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.

Mariners 6 and 7: radio occultation measurements of the atmosphere of Mars.

Radio occultation measurements with Mariners 6 and 7 provided refractivity data in the atmosphiere of Mars at four points above its surface. For an atmosphere consisting predominantly of carbon dioxide, surface pressures between 6 and 7 millibars are obtained at three of the points of measurement, and 3.8 at the fourth, indicating an elevation of 5 to 6 kilometers. The temperature profile measured by Mariner 6 near the equator in the daytime indicates temperatures in the stratosphere about 100 degrees K warmer than those predicted by theory. The measurements of Mariner 6 taken at 79 degrees N at the beginning of polar night indicate that conditions are favorable for the condensation of carbon dioxide at almost all altitudes. Mariner 7 measurements taken at 58 degrees S in daytime and 38 degrees N at night also show that carbon dioxide condensation is possible at altitudes above about 25 kilometers. Measurements of the electron density in the ionosphere show that the upper atmosphere is substantially warmer than it was in 1965, possibly because of increased solar activity and closer proximity to the sun.

Preliminary results on the atmospheres of io and jupiter from the pioneer 10 s-band occultation experiment.

The preliminary analysis of data from the Pioneer 10 S-band radio occultation experinment has revealed the presence of an ionosphere on the Jovian satellite Io (JI) having an electron density peak of about 6 x 10(4) electrons per cubic centimeter at an altitude of approximately 60 to 140 kilometers. This suggests the presence of an atmosphere having a surface number density of about 10(10) to 10(12) per cubic centimeter, corresponding to an atmospheric surface pressure of between 10(-8) and 10(-10) bar, at or below the detection threshold of the Beta Scorpii stellar occultation. A measurement of the atmosphere of Jupiter was obtained down to the level of about 80 millibars, indicating a large temperature increase at about the 20 millibar level, which cannot be explained by the absorption of solar radiation by methane alone and can possibly be due to absorption by particulate matter.

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.

Atmosphere and ionosphere of venus from the mariner v s-band radio occultation measurement.

Measurements of the frequency, phase, and amplitude of the S-band radio signal of Mariner V as it passed behind Venus were used to obtain the effects of refraction in its atmosphere and ionosphere. Profiles of refractivity, temperature, pressure, and density in the neutral atmosphere, as well as electron density in the daytime ionosphere, are presented. A constant scale height was observed above the tropopause, and the temperature increased with an approximately linear lapse rate below the tropopause to the level at which signal was lost, presumably because heavy defocusing attenuation occurred as critical refraction was approached. An ionosphere having at least two maxima was observed at only 85 kilometers above the tropopause.

Bistatic-radar detection of lunar scattering centers with lunar orbiter I.

Continuous-wave signals transmitted from Lunar Orbiter I have been received on Earth after they have been reflected from the surface of the moon. The frequency spectrum of the reflected signals is used to locate discrete, heterogeneous, scattering centers on the lunar surface. The scattering centers are probably distinguished from the surrounding terrain by a higher surface reflectivity. Continuous-wave bistatic radar could provide an important new method for the study and mapping of planetary surfaces.

Venus: lower atmosphere not measured.

The common ranges of pressure and temperature of the atmosphere of Venus measured last October establish the connection between the Soviet Venera 4 altitude scale and the United States Mariner V radial scale. But if the Venera 4 measurements extended to the surface, as claimed, this comparison implies a radius of the planet which is about 25 kilometers greater than the radius deduced from Earth-based radar data. This impasse has been resolved in favor of the smaller value by a new determination of the radius which is more direct than the method used in deriving the radar radius, and which involves concurrent ranging from Earth both to Mariner V near encounter and to the surface of Venus. It is concluded that neither spacecraft reported on atmospheric conditions near the level of the mean surface, but extrapolations of the measurements yield surface values for mid-latitudes of 100 atmospheres pressure (within a factor of 1.5) and 700 degrees K temperature (within 100 degrees ), in distinction to the Soviet values of 19+/-2 atmospheres and 544 degrees +/-10 degrees K. The higher values support radiometric and radar data on temperature and atmospheric absorption. It appears that the Soviet probe was not designed to work through such a thick atmosphere. A particularly simple (times two) ambiguity in the Venera 4 altimeter reading suggests itself, since this would bring all other data into excellent agreement and would explain the reason for the supposition that the probe reached the surface.

Atmosphere of jupiter from the pioneer 11 s-band occultation experiment: preliminary results.

Two additional radio occultation measurements of the atmosphere of Jupiter were obtained with Pioneer 11. The entry measurement leads to a temperature profile that is substantially in agreement with those obtained with Pioneer 10, showing temperatures much higher than those derived from other observations. The exit measurement is not usable because of the discontinuous drift of the spacecraft auxiliary oscillator, presumably due to the trapped radiation belts of Jupiter. The combination of two Pioneer 10 measurements and one Pioneer 11 measurement yields an oblateness of 0.06496 at 1 millibar and 0.06547 at 160 millibars. Measurements in the Jovian ionosphere indicate a number of layers distributed over about 3000 kilometers, with a topside temperature of about 750 K.

Venus: mass, gravity field, atmosphere, and ionosphere as measured by the mariner 10 dual-frequency radio system.

Analysis of the Doppler tracking data near encounter yields a value for the ratio of the mass of the sun to that of Venus of 408,523.9 +/- 1.2, which is in good agreement with prior determinations based on data from Mariner 2 and Mariner 5. Preliminary analysis indicates that the magnitudes of the fractional differences in the principal moments of inertia of Venus are no larger than 10(-4), given that the effects of gravity-field harmonics higher than the second are negligible. Additional analysis is needed to determine the influence of the higher order harmonics on this bound. Four distinct temperature inversions exist at altitudes of 56, 58, 61, and 63 kilometers. The X-band signal was much more rapidly attenuated than the S-band signal and disappeared completely at 52-kilometer altitude. The nightside ionosphere consists of two layers having a peak density of 10(4) electrons per cubic centimeter at altitudes of 140 and 120 kilometers. The dayside ionosphere has a peak density of 3 X 10(5) electrons per cubic centimeter at an altitude of 145 kilometers. The electron number density observed at higher altitudes was ten times less than that observed by Mariner 5, and no strong evidence for a well-defined plasmapause was found.

Mercury: results on mass, radius, ionosphere, and atmosphere from mariner 10 dual-frequency radio signals.

Analysis of the radio-tracking data from Mariner 10 yields 6,023,600 +/- 600 for the ratio of the mass of the sun to that of Mercury, in very good agreement with values determined earlier from radar data alone. Occultation measurements yielded values for the radius of Mercury of 2440 +/- 2 and 2438 +/- 2 kilometers at laditudes of 2 degrees N and 68 degrees N, respectively, again in close agreement with the average equatorial radius of 2439 +/- 1 kilometers determined from radar data. The mean density of 5.44 grams per cubic centimeter deduced for Mercury from Mariner 10 data thus virtually coincides with the prior determination. No evidence of either an ionosphere or an atmosphere was found, with the data yielding upper bounds on the electron density of about 1500 and 4000 electrons per cubic centimeter on the dayside and nightside, respectively, and an inferred upper bound on the surface pressure of 10(-8) millibar.