Deep Impact Soars to Meet Comet

ON JANUARY 12, the Deep Impact Space Craft was launched at Cape Canaveral, Fla., on its journey to an historic encounter with Comet Tempel 1. On July 4, this NASA Discovery Mission led by University of Maryland astronomer Michael A'Hearn will be the first to smash through a comet's surface and reveal the secrets of its interior.

At encounter, some 83 million miles from Earth, the Deep Impact flyby spacecraft will launch a cylindrical copper "impactor" spacecraft into the path of Comet Tempel 1. With its cameras 'rolling,' the 820-pound, 3-ft.-diameter impactor will collide with the speeding comet at about 23,000 miles per hour. The impact is expected to create a crater several hundred feet in size. Nearby, Deep Impact's 'flyby' spacecraft will collect pictures and data of the event and send them back to Earth. In addition, the Hubble and Spitzer space telescopes, the Chandra X-ray Observatory and telescopes on Earth will observe the material flying from the comet?s newly formed crater, adding their data and images to those collected by the Deep Impact spacecraft.

?The information we gain from Deep Impact will improve our understanding of how our solar system formed, says A?Hearn. "It should also increase our knowledge of the density and composition of comets, information that could be important should a comet ever threaten Earth." —LT

For more information on the Deep Impact mission, visit http://deepimpact.umd.edu.

Men and Women Literally See the World Differently

So you're having that discussion about what color to paint the living room. She says, "How about something in an Iced Mauve." He says,"You mean there are colors besides beige." It could be you've encountered an ancient gender color divide that can be chalked up to evolution.

A new University of Maryland study shows that the same kind of gene variety that causes color blindness--usually in men--also may give humans--especially women--a better perception of color.

Sarah Tishkoff, assistant professor of biology, and former Maryland postdoctoral fellow Brian Verrelli, now an assistant professor at Arizona State University, studied DNA from more than 200 subjects from different geographical populations around the world, and, to their surprise, found that one of the genes connected to color vision has maintained an unusual amount of genetic variation, possibly for millions of years of human evolutionary history.

"Usually, it's a bad thing to have too much change in a gene, and natural selection gets rid of it," says Tishkoff, "but in this case, we're seeing the reverse. Natural selection is acting to maintain that variation."

The Maryland researchers found that variation in this color perception gene may have given women in particular the ability to see more subtle shades of colors. Women have two X-chromosomes, men only one. Because this color vision gene resides on the X-chromosome, rare detrimental changes at this gene cause color-blindness in males--eight percent of the world's men are color blind--whereas females are likely to have at least one good copy of the gene.

Tishkoff and Verrelli speculate that in a time when humans were hunter-gatherers, enhanced color perception would have allowed women, who were traditionally gatherers, to better discriminate among colored fruits, insects and background foliage.

"Men and women literally may be seeing the world differently," Tishkoff says.

The findings also suggest, says Tishkoff, that geneticists may want to look at the impact subtle changes have in natural selection, especially in disease prevention. "It's long been thought that if it's not a dramatic change, it doesn?t matter. But we see in this study that subtle changes can make a difference."

Tishkoff uses DNA to search for the origins of modern man, and is especially interested in the role infectious disease has played in humans. In 2003, she was named one of the country?s top 10 "Brilliant Young Scientists" by Popular Science magazine. —ET

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