Ujjwal Raut

Ujjwal Raut
Southwest Research Institute · Department of Earth, Material and Planetary Sciences

PhD

About

52
Publications
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994
Citations

Publications

Publications (52)
Article
Full-text available
We present reflectance spectra of Ganymede's leading and trailing hemispheres in the wavelength range 138–215 nm, obtained by the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) in 2014. The most notable feature of both spectra is the absence of a sharp water absorption edge at ~165 nm, seen in laboratory measurements of ice reflectivi...
Article
Full-text available
Using data from the Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP), we investigate the spectral properties of rayed craters in the far‐ultraviolet (FUV). Because LAMP is sensitive to the uppermost layer of the lunar surface and regolith grains, it is ideal for characterizing regolith maturity and space weathering products suc...
Article
Full-text available
The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument onboard the Rosetta spacecraft has measured molecular oxygen (O2) in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) in surprisingly high abundances. These measurements mark the first unequivocal detection of O2 in a cometary environment. The large relative abun...
Article
We present detailed photometric properties of the Moon at far ultraviolet wavelengths. The far ultraviolet data from the Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP) instrument were used to derive two Hapke photometric parameters, the single-scattering albedo, w, and the asymmetry factor, b, in the single-particle phase fun...
Article
We report new measurements of the far-ultraviolet (FUV) bidirectional reflectance of Apollo soil 10084 from the Southwest Research Institute ultraviolet reflectance chamber. The bidirectional reflectance distribution function of this mare soil, enriched in Ti and Fe content, is rather featureless in the FUV wavelength region of 115–180 nm, except f...
Article
O2, H2, and H2O2 radiolysis from water ice is pervasive on icy astrophysical bodies, but the lack of a self-consistent, quantitative model of the yields of these water products versus irradiation projectile species and energy has been an obstacle to estimating the radiolytic oxidant sources to the surfaces and exospheres of these objects. A major c...
Article
We have investigated the effects of porosity on the crystallization kinetics of amorphous solid water (ASW). Porosity in ASW films, condensed from the vapor phase at varying incidences at 10 K, was characterized using ultraviolet-visible interferometry and quartz crystal microgravimetry. The films were heated to crystallization temperatures between...
Article
Full-text available
To understand the effects of cosmic-ray (CR) impacts on interstellar icy grains immersed in H-2 gas, we have irradiated porous water-ice films loaded with H-2 with 100 keV H+. The ice films were exposed to H-2 gas at different pressures following deposition and during irradiation. A net H-2 loss is observed during irradiation due to competition bet...
Article
Full-text available
Amorphous solid water (ASW) films grown by vapor deposition below 110 K develop negative surface voltages Vs with respect to the substrate. This polarization is due to a partial alignment of the water molecules during condensation. Kelvin probe measurements show that the magnitude of the surface potential, |Vs |, increases linearly with film thickn...
Article
We report ion-induced enhancement of CH4 uptake by H2O ice and formation of new species, suggesting a mechanism for gas trapping on surfaces of TNOs.
Article
We have studied the photodesorption of monolayer coverage of water ice coating amorphous carbon by 193 nm photons. We found that the column density of water decreases exponentially with fluence during irradiation at 120 K and obtain a desorption cross-section of (7.4±0.5)×10–19 cm2. We estimate the lifetime for photodesorption to be ∼14 h for avera...
Article
Full-text available
Inter- and circumstellar ices comprise different molecules accreted on cold dust particles. These icy dust grains provide a molecule reservoir where particles can interact and react. As the grain acts as a third body, capable of absorbing energy, icy surfaces in space have a catalytic effect. Chemical reactions are triggered by a number of possible...
Article
Full-text available
We present results on sputtering and radiation chemistry of CO2 films induced by 100 keV H+ at 25 and 50 K. Using a quartz crystal microbalance, we measure a sputtering yield (SY) between ~10 and 20 CO2 equivalent per ion at 25 K. The yield at 50 K is similar to that at 25 K at low fluences, but increases to ~2400 by mid-1014 H+ cm–2 and declines a...
Chapter
Full-text available
Water ice in the outer solar system can either have condensed from the gas phase or have been brought in by colliding bodies, such as interplanetary ice grains to comets. Since icy bodies lack a protective atmosphere, their surface is subject to irradiation by photons, ions and electrons. This chapter discusses how energetic radiation affects the p...
Article
Full-text available
We report the synthesis of carbon dioxide on an amorphous carbon-13 substrate coated with amorphous water ice from irradiation with 100 keV protons at 20 K and 120 K. The quantitative studies show that the CO2 is dispersed in the ice; its column density increases with ion fluence to a maximum value (in 10(15) molecules cm (2)) of similar to 1 at 20...
Article
We investigate via infrared spectroscopy the synthesis of CO2 by ultraviolet irradiation (6.41 eV) of amorphous carbon covered with solid O-2 at 21 K. Oxidation occurs at the O-2-carbon interface promoted by photon excitation or dissociation of O-2 molecules. The CO2 production is linear with photon fluence with a yield of 3.3 +/- 0.3 x 10(-5) CO2...
Article
Full-text available
We experimentally examine the removal of adsorbed water from lunar highland soil by Lyman-α (121.6-nm) photons and by 193-nm photons. These results will yield lifetimes of H_2O/OH species on the lunar regolith due to the solar photon flux.
Article
Investigations with infrared spectroscopy and microgravimetry show that CO2 forms in small quantities during codeposition of CO and cooled O and O-2 into thin films at 20 K: similar to 3 x 10(14) CO2 cm(-2) within a film containing 2.7 x 10(17) CO cm (2). The reason for the low CO2 yield is that O atoms react preferentially with O to form O-2, and...
Article
Full-text available
The mass uptake of ambient oxygen in nanoporous ice is enhanced by irradiation with 193 nm photons, due to conversion of O2 into H2O2 and O3, with an efficiency that increases with decreasing temperature. These findings show a new way to form H2O2 and O3 on icy surfaces in the outer solar system at depths much larger than are accessible by typical...
Article
Full-text available
We studied quantitatively the photochemistry of solid O(3) and O(2) films at 193 nm and 22 K with infrared spectroscopy and microgravimetry. Photolysis of pure ozone destroyed O(3), but a small amount of ozone remained in the film at high fluence. Photolysis of pure O(2) produced O(3) in an amount that increased with photon fluence to a stationary...
Article
We have studied the synthesis of 13CO2 from 100 keV proton irradiation of 100 nm thick amorphous water ice film on top of an amorphous 13C foil (95% isotopic purity, 50 nm thick) at 20 and 120 K using infrared spectroscopy and microbalance techniques. In contrast to previous work, we use pure carbon instead of hydrogenated carbon grains (Mennella e...
Article
We study radiation-induced amorphization of crystalline ice, analyzing the results of three decades of experiments with a variety of projectiles, irradiation energy, and ice temperature, finding a similar trend of increasing resistance of amorphization with temperature and inconsistencies in results from different laboratories. We discuss the tempe...
Article
We studied the effects of 100 keV proton irradiation on films of ammonia-water mixtures between 20 and 120 K. Irradiation destroys ammonia, leading to the formation and trapping of H(2), N(2), NO, and N(2)O, the formation of cavities containing radiolytic gases, and ejection of molecules by sputtering. Using infrared spectroscopy, we show that at a...
Article
Tenuous O2 atmospheres are known to exist around icy satellites such as Europa and Ganymede and around Saturn's rings and satellites [1,2]. These faint atmospheres with pressures estimated in 10-3 to 10-8 mbar range [2] are thought to be produced from photolysis and radiolysis of surface ice. In efforts to simulate closely the conditions on icy sat...
Article
This thesis presents investigations of various processes responsible for the origin and evolution of the icy mantles on dust grains present in the interstellar medium (ISM). The physical state and the chemical composition of the icy mantles are thought to depend strongly on the environment that harbors the dust grains. The mantles are continually a...
Article
Full-text available
We studied the compaction of microporous vapor-deposited ice films under irradiation with different ions in the 80-400 keV energy range. We found that porosity decreases exponentially with irradiation fluence, with a mean compaction area per ion that scales linearly with the stopping power of the projectile S above a threshold S-t = 4eV angstrom(-1...
Article
Studies of radiation effects in ice are motivated by intrinsic interest and by applications in astronomy. Here we report on new and recent results on radiation effects induced by energetic ions in ice: amorphization of crystalline ice, compaction of microporous amorphous ice, electrostatic charging and dielectric breakdown and correlated structural...
Article
We have characterized the porosity of vapor-deposited amorphous solid water (ice) films deposited at 30-40 K using several complementary techniques such as quartz crystal microgravimetry, UV-visible interferometry, and infrared reflectance spectrometry in tandem with methane adsorption. The results, inferred from the gas adsorption isotherms, revea...
Article
Laboratory simulations of processes on astronomical surfaces that use infrared reflectance spectroscopy of thin films to analyze their composition and structure often ignore important optical interference effects which often lead to erroneous measurements of absorption band strengths and give an apparent dependence of this quantity on film thicknes...
Article
We have studied the compaction of vapor-deposited amorphous solid water by energetic ions at 40 K. The porosity was characterized by ultraviolet-visible spectroscopy, infrared spectroscopy, and methane adsorption/desorption. These three techniques provide different and complementary views of the structural changes in ice resulting from irradiation....
Article
Full-text available
Recently, the Cassini spacecraft observed an unexpected emission of plumes of water vapor, nitrogen, and icy particles from the southern polar region of Saturn's icy moon Enceladus. While these findings support previous ideas of geological activity in this icy moon, there is no experimental evidence explaining how these plumes could be produced at...
Article
Condensed O-2 and ozone on the surfaces of some icy satellites are thought to originate from the radiolytic decomposition of surface water ice by the impact of energetic magnetospheric ions, but decades of laboratory studies have produced no evidence for ozone from the radiolysis of pure water ice. Here we report for the first time the production o...
Article
We present infrared absorption studies on the effects of 50–100 keV Ar+ and 100 keV H+ ion irradiation of water ice films at 20–120 K. The results support the view that energetic ions can produce hydrogen peroxide on the surface of icy satellites and rings in the outer Solar System, and on ice mantles on interstellar grains. The ion energies are ch...
Conference Paper
We will discuss multiple experiments in our laboratory in the last year in relation to the properties of Enceladus, many with application to other icy regoliths. 1) dependence of sublimation on the aggregation state. 2) adsorption, trapping and desorption of atmospheric gases which have been treated independently, but should be considered as a com...
Article
In connection with the observations of Cassini in its encounter with Enceladus, we are studying the thermal and radiation stability of ammonia-water mixtures in the laboratory. We use microbalance, mass-spectrometry, and infrared-spectroscopy to follow the evolution of the ices, and measure the sputtering and the sublimation rates. The results will...
Article
We have studied the effects of ion irradiation on the porosity of amorphous ice using infrared and ultraviolet-visible (uv-vis)spectroscopy. Our findings indicate that ion irradiation induces compaction in porous ice. The density of the ice films rises asymptotically to a saturation value with increasing ion fluence. Irradiation also decreases the...
Article
We have investigated the synthesis of carbon dioxide in amorphous carbon grains coated with amorphous water ice ( 0.1 microns thick) as a result of irradiation with 100 keV protons at 16 K and 120 K. The quantitative studies report a saturation column density of CO2 of the order of 3 - 9 x 1014 molecules/cm2, with more CO2 produced at lower tempera...
Article
Full-text available
We present new experimental results on radiolysis of water ice below 140 K induced by 150-eV electrons and 100-keV ions, obtained to understand processes occurring in the outer solar system and interstellar space. The experimental methods discussed are low-energy electron-energy-loss spectroscopy (EELS) and Fourier-transform-infrared (FTIR) spectro...
Article
There has been a recent interest in the possible production mechanisms of H2O2 in water ice, since the Galileo NIMS instrument reported an absorption band (3.5 mum) on the surface of Europa (Carlson 1999). Here we present results from laboratory studies that show H2O2 creation and destruction by ion bombardment. We have found that 100 keV H+ irradi...
Article
We have measured the sputtering of specific species during ion irradiation of water ice, labradorite, albite, anorthoclase, and olivine targets, to understand the importance of sputtering in the generation of atmospheres around icy satellites of the outer solar system by magnetospheric ions, and around the Moon and Mercury by the Solar wind. We use...
Article
The detection of H2O2 on Jupiter's icy satellite Europa by the Galileo NIMS instrument presented a strong evidence for the importance of radiation effects on icy surfaces. A few experiments have investigated whether solar flux of protons incident on Europa ice could cause a significant if any H2O2 production. These published results differ as to wh...
Article
We present infrared spectra of the OH stretch band of water ice obtained in ultrahigh vacuum, as a function of temperature and dose of irradiating 100 keV Ar ions. The results have potential use for remote sensing of the properties of ices in the outer solar system.
Article
We have measured the xenon near infrared (NIR) scintillation yield in the wavelength range from about 700 to 850nm for gas pressures from 0.3 to 1.5atm. We have found the NIR yield to be nearly constant above 0.9atm, increasing by about a factor of 4.5 as pressure is lowered to 0.3atm. Measured in number of photons emitted we estimate that at 0.3at...
Article
Here we present laboratory studies where we measure, using infrared spectroscopy, the production of CO2 from amorphous carbon grains with a water ice cap that have been irradiated with 100 keV H + ions. We find that CO2 is produced in both thin films where the ions hit the substrate and in thicker films where the ions stop in the ice film. Furtherm...
Article
The detection of condensed O2 and/or ozone on the surfaces of some satellites orbiting within the magnetospheres of Jupiter and Saturn was attributed to the trapping of radiolytic oxygen in their icy surfaces, but previous experiments showed rapid out-diffusion of O2 from laboratory O2-H2O ice mixtures, which suggested that only very small concentr...
Article
Full-text available
Recently the Cassini spacecraft observed unexpected emission of plumes of water vapor and ice particles from the southern polar region of Enceladus. Here we show that similar behavior appears when heating water-ammonia ices that have been irradiated with energetic ions typical of Saturn's magnetosphere. In addition, we also show the rapid decrease...
Article
We will present results from laboratory studies on the radiation effects on ammonia/water mixtures pertaining to the environment of Saturn's icy moon Enceladus. We show that ion irradiation destroys ammonia efficiently, and produces H2 and N2. Thus, this is likely the source of the N2 and N+ detected near Enceladus by Cassini INMS and CAPS instrume...
Article
Vapor-deposited water ice is believed to be present in astronomical environments such as interstellar grains, planetary rings, comets, and icy satellites. Some salient properties are its amorphous molecular structure and its microporosity, which determines its capacity to absorb gas. Since in most astronomical environments these ices are subject to...

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