MARS-LIKE SOILS IN THE DRIEST CORE OF THE ATACAMA DESERT IN NORTHEN CHILE: THE YUNGAY AREA. R. Navarro-González1 and C.P. McKay2, 1Laboratorio de Laboratorio de Química de Plasmas y Estudios Planetarios, Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Apartado Postal 70-543, México D.F. 04510, MEXICO (navarro@nucleares.unam.mx), 2Space Science Division, NASA Ames Research Center, Moffett Field, CA 94035 (chris.mckay@nasa.gov). Introduction: The next set of missions (MSL 2011, Mars 2018 and ExoMars 2018) seeks to understand whether life ever arose on Mars by detecting the chemical building blocks of life (e.g., organic compounds containing the elements CHONSP) in the soil. Because organic compounds are thermally labile, a simple tool for their analysis is the thermal volatilization (TV) method, which consists of heating the soil in an oven to temperatures ranging from 200ºC to 500 ºC or greater up to 1000ºC in order to vaporize small molecules and break down larger ones into smaller organic molecules, and the resultant organic fragments are then detected by mass spectrometry (MS) [1, 2]. This thermal volatilization process has been the method of choice in past space missions starting with Viking [3], the two ill-fated missions (Mars Polar Lander [4] and Beagle 2 [5]), and Phoenix [6], as well as in future missions: MSL 2011 [7] and ExoMars 2018 [8]. The Viking mission detected water at 0.1–1.0 wt% with traces of chloromethane at 15 ppb, at Viking landing site 1, and water at 0.05–1.0 wt% and carbon dioxide at 50–700 ppm, with traces of dichloromethane at 0.04–40 ppb at Viking landing site 2 [3]. However, these chlorohydrocarbons were considered to be terrestrial contaminants, although they were not detected in the blank runs [3]. The Phoenix Lander did not find organics in the soil [6]. Surprisingly, magnesium perchlorate, a thermodynamically unstable but kinetically stable chemical salt was discovered in the Martian Arctic soil by the Phoenix Lander [9]. With the use of terrestrial Mars analogs, it has been possible to realize important limitations in the search of organics on Mars using the TV method. The successful detection of organics depends not only on the sensitivity of the MS, as generally alleged [10], but also that organics are not refractory (e.g., thermally stable) at the temperature regime investigated [1, 11] or that are not combusted to carbon dioxide in the oven by oxidants (e.g., peroxides, superoxides, perchlorates) present in the soil matrix [1, 2, 12-14]. The arid core region of the Atacama Desert in Yungay has played a key role in understanding the Viking and Phoenix results. Yungay contains Mars-like soils in the surface that have no culturable bacteria (<102 colony-forming units per gram), low levels of extractable DNA, and low organic concentrations (20–40 ppm C) that become detectable at temperature regimes greater than investigated by the Viking mission, and the presence of a non-chirally specific oxidant that consumes organics in aqueous solution [11]. The valley of Yungay contained among the largest deposits of nitrates and perchlorates on Earth, which were mined at the start of last century [15]. However, if Yungay soils are spiked with magnesium perchlorate and treated using the Viking protocol, the low level organics are combusted in the oven but surprisingly a trace amount is quenched in the form of chlorohydrocarbons, namely chloro and dichloromethane [14]. Reinterpretation of the Viking results suggests, therefore, the presence of perchlorates at ≤0.1% and organics at ppm levels at mid-latitudes on Mars [14].

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Mission Description: The next set of missions will try to answer the question of whether life ever rose on Mars by searching for the building blocks of life in the soil using the TV method. The Atacama Desert is probably the driest place on Earth, where hyperaridity has persisted for more than 10-15 Myrs [15]. Mars likely became hyperarid after 3.5 Gyr ago [16]. Therefore, if the instruments to be sent to Mars are not able to detect organics in the Yungay soil from past life, it implies that they are not ready for exploring Mars. Science Merit Related to Mission Objectives: The Yungay soil in the Atacama Desert contains the lowest levels of organics in the form of refractory molecules, no culturable bacteria, low levels of extractable DNA, and the presence of non-chirally specific oxidants. Consequently, this is the most barren site on Earth resembling Mars. Satellite imagery datasets of this site are available commercially or non-commercially. Most Important Question Answered by Site: Did life ever arise on Mars? Logistic and Environmental Constraints: Our main work location is the University of Antofagasta Desert Research Station and is located about 1 hour out of Antofagasta, south on Route 5. GPS coordinates of the station are 24º 04' 50.5" S and 69º 55' 11.1" W. The site is readily accessible by car: from Antofogasta, take route 26 east until it merges into highway 5; turn right on Route 5 and go South for about 30 km. There will be a small shack on the left side of the road and a dirt road off to the left. The sign for this road is Socompo. Turn left off Route 5 and continue for 25 km until just past a water pumping plant. There will be a fork in the road with the main road turning right and an old paved road continuing straight. The station is at this junction on the right. The location is a temperate desert that is easily accessible at any time of the year (see Table 1 and Figure1). Table 1: Characteristics of the Mars Analog Site. Site Name Yungay, Atacama Desert Center Coordinates 24° S, 69.9° W Elevation 1.1 km Areal Extent 10 km by 10 km Prime Science Questions What is the chemical nature of refractory

organics and oxidants in the soil?; What is the age of organics? What is the mechanism of destruction of organics in the soil?

Distance of Science Targets from nearest road or airstrip

Less than 25 km

Environmental characteristics Average temp: 16.5ºC; Max temp: 37.5ºC; Min temp: -5.7ºC; Precipitation: <1 mm Vegetation coverage: None

Previous studies at analogue site [1, 11, 14] Primary Landing Site Target e.g., Any site on Mars

6005.pdfAnalogue Sites for Mars Missions (2011)

0.0 0.5 1.0 1.5 2.0 2.5 3.03.5 4.04.55.05.56.0

Longitude ( oW )

71.5 70.0 68.5

28

26

24

Height (km)

69.90 69.87

24.09

24.06

0.95 1.05 1.15 1.25

Height (km)

Lat

itud

e (

o S )

Paci

fic

Oce

an

ChileArgentina

Figure 1. Digital elevation map of the Atacama Desert in Northern Chile at 30 minute resolution showing the historic nitrate mining sites (black counter lines) and a zoom in of the Yungay Area [16]. References: [1] Navarro-González R. et al. (2006) PNAS, 103, 16089-16094. [2] Navarro-González R. et al (2009) Astrobiology, 9, 703-715. [3] Biemann K. et al. (1977) JGR, 82, 4641–4658. [4] Boynton W.V. et al. (2001) JGR,106,17683–17698. [5] Wright I.P. et al (2003) Acta Astronaut., 52, 219–225. [6] Boynton W.V. et al. (2009) Science, 325, 61–64. [7] Mahaffy P. (2008) Space Sci. Rev., 135, 255-268. [8] Cotter R.J. et al (2010) Eur. J. Mass Spectrom., 16, 331-340. [9] Hecht M. H. et al. (2009) Science, 32, 64–67. [10] Biemann K. (2007) PNAS, 104, 10310-10313. [11] Navarro‐González R. et al. (2003), Science, 302, 1018–1021. [12] Valdivia-Silva J.E. et al (2009) Adv. Space Res., 44, 254–266. [13] Iñiguez E. et al (2009) GRL, 36, L21205. [14] Navarro-González R. (2010) JGR, 115, E12010. [15] Ericksen G.E. (1983) Am. Sci., 71, 366–374. [16] McKay C.P. (1998) Gravit. Space Biol. Bull., 11, 41-50. [16] This work was supported by grants from UNAM (DGAPA PAPIIT IN-109110 and DGAPA PAPIME PE103609), the National Council of Science and Technology of Mexico (CONACyT 98466), and the National Aeronautics and Space Administration ASTEP program.

6005.pdfAnalogue Sites for Mars Missions (2011)