Mars ultraviolet reflectance compared with imaging, topography and geology
Explore the source record for details and available documents.
Mars ultraviolet mariners↗
Engineering topics
Simmons, K. E.
Publications and source records attributed to Simmons, K. E..
Description of Data Archiving Activities
Data restoration and archiving activities for this project have resulted in the restoration of 100% of the original Mariner 9 raw data set as well as many of the secondary analysis data sets. These data sets have been submitted to the Planetary Data System (PDS) Atmospheric Node, long with their PDS labels and descriptive metadata.
Simmons, K. E.↗
Description of Data Archiving Associated With the NASA Goddard Grant NAGS-9590
Data restoration and archiving activities for this project have resulted in the restoration of 100% of the original Mariner 9 raw data set as well as many of the secondary analysis data sets. These data sets have been submitted to the Planetary Data System (PDS) Atmospheric Node, along with their PDS labels and descriptive metadata. In addition, a useful visualization and analysis tool has also been developed which allows the user to compare these Mariner 1971 Ultraviolet spectral data with several choices of related data sets: Mariner 9 images, USGS geologic data, MGS MOLA topography, Viking images (Viking MDIM) and thermal inertia data (MGS TES).
Simmons, K. E.↗
Observations of interplanetary Lyman-alpha with the Galileo Ultraviolet Spectrometer: Multiple scattering effects at solar maximum
The Galileo Ultravilet Spectrometer Experiment (UVS) obtained a partial celestial sphere map of interplanetary Lyman-alpha (IP L alpha) on 13-14 December 1990 during the first Earth encounter. The Galileo spacecraft was near the downwind axis of the local interstellar medium flow. These UVS measurements sampled the downwind, anti-sunward hemisphere. The data were modeled using a hot model of the interplanetary hydrogen density distribution with the goal of studying multiple scattering effects in the inner solar system. The derived ratio in the downwind direction of the observed brightness and a single scattering model brightness, both normalized to unity in the upwind direction, is 1.82 +/- 0.2. This brightness ratio requires a multiple scattering correction which is 36% larger than can be accounted for by theoretical calculations. The hot model may require: (1) a temperature perturbation of the interstellar wind velocity distribution or (2) an additional downstream source of interplanetary hydrogen. However, a more likely exlanation which affects the hot model is the latitude dependence of the radiation pressure. This dependence, based on the known solar L alpha flux latitude variation at solar maximum, causes a downwind brightness enhancement by preferential focusing of H-atoms with trajectory planes containing the solar poles. This result implies that radiation pressure near the solar poles is nearly independent of solar cycle and is insufficient to lead to a net repulsion of hydrogen atoms by the sun, as can occur near the ecliptic plane during the solar maximum. In addition, the UVS performed 13 observations of IP L alpha while in cruise between Venus and the Earth in 3 directions fixed in ecliptic coordinates.
Ajello, J. M.↗
(abstract) Interplanetary Lyman-alpha Observations with the Galileo Ultraviolet Spectrometer: Solar Wind Latitude Variations and Multiple Scattering at Solar Maximum
The Galileo Ultraviolet Spectrometer obtained a Lyman-alpha celestrial sphere map on 13,14 December 1990 near the first Earth encounter, with spacecraft near the interstellar wind downwind axis. The data show solar flux longitudinal and latitudinal asymmetries which are modeled with He 10830 Ssolar images. The difference between the observed brightness and a single scattering model is attributed to multiple scattering effects, which we also calculate. The data constrain the solar wind flux latitude variation at solar maximum. Other 1990-1992 Galileo Lyman-alpha data will be discussed.
solar wind ultraviolet spectrometer solar flux cel↗
The Galileo and Pioneer Venus ultraviolet spectrometer experiments - Solar Lyman-alpha latitude variation at solar maximum from interplanetary Lyman-alpha observations
Solar Ly-alpha latitude variation at solar maximum is examined on the basis of interplanetary Ly-alpha observations made during the Galileo and Pioneer Venus UV spectrometer experiments. A comparison is made of the latitude variation of the interplanetary (IP) Ly-alpha signal in 1986 at solar minimum from Pioneer Venus and in 1990 at solar maximum from Galileo. The Galileo EUV spectrometer shows that a large enhancement of the IP Ly-alpha emission occurred over the intervening four years near the solar equator. An IP Ly-alpha model is developed which considers the latitude variation of the solar Ly-alpha flux. The model fit to the data shows a 25-percent decrease of the full disk solar Ly-alpha flux from solar equator to solar pole in 1990. A detailed study of the Galileo IP Ly-alpha observations on day-of-year 190, 193, 197, and 200 in 1990 reveals that large variations occur in response to the 27-d solar variation. Analysis of these data shows that a maximum variation of 20 percent can be expected in the IP Ly-alpha upwind intensity over this 27-d period.
Pryor, W. R.↗
Galileo ultraviolet spectrometer experiment - Initial Venus and interplanetary cruise results
The Galileo Extreme Ultraviolet Spectrometer obtained a spectrum of Venus atmospheric emissions in the 55.0- to 125.0-nm wavelength region. Emissions of helium (58.4 nm), ionized atomic oxygen (83.4 nm), and atomic hydrogen (121.6 nm), as well as a blended spectral feature of atomic hydrogen (Lyman-beta) and atomic oxygen (102.5 nm), were observed at 3.5-nm resolution. During the Galileo spacecraft cruise from Venus to earth, Lyman-alpha emission from solar system atomic hydrogen (121.6 nm) was measured. The dominant source of the Lyman-alpha emission is atomic hydrogen from the interstellar medium. A model of Galileo observations at solar maximum indicates a decrease in the solar Lyman-alpha flux near the solar poles. A strong day-to-day variation also occurs with the 27-day periodicity of the rotation of the sun.
Hord, C. W.↗
Temperature and aerosol structure of the nightside Uranian stratosphere from Voyager 2 photopolarimeter stellar occultation measurements
Voyager 2 UV-photopolarimeter occultation observations toward Gamma Peg, obtained on the nightside of Uranus at planetocentric latitude 68.9 deg N on January 24, 1986, are used to probe the structure of the Uranian atmosphere. The data are presented graphically and compared with the predictions of model atmospheres. The temperature profile for an aerosol-free atmosphere ranges from 85 + or - 2.3 K at 2.7 mbar to 96 + or - 13 K at 370 microbar, and the 1-mbar radius is found to be 25,219 + or - 6.3 km. The extinction coefficient for an aerosol haze layer at 1 mbar or higher is shown to be less than or equal to about 0.0001/km, but it is suggested that a well-mixed haze layer consisting of meteor or ring dust and/or photochemical condensates may well be present below 3 mbar.
West, R. A.↗
Photometry from Voyager 2 - Initial results from the Uranian atmosphere, satellites, and rings
The results of Voyager 2 photopolarimetry (PPS) surveys of Uranus, the ring system, occultation experiments and observations of the Uranian moons are reported. Dual-channel photometry and polarimetry data obtained of the atmosphere at various emission and phase angles are delineated and compared with characteristics of the Saturn and Jupiter atmospheres. The results of temperature, UV absorption and density profile calculations are also discussed. Extensive ring dimensional data, based on two occultation experiments, are provided in tabular form noting that the rings contain no dust. Finally, the geometric albedos of the five major moons and the phase curve of the moon Titania are presented. The latter data indicate that Titanian surface features are not the result of recent events such as volcanism or ice slurry outflows.
Lane, A. L.↗
Evidence for material between Saturn's A and F rings from the Voyager 2 photopolarimeter experiment
The region in the Saturn system between the F ring and the outer edge of the A ring is an area that appears, in images from the imaging experiment, to be virtually devoid of material except for three small satellites. Near the orbit of 1980S28, Atlas - the innermost satellite - the Voyager Photopolarimeter Stellar Occultation data show a discontinuity in count rate which marks a boundary between the tenuous material near the outer edge of the A ring and the orbit of Atlas. The data pertaining to this region have been examined with the aid of statistics and models generated from other similar ring structures. It is concluded that the discontinuity is real, implying the existence of tenuous material of normal optical depth of 0.01 to 0.006 in this region.
Graps, A. L.↗
Voyager photopolarimeter stellar occultation of Saturn's rings
On Aug. 25, 1981, the Voyager 2 photopolarimeter system observed a stellar occultation by Saturn's rings. A brief description of this experiment along with details of the data reduction are presented. The occultation results are given in tabular and graphical form at a resolution of 60 km. Histograms of the frequency of optical depth show dominantly unimodal distributions in each of the classical ring elements. The frequency distribution of the entire ring system shows three modes at tau values of about 0.08, 0.5, and more than 2.5.
Esposito, L. W.↗
Photometry and polarimetry of Saturn at 2640 and 7500 A
Voyager 2 photometric and polarimetric data are reduced and tabulated, with spatially resolved limb-to-terminator scans across Saturn's equatorial zone providing information on the altitude distribution of UV-absorbing hazes, together with the phase function and polarizing properties of stratospheric and tropospheric aerosols. It is found that the UV photometry and polarimetry are best fit by Rayleigh's phase matrix. A stratospheric haze of small particles is allowed as long as the optical depth is near unity or less, and the center of the haze layer is in the 30 to 70 mbar region. The altitudes presently derived for three latitudes agree with those obtained by ground-based methane band studies and analyses from Pioneer 11. A high altitude absorber is abundant in the polar regions.
West, R. A.↗
Voyager 2 photopolarimeter observations of Titan
Observations of Titan's whole-disk polarization at 2460 and 7500 A are presented and analyzed in terms of model scattering atmospheres. If the Titan aerosols are spherical or nearly spherical, no single combination of refractive index and size distribution is able to fit data at both wavelengths. However, a vertically inhomogeneous distribution suggested by Tomasko and Smith (1980), characterized by a size gradient with altitude, fits the data at 2640 A moderately well but must be modified at intermediate and large optical depths to fit the 7500-A data. Results for synthetic phase functions indicate that the single-scattering polarization must be 70 percent or larger in the UV and 78 percent or larger in the near-IR at 90-deg phase angle, depending on the phase function. If the correct phase function is similar to that for 0.5-micron-radius spheres, the UV single-scattered polarization must be 84 percent and the near-IR single-scattered polarization must be over 90 percent. Such large polarizations are impossible for 0.5-micron-radius spheres but may be possible for nonspherical particles with effective radii near 0.5 micron, although the existence of nonspherical particles with the scattering properties required by these and other observations has not been demonstrated.
West, R. A.↗
Voyager photopolarimeter observations of Saturn and Titan
The Voyager 2 photopolarimeter experiment observed the intensity and polarization of scattered sunlight from the atmospheres of Saturn and Titan in the near-UV at 2640 A and in the near-IR at 7500 A. Measurements of Saturn's limb brightening and polarization at several phase angles up to 70 deg indicate that a significant optical depth of UV absorbers are present in the top 100 mbar of Saturn's atmosphere in the equatorial zone and north polar region, and possibly at other latitudes as well. UV absorbers are prominent in polar regions, suggesting that charged particle precipitation from the magnetosphere may be important in their formation. The whole-body polarization of Titan is strongly positive in both the UV and near IR. If spherical particles are responsible for the polarization, no single size distribution or refractive index can account for the polarization at both wavelengths. The model atmosphere proposed by Tomasko and Smith (1982), characterized by a gradient in particle size with altitude, seems capable of explaining the Voyager observations.
West, R. A.↗
The source of Saturn electrostatic discharges
During both Voyager encounters with the saturnian system, the Planetary Radio Astronomy experiment detected strong discrete episodic bursts of radio emission, termed Saturn electrostatic discharges (SED). An examination of Voyager 2 photopolarimeter data now reveals a narrow feature (possibly a gap) in Saturn's B ring. A single, unique object appears to be responsible for both the SED and this feature.
Evans, D. R.↗
Photopolarimetry from Voyager 2 - Preliminary results on Saturn, Titan, and the rings
The Voyager 2 photopolarimeter was reprogrammed prior to the August 1981 Saturn encounter to perform orthogonal-polarization, two-color measurements on Saturn, Titan, and the rings. Saturn's atmosphere has ultraviolet limb brightening in the mid-latitudes and pronounced polar darkening north of 65 deg N. Titan's opaque atmosphere shows strong positive polarization at all phase angles (2.7 deg to 154 deg), and no single-size spherical particle model appears to fit the data. A single radial stellar occultation of the darkened, shadowed rings indicated a ring thickness of less than 200 meters at several locations and clear evidence for density waves caused by satellite resonances. Multiple, very narrow strands of material were found in the Encke division and within the brightest single strand of the F ring.
Lane, A. L.↗
The C ring of Saturn: A high resolution view of some of its structure
Voyager 2 photopolarimeter stellar occultation data on Saturn C ring are discussed. The overall shape is much like the W-shape of other Saturnian rings and the Uranian epsilon ring. The inner structure is quite complex and it is not possible to locate the region of the weaker 1980S27 resonance. There appear to be pseudoperiodic structures, with very pronounced variations in optical depth. Possibly two isolated resonances in close proximity can develop a gravitational interaction that leads to wave patterns imposed upon the intervening ring material. The strength of the variations noted in optical depth between 90140 and 90175 km is too large to be an artifact. It could be temporal, however.
Lane, A. L.↗
Near-ultraviolet scattering properties of Jupiter
Voyager 2 photometric observations of Jupiter at four phase angles between 20 and 80 deg and at various illumination angles are used to determine the altitude distribution and scattering properties of the material responsible for Jupiter's low geometric albedo at 2400 A. Center-to-limb measurements at midlatitudes indicate that most of the absorbing material lies deeper than 100 mbar, while the latitudinal distribution of stratospheric absorbers suggests that energy deposition from the magnetosphere is important in the formation of the absorbers. Scattering properties of model atmospheres containing three distinct aerosol size distributions are examined, and an upper limit to the column abundance of particles larger than the 0.05 micron radius in the north tropical zone and equatorial belt are derived. Rayleigh scattering fits the variation of intensity with phase angles between 20 and 80 deg better than any of the considered particle phase functions, although the Rayleigh scattering from the top 100 mbar obscures effects due to scattering from deeper absorbing particles.
West, R. A.↗