Near-Infrared Mapping Spectrometer Experiment on Galileo

Carlson, R. W.; Weissman, P. R.; Smythe, W. D.; Mahoney, J. Colin

doi:10.1007/978-94-011-2512-3_18

Cited by 62 publications

(74 citation statements)

References 15 publications

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“…These were further processed into reflectance spectra and spectral-property maps and were interpreted in terms of surface composition. The characteristics of the NIMS, the measurement process and the resulting data sets were described earlier [e.g., Carlson et al, 1992;McCord et al, 1998b]. The flyby geometries, their short duration, and limitations on total data return required decisions on given orbits to strike balances among spatial and spectral coverage and resolution.…”

Section: Observationsmentioning

confidence: 99%

Hydrated salt minerals on Europa's surface from the Galileo near‐infrared mapping spectrometer (NIMS) investigation

McCord¹,

Hansen²,

Matson³

et al. 1999

J. Geophys. Res.

301

240

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Abstract. We reported evidence of heavily hydrated salt minerals present over large areas of Europa's surface from analysis of reflectance spectra returned by the Galileo mission near infrared mapping spectrometer (NIMS) [McCord et al., 1997a[McCord et al., , b, 1998a. Here we elaborate on this earlier evidence, present spatial distributions of these minerals, examine alternate water-ice interpretations, expand on our hydrated-salts interpretation, consider salt mineral stability on Europa, and discuss the implications. Extensive well-defined areas on Europa show distinct, asymmetric water-related absorption bands in the 1 to 2.5-gm region. Radiative transfer modeling of water ice involving different particle sizes and layers at Europa temperatures does not reproduce the distinctive Europa water bands. However, ice near its melting temperature, such as in terrestrial environments, does have some characteristics of the Europa spectrum. Alternatively, some classes of heavily hydrated minerals do exhibit such water bands. Among plausible materials, heavily hydrated salt minerals, such as magnesium and sodium sulfates, sodium carbonate and their mixtures, are preferred. All Europa spectral features are present in some salt minerals and a very good match to the Europa spectrum can be achieved by mixing several salt spectra. However, no single or mix of salt mineral spectra from the limited library available has so far been found to perfectly match the Europa spectrum in every detail. The material is concentrated at the lineaments and in chaotic terrain, which are tectonically disrupted areas on the trailing side. Since the spectrum of the material on Europa is nearly the same everywhere so-far studied, the salt or salt-mixture composition may be nearly uniform. This suggests similar sources and processes over at least a near-hemispheric scale. This would suggest that an extensive subsurface ocean containing dissolved salts is the source, and several possible mechanisms for deposit emplacement are considered. The hydrogen bonds associated with hydration of these salts are similar or greater in strength and energy to those in pure water ice. Thus, once on the surface, the salt minerals should be as stable to disruption as water ice at the Europa temperatures, and mechanisms are suggested to enhance the stability of both materials. Spectra obtained of MgSO4o6H20 at 77 K show only small differences from room temperature spectra. The main difference is the appearance of the individual absorptions composing the broad, composite water features and associated with the several different H20 sites in the salt hydrate molecule. This suggests that the Europa absorption bands are also composites. Thus higher spectral resolution may reveal these diagnostic features in Europa's spectrum. The specific salts present and their relative abundances would be indicators of the chemistry and conditions of an ocean environment, and areas of fresh, heavy concentration of these minerals should make ideal lander mission sampling sites.

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Section: Observationsmentioning

confidence: 99%

Hydrated salt minerals on Europa's surface from the Galileo near‐infrared mapping spectrometer (NIMS) investigation

McCord¹,

Hansen²,

Matson³

et al. 1999

J. Geophys. Res.

301

240

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“…The first i s instrument noise arising from effects such as Johnson noise in the detectors and may be estimated, for a particular detector and focal plane temperature, from the calibration of the instrument [Carlson et al, 1992]. For all detectors this source of error is very small and is of the order of 0.1%.…”

Section: Errorsmentioning

confidence: 99%

Cloud structure and atmospheric composition of Jupiter retrieved from Galileo near‐infrared mapping spectrometer real‐time spectra

Irwin¹,

Weir²,

Smith³

et al. 1998

J. Geophys. Res.

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Abstract. The first four complete spectra recorded by the near infrared mapping spectrometer (NIMS) instrument on the Galileo spacecraft in 1996 have been analyzed. These spectra remain the only ones which have been obtained at maximum resolution over the entire NIMS wavelength range of 0.7 -5.2 gm. The spectra cover the edge of a "warm" spot at location 5øN, 85øW. We have analyzed the spectra first with reflecting layer models and then with full multiple scattering models using the method of correlated-k. We find that there is strong evidence for three different cloud layers composed of a haze consistent with 0.5-gm radius tholins at 0.2 bar, a cloud of 0.75-gm NH 3 particles at about 0.7 bar, and a two-component NH4SH cloud at about 1.4 bars with both 50.0-and 0.45-gm particles, the former being responsible for the main 5-gm cloud opacity. The NH 3 relative humidity above the cloud tops is found to decrease slightly as the 5-gm brightness increases, with a mean value of approximately 14%. We also find that the mean volume mixing ratio of ammonia above the middle (NH4SH) cloud deck is (1.7+0.1) x 10 -4 and shows a similar, though less discernible decrease with increasing 5-gm brightness. The deep volume mixing ratios of deuterated methane and phosphine are found to be constant and we estimate their mean values to be (4.9+0.2) x 10 -7 and (7.7+0.2) x 10 -7, respectively. The fractional scale height of phosphine above the 1 bar level is found to be 27.1+1.4% and shows a slight decrease with increasing 5-gm brightness. The relative humidity of water vapor is found to be approximately 7%, but while this and all the previous observations are consistent with the assumption that "hot spots" are regions of downwelling, desiccated air, we find that the water vapor relative humidity increases as the 5-gm brightness increases.

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“…The spectral data used here are from the Galileo Near-Infrared Mapping Spectrometer (NIMS) [Carlson et al, 1992]. These data were used to show that a principal radiolysis product of ice, hydrogen peroxide, exists in Europa's optical surface [Carlson et al, 1999a].…”

Section: Introductionmentioning

confidence: 99%

Electron bombardment of Europa

Paranicas

Carlson

Johnson

2001

Geophysical Research Letters

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119

170

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Abstract. Energetic electrons trapped in Jupiter's magnetic field are a principal source of energy for driving chemistry on the surface of Europa. Here we show that energetic (10 keV-10 MeV) electrons precipitate primarily on the trailing hemisphere, and we give the spatial distribution of the dose-rate deposited in Europa's surface. Based on this we propose that energetic electrons are a primary agent in determining the hemispherical differences in Europa's albedo, which have been attributed to differences in the incident ion flux. We compare the spatial distribution in the dose-rate deposited by the energetic electrons to the spatial distribution in the hydrate (likely frozen, hydrated sulfuric acid) determined by Galileo's near-infrared mapping spectrometer. This comparison supports the idea that radiolysis by the energetic electrons contributes significantly to producing the hydrate.

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Near-Infrared Mapping Spectrometer Experiment on Galileo

Cited by 62 publications

References 15 publications

Hydrated salt minerals on Europa's surface from the Galileo near‐infrared mapping spectrometer (NIMS) investigation

Hydrated salt minerals on Europa's surface from the Galileo near‐infrared mapping spectrometer (NIMS) investigation

Cloud structure and atmospheric composition of Jupiter retrieved from Galileo near‐infrared mapping spectrometer real‐time spectra

Electron bombardment of Europa

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