Letters

Defining death Allowing doctors to absolutely define death (“Doctors debate death definition for transplants,” SN: 9/13/08, p. 5) as “irreversible brain damage” is a slippery slope. There is a lot of pressure from transplant coordinators for body parts. While there is no absolute point in brain damage, heart stoppage is an absolute point. Allowing a vague definition will certainly lead to earlier and earlier use of such a definition. Temptation—the need for organs to maintain transplant programs and the cost of caring for a dying child—will certainly increase the pressure to back up the diagnosis. F. E. Rector Jr., Grosse Pointe Shores, Mich. Reality bytes The introduction to Alex Szalay’s commentary (“Preserving digital data for the future of eScience,” SN: 8/30/08, p. 32) says “… files that will soon approach the petabyte (1015—or quadrillion—byte) scale.” But bytes are not measured in powers of ten but rather powers of two. A kilobyte is not 103 or 1,000 bytes, but 210 or 1,024 bytes, a difference of 24 bytes. As the number of bytes grows, the inaccuracy of these approximations grows as well. I recently purchased a Western Digital “terabyte” disk drive. When I installed it on my computer, the computer immediately recognized its capacity as one trillion bytes, 1012 bytes, rather than a terabyte, 240 bytes. It’s short by 9.1 percent. A petabyte is not 1015 or 1,000,000,000,000,000 bytes but rather 250 or 1,125,899,906,842,624 bytes, a difference of 12 percent. Matthew H. Fields, Ann Arbor, Mich. Petabyte can refer to either 1015 bytes or 250 bytes. As the reader correctly points out, the term is not well-defined. —Alex Szalay Population pressure Regarding “Science should be prominent in U.S. foreign policy” (SN: 8/2/08, p. 32): Science and technology have bettered the lives of millions, and the future remains bright as long as human imagination thrives. A troubling trend, though, is that no new farmland is being created, and neither is air or open space. The question is not whether science can continue to pull off miracles. And it’s not whether human population will continue to grow. The real question is at what point will science not deliver enough to stop humans from crowding themselves and every living thing off our planet? If we don’t seek an equilibrium, Mother Nature will enforce one. If we don’t stop the population from growing, not even science will be able to save us. Why isn’t this a component of our foreign policy? Barry Demchak, La Jolla, Calif. Chemical on Mars In the article titled “Mars lander confirms water ice” (SN: 8/30/08, p. 11), the author says the chemical compound perchlorate was found. Does this compound occur in a state of nature or is it only synthetic, made by man? If it is not natural, how did it end up on Mars? Jeanette Grimshaw, Royal Oak, Mich. On Earth, perchlorates occur in nature. After first discovering the perchlorate on Mars, researchers thought it might be a contaminant from rocket fuel. But the Phoenix Mars Lander’s instruments have now confirmed that the compound’s abundance is too high to have leached from the spacecraft’s rockets. Perchlorate, therefore, naturally occurs on Mars, scientists say. —Ashley Yeager A triathlon of sorts I very much enjoyed Susan Milius’ feature article on animal athletes (“Built for speed,” SN: 8/16/08, p. 14). Before relegating humans to the root cellar of couch potatoes, however, name an animal capable of besting a human (and not just an Olympian) running a mile, swimming a mile and then climbing a tree. Ralph Protsik, Brookline, Mass.