Cold,Dry,Windy,and UV Irradiated: Surveying Mars-Relevant Conditions in Ojos del Salado Volcano (Andes Mountains,Chile)

1. Introduction

This special issue of Astrobiology covers the results of analog research that took place in 2018 at a Mars-relevant area on Earth, the Atacama–Altiplano region. This is a wider Atacama Desert area at the rarely visited Ojos del Salado volcano. The term “site” in this work is used for areas that are several 10 s or some 100 km in diameter and show similar Mars-relevant characteristics. Therefore, these site areas could be considered, in aggregate, a “single site” that covers a large area. This site hosts the highest volcano on Earth, where desiccated lakebeds, hot springs, volcanic alluvium within the combined occurrence of permafrost, ephemeral snow, and extreme UV irradiation occur. This terrain is eroded and was once glaciated but is currently desiccated and strongly wind-chilled, making it an interesting target for astrobiological research. The major findings are summarized briefly below and are grouped into main topics according to the corresponding papers in this special collection. A comparison with other Mars analog sites is presented in the Discussion section.

Ojos del Salado (6893 m, 27°06′34″ S, 68°32′32″ W) is the highest volcano on Earth (Óscar, 1995), with an elevation of 6893 m, located in the Atacama Desert–Altiplano region of the Dry Andes, above the Puna de Atacama plain (Fig. 1). The volcano probably represents a Pliocene-Quaternary volcanic arc in the Andes (Rubiolo and Hickson, 2002). Its activity began at ∼26 Ma (million years) ago (Mpodozis et al., 1996), and produced rocks mostly of evolved geochemistry and complex petrography (DeSilva and Francis, 1991) with a recent shift toward more acidic compositions (Bakero et al., 1987). The last volcanically active period was ∼30 ka ago (Moreno and Gibbons, 2007); currently, only fumarolic activity is observed. This volcano represents the latest, and possibly currently active, episode of volcanism from the Miocene until the Pliocene (Goss, 2008) with variations related to Nazca–South American plate convergence parameters and the consequence of subduction of the Juan Fernández Ridge hotspot track (Kay and Mpodozis, 2002). The region is a desert without continuous vegetation or soil cover. Despite the weak and rare precipitation at the closed basins, several salty lakes or their dried-up deposits can be found there. Undulating topography and high-altitude permafrost are present (Cobos and Corte, 1990; Ahumada, 2002) with some glacier remnants (Oyarzun, 1987). The morphology of the surface is generally dominated by rocks and boulders, although at a few locations ripples (rarely dunes) are also observable.

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FIG. 1.

General overview of the Ojos del Salado region based on GoogleMaps images: (a) Southern America, (b) the meridional range of the Andes Mountain, (c) part of the Altiplano–Atacama Desert region, (d) the Ojos del Salado region, (e) the northern slopes of the target mountain, (f) perspective view of the target area. North is upward in all insets, except the last one (f). The locations of the images in the following figures are indicated in “c” and “e” panels.

Ojos del Salado has a high-altitude snowline [no measured data exist as this or higher elevations at this site; Clapperton (1994)]; however, >6500 m the terrain is mostly, though not always, snow covered (Ammann et al., 2001) and has the highest altitude lakes and desert region on Earth. The climatic conditions are only moderately known, partly because of the stochastic changes and the poor coverage with observations; however, general dryness and coldness are expected.

There are no glaciers in the region at present; however, there were several active glaciers (Nagy et al., 2019) during the Last Glacial Maximum ∼19 ka (thousand years) (Ammann et al., 2001). A range of regolith-covered ice and sand masses occur in various geological settings. Permafrost is present in the form of patches >5200 m and continuously >5600 m. Degradation of permafrost is an important water source, where, based on model calculations, gradually increased temperature is expected for the next decades. The climatic change, however, will probably not turn this region more humid. The annual precipitation is <150 mm/year, but it is difficult to obtain an exact measure as there have been only scattered observations made [for more details see the accompanying paper of Breuer et al. (2020) in this Spec. Coll.]. Long-term cryosphere monitoring started in 2012 with the installation of loggers at five different altitudes. Monitoring has been ongoing ever since; specific details of related analyses are presented by Nagy et al. (2020) in this issue.

The interaction between rare snow events and strong wind-transported sediments produces buried snow masses that are shielded from sublimation. This joint occurrence is rare among Mars analog sites. Even though melting could arise occasionally, the modification of the surface is dominated by desiccation of the cryosphere and by wind activity. The ephemeral surface runoff produces evaporitic sediments that are composed of carbonate, aragonite, anhydrite, talc, and clay minerals, all partly desiccated after deposition. The UV-induced surface modification is strongest here in comparison with other Mars analog sites. A favorable logistical characteristic of this site is its accessibility, with moderately low transport costs, as it is reachable up to 5200 m altitude with a 4–5 h drive by four-wheel drive-supported pickup cars from larger cities such as Copiapó.

2. Key Results Presented in This Special Collection of Papers

Specific climatic characteristics of the Ojos del Salado volcano area are described in the paper “Analog Site Experiment in the High Andes-Atacama Region: Surface Energy Budget Components on Ojos del Salado from Field Measurements and WRF Simulations” (Breuer et al., 2020). The meteorological modeling provides new information in at least two aspects. First, it shows examples of how to extrapolate results to larger areas ∼100 km in diameter by using a few locations where meteorological data have been acquired at the surface. Such work is critical for future Mars exploration, given that surface measurements on the Red Planet will be available from only a few, scattered locations. The second aspect is modeling at an undulating surface with the kind of overall dryness and reduced atmospheric pressure that typifies the Ojos del Salado region. The handling of meteorological data and forecasting under such conditions might provide useful experience for similar calculations applicable to the even lower atmospheric pressure and drier conditions of a martian near-surface layer (Weidinger et al., 2009). Remote sensing data for Mars are abundant, though surface in situ verification is rare. Earth-based methodological improvement thus helps extrapolate below the surface-based data. The Weather Research and Forecasting (WRF) model used here was verified through surface conditions and energy budget calculations. The results show that near-surface atmospheric conditions can be simulated well, although modeling of the effects of water-phase changes should be improved.

Another paper in this special issue, “The Thermal Behavior of Ice-Bearing Ground: The Highest Cold, Dry Desert on Earth as an Analog for Conditions on Mars, at Ojos del Salado, Puna de Atacama-Altiplano Region” by Nagy et al. (2020) describes results for monitoring and modeling of continuously changing frozen ground. The temperature variation of the regolith has been monitored hourly since 2012, that is, between 4200 and 6893 m of altitude, which makes this the highest shallow ground-temperature monitoring system on Earth. The temporal change of water/ice phases was determined, the results of which show that the dryness and cold control the evolution of landforms simultaneously, as is the case for Mars. The presence of permafrost and ground ice was found to be discontinuous >5200–5300 m and continuous >5800 m. Above 6500 m, the active layer is either missing or extremely thin. The presence of pore ice allows the highest ponds on Earth to exist continuously, though permafrost degradation threatens the extreme wetland habitat.

One of the most interesting possibilities, the potential emergence of liquid water, is discussed in the paper titled “Unique and Potentially Mars-Relevant Flow Regime and Water Sources at a High Andes-Atacama Site” by Kereszturi (2020). This work documents the discovery of two types of flow-produced structures and a unique flow regime. Among them, the so-called infilled valleys showed activity only during daytime in a spatially sectioned distribution, originating from three distinct sources: buried snow, surface snow, and ice left behind from liquid water that emerged the day before. Ojos del Salado is a unique ecological site, where material from rare snow events may be protected by the burial of strong wind-transported sediments, which also support ephemeral melting over the long term.

The paper titled “Effects of Active Volcanism on Bacterial Communities in the Highest-Altitude Crater Lake of Ojos del Salado” by Aszalós et al. (2020a) provides examples for locations of extremophiles at the highest altitude lake (6480 m) on Earth. This lake is heated by geothermal activity, where acidic conditions are produced by fumaroles. Cultivation of sampled organisms showed the presence of psychrophilic taxa that belong to Proteobacteria, Bacteroidetes, and Actinobacteria. Characteristically different bacterial communities were identified in the warm and cold water-covered sediments, with acidophilic iron-oxidizers and iron-reducers in the fumaroles' runoff channel or creek.

Further analysis of these extreme habitats is presented in the paper titled “Bacterial Diversity of a High-Altitude Permafrost Thaw Pond Located on Ojos del Salado” by Aszalós et al. (2020b), which characterizes extremophiles in permafrost degradation-produced thaw ponds at 5900 m altitude. Water from the thaw pond was dominated by Bacteroidetes and Proteobacteria, while in the sediment of the lake and permafrost, members of Acidobacteria, Actinobacteria, Bacteroidetes, Patescibacteria, Proteobacteria, and Verrucomicrobia groups were abundant. The lower altitude part of Atacama sites also provides insight, in general, on the methods and problems encountered during laboratory analysis of extremophiles.

The paper titled “Biosignature Analysis of Mars Soil Analogs from the Atacama Desert: Challenges and Implications for Future Missions to Mars” by Aerts et al. (2020) examines biological fingerprints at several locations at the elevated Andean highlands. It was revealed that although the amino acid load, organic carbon, and nitrogen quantities were generally low, most of the soil samples harbored complex microbial communities dominated by halophilic microorganisms. While the Atacama Desert and higher altitude sites, such as the Ojos de Salado volcano, contain some of the driest, harshest, and highest altitude environments on Earth, a singular lesson from their study is that, regardless of these kinds of conditions, life is able to survive and potentially be preserved. Salars and salt flats can, therefore, be considered targets of interest.

3. Discussion: Comparison with Other Mars Analog Sites

Collectively, the papers in this special collection of Astrobiology contribute to a better understanding of the geology and astrobiology of Mars through a systematic comparison (Table 1) of the Ojos del Salado site with other potential Mars analog locations on Earth, including many of those previously studied (Hipkin et al., 2014).

Based on Table 1, the Ojos del Salado site is unique in two main aspects. First, there is high UV irradiation, which is more intense here than at any other currently used analog site. It is possibly higher than other potential Altiplano sites such as Llullaillaco (elevation 6723 m), Licancabur (5920 m), and Socompo (6051 m) volcanoes. The second is the presence of geothermal activity and permafrost within a surface terrain that is cold and dry. In Iceland, volcano–ice interactions occur with the surface ice under a cold, though humid, climate, where liquid water produced by melting could be moderately stable. This provides interesting targets, though without the presence of permafrost and an overall dryness, such an environment is a bit less Mars relevant than Ojos del Salado. The Antarctic Dry Valleys site also provides low temperature and permafrost, but without much geothermal activity.

The Ojos del Salado site is more Mars relevant than most sites due to the joint occurrence of ephemeral snow precipitation, extreme dryness, low temperatures coupled with strong winds, and easily transportable, low-density volcanic grains. This setting provides ideal conditions for the fast burial and maintenance of snow masses under dry and cold conditions. These serve as a potential analog for the formation of the martian latitude-dependent mantle, and for the ice-containing layer on Mars (Schon et al., 2009). The strong wind and easily transportable material are necessary to make such interactions possible. These conditions are absent at other Mars analog sites, with the possible exception of the Antarctic Dry Valleys—surface debris may be less erodible there, however, than at the Ojos de Salado. The existence of permafrost at a dry terrain is rare by itself, and therefore only the Antarctic Dry Valleys could be considered an analog site with similar conditions in this aspect.

4. Conclusion: The Unique Characteristics of Ojos del Salado

The papers in this special collection demonstrate that the Ojos del Salado region in the Altiplano and larger Atacama Desert area provides several additional analog environments that are comparable with other Mars analog sites on Earth. The unique characteristics of the Ojos del Salado site include strong UV irradiation, permafrost in dry terrains, geothermal heat/activity combined with the presence of permafrost, and a strong interaction between ephemeral snow and wind activity. One of the main benefits of this site, when compared with other extreme sites with such dryness and low-temperature conditions, is the low cost and simple site access by pickup trucks. This unique setting provides ideal conditions for the analysis of weathering in dry terrains, permafrost, snow burial, and related geomorphological aspects.

The extremophiles identified and described in this special issue provide insight into the characteristics of microbial communities in dry and cold, geothermally heated terrains, together with the potential to test technological and observational aspects. This special collection of Astrobiology presents insight into the potential Mars analog site, Ojos del Salado, and those unique research opportunities that the region has to offer.