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Advances in Space Research 48 (2011) 689–696

Analog environments for a Europa lander mission

Ralph D. Lorenz a,*, Damhnait Gleeson b, Olga Prieto-Ballesteros c, Felipe Gomez c,Kevin Hand d, Sergey Bulat e

a JHU Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USAb Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA

c Centro de Astrobiologia (INTA-CSIC), Torrejon de Ardoz, 28850, Madrid, Spaind Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USAe Petersburg Nuclear Physics Institute, 188300, St. Petersburg-Gatchina, Russia

Received 25 January 2010; received in revised form 1 May 2010; accepted 5 May 2010Available online 11 May 2010

Abstract

This paper reviews the utility of analog environments in preparations for a Europa lander mission. Such analogs are useful in thedemonstration and rehearsal of engineering functions such as sample acquisition from an icy surface, as well as in the exercise of thescientific protocols needed to identify organic, inorganic and possible biological impurities in ice. Particular attention is drawn to Ant-arctic and Arctic analog sites where progress in these latter areas has been significant in recent years.� 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.

Keywords: Europa; Ice; Astrobiology; Analog field studies; Antarctica

1. Introduction

The scientific success of a Europa lander mission willdepend on the safe delivery of instrumentation and its sup-port equipment to the surface of Europa, followed by theoperation of that instrumentation in, and its interactionwith, the Europa environment. That environment is notcompletely known, and while some major features can beanticipated and reproduced, e.g. in large space simulationchambers, experience shows that much additional insightcan be gained from real-world analog environments. Thisis particularly the case for the rehearsal of scientific inves-tigations which by definition may encounter unanticipatedeffects. The utility of analog environments for space explo-ration in general (notably human exploration) is well-doc-umented: for example, some of the logistical andenvironmental analogies that make Antarctica a useful

0273-1177/$36.00 � 2010 COSPAR. Published by Elsevier Ltd. All rights rese

doi:10.1016/j.asr.2010.05.006

* Corresponding author. Tel.: +1 443 778 2903; fax: +1 443 778 8939.E-mail address: Ralph.lorenz@jhuapl.edu (R.D. Lorenz).

analog for space exploration in the broader sense are dis-cussed by Ardanuy et al. (2005).

A Europa lander will likely perform a variety of scien-tific investigations (see the companion paper by Korablevet al. (2011); see also Balint, 2004), some familiar (suchas survey by panoramic cameras and spectrometers andthe acquisition of surface materials for analysis on-board),some not. These more novel investigations might includegeophysical instrumentation such as seismometers, as wellas sample analysis with a particular emphasis on astrobiol-ogy. The autonomous emplacement of geophysical instru-mentation on an ice surface is a challenge that wouldbenefit from field rehearsal. More important, perhaps, arethe astrobiological sample analysis techniques and contam-ination avoidance protocols (which may have many simi-larities with those which may be necessary at Mars)wherein the avoidance of false positive results is crucial.

While (as we discuss later) our moon, or some of thesmall bodies of the solar system, may be more useful engi-neering analog environments, scientifically the explorationof Mars has some particular lessons. Specifically, the

rved.

690 R.D. Lorenz et al. / Advances in Space Research 48 (2011) 689–696

astrobiological measurements of the Viking landers in 1976are now reasonably understood, but at the time were con-fusing owing to the unexpected oxidant activity in the soil(mimicking metabolism) whereas mass spectrometry indi-cated that organic compounds were not detectably present.Since astrobiology is a key aspect of Europa’s interest as ascientific target, it is important that the scientific measure-ments to look e.g. for biomarkers be understood wellenough for an unambiguous result to be obtained.

A second lesson comes from the recent Phoenix lander,where it was found that soil samples were difficult to ingestinto an instrument because they were unexpectedly cloddyor sticky, this mission landing at high northern latitudeswhere soil moisture was evidently higher than at otherregions of the planet that have been investigated in situ.Exposure of instrumentation – and the scientists directingit – to as wide a variety of possible environments as possi-ble can help to avoid unintended effects like this.

We would contend that analog environment testing ful-fils another important function – that of providing a visualstimulus for the wider community. Many space endeavoursare rather abstract, yet the image of a vehicle in even animperfect analog environment is a powerful motivator (wit-ness, e.g. the sandboxes in which Mars rover operations arerehearsed by operators, and are replicated in miniatureworldwide in schools and robotics clubs). Similarly,accounts with photographs of scientific exploration (andhuman investigators) e.g. in polar regions make planetaryscience a much more tangible and appealing enterprise.The outreach, education and public relations utility ofthese aspects should not be underestimated.

In this paper, we review several areas of Europa terres-trial analog research. First, we consider astrobiologicalanalog studies in general. We first discuss the Antarcticsubglacial Lake Vostok, widely recognized as probablythe most important terrestrial analog for Europa studiesand in particular the astrobiological investigation of theice core above the Lake. We also mention astrobiologicalstudies of saline Lake Tırez in Spain, whose waters mayhave some chemical similarities with the Europan subsur-face ocean. We then discuss a suite of research in springsat Borup Fiord Pass in the Canadian High Arctic wheresulfur minerals appear in a glacial context, providing ana-logs for remote sensing at Europa as well as a site formicrobial sulfur cycling in a plausibly Europan-like envi-ronment. Other studies in Arctic and mountain glacialenvironments are also described. Finally, we note the scien-tific and engineering experience relevant for Europa thatmay be derived from forthcoming missions to other solarsystem targets.

2. Analog research

Analog environments on Earth must be considered inthe context of how they can inform our search for life onother worlds, not just in how they map onto the con-

ditions we think may exist on such worlds. The deep sea

hydrothermal vents provide a useful example of this dis-tinction. The remarkable ecosystems of the hydrothermalvents provide a terrestrial ‘proof-of-concept’ that life canthrive in the dark depths of the ocean utilizing chemosyn-thesis as the base of the food chain. The broad extrapola-tion can then be made that were geologically activeseafloors to exist in the oceans of the moons of Jupiterand Saturn, then it might be possible for life to exist atanalogous site on those worlds.

But how does that comparison inform our search forsuch ecosystems? Certainly it is useful to consider thechemistry of such sites and how that might influence thebulk ocean chemistry, but ultimately the next few decadesof our search for life on icy worlds will be largely con-strained to surface and near-subsurface regions. Submers-ibles that can actively explore the depths of these alienoceans are a long way off. The icy surfaces of these moonswill serve as our window to the interior and our efforts tosearch for biosignatures should reflect this constraint. Ana-log environments on Earth that can inform our search forlife on the icy surfaces of these worlds improve our abilityto detect biosignatures and assist in mission and instrumentdesign.

While hydrothermal vent ecosystems may map onto theconditions thought to exist in the depths of worlds likeEuropa, the vent ecosystems on Earth have essentially noexpression or detectable signature on the surface of ourocean (Winn et al., 1986; Hand, 2009). Without a surfaceexpression – both for the case of Earth and Europan sys-tems – such ecosystems are not detectable from orbit orwith a lander investigating the near-subsurface. In the sec-tions that follow we explore several terrestrial analogs thatprovide some context for search capabilities that might beutilized either remotely or in situ on future missions.

2.1. Lake Vostok

Lake Vostok (Seigert et al., 2001) is a 240 � 50 kmLake, some 4 km beneath the surface of the East Antarcticice sheet. Inasmuch as the Europan ocean likely liesbeneath �15 km of ice (a recent summary of ice thicknessestimates for Europa is that by Billings and Kattenhorn(2005) – it should be noted that many of the thinner esti-mates relate to that thickness of ice which is brittle or elas-tic on some timescale, rather than the total thickness. Inparticular, thermal models and impact cratering morphol-ogies tend to suggest thicknesses in excess of several km),Vostok is a powerful analog – indeed, the radio echo-sounding (i.e. ice-penetrating radar) means by which theLake was discovered is expected to be a valuable techniqueat Europa.

The hydrostatic pressure at the base of the ice may berather similar on both worlds, given Europa’s lower grav-ity. However, whereas Europa’s ocean is some 100 kmthick, Vostok is only about 1.6 km at most. The ice sheetis likely 14 million or more years old, and thus Lake Vos-tok may have existed as an at least partly-isolated system

R.D. Lorenz et al. / Advances in Space Research 48 (2011) 689–696 691

for that time, although both the Lake waters themselves,and the ice presently lying above the Lake, are likely tobe much younger. It is estimated that the residence timeof water in the Lake is of the order of 80,000 years, whilethe ice above the Lake may have been precipitated fromthe atmosphere about 2 Myr ago at most.

These considerations highlight that the Lake is adynamic system, not merely a stagnant pool of water atthe base of a stagnant mass of ice. The geothermal heatflow at the base of the Lake is estimated at 42 mW/m2, per-haps not too different from values expected for Europa.Thermal convection may drive some circulation both onVostok and on Europa, although on Europa the gravita-tional tides are likely to play a much more significant role.In Vostok, as at other subglacial Lakes in hydrostatic equi-librium, the surface gradient that drives the flow of ice isassociated with a steeper, opposite gradient in the ice:waterinterface, such that the northern end of the Lake is at adepth of 4200 m, while the poleward end is at 3750 km.

An ice core (see Fig. 1) was obtained from the Vostokstation, reaching down to 3667 m depth, stopping about80 m above the Lake surface. While most of the columnbecame solid as snow in the atmosphere, accumulatingover the last 4 ice age cycles, the lowest 130 m of the core(and thus the lowest �210 m of the ice column) is ice frozenfrom the Lake. This basal ice therefore represents a frozensample of Lake Vostok.

An additional complication in the ice/water chemistry isthe presence of clathrates in the ice. In particular, oxygen-bearing gas clathrates may be involved in the introductionof oxygen into the Lake waters. Such high oxygen tensionmay be important in forbidding known permitting meta-bolic processes while permitting novel ones (similarly, thedelivery of radiolytic oxidants from the surface of Europato the Europan ocean may be vital in providing chemicaldisequilibrium to permit metabolism).

Fig. 1. A sample of Lake Vostok ice from nearly 4 km deep. The extreme clarimay be a good analog of a Europan ice sample.

The question of possible biota in Lake Vostok is a chal-lenging one. Priscu et al. (1999) identified a variety ofmicrobes at concentrations of several to tens of thousandsof cells per ml in the basal ice. They also detected dissolvedorganic carbon at levels (�0.5 mg/l) that could support het-erotrophic organisms. Bulat et al. (2004) detected the DNAsignature of only thermophilic bacteria in the ice. In a sep-arate study, Bulat et al. (2009) found instead that the ice isessentially germ-free.

It is possible that these discrepant results may be due toextreme heterogeneity in the biotic content of the ice sam-ples. In any case, to be sure of the results, it is clear thatextreme attention must be paid to stringent ice and tooldecontamination procedures to meet chemistry and traceDNA analysis standards, and to the certification of variousenvironments in contact with ice samples for biologicalcontent (including drill fluids, etc.)

The application of multiple avenues of investigation isan additional means to ensuring the robustness of lifedetection. For example, in addition to detecting the pres-ence of biological material (via detection of DNA via Poly-merase Chain Reaction or similar methods) it would bedesirable to verify the presence of an organism via somemetabolic influence on the environment (e.g. the localdepletion of some nutrient around the organism). For ter-restrial samples, it would be desirable to replicate analysesat an independent laboratory: for Europa this will ofcourse not be practical.

2.2. Tırez Lake and other hypersaline environments

While Vostok ice represents an end-member Europaanalog of rather pure water composition, non-ice compo-nent of Europa defines the other end-member, that of sul-fates. These non-ice materials, concentrated alonggeological features on the surface of Europa, can be

ty of the ice may be noted, although clasts of rock are present. Vostok ice

Fig. 2. Phylamentous algae (Zynemopsis gen.) from Tırez Lake, photo-synthetizers growing in high salt concentration liquid.

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distinguished from the ubiquitous background signature ofice in Galileo’s near infrared mapping spectrometer(NIMS) data on the basis of distorted water absorptionbands (Carlson et al., 1999; McCord et al., 1998, 1999).These authors cite heavily hydrated (n�H2O where n = 8–14) sulfur-bearing minerals as the closest spectral matchesfor these materials, with candidate minerals includinghydrated magnesium or sodium sulfates, hydrated sulfuricacid, or polymerized allotropes of sulfur. Laboratory spec-tra at temperatures relevant to Europa have improved thefit of spectral matches (Dalton, 2003; Dalton et al., 2005),and mixtures produced both experimentally (Orlandoet al., 2005), and by spectral modeling (Dalton, 2007),which incorporate both hydrated sulfuric acid and sulfatesalts have been proven to most closely approximate near-IR spectra.

These materials may be sourced endogenously fromEuropa’s subsurface ocean (Zolotov and Shock, 2001)and delivered to the surface by convective activity such asdiapiric upwelling within the ice shell (Pappalardo andBarr, 2004). This activity could produce localized zonesof water-rich plumbing (Greeley et al., 2004) or partial melt(Collins et al., 2000) within the ice. An alternative hypoth-esis proposes that these materials may be delivered to thesurface exogenously in the form of implanted sulfur ionsfrom Io’s volcanoes which subsequently become radiolyzed(Carlson et al., 1999). If internal processes extrude thesematerials, they may hold clues to the habitability of thesubsurface ocean and have the potential to contain biosig-natures (Kargel et al., 2000). Sites of recent activity aremost likely to prove fruitful in this regard (Figueredoet al., 2003).

Based on the comparison of its hydrogeochemistry withthe geochemical features of the alteration mineralogy ofmeteoritic precursors and with Galileo NIMS data, TırezLake (Spain) has been proposed as a terrestrial analog ofthe Europan ocean (Prieto-Ballesteros et al., 2003).Hydrogeochemical and mineralogical analyses showed thatTırez waters correspond to Mg–Na–SO4–Cl brines withepsomite, hexahydrite and halite as end mineral members.Frozen Tırez brines have been analyzed by Fourier Trans-form InfraRed (FTIR) spectroscopy, providing similarspectra to the Galileo spectral data. Calorimetric measure-ments of Tırez brines showed pathways and phase metasta-bility for magnesium sulfate and sodium chloridecrystallization which may aid in understanding the pro-cesses involved in the formation of Europa’s icy crust(see e.g. Zolotov and Shock, 2001). It may be noted thatDifferential Scanning Calorimetry (DSC) instruments suchas those used in the study of frozen Tırez brines have flownin space – specifically, the Thermal and Evolved Gas Ana-lyzer on the Mars Polar Lander and Phoenix missions.

Prokaryotic halophiles that can grow in waters with veryhigh salt concentrations have been reported in brines andhypersaline lagoons: some not only tolerate, but requirehigh salt concentrations to survive (2–4 M, equivalent to12–23% NaCl). Several examples of these organisms can

develop up to saturation (5.5 M salt, up to �32–37%). InTırez Lake two different microbial domains have beenfound: a photosynthetically sustained community repre-sented by planktonic/benthonic forms and microbial matcommunities, and a subsurficial anaerobic realm in whichchemolithotrophy predominates. As discussed in Prieto-Ballesteros et al. (2003), light microscopy with fluorescentstains, and fluorescent “in situ” hybridization to identifyspecific DNA sequences have been used for microbiologicalanalysis of this habitat. Photosynthetic prokaryotes andalgae belonging to the Chlorophyta (see Fig. 2) divisionwere located on the water column. This photosyntheticcommunity of primary producers is also exploited by someheterotrophic protists. Despite the obvious and major dif-ferences in physical conditions between Europa’s surfaceand Tırez Lake, the chemistry of the dissolved salts are auseful analog. Furthermore, the experience in microbialdetection via fluorescent techniques suggests that similartechniques might be applied at Europa.

2.3. Borup Fiord Pass supraglacial deposits

The supraglacial spring system of Borup Fiord Pass onEllesmere Island in the Canadian High Arctic representsthe first opportunity to investigate sulfur minerals in asso-ciation with ice in a terrestrial context, which as discussedabove represents the best chemical analog to the Europansurface. Alkaline spring waters high in sulfide and sulfateaccess the surface of the ice during the melt season eachyear, depositing elemental sulfur, gypsum and calciteacross the glacier and exsolving H2S (Grasby et al., 2003).

Anhydrite evaporites of the Otto Fiord Formation arethe only abundant source of sulfur in the area and o34Smeasurements indicate that sulfate-reducing bacteria areplaying a role in the reduction of the anhydrite to sulfide(Grasby et al., 2003). Sulfide in spring waters is subse-quently becoming incompletely reoxidized to sulfur whenspring waters come in contact with atmospheric oxygen

R.D. Lorenz et al. / Advances in Space Research 48 (2011) 689–696 693

and cultivation experiments have shown that microbialcommunities present in the deposits can mediate this reac-tion (Gleeson et al., submitted for publication). Microbialrates of sulfide oxidation typically outpace abiotic ratesby several orders of magnitude (Millero, 1986; Eary andSchramke, 1990; Kuhl and Jorgensen, 1992). Thus, the geo-chemical (and consequent spectral) signatures of materialsprecipitated at the surface plausibly provide evidence of theecosystem operating in and on the glacial ice.

Due to limited spectral libraries of candidate materialsand low spectral resolution of NIMS data (5–30 km), theexact nature of conditions on the surface of Europaremains uncertain. Borup Fiord Pass (see Fig. 3) providesan opportunity to investigate in a terrestrial environmenthow sulfur-on-ice mineralogy on the ground is reflectedin orbital data. Spectral features diagnostic of compositioncan be evaluated in a real-world setting by comparisonsbetween satellite coverage and field data, and potentialinterferences between candidate materials identified.Observations of the precipitation of mixtures in the fieldcan also provide new insights into mineral partitioningeffects, which can physically obscure certain components.

As any future investigation of Europa will have explor-atory elements, autonomous classification and changedetection techniques that minimize memory and processingrequirements and allow rapid response to unanticipatedevents would be useful. The sulfur signature of the springdeposits of Borup Fiord is extensive enough to be detectedand monitored from orbital satellite observations collectedby the hyperspectral Hyperion instrument aboard the EO-1satellite (Castano et al., 2008; Gleeson et al., in review), andautonomous collection of these data have been utilized toprovide temporal coverage of spring activity. Landing siteselection at Europa is likely to be carried out on the basisof tracking sites of recent activity on the surface on themoon and refining relevant techniques will increase datareturn.

Sulfur metabolisms (e.g. McCollom, 1999) can proceedin the absence of O2 and metabolic biosignatures generatedby these processes on Europa could become entrained inmobile ice and carried to the surface. On the other hand,

Fig. 3. Borup Fiord Pass minerals discolor the ice visibly in remote sensing dathe utility of analog studies at length scales spanning 9 orders of magnitude.

while life on Europa is likely to be oxidant-limited (e.g.Hand et al., 2007), oxidants can be formed by radiolysisin ice (Johnson and Quickenden, 1997).

Microbial sulfur cycling in cold environments has beenunderstudied to date and considerable work is required inthis area to determine what types of biosignatures are gen-erated under low temperature and nutrient limited condi-tions, where chemotrophic sulfur cycling is likely to bethe dominant metabolism. Borup Fiord Pass is the firstenvironment where microbial sulfur cycling on ice has beendescribed, and will inform future lander missions by iden-tifying a range of potential biosignatures relevant toEuropa.

2.4. Alpine (mountain glacier and snow) studies

While the identification of the faint or overlapping sig-natures of inorganic minerals via remote spectroscopycan be challenging (as the long debate on interpretationof Galileo NIMS spectra at Europa attest), certain biogenicorganic compounds are strongly photoactive. Indeed, theyare tuned through eons of selection to strongly absorb,reflect, and emit in very specific wavelength regions to per-form specific functions such as UV shielding (carotenoids),sensing (rhodopsins) and of course photosynthesis (chloro-phyll, phycocyanin etc.). Indeed, the spectral activity ofsuch compounds is such that photosynthesis might be con-sidered evolution’s gift to spectroscopists! It may be opti-mistic, but it must nonetheless be considered, that ifbiota is present in Europa, that it may contain such photo-active compounds.

The faint red blooms of the algae in the snowfields andglaciers of the Sierra Nevada Mountains in California serveas useful example of life in ice on Earth that is detectableusing remote spectroscopic techniques. The visible-wave-length signatures of carotenoids in the snow algae Chla-

mydomonas nivalis could be measured by NASA’sAirborne Visible and Infrared Spectrometer (AVIRIS,Painter et al., 2001). Specifically, a 5.5 km2 area wasimaged which had a concentration of 1300–1700 cells/ml,or a biomass density of 0.033 g/m2. Such ecosystems

ta, and have striking and unexpected microscopic textures. This highlights

694 R.D. Lorenz et al. / Advances in Space Research 48 (2011) 689–696

provide a baseline against which we can begin to addressthe challenges spectroscopists will face as we attempt toidentify signs of life from orbit on distant worlds.

Another aspect of snowpacks – especially for high-alti-tude equatorial sites – that should be noted is that photol-ysis in the upper layers can drive oxidant chemistry thatmay have significant parallels with radiolysis and photoly-sis in Europan ice. Specifically, OH radicals are produced,enhancing the oxidative capacity of the atmosphere – theseradicals can convert organic matter into carbonyl com-pounds and halides into halogens. Emissions of nitrogenoxides, nitrous acid, light aldehydes, acetone, and molecu-lar halogens have also been detected (Domine and Shep-son, 2002).

A related opportunity for analog studies pertains to per-mafrost regions such as Siberia and Alaska. In these areasmethane and other organic compounds may be releasedinto the atmosphere, particularly during the thaw season.Already it is possible for airborne and spaceborne spectros-copy to detect such emissions (and those from rice paddiesand other agricultural operations, as well as from marinemethane seeps). A new challenge, with application toEuropa, is how in situ measurements may be able to iden-tify the source (recent biogenic, or fossil, or abiogenic) ofsuch emissions.

3. Planetary environments

A variety of terrestrial environments (see Table 1) mightbe usefully used to test individual instruments or sampling

Table 1Planetary analog environments.

Environment Similarities with Europa DifferEurop

Subaerial saline Lakes Dissolved salts (Man

Arctic/Alpine Ice (and associated sulfurmineralogy, for Borup Fiord)

AtmoMuchtempeGraviShallo

Antarctica/Greenland ice sheetand subglacial Lakes

Ice AtmoHigheGravi

Moon Space environment (UV, vacuum,etc.) gravity similar

BulksilicatLargerange

Small bodies (Phobos/Deimos/Comet/ Asteroid)

Space environment (UV, vacuum,etc.) diurnal cycle

Low gBulklikelyLargerange

Mars polar cap Ice AtmoLow temperature GraviDiurnal cycle

mechanisms, or perhaps even a full-scale model Europalander. The difficulties of working in remote locations withmineral samples of varying consistencies cannot be overem-phasized, as has been recently illustrated by sampling diffi-culties encountered by the Phoenix mission to the MartianPole. Any instruments proposed for inclusion on a futurelander mission should be exhaustively field-tested under arange of relevant conditions. While Arctic/Antarctic/Alpine environments are not subject to the very low tem-peratures and harsh radiation environment of Europa, theysupply remote and challenging environments in their ownright, with some parallels to Europa’s icy surface. Forexample, air-dropped penetrators for seismometry havebeen tested in Antarctica (Matsushima et al., 2003), givingimportant experience for the application of similar vehicles– originally developed for lunar application – in other iceenvironments like Europa. It should be noted that instru-ment or sampling tests might also usefully employ materi-als from analog sites (such as the Borup Fiord deposits inSection 2.2) but could bring them to the laboratory andflash freeze and/or irradiate them to render them more use-ful still as testing materials for instruments.

In terms of planetary diameter and gravity, hard vac-uum and variable illumination, our own Moon has somesimilarities with Europa, and it is not inconceivable thatopportunities to evaluate sampling systems or other devicesat the moon might emerge in the next decade, in time forlessons learned to be applied for a Europa Lander mission.Generally, however, the surface composition of the moon isquite different. An exception is the possible presence of ice

ences witha

Comments (science/technical discipline addressed)

y) e.g. Tırez Lake.Mineralogical and microbial

sphere Principally microbial, some mineralogicalhigher

raturety higherw ice

sphere e.g. Lake Vostok.Technical (drilling etc.) as well as microbial andpossible mineralogical

r temperaturety higher

surface material ise

Plans for missions in the next decade

r temperature Landing systems, surface sampling in vacuum, gravity.Volatile behavior (lunar poles)

ravity Plans for missions in the next decade. Surface sampling,volatile behavior in vacuumsurface material

ice-poorr temperature

sphere Surface samplingty slightly higher

R.D. Lorenz et al. / Advances in Space Research 48 (2011) 689–696 695

deposits in permanently-shadowed areas of the moon.These locations may indeed be quite Europa-like. Issuessuch as photoelectric charging and the transport of dust(whose effects are not yet fully understood) may occur onthe moon, and might offer useful lessons for similar pro-cesses that could occur (but have not been considered) onEuropa.

Interaction of a spacecraft with a cometary surface isanticipated in 2014, when the ESA Rosetta mission arrivesat Comet 67P/Churyumov-Gerasimenko. The spacecraftwill deposit a small lander which will anchor itself with har-poons and deploy a self-hammering spike into the surface.The surface composition may or may not be Europa-like,depending on whether only sublimation lag is present orif substantial volatiles such as water ice dominate the sur-face. A key difference, of course, is the low cometary grav-ity which introduces complications that will not occur atEuropa (specifically, the reaction force on drills or similardevices). Asteroids and the moons Phobos and Deimosmight also be visited on a timescale relevant for Europalander preparations, however, these environments are lessuseful as Europa analogs than either the moon or a comet.

A final planetary environment of interest is Mars, and inparticular the polar caps. Although temperatures in winterand at night may approach those at Europa, the presenceof even the thin Martian atmosphere introduces convectiveheat transfer mechanisms are quite different from thepurely radiative setting at Europa. Another potential issuein the thin Martian atmosphere, especially for instrumenta-tion using high voltages, is the potential for electricalbreakdown.

4. Conclusions

A variety of research is underway in remote terrestriallocations which address the same types of biomarker detec-tion problem which is likely to be a cornerstone of landedEuropa science. No individual environment is a perfectanalog to Europa – either on Earth or on planetary bodieswhich we might expect to visit in coming years before aEuropa mission. However, the usefulness of analog studiesis principally to find the unexpected in the hope of beingbetter prepared for the unexpected at Europa. The utilityof analog studies for outreach and education is also noted.

Acknowledgements

This paper was prompted by discussions at the EuropaLander Workshop at IKI in Moscow, Russia in February2009. We thank the participants of that workshop for stim-ulating ideas. We thank the editors of the Special Issue fortheir patience.

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