The Solar System

In studying the Solar System, we find an important exception to our concept of astronomical objects being so remote that we cannot hope to visit them in the foreseeable future. People have already visited our nearest neighbor in the Solar System, the Moon, and brought back pieces to study in normal Earth-bound laboratories. Unmanned probes have landed on Venus and Mars and have visited all the other planets. Clearly, the opportunity for even limited close-up viewing has had a major impact on our understanding of the Solar System.

However, the study of the Solar System is not simply devoted to sending probes when we feel like it.The spacecraft have followed literally centuries of study by more traditional astronomical methods. By the time the first probe was launched to any planet, astronomers had already developed a picture of what they expected to find. Many of these pictures did not survive the planetary encounters, but they did provide a framework for asking questions, and for deciding what instruments were important to place on the various probes.

We have also had the advantage of having the Earth as an example of a planet to study. It has been possible to develop ideas about planetary surfaces, interiors, atmospheres and magnetospheres by studying the Earth. For that reason, we have devoted one whole chapter of this Part to the Earth, viewed not as our home base, but as just one planet. In studying the Earth, we will generate ideas which we will extend to studying other planets.

We will study the other planets in two groupings of similar planets, the inner and outer planets.Within each grouping, we don't study all aspects of a given planet before going on to the next planet. Instead, we study a given aspect, e.g. atmospheres, of all the planets for the group.This allows us to extend common ideas to similar objects, looking for similarities and differences.

We will also see how much of the physics we have used in other astronomical problems - orbits, energy transport, hydrostatic equilibrium, tidal effects, and using spectroscopy to study remote objects, to mention a few examples - fit very naturally into our study of the Solar System. Therefore, rather than trying to give a complete list of all the facts revealed by various probes, we emphasize the underlying physics.

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