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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

How Surface Composition and Meteoroid Impacts Mediate Sodium and Potassium in the Lunar Exosphere

Despite being trace constituents of the lunar exosphere, sodium and potassium are the most readily observed species due to their bright line emission. Measurements of these species by the Ultraviolet and Visible Spectrometer (UVS) on the Lunar Atmosphere and Dust Environment Explorer (LADEE) have revealed unambiguous temporal and spatial variations indicative of a strong role for meteoroid bombardment and surface composition in determining the composition and local time dependence of the Moon's exosphere. Observations show distinct lunar day (monthly) cycles for both species as well as an annual cycle for sodium. The first continuous measurements for potassium show a more repeatable variation across lunations and an enhancement over KREEP (Potassium Rare Earth Elements and Phosphorus) surface regions, revealing a strong dependence on surface composition.

Colaprete, A.↗
NASA NTRS2018

The Unknown Hydrogen Exosphere: Space Weather Implications

Recent studies suggest that the hydrogen (H) density in the exosphere and geocorona might differ from previously assumed values by factors as large as 2. We use the SAMI3 (Sami3 is Also a Model of the Ionosphere) and Comprehensive Inner Magnetosphere-Ionosphere models to evaluate scenarios where the hydrogen density is reduced or enhanced, by a factor of 2, relative to values given by commonly used empirical models. We show that the rate of plasmasphere refilling following a geomagnetic storm varies nearly linearly with the hydrogen density. We also show that the ring current associated with a geomagnetic storm decays more rapidly when H is increased. With respect to these two space weather effects, increased exosphere hydrogen density is associated with reduced threats to space assets during and following a geomagnetic storm.

Krall, J.↗
NASA NTRS2018

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H2 Exosphere

The solar wind implants protons into the top 20–30 nm of lunar regolith grains, and the implanted hydrogen will diffuse out of the regolith but also interact with oxygen in the regolith oxides. We apply a statistical approach to estimate the diffusion of hydrogen in the regolith hindered by forming temporary bonds with regolith oxygen atoms. A Monte Carlo simulation was used to track the temporal evolution of bound OH surface content and the H2 exosphere. The model results are consistent with the interpretation of the Chandrayaan‐1 M3 observations of infrared absorption spectra by surface hydroxyls as discussed in Li and Milliken (2017, https://doi.org/10.1126/sciadv.1701471). The model reproduced the latitudinal concentration of OH by using a Gaussian energy distribution of f(U(sub 0) = 0.5 eV, U(sub W) = 0.078–0.1 eV) to characterize the activation energy barrier to the diffusion of hydrogen in space weathered regolith. In addition, the model results of the exospheric content of H2 are consistent with observations by the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter. Therefore, we provide support for hydroxyl formation by chemically trapped solar wind protons.

Tucker, O. J.↗
NASA NTRS2017

The Putative Cerean Exosphere

The ice-rich crust of dwarf planet 1 Ceres is the source of a tenuous water exosphere, and the behavior of thisputative exosphere is investigated with model calculations. Outgassing water molecules seasonally condensearound the winter pole in an optically thin layer.

Schorghofer, Norbert↗
NASA NTRS2018

Understanding Mercury's Exosphere: Models Derived from MESSENGER Observations: Chapter - 15

The observations of Mercury's exosphere described in Chapter 14 have led to many modeling efforts. Early models were based upon a few simple assumptions and primarily explored the dynamics of sodium atoms pushed anti-sunward by radiation pressure [Ip, 1986; Smyth and Marconi, 1995]. More recently, these early models have been superseded by simulations with an increasing number of interdependent source processes [Leblanc and Johnson, 2003; Mura et al., 2009; Leblanc and Johnson, 2010; Burger et al., 2010, 2012, 2014]. We briefly summarize the source and loss processes before describing the published exosphere models, first for the three species observed almost continuously during the MESSENGER mission by the Ultraviolet and Visible Spectrometer (UVVS) channel of the Mercury Atmospheric and Surface Composition2Spectrometer (MASCS), (Na, Mg and Ca), and then more briefly for other species that have been observed or for which new upper limits have been derived.15.1 Overview of Source and Loss Processes15.1.1 Source Processes15.1.1.1 Thermal DesorptionThermal desorption (or thermal evaporation) is the release of adsorbed atoms from a surface via heating. Thermal desorption is related to the binding energy of the atom on the surface and the vibrational frequency of the bound atom, such that the rate of thermal desorption is given by, (15.1)where TD,

Thermal↗
NASA NTRS2019

High-Resolution Potassium Observations of the Lunar Exosphere

We observed lunar exospheric potassium D1 (7,698.9646 Å) emissions using a high-spectral resolution Fabry-Perot spectrometer in 2014. We present the first potassium line profile measurements, which are representative of the potassium velocity distribution. Inferred temperatures are greater during the waxing gibbous phase, 1920 ± 630 K and lower at waning gibbous phase, 980 ± 200 K. Exosphere models suggest that the measured line widths are a combination of photon-stimulated desorption and impact vaporization sources. The relative potassium emission intensity decreases by ∼2.5 between lunar phases 80◦ and 30◦ and is brightest off the northwest limb near the Aristarchus crater, which is a potassium-rich surface region. Additionally, the emissions off the northern limb are brighter than the southern limb. The intensity decrease and the greater line width during the waxing gibbous versus the waning gibbous phase suggests a dawn-dusk asymmetry.

Rosborough, S. A.↗
NASA NTRS2018

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H2 Exosphere

The solar wind implants protons into the top 20–30 nm of lunar regolith grains, and the implanted hydrogen will diffuse out of the regolith but also interact with oxygen in the regolith oxides. We apply a statistical approach to estimate the diffusion of hydrogen in the regolith hindered by forming temporary bonds with regolith oxygen atoms. A Monte Carlo simulation was used to track the temporal evolution of bound OH surface content and the H2 exosphere. The model results are consistent with the interpretation of the Chandrayaan-1 M3 observations of infrared absorption spectra by surface hydroxyls as discussed in Li and Milliken (2017). Themodel reproduced the latitudinal concentration of OH by using a Gaussian energy distribution of f(U(o) = 0.5eV, U(w) = 0.078 – 0.1 eV) to characterize the activation energy barrier to the diffusion of hydrogen in space weathered regolith. In addition, the model results of the exospheric content of H2 are consistent with observations by the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter. Therefore, we provide support for hydroxyl formation by chemically trapped solar wind protons.

O. J. Tucker↗
NASA NTRS2018

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H2 Exosphere

The solar wind implants protons into the top 20–30 nm of lunar regolith grains, and the implanted hydrogen will diffuse out of the regolith but also interact with oxygen in the regolith oxides. We apply a statistical approach to estimate the diffusion of hydrogen in the regolith hindered by forming temporary bonds with regolith oxygen atoms. A Monte Carlo simulation was used to track the temporal evolution of bound OH surface content and the H2 exosphere. The model results are consistent with the interpretation of the Chandrayaan‐1 M3 observations of infrared absorption spectra by surface hydroxyls as discussed in Li and Milliken (2017, https://doi.org/10.1126/sciadv.1701471). The model reproduced the latitudinal concentration of OH by using a Gaussian energy distribution of f(U0 = 0.5 eV, UW = 0.078–0.1 eV) to characterize the activation energy barrier to the diffusion of hydrogen in space weathered regolith. In addition, the model results of the exospheric content of H2 are consistent with observations by the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter. Therefore, we provide support for hydroxyl formation by chemically trapped solar wind protons.

O J Tucker↗