Science is a project in a constant state of revision. Theories are tweaked, probabilities adjusted, limits pushed, elements added, maps redrawn. And every once in a while, a whole chapter gets a rewrite. In the November 2003 issue of Scientific American, "The Unseen Genome," by W. Wayt Gibbs, reviewed one such change currently under way in genetics as new research challenges the long-respected central dogma. In the field of space technology, "The Asteroid Tugboat," by Russell L. Schweickart, Edward T. Lu, Piet Hut and Clark R. Chapman, posited a new way to divert unpredictable Earth-bound asteroids. Reader reactions to these and other innovative ideas from the issue follow.

This article was originally published with the title Letters.

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