Hydrogen Peroxide on the Surface of Europa
Spatially resolved infrared and ultraviolet wavelength spectra of Europa's leading, anti-jovian, quadrant observed from the Galileo spacecraft show absorption features due to hydrogen peroxide.
Jupiter↗
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Near-infrared mapping spectrometer for investigation of Jupiter and its satellites
In the late 1980s, the investigation of the Jupiter system will be continued with the aid of the Galileo spacecraft, which is to be placed in orbit around the planet. The Near-Infrared Mapping Spectrometer (NIMS) is one of several instruments which will be employed in connection with the study of Jupiter and its satellites. The NIMS combines spectroscopic and imaging capabilities. It represents, therefore, a new concept in remote sensing planetary experiments. Information provided by NIMS will be supplemented by results obtained with the aid of the Galileo Solid State Imager (SSI). In the SSI, very high spatial resolution is obtained, but limited spectral information is available. One of the goals of the Galileo mission is related to the investigation of the chemical composition and physical state of Jupiter's satellites, taking into account Io, Europa, Ganymede, and Callisto. Another primary aim involves the study of the Jovian atmosphere, giving attention to chemical composition, atmospheric structure, clouds, energy balance, and atmospheric motions.
Aptaker, I. M.↗
Chemical abundances in the atmospheres of the giant planets and their satellites
Recent results on the composition and structure of the atmospheres of Jupiter, Saturn, Uranus, Neptune, Pluto, and their satellites are summarized with an orientation toward topics of particular interest to the subject of exobiology. The need for an accurate Jovian temperature profile is noted, and current values are given for the known H2, NH3, and CH4 abundances of each planet as well as Titan and Triton. Trace constituents and chromophores in the Jovian atmosphere are discussed, the role of comets as a link between chemical evolution in the solar system and the chemistry of the interstellar medium is examined, and some features in the IR spectrum of Titan are interpreted. The hope is expressed that Titan will remain a useful proving ground for theories of low-temperature abiogenic organic-compound production
Owen, T.↗
Callisto: A World in Its Own Right
This paper presents a discussion on the planetary structure, evolution and composition of the Gallilean Satellite, Callisto. The Jupiter Icy Moons Orbiter (JIMO) mission is currently planned to first orbit Callisto then its two icy sisters Ganymede and Europa to investigate Callisto's actual configuration. The JIMO mission consists of three globally complete mapping sets of Callisto along with spectrographic measurements to answer remaining outstanding questions about the geomorphology of Callisto.
Moore, Jeffrey M.↗
The Galileo mission to Jupiter and its moons
Since 1995, the Galileo mission, despite all the technical troubles, has provided a detailed view of the Jovian system, revealed only fleetingly in the Pioneer and Voyager flybys of the 1970s. The atmospheric probe penetrated the clouds and conducted the first in situ sampling of an outer planet's atmosphere, transmitting data for an hour before it was lost in the gaseous depths. The orbiter, which is still going strong, has photographed and analyzed the planet, its rings, and its diverse moons. Some of the results obtained so far are reviewed.
Jupiter↗
Galileo Ultraviolet Spectrometer experiment
The Galileo ultraviolet spectrometer experiment uses data obtained by the Ultraviolet Spectrometer (UVS) mounted on the pointed orbiter scan platform and from the Extreme Ultraviolet Spectrometer (EUVS) mounted on the spinning part of the orbiter with the field of view perpendicular to the spin axis. The UVS is a Ebert-Fastie design that covers the range 113-432 nm with a wavelength resolution of 0.7 nm below 190 and 1.3 nm at longer wavelengths. The UVS spatial resolution is 0.4 deg x 0.1 deg for illuminated disk observations and 1 deg x 0.1 deg for limb geometries. The EUVS is a Voyager design objective grating spectrometer, modified to cover the wavelength range from 54 to 128 nm with wavelength resolution 3.5 nm for extended sources and 1.5 nm for point sources and spatial resolution of 0.87 deg x 0.17 deg. The EUVS instrument will follow up on the many Voyager UVS discoveries, particularly the sulfur and oxygen ion emissions in the Io torus and molecular and atomic hydrogen auroral and airglow emissions from Jupiter. The UVS will obtain spectra of emission, absorption, and scattering features in the unexplored, by spacecraft, 170-432 nm wavelength region. The UVS and EUVS instruments will provide a powerful instrument complement to investigate volatile escape and surface composition of the Galilean satellites, the Io plasma torus, micro- and macro-properties of the Jupiter clouds, and the composition structure and evolution of the Jupiter upper atmosphere.
Hord, C. W.↗
Channel and physical models of the Jovian subnebula
A semiempirical physical model of the Jovian subnebula was developed by analogy with the primitive solar nebula itself. The chemical aspects of this model are developed according to the principles developed in the study of the thermochemistry and gas kinetic behavior of the solar nebula, but with important modifications to take into account the higher pressures and densities in the Jovian subnebula. The bulk compositions and densities of the inner satellites of Jupiter are calculated. It is proposed that Europa differs from Io chiefly in that in has suffered a less severe thermal history. The general features of this model are applicable with minor modification to the systems of Saturn and Uranus.
Lewis, J. S.↗
The photochemistry of the atmospheres of the outer planets and their satellites
The thermal structure and composition of Uranus, Neptune, Saturn, Jupiter, Titan, and Io are described. Molecular hydrogen is the dominant constituent in the atmosphere of the outer planets. The hydrogen and helium, methane, ammonia and phosphine, and carbon monoxide photochemical reactions of the outer planets are studied. The importance of Jupiter's lightning as a source of organic matter is examined. The aerosol and haze layers of the stratosphere of Jupiter, Saturn, Neptune, and Uranus are observed. The photochemistry of Titan's atmosphere, which includes nitrogen, methane, carbon monoxide, and carbon dioxide reactions, is analyzed. The SO2 atmosphere on Io is discussed.
Strobel, D. F.↗
Ganymede and Callisto: Beauty is only skin deep
Ganymede and Callisto, the two giant icy satellites of Jupiter, have very nearly the same size, composition, and location in the solar system, yet their surfaces are profoundly different. A new scenario of their geologic histories indicates that the differences may be only skin deep.
Croft, S. K.↗
Consideration of probability of bacterial growth for Jovian planets and their satellites
Environmental parameters affecting growth of bacteria (e.g., moisture, temperature, pH, and chemical composition) were compared with current atmospheric models for Jupiter and Saturn, and with the available physical data for their satellites. Different zones of relative probability of growth were identified for Jupiter and Saturn, with the highest in pressure regions of 1-10 million N/sq m (10 to 100 atmospheres) and 3-30 million N/sq m (30 to 300 atmospheres), respectively. Of the more than two dozen satellites, only the largest (Io, Europa, Ganymede, Callisto, and Titan) were found to be interesting biologically. Titan's atmosphere may produce a substantial greenhouse effect providing increased surface temperatures. Models predicting a dense atmosphere are compatible with microbial growth for a range of pressures at Titan's surface. For Titan's surface the probability of growth would be enhanced if (1) the surface is entirely or partially liquid (water), (2) volcanism (in an ice-water-steam system) is present, or (3) access to internal heat sources is significant.
Taylor, D. M.↗
A Shuttle free flyer qualification/acceptance program - Galileo
The next U.S. planetary mission, the Galileo Project, is to be launched in late spring 1986. Primary studies to be conducted are related to the chemical composition and physical state of Jupiter's atmosphere, the chemical composition and physical state of the Jovian satellites, and the structure and physical dynamics of the Jovian magnetosphere. The studies are to be performed with the aid of a planetary Orbiter and an atmospheric entry Probe. At launch and during the interplanetary cruise trip to Jupiter, the Orbiter and Probe will form an integrated spacecraft. The Shuttle will be employed in the launch of the spacecraft. A Centaur high energy upper stage is to transfer the spacecraft from the Shuttle parking orbit to the direct earth-to-Jupiter trajectory. Attention is given to Galileo environmental program special characteristics and major influencing factors.
Schlue, J. W.↗
Galileo mission overview
The Galileo mission has three major and equally important scientific objectives: the investigation of the chemical composition and physical state of the Jupiter atmosphere, the study of the composition and state of the Jovian satellites, and the probing of the structure and physical dynamics of the Jovian magnetosphere. The Galileo spacecraft comprises an Orbiter and an atmospheric entry Probe, which will be released on a ballistic entry trajectory from the Orbiter about 150 days before Jupiter arrival. After Probe release, the Orbiter will overfly the Probe during entry in order to relay its data to earth. The Orbiter will then insert itself into a 200-day orbit around Jupiter. Attention is given to the radio science, remote sensing and fields and particles instruments to be carried for the mission.
Oneil, W. J.↗
Cosmological considerations regarding Uranus
The cosmogony of Uranus is discussed within the context of a picture in which solid condensed materials accumulate to form a large body, which then acquires significant amounts of gas from the primitive solar nebula. Of prime cosmogonical importance is the tilt of the equatorial plane of the planet and of the plane of the satellite orbits by 98 deg with respect to the plane of the planetary orbit. The tilt of the planet can easily occur as a result of a major collision during the formation process; it seems most likely that the tilt of the satellite orbits requires that they were formed from a gaseous disk rotating about the planet after the tilt of the planetary rotational axis had occurred. Possible methods for tilting this gaseous disk are discussed. A strong early magnetic field may have helped in this and may have played an essential role in slowing down the spin of the planet to the present observed value. These processes may have produced significant compositional differences between the satellites of Uranus and those of Jupiter and Saturn.
Cameron, A. G. W.↗
Thermal design of the Galileo bus and Retro Propulsion Module
The Galileo spacecraft (S/C) consists of an Orbiter and Probe which have instruments to investigate the chemical composition and physical state of Jupiter's atmosphere, the Jovian satellites and the structure and physical dynamics of the Jovian magnetosphere. Galileo was at the Kennedy Space Center (KSC) preparing for a May 1986 launch at the time of the Challenger accident. The delay and an incraease in mission time has decreased the Radioisotope Thermoelectric Generator power output significantly. A change to the Inertial Upper Stage from the more powerful Centaur G-Prime has resulted in a trajectory that requires gravity assists once by Venus and twice by earth. The resulting peak solar intensity of this roundabout trajectory is more than twice the previous design value for the direct trajectory. Galileo was returned to the Jet Propulsion Laboratory (JPL) from KSC in February 1987 to begin the rework of the S/C thermal design. Verification of the thermal redesign was completed in the JPL 25' space simulator in August and November of 1988. This paper summarizes the thermal design and redesign of the Bus and Retro Propulsion Model.
Avila, A.↗
Spectral mapping of Jupiter and the Galilean satellites in the near infrared
A near-infrared mapping spectrometer is included in the science complement of the Galileo Mission, which will explore Jupiter and its satellites in the mid-1980s. The objectives of the infrared mapping spectrometer experiment are to map compositional units on the surfaces of the Jovian satellites and to characterize the mineral content of these units. For Jupiter's atmosphere, this experiment will investigate such areas as cloud properties and the spatial and temporal variability of minor species. The instrument consists of a telescope, a plane grating spectrometer, a Si and InSb detector array, and a passive radiative cooler. The spectral range is 0.7-5.2 microns, covered with a resolution of 0.025 micron. A wobbling secondary mirror in the telescope provides one dimension of spatial scanning, while the other dimension is provided by motion of the spacecraft scan platform.
Carlson, R. W.↗
Laboratory reflection spectra for the determination of chemical composition of ice bodies
The visible (0.3 to 1.03 microns) spectral reflectances of N2O, NH3, H2S, and NH4HS frosts and mixtures of these frosts as well as their UV-irradiated products have been measured. These spectra are compared with the spectra of the Galilean satellites of Jupiter, Saturn's rings, and Saturn's satellites to place limits on their surface compositions.
Lebofsky, L. A.↗
Ultraviolet spectrometer experiment for the Voyager mission
An objective grating spectrometer covering the wavelength range of 500 to 1700 A with a 10-A resolution is employed for the Voyager ultraviolet spectrometer experiment. In determining the composition and structure of the atmospheres of Saturn, Jupiter and several satellites, the ultraviolet spectrometer will rely on airglow mode observations to measure radiation from the atmospheres due to resonant scattering of solar flux, and the occultation mode for assessments of the atmospheric extinction of solar or stellar radiation as the spacecraft enters shadow zones. Since it is capable of prolonged stellar observations in the 500 to 1000 A wavelength range, the spectrometer is expected to make important contributions to exploratory studies of UV sources.
Broadfoot, A. L.↗
Spectrophotometric remote sensing of planets and satellites
The most recent comprehensive results on spectrophotometric remote sensing of planets and satellites are reviewed. The moon and terrestrial planets are considered in terms of individual surface elements, reflectance spectra being analyzed to show the composition of the soils of these bodies. For more distant, unresolved objects, including the asteroids, the Galilean satellites, the small satellites of Jupiter, the rings and satellites of Saturn and Uranus, as well as Triton and Pluto, the global or hemispheric averages of surface composition are the objects of study. The absorptions due to methane gas and frost are indicated.
Mccord, T. B.↗