CRATER, ID 310883, ESA/DLR/FU Berlin. mountain rings, etc. This work is a student research project inspired by the discovery of the 12. Christensen, P.R., N.S. Gorelick, G.L. Mehall, and K.C. Murray, THEMIS PubliC Data Releases, Planetary Data System node, Arizona State University, <http://themis-data.asu.edu>. b. RABE CRATER PRESPECTIVE, ID 310887, ESA/DLR/FU Berlin. 13. Brothers, T. C., and J. W. Holt (2016), Three-dimensional structure and origin of a 1.8km thick ice dome within Korolev Crater, Mars, Geophys. Res. Lett., 43, 1443–1449, doi:10.1002/ 2015GL066440 c. HTTPS://WWW.JPL.NASA.GOV/SPACEIMAGES/DETAILS.PHP?ID=PIA22145 14. Esa. (n.d.). Mars Express gets festive: A winter wonderland on Mars. Retrieved from https://www.esa.int/Our_Activities/Space_Science/Mars_Express/Mars_Express_gets_festive_A_winter_wonderland_on_MarsConway, S.J., Hovius, N., Barnie, T., d. HTTPS://WWW.JPL.NASA.GOV/SPACEIMAGES/DETAILS.PHP?ID=PIA22145 so-far-largest fresh impact crater during routine weather inspection of camera imagery from Besserer, J., Le Mouélic, S., Orosei, R., Read, N.A., Climate-driven deposition of water ice and the formation of mounds in craters in Mars’ north polar region, Icarus, 220, 174-193, e. Rabe Crater Dunes, ESP_055160_1360, NASA/JPL/University of Arizona. doi: 10.1016/j.icarus.2012.04.021, 2012. 4. a. PERSPECTIVE VIEW OF LOWELL CRATER, ID 421132, ESA/DLR/FU Berlin. 15. Fenton, L. K. (2006). Dune migration and slip face advancement in the Rabe Crater dune field, Mars. GeophysiCal ResearCh Letters,33(20). doi:10.1029/2006gl027133 b. Christensen, P.R., N.S. Gorelick, G.L. Mehall, and K.C. Murray, THEMIS PubliC Data Releases, Planetary Data System MARCI/MRO [11]. 16. Formation of ring craters. (2018, September 12). Retrieved from https://www.geo.fu-berlin.de/en/geol/fachrichtungen/planet/press_rd/2019_lowell_crater/_content/faq_text/part3.html node, Arizona State University, http://themis-data.asu.edu IMAGE ID V57922003 17. Lowell Crater - a bullseye on Mars.
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  • Giant Saltation on Mars

    Giant Saltation on Mars

    Giant saltation on Mars Murilo P. Almeida†, Eric J. R. Parteli†, Jose´ S. Andrade, Jr.†‡§, and Hans J. Herrmann†‡ †Departamento de Fı´sica,Universidade Federal do Ceara´, 60455-900, Fortaleza, CE, Brazil; and ‡Computational Physics, Institut fu¨r Baustoffe, Eidgeno¨ssische Technische Hochschule Zu¨rich, Schafmattstrasse 6, 8093 Zurich, Switzerland Edited by H. Eugene Stanley, Boston University, Boston, MA, and approved March 11, 2008 (received for review January 9, 2008) Saltation, the motion of sand grains in a sequence of ballistic trajectories close to the ground, is a major factor for surface erosion, dune formation, and triggering of dust storms on Mars. Although this mode of sand transport has been matter of research for decades through both simulations and wind tunnel experi- ments under Earth and Mars conditions, it has not been possible to provide accurate measurements of particle trajectories in fully developed turbulent flow. Here we calculate the motion of saltat- ing grains by directly solving the turbulent wind field and its interaction with the particles. Our calculations show that the minimal wind velocity required to sustain saltation on Mars may be surprisingly lower than the aerodynamic minimal threshold mea- surable in wind tunnels. Indeed, Mars grains saltate in 100 times higher and longer trajectories and reach 5-10 times higher veloc- ities than Earth grains do. On the basis of our results, we arrive at general expressions that can be applied to calculate the length and height of saltation trajectories and the flux of grains in saltation under various physical conditions, when the wind velocity is close to the minimal threshold for saltation.