Dan L. Cain

Occultation Experiment: Results of the First Direct Measurement of Mars's Atmosphere and Ionosphere

Changes in the frequency, phase, and amplitude of the Mariner IV radio signal, caused by passage through the atmosphere and ionosphere of Mars, were observed immediately before and after occultation by the planet. Preliminary analysis of these effects has yielded estimates of the refractivity and density of the atmosphere near the surface, the scale height in the atmosphere, and the electron density profile of the Martian ionosphere. The atmospheric density, temperature, and scale height are lower than previously predicted, as are the maximum density, temperature, scale height, and altitude of the ionosphere.

Viking relativity experiment: Verification of signal retardation by solar gravity

Analysis of 14 months of data obtained from radio ranging to the Viking spacecraft verified, to an estimated accuracy of 0.1%, the prediction of the general theory of relativity that the round-trip times of light signals traveling between the earth and Mars are increased by the direct effect of solar gravity. The corresponding value for the metric parameter gamma is 1.000 plus or minus 0.002, where the quoted uncertainty, twice the formal standard deviation, allows for possible systematic errors.

The atmosphere of Mars from mariner 9 radio occultation measurements

Abstract The Mariner 9 spacecraft was used to perform 160 radio occultation measurements in orbit about Mars during November and December of 1971. At that time, Mars was experiencing a severely obscuring global dust storm. The effect of dust in the atmosphere was reflected in the reduced temperature gradients that were measured in the daytime near-equatorial atmosphere, indicating heating of the atmosphere by solar radiation being absorbed by dust and a simultaneous cooling of the surface. The temperature gradients increased somewhat with time, possibly indicating a gradual clearing of the atmosphere. Measurements made at 65° latitude near the morning terminator showed atmospheric temperatures consistent with condensation of carbon dioxide at low altitude. The surface pressures in the near equatorial regions ranged from a high of 8.9 mbar in Hellas to a low of 2.8 mbar in the Claritas and Tharsis areas, with a mean pressure of 4.95 mbar. The pressures deduced from measurements at 65° latitude ranged from 7.2 to 10.3 mbar, with a mean of 8.9 mbar. The pressure altitudes, referred to a pressure level of 6.1 mbar, show a range in the equatorial regions from a low of −4.4 km in Hellas to a high of 9.6 km in Claritas, with a net excursion of 14.0 km and a mean altitude of 2.7 km. In contrast, the region at 65° longitude shows uniformly negative altitudes, with a mean of −2.6 km. This disparity in pressures, which is also reflected in the measured radii between the near-equatorial and 65° latitude measurements, strongly suggests that the physical shape of Mars is more oblate than the shape of its gravitational equipotential surface, leading to higher atmospheric pressures near the poles than at the equator. However, more measurements at high latitudes are necessary to support this hypothesis. A daytime ionosphere having a peak density of about 1.5 − 1.7 × 10 5 el/cm 3 at an altitude of 140-134 km over a range of solar zenith angles of 56-47° was measured, showing some correlation between the variations in the peak density and the solar flux measured from the earth. The average topside plasma scale height was 38.5 km, showing little correlation with solar flux and solar zenith angle.

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 104 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 1010 to 1012 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.

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.

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�S and 33�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 105 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.

The shape of Mars from the Mariner 9 occultations

Abstract The extinction time of the radio signal, as the Mariner 9 spacecraft was occultated by Mars, together with an accurate ephemeris of the spacecraft were used to determine radii from the mass center to the occulting feature. Similarly estimations were made of the radius to a point where the pressure reached a certain fixed value. Several simple models were proposed to fit both sets of radii data.

Viking Lander Location and Spin Axis of Mars: Determination from Radio Tracking Data

Radio tracking data from the Viking lander have been used to determine the lander position and the orientation of the spin axis of Mars. The areocentric coordinates of the lander are 22.27�N, 48.00�W, and 3389.5 kilometers from the center of mass; the spin axis orientation, referred to Earths mean equator and equinox of 1950.0, is 317.35� right ascension and 52.71� declination.

Radio science experiments - The Viking Mars Orbiter and Lander.

Abstract The objective of the radio science investigations is to extract the maximum scientific information from the data provided by the radio and radar systems on the Viking Orbiters and Landers. Unique features of the Viking missions include tracking of the landers on the surface of Mars, dual-frequency S-and X- band tracking data from the orbiters, lander-to-orbiter communications system data, and lander radar data, all of which provide sources of information for a number of scientific investigations. Post-flight analysis will provide both new and improved scientific information on physical and surface properties of Mars, on atmospheric and ionospheric properties of Mars, and on solar system properties.

Mars Dynamics, Atmospheric and Surface Properties: Determination from Viking Tracking Data

Approximately 3 months of radio tracking data from the Viking landers have been analyzed to determine the lander locations, the orientation of the spin axis of Mars, and a first estimate from Viking data of the planets spin rate. Preliminary results have also been obtained for atmospheric parameters and radii at occultation points and for properties of the surface in the vicinity of lander 1.