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Projects sponsored by the National Science Foundation (NSF) continued to contribute new knowledge about the origins, composition, and dynamics of the universe and Earth's near-space environment. NSF-sponsored scientists have discovered many new outer solar system objects as a result of ongoing optical surveys. For example, scientists now believe that the region beyond the orbit of Neptune is home to hundreds of thousands of minor planets and perhaps billions of comet-like objects. Astronomers have begun to develop a picture of the relationship between these objects and the formation of planets, the origin of comets, and the existence of dust disks around stars.

In addition, NSF-sponsored scientists began monitoring a previously unremarkable binary star that suddenly began emitting x-rays and radio waves. Scientists believe that one of the pair is either a black hole or a neutron star—both very compact objects. Astronomers theorize that, in such systems, the neutron star or black hole is drawing material away from its companion star and that the material is formed into a rotating disk around the compact companion. The x-rays, they believe, come from superheated material in this "accretion disk" and are ejected at right angles to the plane of the disk. Because scientists do not fully understand the relevant physical processes, astronomers are eager to gain as much new information as possible whenever one of these systems is discovered.

Scientists have discovered a way to study so-called "dark matter"—matter we cannot see because it does not give off any radiation. Astronomers have known for several years that a small galaxy is orbiting our home galaxy, the Milky Way. New calculations indicate that the small galaxy orbits the Milky Way in less than 1 billion years and that it has completed 10 orbits. Amazingly, the strong gravitational forces of the Milky Way have not destroyed the small galaxy as would have been expected. This indicates that the small galaxy contains far more mass than indicated by its number of stars, thus signaling the presence of a significant amount of dark matter. Astronomers think that at least 90 percent of the matter in the universe is dark and hope to clarify the nature of this dark matter.

Radio telescope studies of the fiery afterglow of a gamma ray burst have provided astronomers with the best clues yet about the origins of these tremendous cosmic cataclysms since their discovery more than 30 years ago. Observations with NSF's Very Large Array radio telescope confirm that a blast seen to occur on March 29, 1998, had its origin in a star-forming region of a distant galaxy. There are two leading theories for the causes of gamma ray bursts. According to one theory, the blasts occur when a pair of superdense neutron stars collide. The second is that a single, very massive star explodes in a "hypernova," more powerful than a supernova, at the end of its normal life. Observations favor this second hypothesis.

Astronomers have found evidence for the most powerful magnetic field ever seen in the universe. They have observed a long-sought, short-lived "afterglow" of subatomic particles ejected from a magnetar—a neutron star with a magnetic field billions of times stronger than any on Earth and 100 times stronger than any previously known in the universe. The afterglow is believed to be the aftermath of a massive starquake on the neutron star's surface.

NSF-sponsored researchers at Hughes STX Company developed a method for the early warning of solar events using interplanetary radio bursts observed remotely by both the Ulysses and Wind spacecraft. These emissions are generated when coronal mass ejections create shocks in the interplanetary medium. The investigators have been successful in using the timing of these radio emissions to estimate the arrival time of the shocks on Earth.

Scientists at Science Applications International Corporation in San Diego developed a comprehensive, three-dimensional, magnetohydrodynamic model to use remote observations of the Sun to predict the state of the solar wind at Earth's orbit. Researchers have already used the model to determine the coronal magnetic field and heliospheric current sheet structure during the period from February 1997 to March 1998. Scientists also have used the model to simulate the triggering of a coronal mass ejection, including its appearance as seen by a space-based coronagraph.

Scientists from Cornell University used a sensitive all-sky imaging camera to study the behavior of structured airglow layers in the thermosphere over Puerto Rico. These elongated structures are believed to be a result of enhanced geomagnetic activity. Their behavior is consistent with plasma irregularities commonly seen near the magnetic equator, but scientists do not yet completely understand the connection between the two phenomena.

Researchers at SRI International and the University of Alaska's Geophysical Institute in Fairbanks discovered new evidence for a theory explaining the presence of thin sporadic layers of sodium in Earth's upper atmosphere. Scientists believe that these sporadic layers, distinct from the better understood layer of neutral sodium atoms found between 80 and 100 kilometers altitude, are a byproduct of meteors vaporizing when entering the atmosphere. Using data from the NSF-supported incoherent scatter radar and sodium LIDAR, the investigators demonstrated that thin ion layers are pushed downward to a region in which chemical catalysts recombine the ionized sodium, leaving behind a thin layer of neutral sodium.

NSF-funded scientists at the High Altitude Observatory of the National Center for Atmospheric Research continued to develop instruments to assist in studying solar irradiance—energy flux in the plane of Earth's orbit. Solar irradiance and total solar luminosity vary over time scales from days to years. Not only do astronomers not know the physical mechanisms that cause these changes in the Sun's brightness, but astronomers cannot even identify which of the components of the Sun's visible outer photosphere are responsible for the solar energy flux variations that have been detected by satellite experiments. In response to mounting documentation that terrestrial climate is correlated with such changes in the Sun, NSF researchers have developed a long-range plan and experiment to address how and why the Sun's irradiance changes.

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