Oxygen on Ganymede: Laboratory Studies

Vidal, R.; Bahr, D. A.; Baragiola, R. A.; Peters, M.

doi:10.1126/science.276.5320.1839

Cited by 70 publications

(55 citation statements)

References 32 publications

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“…Further, the relative band depths for pure 0 2 are not a good match to the Ganymede spectra. In the spectrum for the 02/ H20 mixture in Figure 1 of Vidal et al [1997], the combination of absorption peak positions and relative band depths appear to this author most similar to the telescopic data. In both papers the relative band depths are ignored.…”

Section: Introductionsupporting

confidence: 64%

“…Hence the suggestion of Calvin et al [1996] and Johnson and Jesser [1997] (see appendix below) that the 02 exists as radiation-induced inclusions (bubbles) in the icy surface. In BB and in an earlier paper [Vidal et al, 1997], they concluded that the 02 is not trapped in inclusions in the ice. Rather, it was suggested that solid 02 exists on Ganymede either in surface regions with very low temperatures or as 02 ice crystals in Ganymede's atmosphere.…”

Section: Introductionmentioning

confidence: 91%

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Comment on “Laboratory studies of the optical properties and stability of oxygen on Ganymede” by Raul A. Baragiola and David A. Bahr

Johnson¹

1999

J. Geophys. Res.

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IntroductionIt has been over 15 years since Brown et at. [1982] showed that the bombardment of the icy satellites by magnetospheric plasma particles would produce significant quantities of 02, including an 02 atmosphere . It is now accepted that radiolysis and, possibly, photolysis of ice [Johnson and Quickenden, 1997] (see appendix below) produce the 02 observed on the icy satellites, but modeling the fate of this 02 is in its infancy. Baragiela and Bahr [1998] (hereafter BB) recently presented experimental data relevant to the two 02 bands observed in the visible by Spencer et al. [1995] and Calvin and Spencer [1998]. These bands are indicative of some form of condensed 02 [Calvin et al., 1996]. Because the 02 band is seen primarily at low latitudes on Ganymede, the stability of "solid" 02 was thought to be a problem. Hence the suggestion of Calvin et al. [1996] and Johnson and Jesser [1997] (see appendix below) that the 02 exists as radiation-induced inclusions (bubbles) in the icy surface. In BB and in an earlier paper [Vidal et al., 1997], they concluded that the 02 is not trapped in inclusions in the ice. Rather, it was suggested that solid 02 exists on Ganymede either in surface regions with very low temperatures or as 02 ice crystals in Ganymede's atmosphere. Before commenting on this, clarification is required.That the observed bands require "solid-state" 02 densities is not in question; this became clear in the comparisons by Calvin et al. [1996] of earlier laboratory data with the observed spectra. Therefore the proposed 02 inclusions were presumed to have such densities. (The word "inclusion" is used here to indicate the trapping of a number of 02 molecules in a volume, rather than a single 02 in a single defect.) With this in mind, two principal issues need to be addressed in order to understand the observed 02 bands. Since nonoxygen neighbors and lattice structure can affect the spectrum of solid 02, what amount and which lattice structure are required to match the band profile? In addition, noting that the ultimate source is likely to be radiolysis, how is the observed 02 formed? Is it formed by condensation after production or in situ in voids in the surface material?Based on the telescopic observations, it might appear that solid 02 is unique to Ganymede's near-equatorial region. Spencer [1998] . This implies a slower diffusion rate than that for voids or defects. Since stable areas of O: at low latitudes exposed to space are unlikely, this issue needs to be studied for nonporous, crystalline overlayers.It is, of course, possible that the O: observed on Ganymede might not be trapped in ice. It could be in another substance, which is also transparent in the visible and forms trapped-gas inclusions, such as certain salts [Karget, 1991] The conclusion in BB that the observed 02 bands are indicative of the presence of condensed 0 2 is based on matching the positions and shapes of the absorption bands of condensed 0 2 at 22 K with the absorption bands observed by Spencer et al. [1995]. Such a...

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Section: Introductionsupporting

confidence: 64%

Section: Introductionmentioning

confidence: 91%

Comment on “Laboratory studies of the optical properties and stability of oxygen on Ganymede” by Raul A. Baragiola and David A. Bahr

Johnson¹

1999

J. Geophys. Res.

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“…Spectral absorption suggestive of ozone has been detected by the Galileo UVS on Ganymede (Hendrix et al, 1999) and by the Hubble Space Telescope on Ganymede, Rhea, and Dione (Noll et al, 1996b;Noll et al, 1997). Laboratory results are not entirely consistent with Galilean satellite observations, however (Vidal et al, 1997 andBahr, 1998), so being able to compare oxygen chemistry at a variety of temperatures and radiation environments will help in understanding the processes.…”

Section: Surface Composition and Chemistrymentioning

confidence: 85%

The Cassini Ultraviolet Imaging Spectrograph Investigation

et al. 2004

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The Cassini Ultraviolet Imaging Spectrograph (UVIS) is part of the remote sensing payload of the Cassini orbiter spacecraft. UVIS has two spectrographic channels that provide images and spectra covering the ranges from 56 to 118 nm and 110 to 190 nm. A third optical path with a solar blind CsI photocathode is used for high signal-to-noise-ratio stellar occultations by rings and atmospheres. A separate Hydrogen Deuterium Absorption Cell measures the relative abundance of deuterium and hydrogen from their Lyman-α emission. The UVIS science objectives include investigation of the chemistry, aerosols, clouds, and energy balance of the Titan and Saturn atmospheres; neutrals in the Saturn magnetosphere; the deuterium-to-hydrogen (D/H) ratio for Titan and Saturn; icy satellite surface properties; and the structure and evolution of Saturn's rings.

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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: 95%

Energetic Ion and Electron Irradiation of the Icy Galilean Satellites

Cooper

Johnson

Mauk

et al. 2001

Icarus

371

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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Oxygen on Ganymede: Laboratory Studies

Cited by 70 publications

References 32 publications

Comment on “Laboratory studies of the optical properties and stability of oxygen on Ganymede” by Raul A. Baragiola and David A. Bahr

Comment on “Laboratory studies of the optical properties and stability of oxygen on Ganymede” by Raul A. Baragiola and David A. Bahr

The Cassini Ultraviolet Imaging Spectrograph Investigation

Energetic Ion and Electron Irradiation of the Icy Galilean Satellites

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