SCIENCE NOTEBOOK

Monday, March 17, 2008

Flyby Sips Saturn Moon's Geysers

NASA's Cassini spacecraft flew through jets of geyser-like icy water spewing from Saturn's moon Enceladus last week, collecting samples that could help explain whether liquid water -- and perhaps even water with organic material -- is trapped beneath the lunar crust.

Flying through the plumes at 120 miles above the surface, and then taking photos from as close as 30 miles, Cassini also gathered data that will help explain how the ice water collects into a giant halo of ice dust and gas around Enceladus, and how that halo helps supply material to one of Saturn's rings.

The close flyby, which scientists hope to follow with an even closer one later this year, also revealed that the north and south poles of the moon are geologically very different. The northern region is much older and pitted with a variety of craters not seen elsewhere on the moon. The geysers spew water vapor at 800 mph from surface fractures running along the south pole.

The flyby and another one planned for Oct. 9 were designed to allow Cassini's particle analyzers to dissect the body of a plume for clues about its particles' density, size, composition and speed.

Instruments on Cassini, which is a joint mission of NASA, the European Space Agency and the Italian Space Agency, discovered evidence for the geyser-like jets on Enceladus in 2005.

-- Marc Kaufman

Stork Brings Kiwi to National Zoo

A North Island brown kiwi has been born at the National Zoo, a notable event because the bird is one of the world's most endangered species.

The chick hatched at the zoo's Bird House early on March 7 after the chick's father incubated the egg for a month and keepers incubated it for another five weeks, zoo officials said.

The little bird is now being kept in a specially designed brooding box. It will not be on exhibit but can be viewed via a webcam ( http://nationalzoo.si.edu/Animals/Birds/Kiwi/default.cfm). Because kiwis are nocturnal, the best time to take a look is in the evening.

Zookeepers have not yet determined the chick's sex. That's something geneticists are working on by analyzing samples swabbed from inside the egg and the bird's beak.

Only four zoos outside of New Zealand have successfully bred kiwis, and only three U.S. zoos exhibit them. The birth marked just the third time in the National Zoo's history that a kiwi has been hatched. The first, in 1975, was the first to occur outside New Zealand. The second was in 2006.

Kiwis typically mate for life, and both parents care for the egg. Chicks are born fully feathered and able to survive on their own.

There are five species of kiwi, and all are unique to New Zealand. The North Island brown species is New Zealand's national bird. Although kiwis have existed in New Zealand for more than 30 million years, only about 24,000 North Island brown kiwis are believed to remain in the wild.

-- Rob Stein

DEET Fools Mosquito's 'Nose'

For most people trying to avoid being eaten alive by mosquitoes, it is enough to know that DEET works. But for scientists and marketers hoping to invent or sell an even better bug repellent, the goal is to find out why DEET works.

Now researchers at Rockefeller University in New York have solved a big part of that longstanding mystery, finding that DEET blocks a highly specific molecular pathway that tells a bug's brain what it is smelling. In particular, it interferes with an insect's ability to smell 1-octen-3-ol -- a telltale ingredient of human breath -- and the scent of lactic acid, an odoriferous hallmark of sweat.

N,N-diethyl-meta-toluamide, or DEET, is the most widely used insect repellent in the world and was developed 60 years ago by the Agriculture Department and the Army. Among the many six-legged pests that find the stuff offensive are mosquitoes, including the species that transmit malaria -- a disease that kills 1 million people every year -- yellow fever, dengue and West Nile fever.

Leslie B. Vosshall and colleagues measured the electrical pulses coming from nerves in the mosquito's olfactory organ and found that DEET blocks a molecular smell receptor known as OR83b, which detects key components of human sweat and breath.

Experiments in fruit flies confirmed the importance of that smell receptor and its susceptibility to interference by DEET.

The discovery means that scientists can start large-scale screenings of chemicals, including some that might be formulated into more pleasant creams, to see if they are as good or better at blocking OR83b.

Details were published Friday in the journal Science.

-- Rick Weiss