The occultation of Mariner 10 by Mercury

Abstract An analysis of the Mariner 10 dual frequency radio occultation recordings has yielded new information on the radius and atmosphere of Mercury. The ingress measurements which were conducted near 1.1° North latitude and 67.4° East longitude on the night side of the planet, gave a value for the radius of 2439.5 ± 1 km. Egress near 67.6° North latitide and 258.4° East longitude in the sunlit side yielded a radius of 2439.0 ± 1 km. The atmospheric measurements showed the electron density to be less than 10 3 cm −3 on both sides of the planet. From the latter result one may infer an upper limit to the dayside surface gas density of 10 6 molecules per cm 3 .