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Monday, January 28, 2008

Asteroid to Miss Earth Tonight

If you feel a little breeze tonight, look up.

An asteroid as wide as the length of three football fields will be speeding past Earth at the astronomical equivalent of a rather close shave: less than one-and-a-half times the distance to the moon.

Okay, that's not close enough to cause a breeze. And it won't be visible without the help of a telescope. But near-Earth asteroids are unusual enough to have astronomers excited about the event. Among the hundreds of asteroids being tracked, the next of this size or larger to pass this close will not arrive until 2027.

That is why scientists at the Arecibo Observatory in Puerto Rico will be training their instruments on the craggy piece of space debris known as 2007 TU24 to study its features and trajectory.

Scientists at Cornell University, which operates Arecibo for the National Science Foundation, emphasized that TU24 poses no threat. A miss is as good as a mile, after all, and in this case, we're talking about 334,000 miles.

But only two telescopes on the planet can examine such objects in detail -- those at Arecibo and NASA's Goldstone facility in California. Both use radar, a wavelength that can tell with great precision an asteroid's contours, its path through space and how it is spinning.

Goldstone devoted a couple of days to TU24 last week, but Arecibo has the more sensitive instrument, able to discern details as small as 25 feet across. Its radar "allows very accurate predictions of the future orbits of near-Earth asteroids, enabling a much better assessment of the likelihood of an impact with Earth," Cornell astronomy professor Donald B. Campbell said.

-- Rick Weiss

Female Birds Size Up Males

A female bird's taste in males can change radically from year to year. But fickleness or faddishness are not the reasons. Her preferences, instead, arise from another inscrutable attribute: female intuition.

She infers from a long list of fashion choices in her potential mates which combination is most likely to add up to the most chicks at the end of the season.

That's the conclusion of two biologists who reported their work last week in the journal Science.

So-called "secondary sexual traits" -- fancy plumage, rump color, big beaks -- are the product of two forces. One is the competition between males for mates and often for territory. The other is the female's choice of her mate.

Traditionally, biologists believed that females favored male attributes in a predictable and largely unchanging way. But it turns out this isn't true.

Alexis S. Chaine, of France's Laboratory of Evolution and Biological Diversity, and Bruce E. Lyon, of the University of California at Santa Cruz, studied lark buntings, songbirds of the Great Plains. Over the five years they watched the birds, competition was fierce. About 45 percent of males failed to attract a mate; and even when they did, about 25 percent of chicks were fathered by other males.

They found that each year a different constellation of traits was associated with "fitness," allowing the pairs to produce the most offspring. Some traits went out of fashion overnight.

In one example, having a large body and a lot of black rump feathers were marks of reproductive success one year but marks of reproductive failure another year.

Food, predators and weather are constantly in flux in the lark buntings' habitat. The researchers think the female birds somehow discerned which attributes and behaviors were most favorable for each breeding season, and chose their mates accordingly.

-- David Brown

People Infect Chimps With Viruses

Viral infections passed by humans are causing some wild African chimpanzees to get sick and die. Scientists had suspected it for some time, but now German researchers have proven it.

Using evidence gathered about populations of chimps hit by five different respiratory outbreaks between 1999 and 2006 in the Ivory Coast, the researchers found that tissue samples from all that died tested positive for one of two human respiratory viruses.

"Our demographic analyses of chimpanzees suggest that [the infections] started as soon as people got close enough to chimps to transmit diseases," said Fabian Leendertz of Robert Koch-Institut and Max Planck Institute for Evolutionary Anthropology in Germany.

The study, published last week in the journal Current Biology, examined chimps that lived in protected parks where researchers are active but local people don't travel. As a result, researchers concluded, the sources of the viruses were most likely the researchers themselves or possibly poachers.

Despite this, Leendertz said research and ecotourism have had a strong positive effect on the survival of great apes by reducing poaching and giving more "political weight" to apes in protected areas. He said researchers have adopted practices to help minimize the risk of infection by, among other things, maintaining a distance of at least 22 feet, wearing masks and disinfecting their boots regularly.

-- Marc Kaufman

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