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Science Digest

Monday, March 30, 2009

Meteorite Scavengers

NASA scientist Steve Chesley got a call at home last October with bracing news: A telescope in Arizona had spotted an SUV-size asteroid that appeared to be on a collision course with Earth. He raced to work, ran a computer calculation and saw something he had never seen before: a 100 percent chance of direct impact.

He quickly checked to make sure the asteroid was the size advertised. It was. No reason to panic.

Hours later, the asteroid hit the atmosphere over northern Sudan's Nubian Desert and exploded 23 miles up with the force of a thousand tons of TNT. Witnesses saw the fireball and took pictures of the vapor trails in the sky.

That might have been the end of the story, but Peter Jenniskens, an astronomer at the SETI Institute in California, had an idea: Why not search the desert for meteorites -- the fragments from the space rock?

In December, Jenniskens, professor Muawia Shaddad of the University of Khartoum and dozens of Shaddad's students scoured the desert for traces of the asteroid. Finally, they found one -- and then 46 more, the largest the size of an egg.

It was the first time scientists had observed an asteroid telescopically and then recovered its fragments. By comparing the data gleaned from observing the asteroid in space with analysis of the recovered meteorites, researchers can calibrate their telescopic observations of other asteroids. The findings were published last week in the journal Nature.

"It's the first step toward a Rosetta stone for understanding asteroids," Michael Zolensky of NASA's Johnson Space Center and one of the study's authors, told reporters in a conference call.

-- Joel Achenbach

How Video Games Help

Next time you worry about video games ruining your kids' eyesight, you might want to consider some research that suggests the opposite. Video games apparently can improve a key component of eyesight: discerning slight differences in contrast.

Daphne Bavelier of the University of Rochester and her colleagues studied 22 students before and after they played video games. Half of the students played the action video games Unreal Tournament 2004 and Call of Duty 2, while the others played The Sims 2, which is also richly visual but does not have the same level of visual-motor coordination of the other games.

After 50 hours of games over nine weeks, eye tests found that students who played the action games had significant improvement in discerning between shades of gray, while Sims 2 players did not, the researchers reported yesterday in the journal Nature Neuroscience. The benefits lasted as long as two years, the researchers reported.

The findings are particularly surprising because discerning slight differences in shades of gray, which is critical for good eyesight, has long been thought to be a part of the human visual system that cannot be improved.

"To the best of our knowledge this is the first demonstration that contrast sensitivity can be improved by simple training," Bavelier said.

The findings suggest that "video games train the brain to process the existing visual information more efficiently, and the improvements last for months after the game play stopped," she said. "These games push the human visual system to the limits, and the brain adapts to it."

-- Rob Stein

Night Schools for Fish

Some fish form huge schools, known as shoals, that stretch for miles. What triggers hundreds of millions of individuals to form such aggregations that can then move in unison is one of biology's mysteries.

A team of researchers at the Massachusetts Institute of Technology's Center for Ocean Engineering shed some light on the process last week. It turns out that darkness is the first step.

Nicholas C. Makris and collaborators at five other institutions studied Atlantic herring, which shoal up on a fishing ground off Massachusetts known as Georges Bank. They used an underwater imaging technology called Acoustic Waveguide Remote Sensing and conventional fish-finding sonar to observe the herring over several days in autumn when they spawn.

Triggered by the fading light of sunset, fish in scattered groups began swimming much closer to one another than they normally do -- one-twentieth as far apart as before. This set off a chain reaction of similar behavior that spread like a sound wave through the water at a speed far faster than any individual fish could swim.

Some shoals were 25 miles across and 100 feet from top to bottom. They formed in deep water and moved into more shallow areas. As the sun rose, the shoals fell apart.

Forming shoals apparently allows herring to develop their eggs in synchrony, which in turn permits mass spawning. It also protects fish from predators by giving them simple strength in numbers. The report appeared last week in the journal Science.

-- David Brown

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