Does Europa have a subsurface ocean? Evaluation of the geological evidence

Pappalardo, R. T.; Belton, M. J. S.; Breneman, H.; Carr, M. H.; Chapman, C. R.; Collins, G. C.; Denk, T.; Fagents, S. A.; Geissler, P. E.; Giese, B.; Greeley, R.; Greenberg, R.; Head, J. W.; Helfenstein, P.; Hoppa, G. V.; Kadel, S. D.; Klaasen, K. P.; Klemaszewski, J. E.; Magee, K. P.; McEwen, A. S.; Moore, John B.; Moore, W. B.; Neukum, G.; Phillips, C. B.; Prockter, L. M.; Schubert, G.; Senske, D. A.; Sullivan, Robert; Tufts, B. R.; Turtle, E. P.; Wagner, R. J.; Williams, K. K.

doi:10.1029/1998je000628

Cited by 376 publications

(282 citation statements)

References 121 publications

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“…Tidal model estimates for global ice crust thickness generally lie in the range 10 -30 km, consistent with several models of Europan tectonic expression from Galileo images (summarized in [Pappalardo et al, 1999]). Analysis of transitions in crater shape-diameter statistics for craters on Europa may suggest an ice crust thickness of >19 km [Schenk, 2002].…”

Section: Introductionmentioning

confidence: 55%

Persistence of thin ice regions in Europa's ice crust

Buck

Chyba

Goulet

et al. 2002

Geophysical Research Letters

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[1] Extensive data from planetary spacecraft as well as celestial mechanics models support the existence of a subsurface ocean on Europa $100 km thick, maintained by a tidal heat flux. Models in which the overlying ice crust is less than 20 km thick permit breaches in the ice due to impact events or thermal plumes from the tidally heated core. We apply a two-dimensional thermal model to the analysis of the refreezing of a hole in the ice crust following a breach event. Our model incorporates heat produced by tidal heating of Europa in two ways: a basal heat flux from Europa's silicate and iron core, together with volumetric heating of the ice shell. We compare our refreezing timescales to those obtained from a model where viscous flow in the base of the ice crust fills the hole. We find that catastrophic breaches in Europa's ice crust may produce regions of relatively thin ice persisting up to $1 My. These breaches are closed by viscous flow when radii are small (<10-50 km) and by conductive refreezing for larger radii, especially if Europa's crust has a high basal heat flow due to a hot core. Detection of the ice/ocean interface by orbital detection of the temperature anomalies or radar sounding would be most probable in the vicinity of these events.

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Section: Introductionmentioning

confidence: 55%

Persistence of thin ice regions in Europa's ice crust

Buck

Chyba

Goulet

et al. 2002

Geophysical Research Letters

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“…Both present relatively hostile environments for mesophilic terrestrial life, but both seem capable of supporting liquid water, which is generally regarded as a prerequisite for life. In Europa's case, water, if present, resides under a thick ice cap, heated by the dissipation of tidal forces (Reynolds et al 1987;Pappalardo et al 1999). Mars, however, may be capable of maintaining liquid water on or near the surface.…”

Section: Introductionmentioning

confidence: 99%

Terrestrial models for extraterrestrial life: methanogens and halophiles at Martian temperatures

Reid¹,

Sparks²,

Lubow³

et al. 2006

International Journal of Astrobiology

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: Cold environments are common throughout the Galaxy. We are conducting a series of experiments designed to probe the low-temperature limits for growth in selected methanogenic and halophilic Archaea. This paper presents initial results for two mesophiles, a methanogen, Methanosarcina acetivorans, and a halophile, Halobacterium sp. NRC-1, and for two Antarctic coldadapted Archaea, a methanogen, Methanococcoides burtonii, and a halophile, Halorubrum lacusprofundi. Neither mesophile is active at temperatures below 5 xC, but both cold-adapted microorganisms show significant growth at sub-zero temperatures (x2 xC and x1 xC, respectively), extending previous lowtemperature limits for both species by 4-5 xC. At low temperatures, both H. lacusprofundi and M. burtonii form multicellular aggregates, which appear to be embedded in extracellular polymeric substances. This is the first detection of this phenomenon in Antarctic species of Archaea at cold temperatures. The low-temperature limits for both psychrophilic species fall within the temperature range experienced on present-day Mars and could permit survival and growth, particularly in subsurface environments. We also discuss the results of our experiments in the context of known exoplanet systems, several of which include planets that intersect the Habitable Zone. In most cases, those planets follow orbits with significant eccentricity, leading to substantial temperature excursions. However, a handful of the known gas giant exoplanets could potentially harbour habitable terrestrial moons.

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“…A primary result of the Galileo orbiter mission has been the discovery of morphological evidence suggesting but not proving the existence of an aqueous layer beneath an icy H20 crust [Pappalardo et al, 1999] Finally, coregistration of high spectral resolution images from SSI and false color maps showing distribution of spectral features incompatible with H20 ice demonstrated a nearperfect spatial correlation between the "non-H20 ice" material and tectonic or impact induced breaches in the solid H20 [Fanale et al, 1999[Fanale et al, , 2000. Thus it has been assumed that if the mineralogy of the non-H20 ice material could be deciphered, the chemical composition of the aqueous phase could be established.…”

Section: Introductionmentioning

confidence: 99%

An experimental estimate of Europa's “ocean” composition independent of Galileo orbital remote sensing

Fanale¹,

Li²,

Carlo³

et al. 2001

J. Geophys. Res.

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Abstract. We have conducted a series of experiments designed to simulate, in the laboratory, the development of any subsurface aqueous phase on Europa. In our theoretical-experimental approach we select a single natural sample (a CM meteorite) that based on cosmochemical considerations, we consider to approximately represent the bulk material that accreted to form Europa. We then subject the sample to a hot water leaching procedure designed to simulate low-to moderate-temperature aqueous alteration. The resulting leach solution was then subjected to a series of sequential fractional crystallization steps producing a series of ices and residual brines. Then all this brines and ices are multiply analyzed for Na, Ca, Mg, Sr, Ba, Fe, Mn, K, CI, and SO4. Results were found to be remarkably consistent between brines and ices in the same stages of crystallization and also between stages. We found that any putative aqueous phase below Europa's ice crust is probably a brine with cations: Na -Mg > Ca, K> Fe and anions: SO4 >>C1. Our results are in harmony with inferences drawn from one of the two main current interpretations of the orbital spectral data but cannot definitively rule out inferences drawn from the alternative interpretation. This is so because the mineralogy of the top 200/xm may not reflect the chemical composition of bodies of brine below the solid surface owing to extensive alteration caused by magnetospheric bombardment.

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Does Europa have a subsurface ocean? Evaluation of the geological evidence

Cited by 376 publications

References 121 publications

Persistence of thin ice regions in Europa's ice crust

Persistence of thin ice regions in Europa's ice crust

Terrestrial models for extraterrestrial life: methanogens and halophiles at Martian temperatures

An experimental estimate of Europa's “ocean” composition independent of Galileo orbital remote sensing

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