G. Münch

Infrared Thermal Mapping of the Martian Surface and Atmosphere: First Results

The Viking infrared thermal mapper measures the thermal emission of the martian surface and atmosphere and the total reflected sunlight. With the high resolution and dense coverage being achieved, planetwide thermal structure is apparent at large and small scales. The thermal behavior of the best-observed areas, the landing sites, cannot be explained by simple homogeneous models. The data contain clear indications for the relevance of additional factors such as detailed surface texture and the occurrence of clouds. Areas in the polar night have temperatures distinctly lower than the CO2 condensation point at the surface pressure. This observation implies that the annual atmospheric condensation is less than previously assumed and that either thick CO2 clouds exist at the 20-kilometer level or that the polar atmosphere is locally enriched by noncondensable gases.

Mariner 10 infrared radiometer results: Temperatures and thermal properties of the surface of Mercury

Mariner 10 infrared brightness temperatures of the surface of Mercury at 11 and 45 μm are presented. The data were obtained during the first flyby along a nera-equatorial swath extending from 17 hours local time through local midnight to 9 hours local time. For an assumed emissivity of 0.9, derived surface thermal inertias are between 0.0031 and 0.0031 cal cm^(−2)sec^(−12) K^(−1) and the implied minimum predawn surface kinetic temperature for the warm pole at longitude 270° is near 93 K. Several pronounced thermal inhomogeneities were seen, one of which appears to coincide with a region of high radar reflectivity. The derived thermal properties and the electrical skin depth and loss tangent fall within the range of values found on the Moon.

Pioneer 10 Infrared Radiometer Experiment: Preliminary Results

Thermal maps of Jupiter at 20 and 40 micrometers show structure closely related to the visual appearance of the planet. Peak brightness temperatures of 126� and 145�K have been measured on the South Equatorial Belt, for the 20- and 40-micrometer channels, respectively. Corresponding values for the South Tropical Zone are 120� and 138�K. No asymmetries between the illuminated sunlit and nonilluminated parts of the disk were found. A preliminary discussion of the data, in terms of simple radiative equilibrium models, is presented. The net thermal energy of the planet as a whole is twice the solar energy input.

Pioneer 11 Infrared Radiometer Experiment: The Global Heat Balance of Jupiter

Data obtained by the infrared radiometers on the Pioneer 10 and Pioneer 11 spacecraft, over a large range of emission angles, have indicated an effective temperature for Jupiter of 125� � 3�K. The implied ratio of planetary thermal emission to solar energy absorbed is 1.9�0.2, a value not significantly different from the earth-based estimate of 2.5�0.5.

Mariner 1969: preliminary results of the infrared radiometer experiment.

The thermal energy emitted by Mars was measured in the 8- to 12- and 18- to 25-micrometer bands. The minimum temperature derived for the southern polar cap is 150�K, an indication that the cap is formed by frozen carbon dioxide. No significant temperature fluctuations were detected with a 100-kilometer scale.

Infrared thermal mapping experiment: The Viking Mars orbiter

The Mars infrared thermal mapper (IRTM) will be carried on the scan platform of the orbiter of the Viking 1975 mission. The IRTM is a multichannel radiometer with several detectors in each of six spectral regions. This instrument will measure the reflected solar radiation and surface thermal emission from the area viewed by the orbiter imaging system with nominal 5 km resolution. Extensive additional areas will be covered for which simultaneous imaging will not be available. nThe spectral channels are selected to be sensitive to surface emissivity variations and provide good temperature resolution over the entire range of Martian temperatures. These observations will allow determination of the surface kinetic temperature and thermal balance, and by coverage of the dark hemisphere, a search for regions with anomalous cooling can be made. Observations of ground frosts or clouds will help to determine their composition, and in the case of extensive H_2O frosts, will allow the local water vapor pressure to be estimated.

Preliminary Infrared Radiometry of the Night Side of Mercury from Mariner 10

The infrared radiometer on Mariner 10 measured the thermal emission from the planet with a spatial resolution element as small as 40 kilometers in a broad wavelength band centered at 45 micrometers. The minimum brightness temperature (near local midnight) in these near-equatorial scans was 100�K. Along the track observed, the temperature declined steadily from local sunset to near midnight, behaving as would be expected for a homogeneous, porous material with a thermal inertia of 0.0017 cal cm-2 sec-� �K-1, a value only slightly larger than that of the moon. From near midnight to dawn, however, the temperature fluctuated over a range of about 10�K, implying the presence of regions having thermal inertia as high as 0.003 cal cm-2 sec-� �K-1.

Infrared Coronal Lines. II. Observation of [SI x] λ 1.43 μ and [Mg VIII] λ 3.03 μ

The wavelengths and intensities of the coronal lines of the ions Si^(9+) and Mg^(8+), resulting from the airborne observation of the November 12, 1966, total solar eclipse, are given.

Preliminary infrared radiometry of Venus from Mariner 10

The intensity of emission at 45 micrometers, measured with high spatial resolution along a single crossing of the Venus disk, is presented. On the average, the observed darkening toward the limb varies nearly linearly with the cosine of the emission angle. The brightness temperature, extrapolated to normal emission, is 255� K. The limb darkening curve, interpreted in a linear approximation, implies that the atmosphere is quite opaque, with an absorption coefficient of 0.24 per kilometer. Changes in curvature present in the limb darkening curve suggest the existence of thermal inhomogeneities with scale comparable to that of the dark markings shown by ultraviolet images.

The helium abundance on Jupiter

Methods of determining helium on Jupiter (and the Jovian planets) are critically surveyed. Current information is consistent with solar abundance, He/H2 = 0.11 by number. The available lines of evidence are the mean density, spectral-line broadening, and stellar occultations. Methods usable from spacecraft flying by are discussed. Observation of far-infrared emission has great promise, but we may have to await the development of entry probes for the greatest assurance.