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Hendrix, A. R.

Publications and source records attributed to Hendrix, A. R..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

NASA Planetary Mission Concept Study: Assessing: Dwarf Planet Ceres' past and Present Habitability Potential

The Dawn mission revolutionized our understanding of Ceres during the same decade that has also witnessed the rise of ocean worlds as a research and exploration focus. We will report progress on the Planetary Mission Concept Study (PMCS) on the future exploration of Ceres under the New Frontiers or Flagship program that was selected for NASA funding in October 2019. At the time this writing, the study was just kicked off, hence this abstract reports the study plan as presented in the proposal.

Castillo-Rogez, J. C.↗
NASA NTRS2018

Toolbox for Research and Exploration (TREX): Investigations of Fine-Grained Materials on Small Bodies

The Toolbox for Research and Exploration (TREX) is a NASA SSERVI (Solar System Exploration Research Virtual Institute) node. TREX (trex.psi.edu) aims to decrease risk to future missions, specifically to the Moon, the Martian moons, and near- Earth asteroids, by improving mission success and assuring the safety of astronauts, their instruments, and spacecraft. TREX studies will focus on characteristics of the fine grains that cover the surfaces of these target bodies - their spectral characteristics and the potential resources (such as H2O) they may harbor. TREX studies are organized into four Themes (Laboratory- Studies, Moon-Studies, Small-Bodies Studies, and Field-Work). In this presentation, we focus on the work targeted by the Small-Bodies Theme. The Small-Bodies' Theme delves into several topics, many which overlap or are synergistic with the other TREX Themes. The main topics include photometry, spectral modeling, laboratory simulations of space weathering processes relevant to asteroids, the assembly of an asteroid regolith database, the dichotomy between nuclear and reflectance spectroscopy, and the dynamical evolution of asteroids and the implications for the retention of volatiles.

Domingue, D. L.↗
NASA NTRS2012

Seasonal Variability on Saturn's Moons Mimas and Tethys

We present far-ultraviolet (FUV) observations of Mimas and Tethys, which show evidence for likely seasonal variation in UV albedo across their surfaces. The ultraviolet is an important wavelength regime for studying the effects of photolytic and radiolytic processes, because primarily the uppermost layers of the regolith and grains are sensed in this range.

far-ultraviolet (FUV)↗
NASA NTRS2011

Collisional Evolution of the Enceladus Neutral Cloud

Water vapor ejected from Saturn's small moon Enceladus easily escapes its meager gravity to form a Saturn-encircling cloud with a low collision rate. Observations show that the cloud is quite broad in the radial direction, and we show here that collisions, though quite rare, may be largely responsible for this radial spreading. We modeled this cloud using the Direct Simulation Monte Carlo method, as fluid methods would be inappropriate for such a tenuous gas.

magnetic fields↗
NASA NTRS2008

The Saturn System's Icy Satellites: New Results from Cassini

Cassini-Huygens is a multidisciplinary, international planetary mission consisting of an orbiting spacecraft and a probe. The Huygens probe successfully landed on Titan's surface on January 14, 2005, while the orbiter has performed observations of Saturn, its rings, satellites, and magnetosphere since it entered orbit around Saturn on July 1, 2004. The Cassini mission has been prolific in its scientific discoveries about the Saturn system. In this special section, we present new mission results with a focus on the 'icy satellites,' which we define as all Saturn's moons with the exception of Titan. The results included in this section have come out of the Cassini SOST--Satellites Orbiter Science Team--a multi-instrument and multidiscipline group that works together to better understand the icy satellites and their interactions with Saturn and its rings. Other papers included in this issue present ground-based observations and interior modeling of these icy moons.

Cassini↗
NASA NTRS2005

The Saturn System as Observed by Cassini's Ultraviolet Imaging Spectrograph

The Cassini Ultraviolet Imaging Spectrograph (UVIS) has major new findings in all aspects of Saturn science: Saturn, its rings, Titan and the icy satellites, and the Saturn magnetosphere. Dynamic interactions between neutrals, ions, rings, moons and meteoroids produce a highly structured and time variable Saturn system. Highlights and outstanding new results will be reported, focusing on Saturn s moons and their interaction with their environment. The UVIS is one of Cassini s suite of remote sensing instruments. The UVIS instrument includes channels for extreme UV (55 to 110 nm) and far UV (110 to 190 nm) spectroscopic imaging, high speed photometry of stellar occultations, solar EUV occultation, and a hydrogen/deuterium absorption cell. UVIS has detected products of water dissociation, neutral oxygen and OH, which dominate the Saturn inner magnetosphere, in contrast to Jupiter, and H fills the entire magnetosphere apparently extending through the magnetopause at far greater density than the ion population. The O and OH and a fraction of the H are probably the products of water physical chemistry, and derived ultimately from water ice. Observed fluctuations indicate close interactions with plasma sources. Sputtering from the satellites water ice surfaces is insufficient to supply the observed mass. Stochastic events in the E ring may be the ultimate source.

Esposito, L. W.↗
NASA NTRS2005

An Overview of Cassini UVIS Icy Satellite Results So Far

The icy satellites of the Saturn system exhibit a remarkable amount of variability. From dark, battered Phoebe orbiting at 200 R(sub S) to black-and-white Iapetus, the wispy streaks of Dione, heavily cratered Tethys and Mimas, to potentially geologically active Enceladus, the extent of geological phenomena exhibited by these bodies is tremendous. Phoebe, Iapetus and Hyperion all orbit outside Saturn s magnetosphere, while Mimas, Enceladus, Dione Tethys and Rhea all orbit within the magnetosphere. Furthermore, Mimas, Enceladus, Tethys and Dione all orbit within the E-ring so the extent of exogenic effects on these icy satellites is wide-ranging. After 9 months in orbit around Saturn, we present UV results so far from Phoebe, Tethys, Dione, Iapetus, Mimas, Enceladus and Rhea. We expect that the UV signatures of these icy satellites are strongly influenced not only by their composition, but by external effects and magnetospheric environments.

Hendrix, A. R.↗
NASA NTRS2005

Iapetus and Phoebe as Measured by the Cassini UVIS

The bizarre appearance of Iapetus has long intrigued researchers of this Saturnian moon. The leading hemisphere is very dark and reddish in color at visible-near-IR wavelengths. In contrast, the trailing hemisphere is relatively bright and its near-IR spectrum is dominated by water ice. The severe hemispherical brightness dichotomy has been explained by both endogenic and exogenic models. The primary endogenic model involves eruption of dark material onto the leading hemisphere from the interior of Iapetus. Exogenic models include exposure of dark underlying material by micrometeorite bombardment, contamination of Iapetus leading hemisphere by Titan tholin material, and the coating of the leading hemisphere by Phoebe dust. It has been shown that the dark material on Iapetus leading hemisphere is redder in color at visible wavelengths than Phoebe, which is spectrally gray at visible wavelengths. An additional exogenic model involves the coating of both Iapetus leading hemisphere and Hyperion with material from small retrograde satellites, which are reddish in color at visible wavelengths. We present the first FUV spectra of Iapetus and Phoebe to investigate whether the UV wavelength range can contribute to solving the puzzle of Iapetus.

Hendrix, A. R.↗
NASA NTRS2005

Ultraviolet Views of Enceladus, Tethys, and Dione

The Cassini Ultraviolet Imaging Spectrograph (UVIS) has collected ultraviolet observations of many of Saturn's icy moons since Cassini's insertion into orbit around Saturn. We will report on results from Enceladus, Tethys and Dione, orbiting in the Saturn system at distances of 3.95, 4.88 and 6.26 Saturn radii, respectively. Icy satellite science objectives of the UVIS include investigations of surface age and evolution, surface composition and chemistry, and tenuous exospheres. We address these objectives by producing albedo maps, and reflection and emission spectra, and observing stellar occultations. UVIS has four channels: EUV: Extreme Ultraviolet (55 nm to 110 nm), FUV: Far Ultraviolet (110 to 190 nm), HSP: High Speed Photometer, and HDAC: Hydrogen-Deuterium Absorption Cell. The EUV and FUV spectrographs image onto a 2-dimensional detector, with 64 spatial rows by 1024 spectral columns. To-date we have focused primarily on the far ultraviolet data acquired with the low resolution slit width (4.8 angstrom spectral resolution). Additional information is included in the original extended abstract.

Hansen, C. J.↗
NASA NTRS2004

Space Weathering: An Ultraviolet Indicator

We present evidence suggesting that the spectral slope of airless bodies in the UV-visible wavelength range can be used as an indicator of exposure to space weathering. While space weathering generally produces a reddening of spectra in the visible-NIR spectral regions, it tends to result in a bluing of the UV-visible portion of the spectrum, and may in some cases produce a spectral reversal. The bluing effect may be detectable with smaller amounts of weathering than are necessary to detect the longer-wavelength weathering effects.

Hendrix, A. R.↗
NASA NTRS2003

An Ultraviolet Imaging Spectrograph for JIMO

It is vital to include an ultraviolet spectrograph as part of the JIMO payload to Europa, Ganymede and Callisto. Ultraviolet measurements are key for understanding the atmospheres, auroral activity and surfaces of these icy satellites, and a UV imaging spectrograph will also complement a visible camera and near-IR spectrometer, to achieve full wavelength coverage in remote sensing of the icy satellites. The UV instrument proposed for JIMO will be similar to that currently on board the Cassini spacecraft. The design draws on the experience of building UV spectrometers for Mariner, Pioneer, Galileo and Cassini. It will have three spectrographic channels that provide images and spectra of the atmosphere, aurorae and surface: An EUV channel (800-110 nm), an FUV channel (110 to 190 nm) range, and an NUV channel (180 to 350 nm).

Hendrix, A. R.↗
NASA NTRS2003

Space Weathering: An Ultraviolet Indicator

We present evidence suggesting that the spectral slope of airless bodies in the UV-visible wavelength range can be used as an indicator of exposure to space weathering. While space weathering generally produces a reddening of spectra in the visible-NIR spectral regions, it tends to result in a bluing of the UV-visible portion of the spectrum, and may in some cases produce a spectral reversal. The bluing effect may be detectable with smaller amounts of weathering than are necessary to detect the longer-wavelength weathering effects.

Hendrix, A. R.↗
NASA NTRS2002

The lunar phase curve in the near ultraviolet

We present results from an ongoing program to perform UV measurements (215.0 and 237.0 nm) of the Moon at varying solar phase angles to understand the lunar phase curve at ultraviolet wave- lengths.

lunar↗
NASA NTRS2002

Ultraviolet surface properties of the icy galilean satellites from phase curve analysis

In this study, we use ultraviolet observations from the International Utlraviolet Explorer (IUE) and the Galileo Ultraviolet Spectrometer (UVS) to compose the ultraviolet solar phase curves of the icy galilean satellites. Broadband rotation phase curves from 0.26 to 0.32 microns are constructed in order to examine the rotational behavior of the icy Galilean satellites in the ultraviolet. After normalizing the rotational variations, modeling of the solar phase variations are compared to comparable studies in the visible.

International↗
NASA NTRS2002

The Lunar Phase Curve in the Near Ultraviolet

We present the ultraviolet phase curve of the Moon at two wavelengths, 215 and 237 nm, as measured by the Ultraviolet Spectrometer on board the Student Nitric Oxide Explorer. Additional information is contained in the original extended abstract.

Hendrix, A. R.↗