James W. Scott
KIANG REPLIES: Scott raises some excellent, fun points. Even on Earth there is latitudinal adaptation—not so much in pigments to spectral variation in radiation as in a plant’s shape to the sun’s height in the sky. The conical shape of coniferous trees at high latitudes, for instance, is better at intercepting light at low solar elevation angles. So, on a tidally locked planet orbiting a type M star, we might see a longitudinal gradient in plant pigments as well as adaptations to fairly fixed elevation angles of the parent star. The first telescopic missions to obtain planetary spectra will not be able to resolve such gradients, but scientists could make use of variations observed from a planet’s different faces to tease out more information about its surface.
Coming through the Border
Thomas B. Cochran and Matthew G. McKinzie’s description of the exercise where depleted uranium slugs were passed through U.S. ports in “Detecting Nuclear Smuggling” has confirmed what many have long known: radiation portal monitors provide little actual security. The situation is perhaps even worse than portrayed. Not only are the monitors not effective against uranium, but they also do not work against weapons-grade plutonium if one understands the basic physics required to shield it. And those physics are well known around the world.
Jack L. Parker
Los Alamos National Laboratory
Note: This story was originally printed with the title, "Letters".