Virgil G. Kunde

Investigation of the Martian environment by infrared spectroscopy on Mariner 9

Abstract The infrared spectroscopy experiment on Mariner 9 provides extensive information on the Martian environment, including spatial, diurnal, and secular dependences of atmospheric and surface parameters. Measurements obtained during and after the planet-wide dust storm indicate that large diurnal variations in atmospheric temperature existed up to at least 30 km; winds inferred from the temperature fields show a strong tidal component and significant ageostrophic behavior. With the dissipation of the dust, the maximum in the atmospheric temperature field moved from approximately latitude -60° and late afternoon local time to near the subsolar point in latitude and time. Analysis of spectral features due to the atmospheric dust indicates a SiO 2 content of 60 ± 10%, implying that substantial geochemical differentiation has occurred. Water vapor estimates indicate abundances of 10–20 precipitable micrometers, less than has been inferred by ground-based methods in similar phases of previous Martian seasons. Between November 1971 and April 1972 no gross latitudinal or temporal dependence in the water vapor distribution has been detected from the south polar region to the equator. Water vapor has not been detected over the north polar regions. Surface pressure mapping has been carried out from which topographic relief of nearly two pressure scale heights is inferred. Extensive regions have been found where the surface pressure exceeds the triple-point pressure of water.

Infrared Observations of the Jovian System from Voyager 1

The infrared spectroscopy and radiometry investigation has obtained spectra of Jupiter and its satellites between approximately 180 and 2500 cm–1 with a spectral resolution of 4.3 cm–1. The Jupiter spectra show clear evidence of H2, CH4 C2H2, C2H6, CH3D, NH3, PH3, H2O, and GeH4. A helium concentration of 0.11 � 0.03 by volume is obtained. Meridional temperature cross sections show considerable structure. At high latitudes, the stratosphere is warmer in the north than in the south. The upper troposphere and lower stratosphere are locally cold over the Great Red Spot. Amalthea is warmer than expected. Considerable thermal structure is observed on Io, including a relatively hot region in the vicinity of a volcanic feature.

Infrared Observations of the Saturnian System from Voyager 2

During the passage of Voyager 2 through the Saturn system, infrared spectral and radiometric data were obtained for Saturn, Titan, Enceladus, Tethys, Iapetus, and the rings. Combined Voyager 1 and Voyager 2 observations of temperatures in the upper troposphere of Saturn indicate a seasonal asymmetry between the northern and southern hemispheres, with superposed small-scale meridional gradients. Comparison of high spatial resolution data from the two hemispheres poleward of 60� latitude suggests an approximate symmetry in the small-scale structure, consistent with the extension of a symmetric system of zonal jets into the polar regions. Longitudinal variations of 1 to 2 K are observed. Disk- averaged infrared spectra of Titan show little change over the 9-month interval between Voyager encounters. By combining Voyager 2 temperature measurements with ground-based geometric albedo determinations, phase integrals of 0.91 � 0.13 and 0.89 � 0.09 were derived for Tethys and Enceladus, respectively. The subsolar point temperature of dark material on Iapetus must exceed 110 K. Temperatures (and infrared optical depths) for the A and C rings and for the Cassini division are 69 � 1 K (0.40 � 0.05), 85 � 1 K (0.10 � 0.03), and 85 � 2 K (0.07 � 0.04), respectively.

Infrared observations of the neptunian system.

The infrared interferometer spectrometer on Voyager 2 obtained thermal emission spectra of Neptune with a spectral resolution of 4.3 cm-1. Measurements of reflected solar radiation were also obtained with a broadband radiometer sensitive in the visible and near infrared. Analysis of the strong C2H2 emission feature at 729 cm-1 suggests an acetylene mole fraction in the range between 9 x 10-8 and 9 x 10-7. Vertical temperature profiles were derived between 30 and 1000 millibars at 70� and 42�S and 30�N. Temperature maps of the planet between 80�S and 30�N were obtained for two atmospheric layers, one in the lower stratosphere between 30 and 120 millibars and the other in the troposphere between 300 and 1000 millibars. Zonal mean temperatures obtained from these maps and from latitude scans indicate a relatively warm pole and equator with cooler mid-latitudes. This is qualitatively similar to the behavior found on Uranus even though the obliquities and internal heat fluxes of the two planets are markedly different. Comparison of winds derived from images with the vertical wind shear calculated from the temperature field indicates a general decay of wind speed with height, a phenomenon also observed on the other three giant planets. Strong, wavelike longitudinal thermal structure is found, some of which appears to be associated with the Great Dark Spot. An intense, localizd cold region is seen in the lower stratosphere, which does not appear to be correlated with any visible feature. A preliminary estimate of the effective temperature of the planet yields a value of 59.3 � 1.0 kelvins. Measurements of Triton provide an estimate of the daytime surface temperature of 38+3-4 kelvins.

Mars: Mariner 9 spectroscopic evidence for H2O ice clouds

Spectral features observed with the Mariner 9 interferometer spectrometer are identified as those of H2O ice. The measured spectra are compared with theoretical calculations for the transfer of radiation through clouds of ice particles with variations in size distribution and integrated cloud mass. Comparisons with an observed spectrum from the Tharsis Ridge region indicate H2O ice clouds composed of particles with a mean radius of 2.0 micrometers and an integrated cloud mass of 5 x 10-5 grain per square centimeter.

Albedo, internal heat flux, and energy balance of Saturn

Full-disk and high-resolution measurements recorded during the Voyager 1 flyby of Saturn by the radiometer of the infrared instrument, IRIS, indicate a geometric albedo of 0.242 ± 0.012, which is lower than previous estimates. The given error is largely due to uncertainties in systematic corrections; random effects are small. Combining this measurement with the Pioneer-derived phase integral yields a Bond albedo of 0.342 ± 0.030. Infrared spectra recorded at the same time by the Michelson interferometer, along with a model extrapolation to wavenumbers not covered by the instrument, yield an effective temperature of 95.0 ± 0.4°K. As in the case of the radiometer, random instrumental errors are small, and the quoted error in the effective temperature reflects primarily uncertainties in systematic corrections. The rings of Saturn significantly affect both the short- and long-wavelength fluxes. From these measurements the internal heat flux of Saturn is 2.01 ± 0.14 10−4W cm−2, and the energy balance, defined as the ratio of total emitted to total absorbed energy, is 1.78 ± 0.09.

Cassini infrared Fourier spectroscopic investigation

The composite infrared spectrometer (CIRS) is a remote sensing instrument to be flown on the Cassini orbiter. CIRS will retrieve vertical profiles of temperature and gas composition for the atmospheres of Titan and Saturn, from deep in their tropospheres to high in their stratospheres. CIRS will also retrieve information on the thermal properties and composition of Saturns rings and Saturnian satellites. CIRS consists of a pair of Fourier Transform Spectrometers (FTSs) which together cover the spectral range from 10-1400 cm-1 with a spectral resolution up to 0.5 cm-1. The two interferometers share a 50 cm beryllium Cassegrain telescope. The far-infrared FTS is a polarizing interferometer covering the 10-600 cm-1 range with a pair of thermopile detectors, and a 3.9 mrad field of view. The mid-infrared FTS is a conventional Michelson interferometer covering 200-1400 cm-1 in two spectral bandpasses: 600-1100 cm- 1100-1400 cm(superscript -1 with a 1 by 10 photovoltaic HgCdTe array. Each pixel of the arrays has an approximate 0.3 mrad field of view. The HgCdTe arrays are cooled to approximately 80K with a passive radiative cooler.

Infrared Observations of the Uranian System

The infrared interferometer spectrometer (IRIS) on Voyager 2 recorded thermal emission spectra of Uranus between 200 and 400 cm-1 and of Miranda and Ariel between 200 and 500 cm-1 with a spectral resolution of 4.3 cm-1. Reflected solar radiation was also measured with a single-channel radiometer sensitive in the visible and near infrared. By combining IRIS spectra with radio science results, a mole fraction for atmospheric helium of 0.15 � 0.05 (mass fraction, 0.26 � 0.08) is found. Vertical temperature profiles between 60 and 900 millibars were derived from average polar and equatorial spectra. Temperatures averaged over a layer between 400 to 900 millibars show nearly identical values at the poles and near the equator but are 1 or 2 degrees lower at mid-latitudes in both hemispheres. The cooler zone in the southern hemisphere appears darker in reflected sunlight than the adjacent areas. An upper limit for the effective temperature of Uranus is 59.4 kelvins. Temperatures of Miranda and Ariel at the subsolar point are 86 � 1 and 84 � 1 kelvins, respectively, implying Bond albedos of 0.24 � 0.06 and 0.31 � 0.06, respectively. Estimates of phase integrals suggest that these satellites have unusual surface microstructure.

Infrared Spectroscopy Experiment on the Mariner 9 Mission: Preliminary Results

The Mariner 9 infrared spectroscopy experiment has provided goodquality spectra of many areas of Mars, predominantly in the southern hemisphere. Large portions of the thermal emission spectra are significantly affected by dust with a silicon oxide content approximately corresponding to that of an intermediate igneous rock, thus implying that Mars has undergone substantial geochemical differentiation. Derived temperature profiles indicate a warm daytime upper atmosphere with a strong warming over the south polar cap. Atmospheric water vapor is clearly observed over the south polar area and less strongly over other regions.

Study of the Ammonia ice cloud layer in the equatorial region of Jupiter from the infrared interferometric experiment on voyager

Abstract Spectra from the Voyager 1 infrared interferometer spectrometer (IRIS) obtained near the time of closest approach to Jupiter were analyzed for the purpose of inferring ammonia cloud properties associated with the Equatorial Region. Comparisons of observed spectra with synthetic spectra computed from a radiative transfer formulation, that includes multiple scattering, yielded the following conclusions: (1) very few NH 3 ice particles with radii less than 3 μm contribute to the cloud opacity; (2) the major source of cloud opacity arises from particles with radii in excess of 30 μm; (3) column particle densities are between 1 and 2 orders of magnitude smaller than those derived from thermochemical considerations alone, implying the presence of important atmospheric motion; and (4) another cloud system is confirmed to exist deeper in the Jovian troposphere.