Engineering topics

Cook, Jason C.

Publications and source records attributed to Cook, Jason C..

3 records

NASA NTRS2016

Contributions of Solar Wind and Micrometeoroids to Molecular Hydrogen in the Lunar Exosphere

We investigate the density and spatial distribution of the H2 exosphere of the Moon assuming various source mechanisms. Owing to its low mass, escape is non-negligible for H2. For high-energy source mechanisms, a high percentage of the released molecules escape lunar gravity. Thus, the H2 spatial distribution for high-energy release processes reflects the spatial distribution of the source. For low energy release mechanisms, the escape rate decreases and the H2 redistributes itself predominantly to reflect a thermally accommodated exosphere. However, a small dependence on the spatial distribution of the source is superimposed on the thermally accommodated distribution in model simulations, where density is locally enhanced near regions of higher source rate. For an exosphere accommodated to the local surface temperature, a source rate of 2.2 g s-1 is required to produce a steady state density at high latitude of 1200 cm-3. Greater source rates are required to produce the same density for more energetic release mechanisms. Physical sputtering by solar wind and direct delivery of H2 through micrometeoroid bombardment can be ruled out as mechanisms for producing and liberating H2 into the lunar exosphere. Chemical sputtering by the solar wind is the most plausible as a source mechanism and would require 10-50 of the solar wind H+ inventory to be converted to H2 to account for the observations.

Impact↗

NASA NTRS2015

Understanding Temporal and Spatial Variability of the Lunar Helium Atmosphere Using Simultaneous Observations from LRO, LADEE, and ARTEMIS

Simultaneous measurements of helium in the exosphere of the Moon are made from the Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP) and the Lunar Atmosphere and Dust Environment Explorer (LADEE) Neutral Mass Spectrometer (NMS) through the entire 5-month span of the LADEE mission. In addition, the ARTEMIS mission monitored the solar wind alpha particle flux to the Moon. Modeling the lunar helium exosphere, we relate the LAMP polar observations to the LADEE equatorial observations. Further, using the ARTEMIS alpha flux in the Monte Carlo model reproduces the temporal variations in helium density. Comparing the LAMP data to the LADEE data shows excellent agreement. Comparing those with the ARTEMIS data reveals that the solar wind alpha flux is the primary driver to variability in the helium exosphere throughout the LADEE mission. Using a decay time for exospheric helium of 5 days, we determine that the solar wind contributes 64 +/- 5% of the helium to the lunar exosphere. The remaining 36 +/- 5% is presumed to come from outgassing of radiogenic helium from the interior of the Moon. Furthermore, the model reproduces the measurements if 63 +/- 6% of the incident alpha particles are converted to thermalized helium atoms through the interaction between the alphas and the lunar surface. However, these values are dependent on both inferred source rates from LAMP and LADEE observations and on the assumed time constant of the exospheric decay rate.

Moon↗

NASA NTRS2014

Gemini NorthNIRI Spectra of Pluto and Charon: Simultaneous Analysis of the Surface and Atmosphere

94035We report on our analysis of blended Pluto and Charon spectra over the wavelength range 1.4 to 2.5 m as obtained by the NIRI instrument on Gemini North on June 25-28, 2004. The data have a resolving power () around 1500 and a SNR around 200 per pixel. The observed blended spectra are compared to models that combine absorption from the solid ice on the surface using Hapke theory, and absorption from the gaseous atmosphere. We assume the spectrum is a combination of several spatially separate spectral units: a CH4-rich ice unit, a volatile unit (an intimate mixture of N2, CH4 and CO), and a Charon unit (H2O, ammonia hydrate and kaolinite). We test for the presence of hydrocarbons (i.e. C2H6) and nitriles (i.e. HCN) and examine cases where additional ices are present as either pure separate spatial units, mixed with the CH4-rich unit or part of the volatile unit. We conclude that 2-4 of Plutos surface is covered with pure-C2H6 and our identification of C2H6 is significantly strengthened when absorption due to gaseous CH4 is included. The inclusion of Plutos atmosphere demonstrates that low-resolution, high-SNR observations are capable of detecting Plutos atmosphere during a time when Plutos atmosphere may have been undergoing rapid changes (1988-2002) and no high-resolution spectra were obtained. In particular, we identify features at 1.665 and 2.317 m as the Q-branch of the 23 and 3+4 bands of gaseous CH4, respectively. The later band is also evident in many previously published spectra of Pluto. Our analysis finds it is unnecessary to include 13CO to explain the depth of the 2.405 m, which has been previously suggested to be a spectral blended with C2H6, but we cannot definitively rule out its presence. Funding for this work (Cook) has been provided by a NASA-PATM grant.

Charon↗