![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2018\/07\/Mars-Express.jpg\")
<\/p>\nFor the first time in human exploration of Mars, the presence of a stable, subterranean body of salty (briny) water has been strongly suggested by data returned by the European Space Agency\u2019s Mars Express orbiter. Using measurements taken by the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument, a team of Italian researches announced this week the first (probable) discovery of a stable body of liquid water on Mars. But with this discovery comes a host of questions regarding future exploration of the Red Planet.<\/p>\n
A stable, large body of liquid water on Mars:<\/b><\/p>\n
It\u2019s the word \u201cstable\u201d that is the historic and big-ticket item here.<\/p>\n
Prior to this week, liquid water on Mars\u2019 surface had only been observed for very brief periods of time. Briny water droplets were briefly observed on NASA\u2019s Phoenix Polar Lander and orbital terrain images have revealed new surface features carved by flowing water that quickly disappeared.<\/p>\n
But never before had liquid water in large, stable quantities been found on \u2013 or beneath \u2013 Mars.<\/p>\n
Nonetheless, the presence of liquid water underneath the Martian polar caps has long been hypothesized. In fact, it was first suggested as \u201cpossible\u201d over 30 years ago, but conclusive data to either prove or disprove the hypothesis remained elusive.<\/p>\n
<\/p>\n
Mars Express in orbit of Mars. (Credit: ESA)<\/p>\n
Enter the European Space Agency\u2019s (ESA\u2019s) Mars Express orbiter, which has been at Mars since 25 December 2003. <\/p>\n
Since then, it has been dutifully studying the Martian terrain, including its subsurface mysteries, with the Mars Advanced Radar for Subsurface and Ionosphere Sounding, or MARSIS, instrument \u2013 specifically, a region underneath Mars\u2019 Planum Australe (south polar region) known as the South Polar Layered Deposits.<\/p>\n
Space Shuttle (adsbygoogle = window.adsbygoogle || []).push({});<\/p>\n The evidence returned by MARSIS of a persistent liquid water deposit in this region came via a three and a half Earth-year observational period from May 2012 to December 2015, during which MARSIS conducted 29 different radar scans of a 200 km-wide (124 mile-wide), flat area of the Planum Australe.<\/p>\n The radar waves sent from MARSIS penetrated the top layers of the Martian terrain, extending a few kilometers underneath the surface. Those waves were then reflected back toward MARSIS when they encountered various rocks, sediments, and \u2013 in this case \u2013 liquid water.<\/p>\n The MARSIS findings are reported by Dr. R. Orosie et al. in the article \u201cRadar evidence of subglacial liquid water on Mars\u201d and was published in the journal Science can be read here.<\/p>\n (A) Shaded relief map of Planum Australe, Mars, south of 75\u00b0S latitude. The black square outlines the study area. (B) Mosaic produced using infrared observations by the THEMIS (Thermal Emission Imaging System) camera, corresponding to the black square in (A). The red line marks the ground track of orbit 10,737 of Mars Express. The area consists mostly of featureless plains, except for a few large asymmetric polar scarps near the bottom right of (B). (Credit: R. Orosei et al. Science 2018)<\/p>\n The specific discovery was made by measuring what\u2019s known as the dielectric permittivity (or the strength of the reflected radio waves) and via routine (i.e., stable) observations of a highly reflective 20 km-wide (12 mile-wide), 1.5 km (0.9 miles) deep deposit of water over the 3.5 year observational period.<\/p>\n For this discovery, the dielectric permittivity provided the information necessary to understand that it was liquid water causing the strong reflections seen in the MARSIS data and not something else.<\/p>\n In fact, other potential explanations for the high permittivity returns were explored but ultimately rejected based on sound evidence.<\/p>\n Moreover, the extremely strong evidence in the MARSIS data that this is, in fact, stable liquid water also points to this deposit being extremely salty because temperatures in the region are understood to be -68\u00b0C (-90\u00b0F) \u2013 far below the freezing point of freshwater.<\/p>\n Therefore, the water deposit would have to be salty, as the saltier the water, the lower the freezing point is.<\/p>\n<\/p>\n![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2018\/07\/Mars-water-1.jpg\")
<\/p>\n