Mariner 9 s-band martian occultation experiment: initial results on the atmosphere and topography of Mars

A preliminary analysis of 15 radio occultation measurements taken on the day side of Mars between 40 degrees S and 33 degrees S has revealed that the temperature in the lower 15 to 20 kilometers of the atmosphere of Mars is essentially isothermal and warmer than expected. This result, which is also confirmed by the increased altitude of the ionization peak of the ionosphere, can possibly be caused by the absorption of solar radiation by fine particles of dust suspended in the lower atmosphere. The measurements also revealed elevation differences of 13 kilometers and a range of surface pressures between 2.9 and 8.3 millibars. The floor of the classical bright area of Hellas was found to be about 6 kilometers below its western rim and 4 kilometers below the mean radius of Mars at that latitude. The region between Mare Sirenum and Solis Lacus was found to be relatively high, lying 5 to 8 kilometers above the mean radius. The maximum electron density in the ionosphere (about 1.5 x 10(5) electrons per cubic centimeter), which was found to be remarkably constant, was somewhat lower than that observed in 1969 but higher than that observed in 1965.     

Mariner 9 ultraviolet spectrometer experiment: initial results

The ultraviolet airglow spectrum of Mars has been measured from an orbiting spacecraft during a 30-day period in November-December 1971. The emission rates of the carbon monoxide Cameron and fourth positive bands, the atomic oxygen 1304-angstrom line and the atomic hydrogen 1216-angstrom line have been measured as a function of altitude. Significant variations in the scale height of the CO Cameron band airglow have been observed during a period of variable solar activity; however, the atomic oxygen and hydrogen airglow lines are present during all the observations. Measurements of the reflectance of the lower atmosphere of Mars show the spectral characteristics of particle scattering and a magnitude that is about 50 percent of that measured during the Mariner 6 and 7 experiments in 1969. The variation of reflectance across the planet may be represented by a model in which the dominant scatterer is dust that absorbs in the ultraviolet and has an optical depth greater than 1. The atmosphere above the polar region is clearer than over the rest of the planet.     

Mariner 9 ultraviolet spectrometer experiment: seasonal variation of ozone on Mars

Ozone is observed to be present in the polar regions of Mars and to have a seasonal variation. In the summer, the amount present in the polar atmosphere is less than 3 micrometer-atmospheres. In the fall, ozone increases in amount and is found in association with the formation of the polar hood. In winter, the maximum amount of ozone is present, 57 micrometer-atmospheres over the polar hood and 16 over the polar cap. In spring, the amount over the polar cap decreases monotonically until by the beginning of summer the ozone disappears. Ozone is not observed in the equatorial region during any season.     

Mariner 9 celestial mechanics experiment: gravity field and pole direction of Mars

Analysis of the Mariner 9 radio-tracking data shows that the Martian gravity field is rougher than that of Earth or the moon, and that the accepted direction of Mars's rotation axis is in error by about 0.5 degrees . The new value for the pole direction for the epoch 1971.9, referred to the mean equatorial system of 1950.0, is right ascension alpha= 317.3 degrees +/- 0.3 degrees , declination delta = 52.6 degrees +/- 0.2 degrees . The values found for the coefficients of the low-order harmonics of Mars's gravity field are as follows: J(2)=(1.96+/-0.01)x10(-3), referred to an equatorial radius of 3394 kilometers; C(22) = -(5 +/- 1) x 10(-5); and S(22) = (3 +/- 1) x 10(-5). The value for J(2) is in excellent agreement with the result from, Wilkins' analysis of the observations of Phobos. The other two coefficients imply a value of (2.5 +/- 0.5) x 10(-4) for the fractional difference in the principal equatorial moments of inertia; the axis of the minimum moment passes near 105 degrees W.     

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 degrees K, an indication that the cap is formed by frozen carbon dioxide. No significant temperature fluctuations were detected with a 100-kilometer scale.     

Mars: Mariner 9 Spectroscopic Evidence for H2O Ice Clouds

Spectral features observed with the Mariner 9 interferometer spectrometer are identified as those of H(2)O 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 H(2)O 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.     

Atmosphere of Mars: Mariner IV Models Compared

Three classes of models for the atmosphere of Mars differ in identifying the main ionospheric layer measured by Mariner IV as being analogous to a terrestrial F(2), F(1), or E layer. At an altitude of several hundred kilometers, the relative atmospheric mass densities for these models (in the order named) are approximately 1, 10(2), and 10(4), and the temperatures are roughly 100 degrees , 200 degrees , and 400 degrees K. Theory and observation are in best agreement for an F, s model, for which photodissociation of CO(2), and diffusive separation result in an atomic-oxygen upper atmosphere, with O(+) being the principal ion in the isothermal topside of the ionosphere. The mesopause temperature minimum would be at or below the freezing point of CO(2), and dry ice particles would be expected to form. However, an F(1) model, with molecular ions in a mixed and warmer upper atmosphere, might result if photodissociation and diffusive separation are markedly less than would be expected from analogy with Earth's upper atmosphere. The E model proposed by Chamberlain and McElroy appears very unlikely; it is not compatible with the measured ionization profile unless rather unlikely assumptions are made about the values, and changes with height, of the effective recombination coefficient and the average ion mass. Moreover our theoretical heat-budget computations for the atmospheric region probed by Mariner IV indicate markedly lower temperatures and temperature gradients than were obtained for the E model.     

Viking orbital colorimetric images of Mars: preliminary results

Color reconstruction and ratios of orbital images of Mars confirm Earth-based measurements showing red/violet ratios for bright areas to be roughly 1.5 times greater than dark areas. The new results show complex variation among dark materials; dark streaks emanating from craters in southern cratered terrains are much bluer than dark materials of the north equatorial plains on which Viking 1 landed.     

Mariner 6: ultraviolet spectrum of Mars upper atmosphere

Emission features from ionized carbon dioxide and carbon monoxide were measured in the 1900- to 4300-angstrom spectral region. The Lyman alpha 1216-angstrom line of atomic hydrogen and the 1304-, 1356-, and 2972-angstrom lines of atomic oxygen were observed.     

Mariner 6: origin of Mars ionized carbon dioxide ultraviolet spectrum

The predicted intensities of the ionized carbon dioxide (CO(2)+) emission feature at 2890 angstroms and the Fox-Duffendack-Barker bands are 5.2 and 19.9 kilorayleighs, respectively, for a vertical column. Direct photoionization of carbon dioxide by solar radiation contributes 3.5 and 4.1 kilorayleighs, respectively, and fluorescent scattering by C0(2)+, 1.6 and 15.3 kilorayleighs, respectively. Photoelectron impacts are less important.     

Mariner 10 pictures of mercury: first results

Mercury has a heavily cratered surface cotntaining basins up to at least 1300 kilometers diameter flooded with mare-like material. Many features are closely similar to those on the moon, but significant structural differences exist. Major chemical differentiation before termination of accretion is implied.     

Viking bistatic radar observations of the hellas basin on Mars: preliminary results

Preliminary reduction of Viking bistatic radar data gives root-mean-square surface slopes in the Hellas basin on Mars of about 4 degrees on horizontal scales averaged over 10 centimeters to 100 meters. This roughness decreases slightly with position along the ground track, south to north. The dielectric constant in this area appears to be approximately 3.1, greater than the martian average. These values are characteristic of lunar maria and are similar to those found near the Viking lander site in Chryse with the use of Earth-based radar.     

Mariner 9 ultraviolet spectrometer experiment: stellar observations

Photoelectric spectra have been obtained for a number of early-type stars in the 1100- to 2000-angstrom region with the Mariner 9 ultraviolet spectrometer. The resonance lines of H I, Si IV, and C IV are easily identified, as are features due to C II, C III, Si III, Fe II, N IV. The absolute energy distribution derived from the data lie about 20 percent below those of OAO-2 in the 1200- to 2000-angstrom region.     

Global distribution of neutrons from Mars: results from Mars odyssey

Global distributions of thermal, epithermal, and fast neutron fluxes have been mapped during late southern summer/northern winter using the Mars Odyssey Neutron Spectrometer. These fluxes are selectively sensitive to the vertical and lateral spatial distributions of H and CO2 in the uppermost meter of the martian surface. Poleward of +/-60 degrees latitude is terrain rich in hydrogen, probably H2O ice buried beneath tens of centimeter-thick hydrogen-poor soil. The central portion of the north polar cap is covered by a thick CO2 layer, as is the residual south polar cap. Portions of the low to middle latitudes indicate subsurface deposits of chemically and/or physically bound H2O and/or OH.     

Morphology and composition of the surface of Mars: Mars Odyssey THEMIS results

The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrock are observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified.     

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.