Christopher P. McKay’s research while affiliated with National Aeronautics and Space Administration and other places

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Publications (642)


The Viking biology experiments on Mars revisited
  • Article

January 2025

Icarus

Christopher P. McKay

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Richard C. Quinn

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Carol R. Stoker

Fig. 1. Rock 1, a sample of Beacon sandstone from Battleship Promontory colonized by cryptoendolithic lichens. The background grid is 0.5 cm squares.
Fig. 2. a. Rock 2, a sample of Beacon sandstone from Battleship Promontory colonized by cryptoendolithic lichens. The background grid is 0.5 cm squares. b. A close-up image showing the black colonized zone.
Fig. 6. The fraction of water retained as the rock dries, shown as black lines. The square symbols and solid black lines are for Rock 1; the circle symbols and dashed black lines are for Rock 2. Unfilled symbols are for drying at 20°C; filled symbol are for drying at 5°C. The blue solid line is the equilibrium relative humidity of Rock 1 during the drying process computed from the results in Fig. 5. The arrows indicate the times at which the relative humidity falls below 98 (19 h) and below 80% (68 h).
Pore size distribution and water retention in colonized Antarctic Beacon sandstone
  • Article
  • Full-text available

November 2024

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18 Reads

Antarctic Science

We report on the pore size distribution and water retention of Beacon sandstone from Antarctica that harbours a cryptoendolithic community, predominantly lichens, just below the surface. We measured the pore size distribution, drying time and equilibrium relative humidity of sandstone samples that were colonized by lichens. The incremental pore volume distribution peaks at ~10 μm radius, but ~20% of the pore volume occurs for a radius < 0.02 μm. Water from snowmelt fills ~20% of the total pore volume. It takes ~4–5 days of evaporation to lose 90% of the water. As the rock loses water, the equilibrium relative humidity remains at 99% until an appreciable amount (80–90%) of the pore water is lost, after which the equilibrium relative humidity starts to decrease. The relative humidity remains at > 80% (68 h) long after the water content falls to < 98% (19 h) - the point at which liquid water is estimated no longer to be present. Lichens can remain active in air with high relative humidity (> 80%). Thus, the pore size distribution of the sandstone may play a role in explaining why lichens dominate these sandstones.

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Hypolith Distribution Within a Dewy Drainage Basin: Possible Link to Dew or Rather to Rain?

October 2024

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10 Reads

Ecohydrology

The water source of hypoliths is a matter of controversy, with some scholars advocating the role of nonrainfall water (NRW), principally dew or fog as the main water sources, while others maintain that it is rain. In the Negev Highlands, where lichens cover > 90% of the upper surfaces of cobblestones, hypoliths may also reside on the undersides of these cobblestones. In an attempt to evaluate the possible role of rain, dew and fog, the abundance, cover and chlorophyll content of the hypoliths on 10–20 cm × 5–10 cm cobblestones was measured at five slope locations at the hilltop (HT) and the upper parts of the north‐facing (NF), south‐facing (SF), east‐facing (EF) and west‐facing (WF) slopes, which were characterised by contrasting abiotic conditions. Within each slope location, 50 and 10 cobblestones were randomly, respectively, collected to evaluate the abundance and cover and to measure their chlorophyll content. In addition, field measurements were conducted to evaluate the ability of rain, dew and fog to wet the hypoliths. Our results indicate that (a) hypoliths were confined to cobblestones lying loosely on the ground; (b) while similar chlorophyll content characterised patches with hypoliths at all slope locations, their abundance and cover were the highest at NF and WF, followed by HT, with SF and EF exhibiting the lowest values; (c) our measurements did not show direct wetting by dew, fog or rain. We therefore suggest that distillation may be the main source of water. Our suggestion implies that a reduction in rain, but even more importantly, elevated nocturnal temperatures during the rainy period, may have a great negative effect on the hypolithic population.


Vapor flux induced by temperature gradient is responsible for providing liquid water to hypoliths

October 2024

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67 Reads

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1 Citation

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Rafael Kronenfeld

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[...]

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Dani Or

Commonly comprised of cyanobacteria, algae, bacteria and fungi, hypolithic communities inhabit the underside of cobblestones and pebbles in diverse desert biomes. Notwithstanding their abundance and widespread geographic distribution and their growth in the driest regions on Earth, the source of water supporting these communities remains puzzling. Adding to the puzzle is the presence of cyanobacteria that require liquid water for net photosynthesis. Here we report results from six-year monitoring in the Negev Desert (with average annual precipitation of ~ 90 mm) during which periodical measurements of the water content of cobblestone undersides were carried out. We show that while no effective wetting took place following direct rain, dew or fog, high vapor flux, induced by a sharp temperature gradient, took place from the wet subsurface soil after rain, resulting in wet-dry cycles and wetting of the cobblestone undersides. Up to 12 wet-dry cycles were recorded following a single rain event, which resulted in vapor condensation on the undersides of the cobblestones, with the daily wet phase lasting for several hours during daylight. This ‘concealed mechanism’ expands the distribution of photoautotrophic organisms into hostile regions where the abiotic conditions limit their growth, and provides the driving force for important evolutionary processes not yet fully explored.


Temperatures and treeline elevation in the Sierra Nevada de Mérida of the Venezuelan

September 2024

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27 Reads

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2 Citations

We report here on two extensive data sets across the tree line in the Sierra Nevada de Mérida in the Venezuelan Andes. First, we describe the tree distribution with elevation at this site. Second, we report on several years of temperature data beginning in 2001 for the soil surface, 10, 20, and 40 cm depth from 2,000 to 4,978 m elevation. The tree line at this site is dominated by Polylepis and is located near 4,100 m. At the tree line, the annual mean temperature at 10 cm depth was 6.66°C with an annual maximum temperature of 13°C and an annual minimum temperature of 1.4°C; the lowest maximum temperature for any day of the year was 6°C, so though there is not continuous growth, every day of the year the temperature gets high enough that some growth is possible. The mean annual air temperature was 6.4°C. The topographic lapse rate across the tree line is 5.7°C/km for all depths. Below 3,500 to 2,500 m elevation in the cloud forest zone the topographic rate decreases to 0.9°C/km. Our results are consistent with the emerging model of temperature correlation with the elevation of tree line. Temperature archive data set identifier: https://zenodo.org/records/12628498. ARTICLE HISTORY


Site map of Death Valley. The Furnace Creek site is the small patch of green as indicated. The Badwater site is on the edge of the salt flat. The Black Mountains and the Panamint range are indicated. Base image is from Copernicus Sentinel‐2 LA2, taken 27 April 2024 and processed with EO Browser.
Temperature throughout the day on 17 July 1998 which included the highest temperature measured that summer. Blue solid lines are the maximum and average from the Badwater aspirated RTD temperature sensor. The red dotted lines are the maximum and average from the Badwater passively shielded 207 thermistor sensor. Temperature averaged over 30‐minute intervals (lower lines) and the maximum temperature of instantaneous samples every minute (upper lines) are shown. The peak temperature was 53.6 ± 0.1°C recorded at 15:44 local standard time. Winds were light (less than 4 m/s) and blowing towards the west (220–320°) during the afternoon.
Scatter plot comparison of the temperature averaged over 30‐min intervals for the Badwater 207 thermistor versus the Badwater RTG temperature sensor for the months of July, August and September in 1998. The upper and lower reference lines indicate the linear regression (equivalent to y = x + 1) and 1:1 values, respectively.
Correlation between maximum and minimum temperatures for Furnace Creek, Death Valley and from the station at Badwater, Death Valley, over the period of April 1998 to September 2000. Panel a shows that the maximum temperatures are in good agreement for summertime high temperatures while the Badwater Station is about 1°C cooler for wintertime temperatures. Panel b shows the minimum temperatures at the Badwater site are about 2–3°C warmer than at the Furnace Creek.
Meteorological data from Badwater, Death Valley National Park 1998 to 2019

We installed a meteorological recording system at Badwater (elev. −75 m), the lowest point in Death Valley, California and recorded data over the period 1998–2019. A second station (the Outhouse Station) was established nearby from 2014 to 2019. Here, we report on and publicly archive the data from these two stations. Of interest was the comparison between two air temperature measurements at the Badwater Station, the first with an aspirated platinum resistance temperature device and the second with a thermistor probe in a passive sun shield. During the hottest periods of the summer when temperatures were typically between 30°C at night and 50°C daily peak, the passively shielded sensor indicated up to 0.5°C warmer than the aspirated temperature sensor due to radiative effects. The data suggest a correction for radiative heating of (T–35)/30, for T > 35°C, where, T, is the uncorrected temperature reading of a passively shielded sensor subtracted after any calibration at lower temperatures. Our station was the first precision temperature measurements at Badwater. A longer record exists for the reporting station near the visitor's centre at the Furnace Creek. The summer temperature maxima at the Badwater site correlate well with the values the same day from the Furnace Creek site. The daily maximum temperatures in winter at the Badwater site appear to be about 1°C lower than at the Furnace Creek site. The largest differences are in the minimum temperatures for which the Badwater site averages about 2–3°C warmer than the Furnace Creek site.


Active microbiota persist in dry permafrost and active layer from Elephant Head, Antarctica

January 2024

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107 Reads

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4 Citations

ISME Communications

Dry permafrost is a challenging environment for microbial life due to the cold, dry, and often oligotrophic conditions. In 2016, Elephant Head, Antarctica was confirmed as the second site on Earth to contain dry permafrost. It is geographically distinct from the McMurdo Dry Valleys where dry permafrost has been studied previously. Here we present the first study of the microbial activity, diversity, and functional potential of Elephant Head dry permafrost. Microbial activity was measured using radiorespiration assays with radiolabelled acetate as a carbon source at 5, 0 and − 5°C. Low, but detectable, rates of microbial activity were measured in some samples at 0 and − 5°C. This is distinct from previous studies of McMurdo Dry Valley dry permafrost which concluded that dry permafrost represents a cold-arid limit to life on the planet. The isolation of cold adapted organisms from these soils, including one capable of sub-zero growth further supports that Elephant Head dry active layer and dry permafrost harbor viable microbial life which may be active in situ. Metagenomic, 16S rRNA gene and ITS and amplicon sequencing identified similar microbial communities to other Antarctic and cold environments. The Elephant Head microbial community appears adapted for survival in cold, dry, and oligotrophic conditions based on the presence of cold adaptation and stress response genes in the metagenomes. Together our results show that dry permafrost environments do not exclude active microbial life at sub-zero temperatures and suggests that the cold, dry soils of Mars may also not be as inhospitable as previously thought.


In Situ Real-Time Monitoring for Aseptic Drilling: Lessons Learned from the Atacama Rover Astrobiology Drilling Studies Contamination Control Strategy and Implementation and Application to the Icebreaker Mars Life Detection Mission

December 2023

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51 Reads

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3 Citations

Astrobiology

In 2019, the Atacama Rover Astrobiology Drilling Studies (ARADS) project field-tested an autonomous rover-mounted robotic drill prototype for a 6-Sol life detection mission to Mars (Icebreaker). ARADS drilled Mars-like materials in the Atacama Desert (Chile), one of the most life-diminished regions on Earth, where mitigating contamination transfer into life-detection instruments becomes critical. Our Contamination Control Strategy and Implementation (CCSI) for the Sample Handling and Transfer System (SHTS) hardware (drill, scoop and funnels) included out-of-simulation protocol testing (out-of-sim) for hardware decontamination and verification during the 6-Sol simulation (in-sim). The most effective five-step decontamination combined safer-to-use sterilants (3%_hydrogen-peroxide-activated 5%_sodium-hypochlorite), and in situ real-time verification by adenosine triphosphate (ATP) and Signs of Life Detector (SOLID) Fluorescence Immunoassay for characterization hardware bioburden and airborne contaminants. The 20- to 40-min protocol enabled a 4-log bioburden reduction down to <0.1 fmoles ATP detection limit (funnels and drill) to 0.2-0.7 fmoles (scoop) of total ATP. The (post-cleaning) hardware background was 0.3 to 1-2 attomoles ATP/cm2 (cleanliness benchmark background values) equivalent to ca. 1-10 colony forming unit (CFU)/cm2. Further, 60-100% of the in-sim hardware background was ≤3-4 bacterial cells/cm2, the threshold limit for Class <7 aseptic operations. Across the six Sols, the flux of airborne contaminants to the drill sites was ∼5 and ∼22 amoles ATP/(cm2·day), accounting for an unexpectedly high Fluorescence Intensity (FI) signal (FI: ∼6000) against aquatic cyanobacteria, but negligible anthropogenic contribution. The SOLID immunoassay also detected microorganisms from multiple habitats across the Atacama Desert (anoxic, alkaline/acidic microenvironments in halite fields, playas, and alluvial fans) in both airborne and post-cleaning hardware background. Finally, the hardware ATP background was 40-250 times lower than the ATP in cores. Similarly, the FI peaks (FImax) against the microbial taxa and molecular biomarkers detected in the post-cleaned hardware (FI: ∼1500-1600) were 5-10 times lower than biomarkers in drilled sediments, excluding significant interference with putative biomarker found in cores. Similar protocols enable the acquisition of contamination-free materials for ultra-sensitive instruments analysis and the integrity of scientific results. Their application can augment our scientific knowledge of the distribution of cryptic life on Mars-like grounds and support life-detection robotic and human-operated missions to Mars.




Citations (71)


... In this sense, it has been postulated that greater proportions of the families of Sphingomonadaceae and Chitinophagaceae can be found in both the early stages of deglaciation and in older moraines [22,65]. Members of Sphingomonadaceae and Chitinophagaceae family are also present in ice-free soils and dry permafrost from different Antarctic regions [66,67]. Representatives of the Chitinophagaceae family, with relative abundance ranging from 2.9% to 17.5%, were detected in the three types of soils; this group includes chemoheterotrophic bacteria able to degrade chitin and other soil organic compounds [68,69]. ...

Reference:

Microbial Communities in Permafrost, Moraine and Deschampsia antarctica Rhizosphere Soils near Ecology Glacier (King George Island, Maritime Antarctic)
Active microbiota persist in dry permafrost and active layer from Elephant Head, Antarctica

ISME Communications

... Given the sensitivities of both a simulation running on prototypes and brassboard equipment (requiring out-ofsimulation replenishment, servicing, and maintenance by field staff) and looking for local biosignatures and extant Atacama organisms (while minimizing and controlling external cross-contamination), a mission simulation contamination control plan was developed in early 2019 and was tested/calibrated in dry-runs beforehand. Details are discussed in the work of Bonaccorsi et al. (2023). The in-situ real-time adenosine triphosphate (ATP) luminometric assay (invisible to the simulation) was used to monitor the efficiency of the cleaning/microbial reduction protocols and for bioburden monitoring of the ARADS hardware during the simulation. ...

In Situ Real-Time Monitoring for Aseptic Drilling: Lessons Learned from the Atacama Rover Astrobiology Drilling Studies Contamination Control Strategy and Implementation and Application to the Icebreaker Mars Life Detection Mission
  • Citing Article
  • December 2023

Astrobiology

... It holds promise as a key biosignature in the search for life on Mars, as substantial salt stresses is to be expected in Martian environments. While it may be challenging to encounter liquid water in the near-surface environment that is accessible to a landed spacecraft (i.e., the upper 2 m of Martian surface) [68], there are likely still near-surface environments, even in hyperarid regions, where liquid water exists. Potential habitats include (1) (meta)stable brines [16] (however, these brines would only exist at very low temperatures and for short durations when high humidity permits brine formation, presenting significant challenges for life), (2) deliquescent environments in NaCl-rich salt rocks, especially in Mars' Southern Highlands [23], and (3) topographically low locations, such as at the bottom of Valles Marineris (or inside caves), where atmospheric pressures may be sufficient to support liquid (salty) water [69]. ...

The habitability conditions of possible Mars landing sites for life exploration
  • Citing Article
  • October 2023

Icarus

... Moreover, such alternative life forms might not be detectable through biomolecule-based biosignatures but would depend on agnostic biosignatures [86]. Examples of such "bio"signatures are unique molecular frequency patterns that are different from their abiotic chemical space [85], higher enantiomeric excess of compounds, or even the signs of catalytic activities [93]. ...

Organic Catalytic Activity as a Method for Agnostic Life Detection

Astrobiology

... As for the inclined north-facing bedrocks, while Kidron et al. Science of the Total Environment xxx (xxxx) 168753 receiving only moderate amounts of dew, dew duration there lasts for long (Kidron et al., 2011(Kidron et al., , 2023. Strips and patches (several meter wide) of loessial soil and large (up to dozens of meter wide) of colluvial-alluvial loessial soil cover the spaces in between the rocks at the slopes and at the footslopes, respectively. ...

The effect of the water source on niche partioning of chlorolichens and cyanobacteria—implications for resilience?

Planta

... This phenomenon has been observed in previous literatures, which likely affects the FEAST source apportionment results. 55,56 Therefore, the associations between the CR microbiome and indoor environmental, human microbiome were estimated with the OTUbased taxonomic data. The potential contribution of environmental and human samples to cockroaches was evaluated by assuming the cockroach was a sink and others as sources. ...

Contribution of soil bacteria to the atmosphere across biomes

The Science of The Total Environment

... Mars analog research has a rich literature describing arid, low a w deserts such as the Atacama Desert in Chile (Azua-Bustos et al., 2023;Connon et al., 2007;DiRuggiero et al., 2013;Finstad et al., 2017;Kobayashi et al., 2022;Navarro-González et al., 2003;Robinson et al., 2015;Skelley et al., 2007;Warren-Rhodes et al., 2007) and the McMurdo Dry Valleys of Antarctica (Archer et al., 2017;Mikucki et al., 2015;Murray et al., 2012). Concurrently, microbiology research in aqueous low a w environments has been active for over four decades (Anati, 1999;Berard et al., 2013;Buffo et al., 2022;Edgcomb and Bernhard, 2013;Emerson et al., 2013;Magnuson et al., 2022;Des Marais, 1995;Pachiadaki et al., 2014;Pérez and Chebude, 2017;Pontefract et al., 2017;Samarkin et al., 2010;Shokes et al., 1977;Tuovila et al., 1987). ...

Biomarkers in the Atacama Desert along the moisture gradient and the depth in the hyperarid zone: Phosphatase activity as trace of microbial activity

International Journal of Astrobiology

... Desert ecosystem, characterized by its arid conditions and scarce availability of water, represents a quintessential example of a fragile ecosystem, often exhibiting a significantly diminished level of biodiversity owing to the harsh and inhospitable nature of its surroundings (Whitford and Duval 2020;Rocha et al. 2021;Warren-Rhodes et al. 2022). Badain Jaran Desert is a typical desert in Northwest China, where several desert plant species and large animals such as camels survived since ancient times (Wang and Zhou 2018;Li et al. 2020;Lu et al. 2023). ...

Insights of Extreme Desert Ecology to the Habitats and Habitability of Mars
  • Citing Chapter
  • July 2022