See Inside November 2007

Whatever happened to...?

Cosmic Radiation -- Smoking and Genes -- Shrubs 1, Grasses 0 -- Corona Heat

Radiation Redux
NASA has worried that cosmic rays could undermine a human voyage to Mars. New simulations and calculations, though, suggest that such lengthy exposure to space radiation may pose only half the health risk that NASA had expected.

The best U.S. space radiation simulations take place at Brookhaven National Laboratory’s Booster accelerator, where a facility for space research opened in 2003. The device sends beams of protons, iron and other cosmic elements down a 100-meter-long tunnel to strike human cells, mice and rats. Biologists then assess DNA damage. The Booster has enabled NASA to conduct regular, more realistic experi-ments beyond the one-week-a-year timetable of the past.

One interesting preliminary finding, according to Brook-haven radiobiologist Betsy Sutherland, is that the lower a proton’s energy, the more damage it does. Apparently, lower-energy protons, which travel more slowly, have more time to interact with tissues. In lowering its assessment of risk, NASA also factored in astronauts’ better-than-average health and switched from “whole-body” radiosensitivity to organ-by-organ measurements, where new studies have found lower risks for lungs, breasts and the blood system.

Such analyses, if they prove correct, could mean that Mars mission astronauts might not need radioprotective drugs at all, says Francis Cucinotta, NASA’s chief scientist for human radiation research. For solar storms and other acute risks, he adds, “we might want to carry them just in case.” Possible drugs include retinoids—vitamins that work as antioxidants—and compounds that delay cell division long enough for damaged cells to repair themselves before they can propagate mutations.
—John Dudley Miller

Tobacco Turnoff
The dangers of tobacco smoking are well known. But the risks persist even after quitting. A possible explanation: smoking permanently affects some genes. Researchers came to this conclusion after analyzing lung samples from 24 current and former smokers and those who have never inhaled. Genes irreversibly affected include those that repair DNA and combat the development of lung cancer. The study appears in the August 29 BMC Genomics.

Shrubby Frontier
Scientists have observed how climate change has altered global ecosystems. A five-year experiment reveals details of just how. Researchers exposed sections of a short-grass prairie to twice the amount of carbon dioxide it ordinarily would receive. The balance of plant species changed; the area became dominated by a 40 percent rise in woody shrubs, which metabolize CO2 more efficiently than grasses do. The results, appearing in the September 11 Proceedings of the National Academy of Sciences USA, confirm the hypothesis that, in a CO2-enriched world, woody shrubs will replace grasses on the American rangeland. The change could affect livestock and other grazers—certainly the deer and the antelope will have fewer places to play.

Heat Waves
Travel away from the sun’s surface, and it actually gets hotter, increasing from 5,000 to two million degrees Celsius. Just how the sun’s atmosphere, or corona, heats up so much has puzzled physicists. One proposed heating mechanism is magnetic oscillations. These oscillations, called Alfvén waves, would transport energy from the surface to the corona, which extends millions of kilometers. Astronomers have now detected Alfvén waves in the corona for the first time. In the August 31 Science, researchers describe how they measured these waves, which roughly follow the sun’s magnetic field. The detected Alfvén waves alone do not carry enough energy to heat the corona to its blazing levels, but the team suspects that more accurate measurements will show that Alfvén waves are actually larger and able to deliver the heat.

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