Anderson J D, Null G W, Biller E D, Wong S K, Hubbard W B, Macfarlane J J
Science. 1980 Jan 25;207(4429):449-53. doi: 10.1126/science.207.4429.449.
During the Pioneer Saturn encounter, a continuous round-trip radio link at S band ( approximately 2.2 gigahertz) was maintained between stations of the Deep Space Network and the spacecraft. From an analysis of the Doppler shift in the radio carrier frequency, it was possible to determine a number of gravitational effects on the trajectory. Gravitational moments ( J(2) and J(4)) for Saturn have been determined from preliminary analysis, and preliminary mass values have been determined for the Saturn satellites Rhea, Iapetus, and Titan. For all three satellites the densities are low, consistent with the compositions of ices. The rings have not been detected in the Doppler data, and hence the best preliminary estimate of their total mass is zero with a standard error of 3 x 10(-6) Saturn mass. New theoretical calculations for the Saturn interior are described which use the latest observational data, including Pioneer Saturn, and state-of-the-art physics for the internal composition. Probably liquid H(2)O and possibly NH(3) and CH(4) are primarily confined in Saturn to the vicinity of a core of approximately 15 to 20 Earth masses. There is a slight indication that helium may likewise be fractionated to the central regions.
在“先驱者”号飞越土星期间，深空网络的各站点与航天器之间保持着S波段（约2.2吉赫兹）的连续往返无线电链路。通过对无线电载波频率中的多普勒频移进行分析，可以确定一些对轨道的引力效应。已从初步分析中确定了土星的引力矩（J(2)和J(4)），并确定了土星卫星土卫五、土卫八和土卫六的初步质量值。对于这三颗卫星来说，密度都很低，这与冰的成分相符。在多普勒数据中未检测到土星环，因此对其总质量的最佳初步估计为零，标准误差为3×10^(-6)土星质量。文中描述了针对土星内部的新理论计算，这些计算使用了最新的观测数据，包括“先驱者”号飞越土星的数据，以及用于内部成分的最先进物理学理论。液态水可能是土星内部的主要成分，氨和甲烷可能也存在，它们主要集中在质量约为15至20个地球质量的核心附近。有迹象表明，氦可能同样会在中心区域发生分馏。
