Planetary exploration has become one of incredible and vast accomplishments, in which huge amounts of data have now accumulated. Much of it has relied exclusively or largely on remote sensing. It is, regrettably, impractical to go into these fascinating results in the detail that this writer would like, because of the limitations of Web space allotted to this tutorial. Even so, this section is by far the longest in the series. The intention is to provide a thumbnail view of the major missions to the planets, but with the restriction that we show only surface images¾ usually no more than two or three representatives of each mission. Despite the importance of learning about planetary atmospheres, we do not say much about the results of remote sensing of these gaseous envelopes.

There are many sources of additional images and descriptive information. Among the best of these currently online is a replica of Chapter 5: Planetary Geology, by James Bell, Bruce Campbell, and Mark Robinson, in the 3rd Edition of the Manual of Remote Sensing: Earth Sciences Volume, 1996, at http://marswatch.tn.cornell.edu/rsm.html. This lengthy and detailed review focuses on remote sensing approaches to planetary exploration. Its one drawback is a sparsity of images (compared with this Section 19 overview). Another site worth visiting is the Home Page of the Jet Propulsion Laboratory (http://www.jpl.nasa.gov) where you can get addresses to visit other sites dealing with terrestrial and planetary space programs. JPL has recently selected choice images of the planets from various missions in a special Web site called the Planetary Photojournal, which you can access at http://photojournal.wr.usgs.gov/. Some images used in this section come from that source. Another NASA source is the National Space Science Data Center (http://nssdc.gsfc.nasa.gov/image/planetary. Two other exceptional Home Pages are The Nine Planets, by Bill Arnett of the Lunar and Planetary Laboratory, University of Arizona (http://seds.lpl.arizona.edu/ nineplanets/nineplanets) and Views of the Solar System, by C.J..Hamilton of the Los Alamos National Laboratory (http://spaceart.com/solar/). Books that treat planetary remote sensing include the aforementioned one by Billy Glass of the University of Delaware, and a now out-of-print text by this tutorial's author (Nicholas M. Short, Planetary Geology, 1975, Prentice-Hall Publ.), still in libraries. More recent are Planetary Landscapes by R. Greeley, 1985, Allen & Unwin, and Exploring the Planets by W.K. Hamblin and E.H. Christiansen, MacMillan, 1990.

Before we start our tour of the planets, you may wish to review some of the main principles and concepts of astronomy. The writer has developed a synopsis of "The Origin and Development of the Universe," emphasizing cosmology, as part of an aborted textbook on introductory geology. We place this review as a link for you to access if you Appendix A - Cosmology. While the synopsis is not really a remote sensing document, it is an efficient overview of several aspects of cosmic science that draw upon some of the same concepts that underlie planetary science. Besides, the subject is incredibly fascinating and was great fun to prepare. But, be advised: this distillation of the current views on cosmology appears as though the topics are almost "gospel," but the subject, with all its ramifications, is ever evolving, speculative, and still inexact in many aspects. We play down some of the more exotic ideas (such as "multiverses" and "virtual creation"). We do treat these astounding notions briefly towards the close.

We concentrate in this section almost entirely on the planetary bodies of the solar system (for information on the Sun, check http://seds.lpl.arizona.edu/nineplanets/nineplanets/sol.html and/or http://spaceart.com/solar) , excluding Earth. To set a framework for our survey, look first at the illustration below, which shows the relative sizes of the nine planets of our solar system (the distances between them are not to scale). From their appearance, how many can you name?

Collaborators: Code 935 NASA GSFC, GST, USAF Academy
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