NASA MISSION SET TO RENDEZVOUS WITH A COMET
NASA's Comet Nucleus Tour, or CONTOUR, is scheduled for launch on July 1 and visit at least two comets as they speed toward the sun. The mission should provide the first detailed look at these primitive building blocks of the solar system. CONTOUR's flexible four-year plan includes encounters with comets Encke on Nov. 12, 2003 and Schwassmann-Wachmann 3 on June 19, 2006. The spacecraft can add a study of a new comet if one is discovered in time to catch it. CONTOUR will examine each comet's "heart," or nucleus, which scientists theorize is a chunk of ice and rock, often just a few miles across and hidden from Earth-based telescopes beneath a dusty atmosphere and long tail. The 8-sided solar-powered craft will fly as close as 62 miles to each nucleus, at top speeds of about 20 miles per second. A 5-layer dust shield of heavy Nextel and Kevlar fabric will protect the spacecraft from comet dust and debris.
FOREST BIODIVERSITY
Biologists studying tree seeds in the Appalachian Mountains have found evidence that helps explain how forests develop their diversity. The findings suggest natural enemies play a role in promoting diversity in both temperate and tropical forests -- therefore preserving diversity might also depend on preserving the natural enemies of trees. Researchers from Duke University tested whether a process called "density-dependent mortality" was at work in temperate forests, just as other researchers had found evidence for the process in tropical forests. "Basically, the idea of density-dependent mortality is that near adult trees of a given species, there is a concentration of natural enemies -- for example pathogens or predators of seeds or seedlings," researchers said. "If the natural enemies of these trees congregate in the neighborhood of adult trees, then there would be disproportionate mortality of seeds and seedlings." That means even if a given species is a better competitor for light or nutrients, density-dependent mortality would tend to neutralize the advantage and promote diversity. Sure enough, researchers measured the mortality of seeds from five tree species -- red maple, birch, ash, tulip poplar and oak -- as they progressed through germination to older seedlings. They found the mortality at each stage depended on how many adult trees of that species were clustered nearby -- demonstrating that density-dependent mortality was at work in a temperate forest, just as it is in tropical forests.
STUDY TRACKS CO-EVOLUTION
A surprisingly complex relationship between a common wildflower and a little gray moth is showing biologists how species can co-evolve. The wildflower, known as Lithophragma parviflorum, goes by the common names woodland star or prairie starflower. Its life history is entwined with that of a moth called Greya politella. Both species have co-evolved in a variety of habitats throughout Idaho, Washington and Oregon. The moth is both a pollinator of L. parviflorum flowers and a consumer of its seeds, a combination of effects that seems to have widely varying outcomes in different habitats. The interaction covers the full range of possibilities, from mutually beneficial to antagonistic, researchers said. In extensive field surveys, biologists found the moths associated with every population of L. parviflorum they sampled. Further studies focused on 12 sites in contrasting habitats, including open grassland, ponderosa pine woodland, and streamside canyons. In all but one of the sites, the moths were completely dependent on L. parviflorum for food -- nectar for adult moths and seeds for their larvae -- and for mating sites.
FAINT COMPANIONS FOUND AROUND BRIGHT STARS
Three small, faint stars, apparently locked by gravity in orbits around much larger and brighter companions, have been discovered by a new infrared camera with innovative optics on the 100-inch telescope at the Mount Wilson Observatory in Pasadena, California. The optics are part of new technology being developed to help NASA's forthcoming Terrestrial Planet Finder, a giant space observatory scheduled to be launched in 2012 to look for Earth-like planets around other stars. Each of the three dwarf stars is less than one-tenth the mass of the sun. All give off a dark-red glow. One of the stars is about 50 light-years from Earth, another is about 27 light-years away, and the third is about 200 light-years away. Astronomers consider all three our neighbors in this corner of the galaxy. The camera has a specially shaped mask installed over the "pupil" of its eye to allow fainter companions to be seen around bright objects. The shaped mask is an improvement over the circular masks that astronomers have been using to block the light from bright stars in an attempt to see a nearby fainter objects.
(Editors: For more information on COMET MISSION, contact Michael Buckley at 240-228-7536 or [email protected]. For FOREST DIVERSITY, Dennis Meredith at 919-681-8054 or [email protected]. For CO-EVOLUTION, Tim Stephens at 831-459-4352 or [email protected]. For FAINT COMPANIONS, Bob Eklund at 310-333-3478 or [email protected])
