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J. Hunter Waite

Bio: J. Hunter Waite is an academic researcher from Southwest Research Institute. The author has contributed to research in topics: Enceladus & Titan (rocket family). The author has an hindex of 29, co-authored 86 publications receiving 2884 citations. Previous affiliations of J. Hunter Waite include University of Nantes & University of Texas at San Antonio.


Papers
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Journal ArticleDOI
14 Apr 2017-Science
TL;DR: The Ion Neutral Mass Spectrometer onboard the Cassini spacecraft is used to detect molecular hydrogen in the plume of escaping material on Enceladus, finding that the most plausible source of this hydrogen is ongoing hydrothermal reactions of rock containing reduced minerals and organic materials.
Abstract: Saturn's moon Enceladus has a subsurface ocean covered by a layer of ice. Some liquid escapes into space through cracks in the ice, which is the source of one of Saturn's rings. In October 2015, the Cassini spacecraft flew directly through the plume of escaping material and sampled its chemical composition. Waite et al. found that the plume contains molecular hydrogen, H2, a sign that the water in Enceladus' ocean is reacting with rocks through hydrothermal processes (see the Perspective by Seewald). This drives the ocean out of chemical equilibrium, in a similar way to water around Earth's hydrothermal vents, potentially providing a source of chemical energy. Science , this issue p. [155][1]; see also p. [132][2] [1]: /lookup/doi/10.1126/science.aai8703 [2]: /lookup/doi/10.1126/science.aan0444

396 citations

Journal ArticleDOI
01 Jun 2018-Nature
TL;DR: The detection of complex organic molecules with masses higher than 200 atomic mass units in ice grains emitted from Enceladus indicates the presence of a thin organic-rich layer on top of the moon’s subsurface ocean.
Abstract: Saturn’s moon Enceladus harbours a global water ocean1, which lies under an ice crust and above a rocky core2. Through warm cracks in the crust3 a cryo-volcanic plume ejects ice grains and vapour into space4–7 that contain materials originating from the ocean8,9. Hydrothermal activity is suspected to occur deep inside the porous core10–12, powered by tidal dissipation13. So far, only simple organic compounds with molecular masses mostly below 50 atomic mass units have been observed in plume material6,14,15. Here we report observations of emitted ice grains containing concentrated and complex macromolecular organic material with molecular masses above 200 atomic mass units. The data constrain the macromolecular structure of organics detected in the ice grains and suggest the presence of a thin organic-rich film on top of the oceanic water table, where organic nucleation cores generated by the bursting of bubbles allow the probing of Enceladus’ organic inventory in enhanced concentrations.

263 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used a thermodynamic model of carbonate speciation to determine the pH of the ocean of Enceladus using data from the Cassini spacecraft.

210 citations

BookDOI
01 Dec 2010
TL;DR: Titan in the Cassini-Huygens Extended Mission: The Origin and Evolution of Titan, and Mapping Products of Titan's Surface.
Abstract: Preface.- Chapter 1 Overview.- Chapter 2 Earth-based Perspective and pre-Cassini-Huygens Knowledge of Titan.- Chapter 3 The Origin and Evolution of Titan.- Chapter 4 Titan's Interior structure.- Chapter 5 Geology and Surface Processes on Titan.- Chapter 6 Composition of Titan's Surface.- Chapter 7 Volatile Origin and Cycles: Nitrogen and Methane.- Chapter 8 High-altitude Production of Titan's Aerosols.- Chapter 9 Titan's Astrobiology.- Chapter 10 Atmospheric Composition and Structure.- Chapter 11 Composition and Structure of the Ionosphere and Thermosphere.- Chapter 12 Aerosols in Titan's Atmosphere.- Chapter 13 Atmospheric Dynamics and Meteorology.- Chapter 14 Seasonal Change on Titan.- Chapter 15 Mass loss processes in Titan's Upper Atmosphere.- Chapter 16 Energy Deposition Processes in Titan's Upper Atmosphere and Its Induced Magnetosphere.- Chapter 17 Titan in the Cassini-Huygens Extended Mission.- Chapter 18 Titan Beyond Cassini-Huygens.- Chapter 19 Mapping Products of Titan's Surface.- Appendix.

195 citations

Journal ArticleDOI
TL;DR: In this article, a one-dimensional model coupling a two-stream electron transport model of energy deposition with a 1-D thermal conduction model has been developed to investigate the links between auroral heat input and the vertical temperature of Jupiter's upper atmosphere.
Abstract: A one-dimensional (1-D) model coupling a two-stream electron transport model of energy deposition with a 1-D thermal conduction model has been developed. It is applied to investigate the links between auroral heat input and the vertical temperature of Jupiter's upper atmosphere. Two energy distributions meant to reproduce the emissions of a diffuse and a discrete aurora are used to evaluate the importance of the energy spectrum of the incident electrons for the thermal balance of Jupiter's auroral thermosphere. The values of observable quantities such as the altitude of the H2 emission peak, thermal infrared (IR), ultraviolet (UV) emissions, and temperatures associated with various optical signatures are used to constrain the parameters of these distributions. It is shown that the high-energy component of these energy distributions heats a region of the homosphere between 10−4 and 10−6 bar and mainly controls the H2 temperature and the far-UV (FUV) emission. A 3-keV soft electron component is necessary to heat the region directly above the homopause, between 10−6 and 10−9 bar. It has a large influence on the H2 and H3+ temperatures and on the H3+ near-IR (NIR) emission. It is used in conjunction with a weak 100 eV component which is responsible for heating the thermosphere, from 10−9 to 10−12 bar and exerts a control on the exospheric temperature. The calculated temperatures, UV, and IR emissions suggest that the model probably misses a nonparticle heat source in the 10−5 bar region, that is expected to balance the strong hydrocarbon cooling. Sensitivity tests are performed to evaluate the importance of the parameters of the energy distributions. They show that the FUV color ratio increases with the characteristic energy (or high-energy cutoff) of the high-energy component, while the H2 rovibrational temperature varies inversely. A trade-off is therefore necessary for these two parameters to simultaneously meet their observational constraints. Further tests demonstrate the essential thermostatic role played by H3+, which regulates the net heating in the thermosphere. An increased eddy diffusion reproduces the effect of a possible auroral upwelling of methane but gives rise to an H2 temperature smaller than the observed value.

188 citations


Cited by
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Journal ArticleDOI
TL;DR: The mechanism of Nile Red release was investigated, and the change in size of the micelles over time at acidic pH showed a size decrease over time, eventually reaching the size of a unimer, thus providing evidence for the proposed micelle disintegration.
Abstract: With the goal of developing a pH-responsive micelle system, linear-dendritic block copolymers comprising poly(ethylene oxide) and either a polylysine or polyester dendron were prepared and hydrophobic groups were attached to the dendrimer periphery by highly acid-sensitive cyclic acetals. These copolymers were designed to form stable micelles in aqueous solution at neutral pH but to disintegrate into unimers at mildly acidic pH following loss of the hydrophobic groups upon acetal hydrolysis. Micelle formation was demonstrated by encapsulation of the fluorescent probe Nile Red, and the micelle sizes were determined by dynamic light scattering. The structure of the dendrimer block, its generation, and the synthetic method for linking the acetal groups to its periphery all had an influence on the critical micelle concentration and the micelle size. The rate of hydrolysis of the acetals at the micelle core was measured for each system at pH 7.4 and pH 5, and it was found that all systems were stable at neutral pH but underwent significant hydrolysis at pH 5 over several hours. The rate of hydrolysis at pH 5 was dependent on the structure of the copolymer, most notably the hydrophobicity of the core-forming block. To demonstrate the potential of these systems for controlled release, the release of Nile Red as a "model payload" was examined. At pH 7.4, the fluorescence of micelle-encapsulated Nile Red was relatively constant, indicating it was retained in the micelle, while at pH 5, the fluorescence decreased, consistent with its release into the aqueous environment. The rate of release was strongly correlated with the rate of acetal hydrolysis and was therefore controlled by the chemical structure of the copolymer. The mechanism of Nile Red release was investigated by monitoring the change in size of the micelles over time at acidic pH. Dynamic light scattering measurement showed a size decrease over time, eventually reaching the size of a unimer, thus providing evidence for the proposed micelle disintegration.

526 citations

Journal ArticleDOI
TL;DR: The IAU Working Group on Cartographic Coordinates and Rotational Elements (WGPSN) as mentioned in this paper takes into account the IAU working group for planetary system Nomenclature and the International Astronomical Union (IAUWCN) definition of dwarf planets, and introduces improved values for the pole and rotation rate of Mercury, returns the rotation rates of Jupiter to a previous value, and adds the equatorial radius of the Sun for comparison.
Abstract: Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars’ satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) Steins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn.

484 citations