Laboratory studies of the optical properties and stability of oxygen on Ganymede

Baragiola, R. A.; Bahr, D. A.

doi:10.1029/98je01634

Cited by 44 publications

(34 citation statements)

References 61 publications

(39 reference statements)

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“…Instead, they are redeposited and trapped in the surface ice in colder regions. The presence of molecular oxygen in the solid phase on the surface of Europa is itself a puzzle (Baragiola and Bahr, 1998;. Recently, Hand et al (2006) argued that mixed clathrates of O 2 -CO 2 -SO 2 could solve the trapping problem.…”

Section: Discussionmentioning

confidence: 99%

Energy, Chemical Disequilibrium, and Geological Constraints on Europa

2007

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Europa is a prime target for astrobiology. The presence of a global subsurface liquid water ocean and a composition likely to contain a suite of biogenic elements make it a compelling world in the search for a second origin of life. Critical to these factors, however, may be the availability of energy for biological processes on Europa. We have examined the production and availability of oxidants and carbon-containing reductants on Europa to better understand the habitability of the subsurface ocean. Data from the Galileo Near-Infrared Mapping Spectrometer were used to constrain the surface abundance of CO 2 to 0.036% by number relative to water. Laboratory results indicate that radiolytically processed CO 2 -rich ices yield CO and H 2 CO 3 ; the reductants H 2 CO, CH 3 OH, and CH 4 are at most minor species. We analyzed chemical sources and sinks and concluded that the radiolytically processed surface of Europa could serve to maintain an oxidized ocean even if the surface oxidants (O 2 , H 2 O 2 , CO 2 , SO 2 , and SO 4 2؊ ) are delivered only once every ϳ0.5 Gyr. If delivery periods are comparable to the observed surface age (30-70 Myr), then Europa's ocean could reach O 2 concentrations comparable to those found in terrestrial surface waters, even if ϳ10 9 moles yr ؊1 of hydrothermally delivered reductants consume most of the oxidant flux. Such an ocean would be energetically hospitable for terrestrial marine macrofauna. The availability of reductants could be the limiting factor for biologically useful chemical energy on Europa. Keywords: Europa-Radiolysis-Oxygen-Habitability-Planetary science. Astrobiology 7, 1006-1022. INTRODUCTION WHILE THE MANTRA of "follow the water" has been the call of NASA's search for life beyond Earth, it is really a subset of the mantra "follow the energy." Life as we know it-that is, all life on Earth-requires just two forms of energy: thermal energy for melting water and chemical energy for maintaining and regulating processes considered essential for life. Even organisms that directly absorb light, e.g., for photosynthesis, do so as a means of producing utilizable chemical energy, stored in ATP.The existence of liquid water on any world in our contemporary cold universe (2.725 Ϯ 0.002 K) is the result of energy production (Mather et al., (Haida et al., 1974). Traditional definitions of the habitable zone have, in part, been restricted to liquid water on the surface of Earth-like planets made possible in part by atmospheric and surface heating from the parent star (Kasting et al., 1993). Such definitions of "surface habitability" cannot (nor were they intended to) take into account two energy sources that may be responsible for maintaining the majority of liquid water in our solar system, if not the universe: tidal and radiogenic energy.Within the jovian system, the generation of thermal energy through tidal dissipation and radioactive decay (following initial accretional heating) accounts for what are likely our solar system's three largest oceans. At present, the evid...

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Section: Discussionmentioning

confidence: 99%

Energy, Chemical Disequilibrium, and Geological Constraints on Europa

2007

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“…Contamination by trapped atmospheric O 2 or CO 2 was thought to be low but possibly was not. More recent experiments (Vidal et al 1997, Baragiola andBahr 1998) suggest varied but lower O 2 yields. Baragiola et al (1999) report only small upper limits for direct production of trapped O 2 within ice by 60 keV O + 2 (G O 2 < 5 × 10 −4 ) and 100 keV H + (G O 2 < 4 × 10 −5 ), but higher yields are possible (Johnson 1999).…”

Section: Fig 15mentioning

confidence: 99%

Energetic Ion and Electron Irradiation of the Icy Galilean Satellites

Cooper

Johnson

Mauk

et al. 2001

Icarus

367

437

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at Ganymede's polar cap, the latter being comparable to radiogenic energy input. Rates of change in optical reflectance and molecular composition on Europa, and on Ganymede's polar cap, are strongly driven by energy from irradiation, even in relatively young regions. Irradiation of nonice materials can produce SO 2 and CO 2 , detected on Callisto and Europa, and simple to complex hydrocarbons. Iogenic neutral atoms and meteoroids deliver negligible energy ∼10 4-5 keV (cm 2 -s) −1 but impacts of the latter are important for burial or removal of irradiation products. Downward transport of radiation produced oxidants and hydrocarbons could deliver significant chemical energy into the satellite interiors for astrobiological evolution in putative sub-surface oceans.

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“…Also, studies of 02 absorption band shapes and positions in the red (around 600 nm) showed that 02 had to be in the form of a solid, not a liquid or gas [Baragiola and Bahr, 1998]. These spectroscopic laboratory data imply that solid 02 exists at temperatures much colder than the average temperatures of Ganymede's surface ice.…”

Section: Introductionmentioning

confidence: 99%

“…Evidence for atmospheres came mainly from stellar occultations [Carlson et al, 1973 Baragiola and Bahr [1998] on the grounds of laboratory results that showed that 02 could not be retained in water ice in sufficient amounts to produce the observed absorption bands in Ganymede. Also, studies of 02 absorption band shapes and positions in the red (around 600 nm) showed that 02 had to be in the form of a solid, not a liquid or gas [Baragiola and Bahr, 1998].…”

Section: Introductionmentioning

confidence: 99%

Radiolysis of water ice in the outer solar system: Sputtering and trapping of radiation products

Bahr¹,

Famá²,

Vidal³

et al. 2001

J. Geophys. Res.

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Abstract. We performed quantitative laboratory radiolysis experiments on cubic water ice between 40 and 120 K, with 200 keV protons. We measured sputtering of atoms and molecules and the trapping of radiolytic molecular species. The experiments were done at fluences corresponding to exposure of the surface of the Jovian icy satellites to their radiation environment up to thousands of years. During irradiation, 02 molecules are ejected from the ice at a rate that grows roughly exponentially with temperature; this behavior is the main reason for the temperature dependence of the total sputtering yield. 02 trapped in the ice is thermally released from the ice upon warming; the desorbed flux starts at the irradiation temperature and increases strongly above 120 K. Several peaks in the desorption spectrum, which depend on irradiation temperature, point to a complex distribution of trapping sites in the ice matrix. The yield of 02 produced by the 200 keV protons and trapped in the ice is more than 2 orders of magnitude smaller than used in recent models of Ganymede. We also found small amounts of trapped H20 2 that desorb readily above 160 K.

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Laboratory studies of the optical properties and stability of oxygen on Ganymede

Cited by 44 publications

References 61 publications

Energy, Chemical Disequilibrium, and Geological Constraints on Europa

Energy, Chemical Disequilibrium, and Geological Constraints on Europa

Energetic Ion and Electron Irradiation of the Icy Galilean Satellites

Radiolysis of water ice in the outer solar system: Sputtering and trapping of radiation products

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