Radiative Transfer and Thermal Control

The original source of the collection of papers in this volume was the AIAA/AGU Space Science Conference: Exploration of the Outer Solar System, held in July 1973. Papers were selected from those presented at the meeting, brought up to date as dictated by later events, and supplemented by appropriate additional contributions to make a compact picture of our chosen topics.

The first key element in this aspect of space exploration is the extended heliosphere itself, for the sun projects its material presence far beyond the inner planets by virtue of the constantly streaming, hypersonic solar wind. Study of the solar system, or of the sun as a star, is therefore incomplete without a comprehensive picture of the heliosphere all the way to its boundary with the interstellar medium. The wind is believed to have its boundary-i.e., its transition from solar-generated to interstellar gas somewhere in the "outer" region defined above. This is the subject of the first group of papers.

Whereas the sun and heliosphere constitute the hot material of the solar system, the planets, their satellites, and various minor bodies constitute the cold, or condensed, material of the solar system. In this category, Jupiter and Saturn are the most important of the bodies in regular orbits. These two major planets account for 92% of the condensed mass in the solar system. Moreover, their nonmaterial extensions into the uncondensed solar wind are by no means negligible. The second group of papers concentrates on the giant planets and their immediate environments.

Although the prospect of sending probes directly to bodies at, let alone beyond, the visible perimeter of the solar system is dim in the immediate future, the distant solar system generously sends representatives inward to us so that, if we wish to know something about the matter of which the far region is composed, we need only intercept one of these messengers with one of our own. These samples from the remote reaches of solar gravity are the comets, whose exploration constitutes one of the most rewarding of prospective new endeavors. The third group of papers deals with this topic.