Mercury: Results on Mass, Radius, Ionosphere, and Atmosphere from Mariner 10 Dual-Frequency Radio Signals

Abstract

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.

Some aspects of core formation in Mercury

“…Necessary for such a calculation are the mass and radius of the planet, both sufficiently well known (Smith et al, 1970;Ash et al, 1971;Howard et al, --1974), a nominal temperature profile:, and assumed equations of state for both the mantle and core. Siegfried and Solomon (1974; estimated that a fully differentiated core in…”

“…There is some promise of extracting a reliable value of J 2 for Mercury from tha three Mariner 10 encounters (Howard et al, 1974;Esposito et a l ., 1975). Can the measurement of J 2 be used to estimate C/MR2 using hydrostatic theory?…”

The magnetic field of Mercury, 1

“…In addition, intense bursts of higher-energy electrons (Ee > 170 keV) and protons (Ep > 500 keV) were reported by the charged particle telescope experiment [Simpson et al, 1974] The combination of factors relating to the geometry and positions of the bow shock and magnetopause, which implies a scale size of solar wind interaction larger than the planet, and both the geometry and the magnitude of the magnetic field within the magnetospherelike region are found to be inconsistent with present models of such planetary interactions. The lack of evidence for any appreciable atmosphere or ionosphere [Broadfoot et al, 1974;Howard et al, 1974] suggests that the interaction is unlike that at Venus, wherein a substantial atmosphere-ionosphere is responsible for the deflection of the Copyright ¸ 1975 by the American Geophysical Union. solar wind flow and the development of the detached bow shock wave Ness et al, 1974a].…”

Satellite Atmospheres and Magnetospheres

“…This technique has been used very successfully to measure the characteristics of the ionospheres and atmospheres of Venus (Kliore et al, 1967;Fjeldbo et al, 1971;Kliore and Patel 1980); Mars (Kliore et al, 1965;Kliore et al, 1972a;Lindal et al, 1979); Mercury (Howard et al, 1974); Jupiter (Fjeldbo et al, 1975;Eshleman et al, 1979;Lindal et al, 1981;Hinson et al, 1997); Saturn Tyler et al, 1981;Lindal et al, 1985); Uranus (Lindal et al, 1987); Neptune (Tyler et al, 1989;Lindal 1992); Saturn's rings (Marouf and Tyler 1985); as well as Saturn's satellite Titan (Lindal et al, 1983); Neptune's Triton (Tyler et al, 1989); and Jupiter's satellites Io (Kliore et al, 1975) and Europa (Kliore et al, 1997).…”