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Mimicking the Martian Hydrological Cycle: a Set-Up to Introduce Liquid Water in Vacuum

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Mimicking the Martian Hydrological Cycle: a Set-Up to Introduce Liquid Water in Vacuum sensors Article Mimicking the Martian Hydrological Cycle: A Set-Up to Introduce Liquid Water in Vacuum Jesús Manuel Sobrado Centro de Astrobiología (INTA-CSIC), Torrejón de Ardoz, 28850 Madrid, Spain; [email protected] Received: 24 September 2020; Accepted: 27 October 2020; Published: 29 October 2020 Abstract: Liquid water is well known as the life ingredient as a solvent. However, so far, it has only been found in liquid state on this planetary surface. The aim of this experiment and technological development was to test if a moss sample is capable of surviving in Martian conditions. We built a system that simulates the environmental conditions of the red planet including its hydrological cycle. This laboratory facility enables us to control the water cycle in its three phases through temperature, relative humidity, hydration, and pressure with a system that injects water droplets into a vacuum chamber. We successfully simulated the daytime and nighttime of Mars by recreating water condensation and created a layer of superficial ice that protects the sample against external radiation and minimizes the loss of humidity due to evaporation to maintain a moss sample in survival conditions in this extreme environment. We performed the simulations with the design and development of different tools that recreate Martian weather in the MARTE simulation chamber. Keywords: mars simulation; artificial atmosphere; water cycle; moss survival 1. Introduction There are similitudes and differences between Mars, the red planet, and Earth. One of the requirements for Earth-like life to emerge from a planet habitability perspective is the hydrological cycle. Pressure, temperature, and gas composition allow, for example, extreme microorganisms to live on Earth in different environments [1–4] where these variables are far from the average values. Water is a prerequisite for life [5]. This constitutes the main astrobiology paradigm [6–8]. Water in the gaseous state is found mostly in the universe in the interstellar medium [9]. Water as ice abounds in the interior of some moons, such as Europe [10]; at the poles of rocky planets, such as Earth and Mars [11]; and in interplanetary objects, such as comets and asteroids [12]. In liquid state, water is located on the surface of the Earth and interior of satellites of the giant planets [13]. In principle, liquid water and vacuum are incompatible. Only under special conditions, liquid water can be introduced in a vacuum system. The water vapor pressure indicates that under certain conditions of pressure and temperature [14], it is possible for water to remain in liquid state (Figure1). Sensors 2020, 20, 6150; doi:10.3390/s20216150 www.mdpi.com/journal/sensors Sensors 2020, 20, 6150 2 of 21 Sensors 2020, 20, x FOR PEER REVIEW 2 of 21 Figure 1. Water phase diagram [[14].14]. Comparison of parameters between Mars and Earth. Fortunately, MarsMars has has water, water, as iceas atice the at poles, the poles, as vapor as invapor the atmosphere in the atmosphere with a low with percentage a low in comparison with the main gases (95% CO , 2.7% N ; 1.6% Ar; 0.13% H 0; 0.08% CO) [15], and percentage in comparison with the main gases2 (95% CO2 2, 2.7% N2; 1.6% Ar;2 0.13% H20; 0.08% CO) as[15], liquid and as in liquid subglacial in subglacial layers [ 16layers,17]. [16,17]. Mars hasMars seasons, has seasons, diurnal diurnal and nocturnaland nocturnal variations variations of the of mainthe main environmental environmental variables variables [18] (temperature, [18] (tempera pressure,ture, pressure, radiation, radiation, composition composition of the atmosphere of the andatmosphere humidity), and which humidity), result which in changes result in in the changes state ofin waterthe state in aof short water amount in a short of time amount [19]. of Under time these[19]. Under conditions, these conditions, ice–liquid andice–liquid ice–mineral and ice–mine interfacesral interfaces [20] are the [20] appropriate are the appropriate means for means extreme for microorganismsextreme microorganisms to adapt into thisadapt hostile in this environment hostile envi [ronment21]. Some [21]. of theSome most of the relevant most aspectsrelevant from aspects the pointfrom the of view point of of liquid view of water liquid on water the surface on the of surfac Marse areof Mars found are in found the hydrological in the hydrological cycle [22 cycle] and [22] the dailyand the humidity daily humidity cycle that cycle might that influence might influence hydration hydration on Mars [on23]. Mars The hydrological[23]. The hydrological cycle is related cycle tois therelated seasons, to the the seasons, ice of thethe polarice of caps, the polar and thecaps, gas and flow the in gas the flow atmosphere in the atmosphere [24]. [24]. The existence of waterwater isis essentialessential forfor lifelife toto emerge.emerge. In planetary sciences, there have been developments of simulation systems that include water in habitabilityhabitability and geochemicalgeochemical studies of vacuum samples [[25–28].25–28]. The last calibration of the Ph Phoenixoenix lander in relation to the relative relative humidity sensor [[29,30]29,30] provides the meansmeans under very specialspecial circumstancescircumstances to enableenable thethe existenceexistence ofof liquidliquid water on thethe MartianMartian surfacesurface [[31].31]. According to this last calibration at the location of the PhoenixPhoenix lander (near(near the the North North Pole), Pole), relative relative humidity humidity values values surpassing surpassing 35% have 35% been have recorded. been recorded. In summer, In a water vapor peak (relative humidity) appears due to the minimum CO ice coverage of the water ice summer, a water vapor peak (relative humidity) appears due to the minimum2 CO2 ice coverage of formedthe water in ice the formed bottom in main the partbottom of the main northern part of polar the northern cap. Water polar vapor cap. is Water transported vapor tois transported the equator fromto the the equator polar capsfrom ofthe Mars polar [32 caps,33]. of This Mars increase [32,33]. in Th wateris increase vapor, althoughin water itvapor, is a very although small amountit is a very by volumesmall amount of water by due volume to the of density water ofdue the to atmosphere the density with of the an atmosphere average pressure with ofan ~(6–8) average mbar pressure [34], can of condense~(6–8) mbar on [34], the cooler can condense surfaces on at dawnthe cooler and occasionallysurfaces at dawn at lower and latitudes, occasionally especially at lower at nightlatitudes, [35], similar to what happens with dew on Earth. The average temperature in the air is 218 K ( 55 C), with especially at night [35], similar to what happens with dew on Earth. The average temperature− ◦ in the a maximum of 276.3 K (3.15 C) in the equator, up to 170 K (below 100 C) in the polar cap [36]. Mars air is 218 K (−55 °C), with a maximum◦ of 276.3 K (3.15 °C) in the equator,− ◦ up to 170 K (below −100 °C) hasin the a di polarfference capof [36]. up toMars 30 ◦hasC between a difference the ground of up andto 30 the °C surface between atmosphere the ground [37 and]. On the the surface other hand,atmosphere the increase [37]. inOn diurnal the other temperature, hand, the the increase incidence in ofdiurnal solar radiationtemperature, on the the surface, incidence as well of assolar the fluctuationradiation on and the increase surface, in as pressure well as the due fluctuation to the sublimation and increase of carbon in pressure dioxide due ice, to can the allow sublimation that liquid of watercarbon to dioxide appear asice, ice can near allow the polesthat liquid in short water seasonal to appear periods. as ice near the poles in short seasonal periods.The regions near the poles of the red planet contain large amounts of water ice, both inside [16] and outside,The regions giving near rise the to poles the existenceof the red ofplanet salts contai that producen large amounts a brine [ 38of– water40] of ice, clathrates both inside [41] and[16] perchloratesand outside, [giving42,43]. rise On Mars,to the waterexistence iceand of salts carbon that dioxide produce are a subjectbrine [38–40] to climatic of clathrates and seasonal [41] and dailyperchlorates variations [42,43]. [44]. On We Mars, know water that an ice ice and sheet carbon protects dioxide against are subject life-damaging to climatic ultraviolet and seasonal radiation and anddaily is variations a good thermal [44]. We insulator know that [45,46 an]. ice The sheet main protects example against on our life-damaging planet is found ultraviolet in Antarctica radiation [47], whereand is microa good algae thermal composed insulator mainly [45,46]. of cyanobacteria The main example are capable on our of planet photo synthesizingis found in Antarctica [48,49]. In [47], this setting,where micro one of algae the places composed where mainly water existenceof cyanobacteri is possiblea are in capable several statesof photo as wellsynthesizing as the emergence [48,49]. In of lifethis issetting, in locations one of favored the places by the where hydration water of theexistenc atmosphere.e is possible in several states as well as the emergenceThe goal of oflife this is in paper locations is to presentfavored anby experimentalthe hydration set-up of the andatmosphere. method capable of recreating the appropriateThe goal environmental of this paper conditionsis to present to an favor experime the metabolicntal set-up activity and method of simple capable Earth-based of recreating organisms the appropriate environmental conditions to favor the metabolic activity of simple Earth-based organisms on the Martian surface [50]. We designed an observation in the laboratory similar to the Sensors 2020, 20, 6150 3 of 21 on the Martian surface [50].
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