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August 19, 2002

For more information on these science news and feature story tips, contact the public information officer listed at (703) 292-8070. Editor: Josh Chamot

Team Probes Pluto's Atmosphere During Cosmic Event

Astronomers who observed a rare cosmic event in July have announced that Pluto's atmosphere has undergone drastic changes in the past 14 years.

Pluto, the farthest planet from the sun, has never been seen clearly from Earth, or even from space telescopes. However, in an "occultation" on July 19, the planet passed directly in front of the star P126A, blocking the star's light. Marc Buie of Lowell Observatory in Flagstaff, Ariz., and Oscar Saa of Cerro Tololo Inter-American Observatory in Chile used a 14-inch portable telescope in northern Chile to observe the event. By recording the dimming of the starlight, Buie's team was able to calculate the density, pressure and temperature of Pluto's atmosphere.

During observations of the last occultation in 1988, the light from the star winked out completely, suggesting a "smog" layer over Pluto or a sharp decline in its atmospheric temperature. However, during the recent viewing, the star's light gradually dimmed as the planet passed in front. Comparing the two results, James Elliot of the Massachusetts Institute of Technology said one possible explanation is that the "smog" layer, or the temperature drop, that extinguished the starlight the first time has now dropped to a lower altitude or disappeared. Another possibility, according to Elliot, is that Pluto is undergoing global warming.

The scientists hope to obtain more information during an occultation predicted for August 20, 2002, when Pluto will pass in front of the star P131.1. These events are becoming more common because Pluto is moving into line with the Milky Way, where stars are more abundant, Elliot said.

The National Science Foundation (NSF) partially supports this research, and scientists used NSF's Cerro Tololo observatory to help predict when and where the event could be observed. [Amber Jones]

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National Tragedy Survey Reveals Continuing Impact of 9/11

Although most Americans returned to their normal activities with resilience after the events of September 11, 2001, the impact of the tragedy continued to be felt throughout society, reports the National Opinion Research Center at the University of Chicago in a follow-up to an earlier NSF-supported study.

A research team found that people's feeling of national pride, enhanced by public response to the 9/11 events, continued to be unusually high. They also found that people's faith in others, which was also heightened by the response to the events, did not fade with the passing of time.

However, some groups were more severely affected by the tragedy and are having greater difficulty recovering from 9/11, according to surveys taken three to five months later. For example, New Yorkers were more likely than the rest of the nation to be worried about more terrorist attacks (27 percent versus 17 percent) and Democrats expressed greater worry than Republicans (17 percent versus 3 percent).

On average, people in follow-up interviews were less likely to report negative moods, such as depression, anxiety about being criticized and restlessness than they did immediately after the attacks. However, New Yorkers had a rate of recovery about half that of others in the country, the surveyors found.

Among the other groups that had greater difficulty recovering were those with family incomes less than $40,000 a year and people with less than a high school education. Members of minority groups also reported greater difficulty recovering from the events than the general population.

The findings are part of the study "America Recovers: A Follow-Up to a National Study of Public Responses to the September 11 Terrorist Attacks." The research team, headed by senior research scientist Kenneth A. Rasinski, and Tom W. Smith, Director of the General Social Survey, based the report on re interviews with 805 of the 1,013 people interviewed nationally in the first sample that was taken immediately after September 11. The survey also included 406 people initially interviewed in New York of whom 296 were interviewed in the follow-up.

In addition to NSF, the initial survey was funded by the Russell Sage Foundation and the Robert Wood Johnson Foundation. The MacArthur Foundation funded this second round. [Bill Harms]

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Researchers Get Excitons to go the Distance

Digital photograph of excitons; caption is below
Digital photograph of excitons that have moved hundreds of microns inside a nanoscale structure from the central laser spot where they were created. Excitons travel in a "dark" state from the central laser source where they are created to a ring where their light is turned back "on."
Image Credit: Loren Pfeiffer, Bell Labs and David Snoke, University of Pittsburgh

Scientists have found a new way to create and move a small bit of optical energy called an exciton over long distances. Such motion is an important step in the path to developing semiconductors in which excitons are shuttled and controlled to form "excitonic circuits."

In conventional semiconductors, electrons or their absence (a so-called hole) move in circuits to perform functions such as computation and storage of information. In the exciton research, laser light is used to separate an electron from an atom in a semiconductor. The "excited" electron plus the hole remaining on the atom compose an exciton, which moves like an energy particle and could potentially carry information.

In most cases, the exciton exists for only a few nanoseconds (billionths of a second) and travels only a few microns before the electron and hole "recombine" and re-emit the light.

David Snoke of the University of Pittsburgh, with support from NSF and the Department of Energy, used nanoscale structures to increase the distance traveled by the excitons to several millimeters. Snoke and his colleagues report their findings in the August 15 Nature.

Previous experiments had shown that excitons could be forced to move from one place to another with pressure or an electric field. These studies, combined with the current results on long distance exciton motion, strengthen the possibility that researchers will be able to develop circuits based on exciton movement rather than electron movement.

"This research is an example of rapid developments occurring at the interface of condensed matter physics, which produces semiconductor structures, and optical science," said Hollis Wickman, a program manager in NSF's materials research division. "The interface represents an emerging field called condensed matter optics." [Amber Jones]

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Central American Volcanoes Yield New Clues About Earth's Processes

A chain of Central America's most active volcanoes has given a team of researchers a novel glimpse into fundamental Earth processes. By comparing volatile gasses leaving Guatemalan and Costa Rican volcanoes, scientists tracked elements cycling between Earth's underlying mantle and its surface reservoirs - such as the crust, oceans, and atmosphere.

The study, funded by NSF and affiliated with the University of New Mexico, the Scripps Institution of Oceanography, and Northern Illinois University, was initially conducted on Costa Rican volcanoes in January 2001. A second expedition concentrated on Guatemalan volcanoes in May 2001.

These volcanoes are created by a process called subduction, a process seen around the world, wherein one of the plates that makes up the Earth's crust slips beneath another and is driven down into the planet's interior. The researchers sampled the gasses that escape from the Central American volcanoes and analyzed the nitrogen and helium.

From a study of these elements, the researchers determined whether subducted crust travels deep into the Earth before melting and arising out of a volcano or if the top of the crust is sheared off as the remaining plate drives downward.

"Volcanoes are basically transfer conduits between the Earth's surface and the underlying mantle," explained David Hilton, a geochemist at Scripps.

Having taken samples of sediments offshore, the researchers knew the crust material being driven into the subduction zone were virtually the same in both Guatemala and Costa Rica. However, the volatile gasses that came out - specifically nitrogen gas - surprised the researchers.

In the Guatemalan volcano system, nitrogen from the subducted crust was driven deep down before rising back to Earth's surface. Yet in Costa Rica, the scientists did not find evidence that nitrogen was coming from the subducting plate. The nitrogen data supported other evidence showing that the uppermost sedimentary veneer on this section of crust is removed by the subduction process before it reached the area where magma is generated.

"The research is significant because not much is known about nitrogen coming out of volcanoes," said Tobias Fischer, a volcanologist at University of New Mexico. "We clearly show that in the Guatemalan subduction zone, up to 95 percent of the nitrogen in volcanic gasses comes from subducted marine sediments. The situation is different in Costa Rica, where the nitrogen is predominantly of mantle origin," said Fischer.

The study, one of the first clear descriptions of how and where nitrogen travels during subduction, gives researchers a new glimpse into the long-term evolution of Earth's mantle. The researchers now plan to address nitrogen and helium relationships in other subduction zones bordering the Pacific Ocean (the so called "Ring of Fire"), as well as at mid-ocean ridges and oceanic hotspots such as Hawaii. [Cheryl Dybas]

For descriptions of the expedition, see:

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