Letters from the July 14, 2007, issue of Science News

At least a few years to prepare

“Northern Exposure: The inhospitable side of the galaxy?” (SN: 4/21/07, p. 244) posits that every 64 million years a mass die-off occurs due to increased cosmic rays. When will the cosmic rays again be at their maximum?

Robert Richards
Metairie, La.

The article failed to mention when the next cosmic-ray bath is due. Now, I’m worried that it might be so imminent that Science News didn’t have the heart to provide its readers the bad news.

Steve Bankhead
Watsonville, Calif.

Study coauthor Adrian Melott of the University of Kansas in Lawrence says that as we head to the north side of the galaxy, cosmic ray exposure will get gradually more intense and peak in about 14 million years.—D. Castelvecchi

Fuel me once?

Ethanol is not an alternative to petroleum-based fuel to reduce air pollution (“Not-So-Clear Alternative: In its air-quality effects, ethanol fuel is similar to gasoline,” SN: 5/5/07, p. 278). It is a grow-it-at-home alternative to foreign-source petroleum-based fuel. It takes only 2 years to build an ethanol-extraction plant but 10 years to build a petroleum-extraction plant. Right now, as long as ethanol doesn’t increase air pollution, I’ll take it.

Lin Daniel
Chatsworth, Calif.

I wonder if Mark Jacobson included in his model comparing the air-quality effects of burning ethanol versus gasoline the decrease in automobile gas mileage with ethanol. I regularly track my mileage and routinely suffer a loss of 2 to 3 miles per gallon during the winter months when Albuquerque-area gas stations switch to an ethanol mix. Even if the polluting effects of both fuels were the same, increased efficiency would favor gasoline.

Jackie Ericksen
Placitas, N.M.

The article seems to have overlooked that ethanol, from plants, contains carbon directly removed from the atmosphere.

John Bodenschatz
San Francisco, Calif.