Radar Evidence Of Subglacial Liquid Water On Mars


Radar data collected by MARSIS. (A) Radargram for MARSIS orbit 10737, whose ground track is shown in Fig. 1B. A radargram is a bi-dimensional color-coded section made of a sequence of echoes in which the horizontal axis is the distance along the ground track of the spacecraft, the vertical axis represents the two-way travel time of the echo (from a reference altitude of 25km above the reference datum), and brightness is a function of echo power. The continuous bright line in the topmost part of the radargram is the echo from the surface interface, whereas the bottom reflector at about 160µs corresponds to the SPLD/basal material interface. Strong basal reflections can be seen at some locations, where the basal interface is also planar and parallel to the surface. (B) Plot of surface and basal echo power for the radargram in (A). Red dots mark surface echo power values, while blue ones mark subsurface echo power. The horizontal scale is along-track distance, as in (A), while the vertical scale reports uncalibrated power in decibels (dB). The basal echo between 45km and 65km along track is stronger than the surface echo even after attenuation within the SPLD.

The presence of liquid water at the base of the Martian polar caps has long been suspected but not observed. We surveyed the Planum Australe region using the Mars Advanced Radar for Subsurface and Ionosphere Sounding, a low-frequency radar on the Mars Express spacecraft.

Radar profiles collected between May 2012 and December 2015, contain evidence of liquid water trapped below the ice of the South Polar Layered Deposits. Anomalously bright subsurface reflections were found within a well-defined, 20km wide zone centered at 193°E, 81°S, surrounded by much less reflective areas.

Quantitative analysis of the radar signals shows that this bright feature has high dielectric permittivity >15, matching water-bearing materials. We interpret this feature as a stable body of liquid water on Mars.

R. Orosei, S. E. Lauro, E. Pettinelli, A. Cicchetti, M. Coradini, B. Cosciotti, F. Di Paolo, E. Flamini, E. Mattei, M. Pajola, F. Soldovieri, M. Cartacci, F. Cassenti, A. Frigeri, S. Giuppi, R. Martufi, A. Masdea, G. Mitri, C. Nenna, R. Noschese, M. Restano, R. Seu
(Submitted on 9 Apr 2020)
Comments: 27 pages, 10 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference: Science 361, 490 (2018)
DOI: 10.1126/science.aar7268
Cite as: arXiv:2004.04587 [astro-ph.EP] (or arXiv:2004.04587v1 [astro-ph.EP] for this version)
Submission history
From: Roberto Orosei
[v1] Thu, 9 Apr 2020 15:16:12 UTC (1,864 KB)
https://arxiv.org/abs/2004.04587
Astrobiology

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