According to current theories, the overall architecture of our solar system was established more than 4 billion years ago through an era of planet formation lasting from 10 million to several hundred millions of years. Before we began learning about other planetary systems, it was natural to assume that our own was quite representative. But in the past decade, the discovery of about 100 planetary systems around other stars has challenged this view; these systems display a broad variation in structure and most do not closely resemble our own (see the article by Tristan Guillot on page 63). 1
Observational capabilities currently are limited to the detection of giant, Jupiter-sized planets around other stars, so that we are uncertain of the existence and distribution of smaller Earth-like planets in such systems. Thus planetary scientists rely on our own solar system as the case study for understanding the formation of terrestrial,...