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The Global Search for Liquid Water on Mars from Orbit: Current and Future Perspectives

by 1,*, 2,†, 3,†, 4,†, 5,†, 5,6,†, 7,†, 8,9,†, 7,†, 8,9,†, 10,† and 11,†
1
Istituto di Radioastronomia, Istituto Nazionale di Astrofisica, Via Piero Gobetti 101, 40129 Bologna, Italy
2
School of Atmosphere Sciences, Sun Yat-sen University, 2 Daxue Road, Xiangzhou District, Zhuhai City 519000, China
3
Institute of Remote Sensing and Geographical Information System, School of Earth and Space Sciences, Peking University, Beijing 100871, China
4
School of Engineering, The University of Edinburgh, Alexander Graham Bell Building, Thomas Bayes Road, Edinburgh EH9 3FG, UK
5
Université Grenoble Alpes, CNRS, CNES, IPAG, 38000 Grenoble, France
6
Centrum Badan Kosmicznych Polskiej Akademii Nauk (CBK PAN), Bartycka 18A, 00-716 Warsaw, Poland
7
Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00146 Roma, Italy
8
Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, China
9
University of Chinese Academy of Sciences, No.19(A) Yuquan Road, Shijingshan District, Beijing 100049, China
10
Piesat Information Technology Co., Ltd, Beijing 100195, China
11
State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Life 2020, 10(8), 120; https://doi.org/10.3390/life10080120
Received: 22 June 2020 / Revised: 17 July 2020 / Accepted: 20 July 2020 / Published: 24 July 2020
(This article belongs to the Special Issue Life on Mars)
Due to its significance in astrobiology, assessing the amount and state of liquid water present on Mars today has become one of the drivers of its exploration. Subglacial water was identified by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) aboard the European Space Agency spacecraft Mars Express through the analysis of echoes, coming from a depth of about 1.5 km, which were stronger than surface echoes. The cause of this anomalous characteristic is the high relative permittivity of water-bearing materials, resulting in a high reflection coefficient. A determining factor in the occurrence of such strong echoes is the low attenuation of the MARSIS radar pulse in cold water ice, the main constituent of the Martian polar caps. The present analysis clarifies that the conditions causing exceptionally strong subsurface echoes occur solely in the Martian polar caps, and that the detection of subsurface water under a predominantly rocky surface layer using radar sounding will require thorough electromagnetic modeling, complicated by the lack of knowledge of many subsurface physical parameters. Higher-frequency radar sounders such as SHARAD cannot penetrate deep enough to detect basal echoes over the thickest part of the polar caps. Alternative methods such as rover-borne Ground Penetrating Radar and time-domain electromagnetic sounding are not capable of providing global coverage. MARSIS observations over the Martian polar caps have been limited by the need to downlink data before on-board processing, but their number will increase in coming years. The Chinese mission to Mars that is to be launched in 2020, Tianwen-1, will carry a subsurface sounding radar operating at frequencies that are close to those of MARSIS, and the expected signal-to-noise ratio of subsurface detection will likely be sufficient for identifying anomalously bright subsurface reflectors. The search for subsurface water through radar sounding is thus far from being concluded. View Full-Text
Keywords: habitability; space missions; space technologies habitability; space missions; space technologies
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MDPI and ACS Style

Orosei, R.; Ding, C.; Fa, W.; Giannopoulos, A.; Hérique, A.; Kofman, W.; Lauro, S.E.; Li, C.; Pettinelli, E.; Su, Y.; Xing, S.; Xu, Y. The Global Search for Liquid Water on Mars from Orbit: Current and Future Perspectives. Life 2020, 10, 120. https://doi.org/10.3390/life10080120

AMA Style

Orosei R, Ding C, Fa W, Giannopoulos A, Hérique A, Kofman W, Lauro SE, Li C, Pettinelli E, Su Y, Xing S, Xu Y. The Global Search for Liquid Water on Mars from Orbit: Current and Future Perspectives. Life. 2020; 10(8):120. https://doi.org/10.3390/life10080120

Chicago/Turabian Style

Orosei, Roberto; Ding, Chunyu; Fa, Wenzhe; Giannopoulos, Antonios; Hérique, Alain; Kofman, Wlodek; Lauro, Sebastian E.; Li, Chunlai; Pettinelli, Elena; Su, Yan; Xing, Shuguo; Xu, Yi. 2020. "The Global Search for Liquid Water on Mars from Orbit: Current and Future Perspectives" Life 10, no. 8: 120. https://doi.org/10.3390/life10080120

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