William C. Maguire

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.

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.

Hydrocarbons in Neptune's stratosphere from Voyager infrared observations

Emission from the acetylene and ethane bands at 729 and 822 cm-1detected in the Voyager infrared spectra of Neptune has been analyzed. A large selection of low-spatial resolution spectra was used to derive the disk-averaged abundances of C2H2 and C2H6. Under the assumption of uniform vertical distributions above the saturation region, a C2H2 mixing ratio of 6−4+14 x 10 −8 and a C2H6 mixing ratio of 1.5−0.5+2.5 x 10−6 were inferred. The accuracy of the retrievals is limited by the large uncertainty in the stratospheric temperature structure. The maximum contribution to the observed C2H2 and C2H6emission comes from the 0.2- and 0.7-mbar regions, respectively. Mixing ratio profiles derived from photochemical modeling, which are not constant with height above the saturation region, indicate that the hydrocarbon emission is most sensitive to the assumed eddy diffusion coefficient in the millibar region. Either the C2H2 or the C2H6 emission can be reproduced by the photochemical model to within the accuracy of the retrievals, but not both simultaneously. Best fits to both emission features simultaneously occur with C2H2 mixing ratios a factor of 2 too high and C2H6 mixing ratios a factor of 2 too low. We consider this agreement satisfactory considering the unknowns in the chemical and photolytic processes. A set of Voyager spectra at higher spatial resolution was used to study the latitudinal variation of the C2H2 emission between 30°N and 80°S. Zonal mean radiances at the C2H2 peak show a minimum near 50°–60°S and maxima near the south pole and equator. This behavior is similar to that observed at 350 and 250 cm−1, where the lower stratosphere and troposphere are sounded. The mid-latitude minimum can be explained by a fivefold depletion of acetylene or a temperature decrease of about 15 K (or any combination of the two effects) in the 0.03- to 2-mbar region. The latitude variation in the C2H2emission could result from a circulation pattern forced from deep levels, with upwelling at mid-latitudes and subsidence at low and high latitudes.

The Voyager infrared spectroscopy and radiometry investigation

The infrared investigation on Voyager uses two interferometers covering the spectral ranges 60–600 cm−1 (17–170 μm) and 1000–7000 cm−1 (1.4–10 μm), and a radiometer covering the range 8000–25 000 cm−1 (0.4–1.2 μm). Two spectral resolutions (approximately 6.5 and 2.0 cm−1) are available for each of the interferometers. In the middle of the thermal channel (far infrared interferometer) the noise level is equivalent to the signal from a target at 50 K; in the middle of the reflected sunlight channel (near infrared interferometer) the noise level is equivalent to the signal from an object of albedo 0.2 at the distance of Uranus.For planets and satellites with substantial atmospheres, the data will be used to investigate cloud and gas composition (including isotopic ratios), haze scale height, atmospheric vertical thermal structure, local and planetary circulation and dynamics, and planetary energy balance. For satellites with tenuous atmospheres, data will be gathered on surface and atmospheric composition, surface temperature and thermal properties, local and global phase functions, and surface structure. For Saturns rings, the composition and radial structure, particle size and thermal characteristics will be investigated. Comparative studies of the planets and their satellite systems will be carried out.

Calculated densities of H3O+(H2O)n,NO2− (H2O)n, CO3− (H2O)n and electron in the nighttime ionosphere of Mars: Impact of solar wind electron and galactic cosmic rays

We have calculated the densities of positive ions and negative ions in the ionosphere of Mars at solar zenith angle 106° between height interval 0 km and 220 km. This model couples ion-neutral, electron neutral, dissociation of positive and negative ions, electron detachment, ion-ion, ion-electron recombination processes through 117 chemical reactions. Of the 34 ions considered in the model, the chemistry of 17 major ions (O 2 + , NO + , CO 2 + , H 3 O + H 2 O, H 3 O + (H 2 O) 2 , H 3 O + (H 2 O) 3 , H 3 O + (H 2 O) 4 , O 2 + CO 2 , H 3 O + , CO 4 - , CO 3 - , CO 3 - H 2 O, CO 3 - (H 2 O) 2 , NO 2 - H 2 O, NO 2 - (H 2 O) 2 , NO 3 - H 2 O, and NO 3 - (H 2 O) 2 ) are discussed in this paper. At altitude below 70 km, the electron density is mainly controlled by hydrated hydronium ions and water clusters of NO 2 - and CO 3 - . The ions O 2 + and NO + dominate above this altitude. This calculation suggests that the ionosphere of Mars contains F and D peaks at altitude ~130 km and ~30 km due to precipitation of solar wind electron and galactic cosmic rays respectively. F peak is mainly produced by O 2 + after heavy loss of CO 2 + with atomic oxygen. D peak occurs due to high efficiency of electron attachment to Ox molecules, which entails that concentration of negative ions is higher than that of electron below 30 km. These results are compared with radio measurements made by Mars 4 and Mars 5 in the nighttime ionosphere.

Infrared spectroscopy of the lower stratosphere with a balloon-borne cryogenic Fourier spectrometer.

The IR limb emission of the lower stratosphere has been measured using a balloon-borne liquid nitrogencooled Michelson interferometer with liquid helium-cooled Si:Ga detectors. Portions of the thermal emission spectrum have been recorded between 650 and 2000 cm(-1) with an unapodized spectral resolution of 0.03 cm(-1). This is the highest spectral resolution limb emission thus far obtained. A preliminary description is given of these data along with a discussion of the significant features. Species identified to date include CO(2), O(3), CFCl(3), CF(2)Cl(2), H(2)O, CH(4), HNO(3), N(2)O, NO(2), and ClONO(2). A tentative identification is made for NO, representing the first direct spectroscopic detection of NO in emission.

Branching ratio for radiative pion capture in 6Li and 12C

Abstract The radiative pion capture rate in 12 C and 6 Li leading to bound final states is calculated using the impulse approximation. The T -matrix is obtained from the time-reversed pion photo-production amplitude and initial-state distortion of the bound pion is taken into account. Using recently published capture schedules for pionic atoms the branching ratio R is calculated and compared to experimental values. The agreement is excellent if those experimental values are used that have been obtained by direct observation of the emitted γ-ray and if an optical-model value for the total 2P absorption width in 12 C is used.