SCIENCE

Notebook

Eel Makes Sure Food Goes Down

Remember the science-fiction monster with a jaw within a jaw that terrorized Sigourney Weaver in the "Alien" films? Well, it turns out a similar double-jawed creature actually exists: The moray eel has a second set of jaws located in its throat that snaps forward to grab prey and quickly pull it down into the eel's digestive system.

"This is really an amazing innovation for feeding behavior," said Rita S. Mehta of the University of California at Davis, who documented the second jaws in a report last week in the journal Nature.

Using a high-speed digital camera, X-rays and other imaging technology, Mehta and a colleague captured the action of the second jaws and studied their purpose.

Most fish feed by overtaking their prey, then expanding their mouths and sucking in water with the food or grabbing it with their jaws, using suction to move the food from their mouth to their esophagus.

Because of their anatomy, moray eels have little ability to create suction through their mouths, Mehta found. Instead, they first grab the food with their strong outer jaws. Next, the inner "pharyngeal" jaws, equipped with large, curved teeth, reach forward and seize the prey, pulling it back to be swallowed within a second.

While other fish have similar second jaws, only the moray's can reach forward and grab prey, the researchers reported.

-- Rob Stein

Asteroid Crash Did In Dinosaurs

A cosmic traffic accident in the asteroid belt between Mars and Jupiter 160 million years ago appears to have been the beginning of the end for the dinosaurs.

That was when two large rocks -- one 106 miles across, the other 37 miles -- slammed together, creating a cluster of asteroid fragments known as the Baptistina family that included 300 pieces larger than 6 miles in diameter.

The orbits of these fragments were slowly changed by thermal forces as they absorbed sunlight and then radiated away the heat, a process that gradually drove about 20 percent of the largest rocks out of the asteroid belt, researchers reported last week in Nature. One large piece went on to strike Earth 65 million years ago in what is now the Yucatan Peninsula in Mexico, creating the Chicxulub crater in a gigantic explosion that triggered the mass extinction of the dinosaurs.

The strike was not an isolated incident but part of a broader twofold increase in big asteroid impacts on the moon and Earth over the past 100 million to 150 million years. Using computer simulations to trace the breakup, researchers calculated that other large fragments probably created the Tycho crater on the moon and many large craters on Venus and Mars.

"We are in the tail end of this shower now," said co-author William F. Bottke of the Southwest Research Institute in Colorado. "Our simulations suggest that about 20 percent of the present-day, near-Earth asteroid population can be traced back to the Baptistina family."

-- Christopher Lee

Astronaut Illness Tied to Protein

Researchers have long observed that spaceflight and extended periods of stress to the body can weaken the immune system and have reported that astronauts appear to suffer higher rates of infection after spaceflights. Now, NASA-funded research has identified the protein osteopontin as a likely cause of the lower immunity and organ atrophy that follows chronic stress, such as prolonged weightlessness.

In studies that exposed mice to three days of conditions simulating the weightlessness of space -- which causes body fluids to gravitate toward the head rather than the extremities -- researchers found that those with a gene for osteopontin had fewer infection-fighting white blood cells, which led to weight loss and damage to the spleen and thymus. In addition, those mice had higher levels of corticosterone, a steroid that kills white blood cells. Mice that did not have the gene suffered no significant effects.

"Following periods of prolonged physical stress, such as when astronauts live in microgravity, white blood cells that fight disease die at an increased rate," said Yufang Shi, an investigator at the National Space Biomedical Research Institute and a professor at the University of Medicine and Dentistry of New Jersey. "By determining the role of lymphocyte death in a stressed immune system, we may be able to develop therapies."

The team is already researching an antibody that can remove osteopontin from blood.

With NASA planning to send astronauts back to the moon and possibly to Mars in future decades, the many physical problems associated with weightlessness and exposure to cosmic radiation have become a major focus of research. NASA now views the international space station primarily as a setting to study the effects of living in space.

-- Marc Kaufman