Secrets Of Feather Formation
Posted: Wednesday, October 30, 2002
Source: American Geophysical Union
WASHINGTON - Researchers have found that a portion of anomalous cosmic rays -- charged particles accelerated to enormous energies by the solar wind -- results from interactions with dust grains from a belt of comet-sized objects near Pluto's orbit. These objects make up what is known as the Kuiper Belt, a remnant of the formation of the solar system.
"This novel finding shows how dust in the cosmos may play an important role for producing the most energetic particles known," says Dr. Nathan Schwadron, a senior research scientist in the Space Science and Engineering Division of Southwest Research Institute (SwRI) in San Antonio, Texas. The study by Schwadron and colleagues at SwRI and the University of Michigan was published October 30 in Geophysical Research Letters, a journal of the American Geophysical Union.
"Dust grains are produced in vast amounts through collisions of Kuiper Belt objects," says Schwadron. "These particles give us a glimpse of the early stages of our solar system when the dust content was much larger, and could parallel other more dusty stellar systems that exist now."
Recent observations of anomalous cosmic rays are puzzling because of the unexpected presence of iron, silicon and carbon, notes Schwadron. "This finding varies from the traditional explanation of anomalous cosmic rays which were thought to be devoid of easily charged elements."
The interstellar medium has lots of carbon, silicon and iron atoms, but electrical charging (ionization) of these elements prevents them from penetrating deeply within the solar system. "Our team looked for a source already inside the solar system to account for the unusual anomalous cosmic rays -- and we found one in the tiny comet-like grains from the nearby Kuiper Belt," says Schwadron.
As the grains produced by collisions in the Kuiper Belt drift in toward the sun, they are bombarded by solar wind particles, which causes sputtering and frees the carbon, silicon and iron atoms from within. At that point, those particles interact with solar radiation, transforming them into ions (charged particles). The solar wind then sweeps them out and accelerates them to anomalous cosmic ray energies at the edge of the solar system, where they are bounced to and fro by magnetic fields in the solar wind and in the medium beyond the solar system, according to Schwadron.
Tom Bogdan, program director in the NSF Division of Atmospheric Sciences, which partly funded the research, says, "This is a big step toward solving the long-standing mystery of the origin of the anomalous component of cosmic rays. The research underscores the power of remote sensing: Sampling of Kuiper Belt material with unmanned space probes is a huge and difficult enterprise. The detection locally of the anomalous cosmic ray component provides information on the conditions that prevail in this remote region of our solar system."
"Anomalous cosmic rays" are so named because they form in the relative vicinity of the Earth, near the sun, and have lower energy than galactic and intergalactic cosmic rays, which form in the far reaches of the galaxy and beyond. Cosmic rays, the most energetic particles in the cosmos, move throughout the universe at light speed and constantly bombard the Earth.
"The discovery that anomalous cosmic rays can be generated from material in the Kuiper Belt provides a tool for understanding its mass distribution and composition and for probing the plasma-dust interactions in space," says Schwadron.
Cosmic rays also are believed to play a role in evolution. "Cosmic rays are a double-edged sword. They cause genetic mutation and are harmful to living organisms, but on the upside stimulate biological evolution," Schwadron says. "Cosmic rays are our only available sample of matter from the far reaches of the distant galaxy, and from other galaxies. They can tell us a lot about what's in the universe, and we can now use them to study what's in the Kuiper Belt. Their relationship to the creation or maintenance of life is also worth a closer look."
This program was supported with funding from NSF, NASA, and SwRI.
Editor's Note: The original news release can be found at:
Send page by E-Mail Chromatin Support Chromosomes During Cell Division
Posted: Tuesday, October 29, 2002
Source: University Of Illinois At Chicago
When cells divide and transfer copies of genes to daughter cells, the process includes a phase where the replicated chromosomes are tightly condensed into durable packages called mitotic chromosomes. These chromosomes must survive the trying ordeal of holding firm during cell division. Some scientists think protein provides the scaffolding-like support in this process.
But researchers at the University of Illinois at Chicago have discovered it is not protein, but chromatin, the portion of the cell nucleus that contains DNA, which provides this support.
"What we've shown is that the mitotic form of chromosomes, when they're folded up for transmission during cell division -- the long, chromatin fibers made of DNA complexed with a lot of protein -- are linked at cross-link points, kind of like playground monkey bars," said John Marko, associate professor of physics at UIC. "And the bars are just chromatin."
The findings will be reported in the online edition of the Proceedings of the National Academy of Sciences the week of Oct. 28.
Marko, who also holds a courtesy appointment in bioengineering, was assisted by Michael Poirier, a former Ph.D. student in physics at UIC, who is now doing post-doctoral research at the Université Louis Pasteur in Strasbourg, France.
Marko and Poirier discovered the protein-support idea literally did not hold up following a series of experiments involving newt chromosomes, chosen because they are large and easy to grasp and manipulate under the microscope. After treating the chromosomes with low concentrations of enzymes that cut DNA at specific points, they discovered there was no support left, and the chromosomes dissolved.
The chromosomes were removed from cells and held in place by hair-like glass tube pipettes. The DNA digestion was done in free solution. This methodology was never previously used. The technique may prove useful in unlocking the puzzle of how cells divide.
Marko began his work about seven years ago while a research fellow at Rockefeller University in New York. He and Poirier began work on this reported research at UIC about four years ago.
"We realized that although a lot was understood biochemically about how chromosomes were organized, not so much was understood about what the physical properties of chromosomes were and how that might be a useful probe to look at their structure," Marko said.
"We're trying to understand the mechanics of cell division, which is still largely considered as a 'black box,' where chromosomes go in, and duplicate chromosomes come out. There are still a lot of questions about how this machinery works, particularly about maintenance, duplication and segregation of the DNA."
"Our study can provide very severe constraints on how other researchers should think about the state of the chromosome during cell division. We say there is no internal protein structure perhaps made by all these proteins sticking together. Instead, these proteins are distributed through a network of chromatin."
The research was funded by grants from the University of Illinois, the National Science Foundation, the Whitaker Foundation, a Johnson & Johnson corporation award, a Research Corporation award and a grant from the Petroleum Research Foundation of the American Chemical Society.
Send page by E-Mail Comparing Monkey And Human Brains
Posted: Tuesday, October 22, 2002
Source: Ohio State University (http://www.acs.ohio-state.edu/)
COLUMBUS, Ohio - Researchers have developed a new way to use a decade-old imaging method to directly compare the brains of monkeys with those of humans. Their report appeared in the journal Science.
The method uses functional Magnetic Resonance Imaging (fMRI) - a technique that measures blood volume and flow and blood-oxygen levels in the brain. It also provides an indirect measure of neuronal activity in different regions of the brain.
Neurons need oxygen and glucose to work. Blood carries both substances, and both can cross the blood-brain barrier. When a particular region of the brain is activated, the blood flow to that area temporarily increases in order to supply the neurons with fresh oxygen and glucose.
"What we're doing is an indirect measurement of the human brain's electrical activity," said Wim Vanduffel, the report's lead author and an instructor at the Athinoula A. Martinos Center for Biomedical Imaging in Charlestown, Mass.
"It's the best way at present for investigating patterns of neural activity in humans," he said.
The researchers used the same fMRI technique on humans and on monkeys to compare activity in an area of the brain called the visual cortex, the region that processes vision and motion. While each species shares similar traits in the visual cortex, the researchers did find distinct differences between the species in two key areas.
"Implicit in the neuroscience community was that the monkey cortex is a good model for the human cortex," said James Todd, a study co-author and a professor of psychology at Ohio State University. "Scientists didn't have any choice but to make that assumption, as the monkey brain was the only model we had to work with."
What set the fMRI technique used in this study apart from past fMRI experiments on monkeys is that the monkeys remained conscious during the experiments.
"Until this point, anybody who has used fMRI on monkeys did so while the animals were sedated," Todd said. "That presents a real problem since sedation may alter the patterns of neural activity that occur when monkeys are awake."
Eleven human subjects each participated in 14 separate fMRI scan sessions, and three juvenile macaques participated in at least eight sessions. While each session produced data, some of the sessions produced weak signals. Therefore, the researchers averaged together the sessions in order to obtain reliable results.
The experiments were conducted in a laboratory run by Guy Orban, head of the division of neurophysiolgy at Katholieke Universiteit Leuven in Belgium, where Wim Vanduffel also holds a postdoctoral position. Todd was responsible for designing the images viewed by all of the subjects.
For each session, a human subject lay on his back inside the fMRI and watched as nine randomly connected lines began to rotate on a monitor inside the machine. This procedure could not be used on the monkeys, however, because monkeys don't like lying on their backs. Instead, the researchers used juvenile monkeys that could be seated within the fMRI apparatus.
The researchers looked for areas of the visual cortex that were activated while the subjects watched rotating 3-D images. Each portion of a subject's visual cortex was scanned during each session in the fMRI. In order to better see the areas of activity in the monkey brain, the macaques were injected with a solution that enhanced the contrast shown in the final scans.
"For unknown reasons, the fMRI signals from the monkeys were weaker than those from the humans," Orban said. "Since the monkey brain is smaller, we needed to use a contrasting agent to increase the fMRI's ability to pick up a signal."
While a regular MRI measures tissue density and structure, fMRI measures the flow, volume and oxygenation of blood in tissue. In the current study, this technique was used to investigate regions of the brain that were activated when the subjects looked at the moving 3-D images.
"The advantage of functional MRI is that scientists can see which regions of the brain are active," Orban said.
The results showed pronounced differences between the two species: in an area of the human visual cortex called V3A - an area thought to be responsible for a variety of visual functions, such as motion processing and stereoscopic depth - and also in the intraparietal cortex. The researchers noted that, in humans, four distinct areas of the intraparietal cortex were involved in processing the rotating 3-D images. There is no clear counterpart to this region in monkeys.
"The results suggest that, as humans evolved, some portions of their brains adapted to produce specific abilities, such as controlling fine motor skills," Orban said.
The results don't mean that monkeys don't have 3-D visual capabilities. The findings do show that researchers now have a technique enabling them to make reliable comparisons between a monkey brain and a human brain.
"This study provides the first evidence of a functional difference between the human and the monkey brain," Todd said. "The results show that, in at least one important aspect, the brains function quite differently."
"We were in a paradoxical situation before we had these results," Orban said. "On one hand, it's obvious that humans and monkeys are different.
"On the other hand, when we use the physiology of the monkey brain as a model to explain what we see in a human functional MRI scan, we had assumed that the activity was occurring in the same region in each brain. We had to make an assumption, which we knew would be wrong from time to time. We just didn't know when that assumption would be wrong."
"Now we have a way to verify when the monkey model does not apply and when it really can apply," Orban said. "And we can be much more precise in extrapolating findings from monkeys to humans."
Support for this research came from the Inter-University Attraction Poles (a Belgian research foundation); GOA (a regional research support foundation in Belgium); the Fund for Scientific Research - Flanders (FWO-Flanders); and the Queen Elisabeth Medical Foundation. Todd, Orban and Vanduffel conducted the study with Denis Fize, Hendrik Peuskens, Katrien Denys and Stefan Sunaert, all of Katholieke Universiteit Leuven.
Editor's Note: The original news release can be found at http://www.osu.edu/researchnews/archive/monkysci.htm
Send page by E-Mail Tokamak Fusion Test Reactor Removal Completed
Posted: Monday, October 21, 2002
Source: Princeton Plasma Physics Laboratory (http://www.pppl.gov/)
Plainsboro, New Jersey - One of the world's largest and most successful experimental fusion machines has been safely disassembled and cleared away. In September, staff at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) completed the dismantling and removal of the Tokamak Fusion Test Reactor (TFTR), which shut down in 1997 following 15 years of operation. During its experimental life, TFTR set records for fusion performance and made major contributions to the development of fusion as a long-term energy alternative. The PPPL team finished the removal of TFTR on schedule and under budget.
"This marks the end of an important chapter in the history of fusion," said Raymond L. Orbach, Director of the Office of Science, which oversees PPPL for the U.S. Department of Energy. "The Tokamak Fusion Test Reactor achieved many firsts that brought us closer to an era of fusion power. Now that the decommissioning of TFTR has been completed safely, on schedule and under budget, in keeping with Office of Science best practices, we look forward to continued contributions in fusion power research from PPPL."
PPPL Director Robert J. Goldston noted, "The unprecedented scientific success of TFTR experiments has now been followed by its safe dismantling and removal. Not only did TFTR greatly advance fusion science, but its safe, cost-effective, and efficient decommissioning also demonstrates the promise of fusion as an environmentally attractive, economical energy source."
TFTR was the world's first magnetic fusion device to perform extensive scientific experiments with plasmas composed of 50/50 deuterium/tritium (D-T), the fuel mix required for practical fusion power production, and also the first to produce more than 10 million watts of fusion power. In 1995, TFTR attained a world-record temperature of 510 million degrees centigrade - more than 25 times that at the center of the sun.
Since the completion of D-T experiments on TFTR in 1997, PPPL has focused on nurturing the best new ideas in fusion research, both in advanced tokamaks and in innovative confinement configurations. Two major experimental projects, along with increased theory and computation, will anchor this program. The first, the National Spherical Torus Experiment (NSTX), is already producing an increased understanding of fusion physics. The second, the National Compact Stellarator Experiment (NCSX), now being designed, will provide further insight into the capabilities of stellarators, particularly for stable, continuous operation.
Work on the removal of TFTR began in October of 1999. The experiment stood 24-feet tall with a diameter of 38 feet. It contained an 80-ton doughnut-shaped vacuum chamber, 587 tons of magnetic field coils, a 15-ton titanium center column, and a massive stainless-steel support structure. TFTR's use of a fuel mixture containing tritium, a mildly radioactive form of hydrogen, added to the challenge of its safe and environmentally sound removal.
The most challenging aspect of the TFTR disassembly was the segmentation of the 100-cubic-yard vacuum vessel. Use of conventional technologies such as abrasive sawing and flame cutting could not satisfy health and safety concerns. PPPL's engineering team effectively addressed all challenges by developing an innovative system - Diamond Wire Cutting used in conjunction with a concrete filling technique - which reduced worker radiation exposure, airborne emissions, and waste generation. PPPL's unique and innovative application of Diamond Wire Cutting earned the Laboratory the New Jersey Society of Professional Engineers' 2002 Outstanding Engineering Achievement Award.
In the fusion process, matter is converted to energy when the nuclei of light elements, such as hydrogen, join or fuse to form heavier elements. In experiments such as TFTR, physicists employ magnetic fields to confine hot, ionized gases called plasmas, which fuel the fusion reactions. Compared to fossil fuels and fission, now used in commercial power plants, fusion would have distinct advantages, including an inexhaustible fuel supply; no chemical combustion products; and inherent safety, with minimal production of waste.
PPPL, funded by the U.S. Department of Energy and managed by Princeton University, is a collaborative national center for science and innovation leading to an attractive fusion energy source. The Laboratory is on Princeton's James Forrestal Campus, off U.S. Route 1 in Plainsboro, NJ.
Editor's Note: The original news release can be found at http://www.pppl.gov/news/pages/tftr_removal.html
Send page by E-Mail Newly Discovered Clouds High Above Milky Way
Posted: Monday, October 21, 2002
Source: National Radio Astronomy Observatory (http://www.nrao.edu)
Green Bank, WV - New studies with the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) have revealed a previously unknown population of discrete hydrogen clouds in the gaseous halo that surrounds the Milky Way Galaxy. These clouds were discovered in the transition zone between the Milky Way and intergalactic space, and provide tantalizing evidence that supernova-powered "galactic fountains" continually blast superheated hydrogen gas into our galactic suburbs.
Extending far above the star-filled disk of the Milky Way is an atmosphere, or halo, of hydrogen gas. "By studying this halo, we can learn a great deal about the processes that are going on inside our Galaxy as well as beyond its borders," said Jay Lockman, an astronomer with the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia. "It has remained a mystery, however, how this halo formed and what has prevented gravitational forces from collapsing the gas into a thin layer long ago."
Some astronomers have speculated that this gas is distributed as a diffuse mist held up by either magnetic fields or cosmic rays streaming out of the plane of the Milky Way. Others believed that it is made of innumerable long-lived hydrogen clouds bobbing up and down like balls tossed by a juggler.
Early observations with other telescopes discovered that there was some neutral hydrogen gas floating far above the Galaxy's plane, but these instruments were not sensitive enough to reveal any structure or resolve questions about its origin.
Lockman's studies for the first time show a clear picture of the structure of the gas. Rather than a mist, the halo is in fact full of discrete clouds, each containing 50-to-100 solar masses of hydrogen and averaging about 100 light-years in diameter. "These objects were just below the ability of the older telescopes to detect," said Lockman, "but I looked with the GBT, and they popped right out." Lockman's results will be published in the Astrophysical Journal Letters.
The clouds were discovered about 15,000 light-years from Earth toward the center of our Galaxy, and about 5,000 light-years above the Galaxy's plane.
One of the most compelling facts revealed by the GBT is that the clouds are coupled dynamically to the disk of the Galaxy; that is, they follow along with the rotation of the rest of the Milky Way. Material from other sources crashing into the Milky Way would have different velocities and also appear quite different. "These are home grown objects, and not interlopers from outside our own Galaxy," said Lockman.
Although the origin of these newly discovered clouds is not yet known, one mechanism to explain how this gas could be lifted into the halo is through supernova explosions. When a massive star reaches the end of its life it erupts in a cataclysm that produces a burst of cosmic rays and an enormous expanding bubble of gas at a temperature of several million degrees Celsius. Over time, this hot gas can flow outward into the Milky Way's halo.
The question remains, however, what happens to this gas once it's ejected into the halo. One possibility is that it leaves the Galaxy as a wind, never to return. Some astronomers predict, however, that as the gas slowly cools it would condense into hydrogen clouds, eventually falling like raindrops back into the Milky Way, and forming what is referred to as a galactic fountain.
"If the clouds were formed by material ejected from the Galactic plane into the halo," Lockman said, "then it's possible that they are now falling back onto the Galaxy. This would then require a continuing flow of new material from supernova explosions into the halo to replenish the hydrogen gas that has rained back into the disk."
The researcher comments that further observations, now in progress, should clarify the properties of these halo clouds, determine their distribution throughout the Galaxy, show how they are related to other types of clouds, and reveal their internal structure.
Radio telescopes are able to detect the naturally occurring radio emission from neutral atomic hydrogen. As hydrogen atoms move about in space, they can absorb small amounts of energy, sending the atom's single electron to a higher energy state. When the electron eventually moves back to its lower energy -- or resting state, it gives up a small amount of electromagnetic radiation at radio frequencies. The individual energy of a single atom is very weak, but the accumulated signal from vast clouds of hydrogen is strong enough to be detected by sensitive radio telescopes on Earth.
The GBT, dedicated in August of 2000, is the world's largest fully steerable radio telescope. Its 100 by 110 meter dish is composed of 2004 individually hinged panels. It also has a unique offset feed arm, which greatly enhances the performance of the telescope, making it ideal for observations of faint astronomical objects. The GBT is completing its commissioning and early science program and will be moving into full time operation.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement with Associated Universities, Inc.
Editor's Note: The original news release can be found at http://www.aoc.nrao.edu/epo/pr/2002/mwclouds/
Send page by E-Mail Center Of The Milky Way, Supermassive Black Hole
Posted: Thursday, October 17, 2002
Source: Weizmann Institute (http://www.weizmann.ac.il/)
Zooming Star Points To Supermassive Black Hole At The Center Of The Milky Way
Rehovot, Israel – October 16, 2002--Supermassive black holes – the name given to black holes whose mass is more than 1,000,000 times the mass of the sun – can be found at the center of many galaxies. Scientists from the Weizmann Institute of Science, the Max Planck Institute for Extraterrestrial Physics, and several institutions in France have succeeded in tracking a star racing around a dark mass at the center of our galaxy. This achievement offers more support for the widely held view that the dark mass is a supermassive black hole. The findings were published in the current issue of Nature. The scientists tracked, for the first time, a star completing an orbit around a known unusual source of radiation (a black hole candidate) in the center of our galaxy. This discovery heralds a new epoch of high precision black hole astronomy and that might help us better understand how galaxies are born and evolve.
Supermassive black holes are thought to evolve when many smaller black holes merge at the center of a galaxy, and start swallowing everything that comes their way. Such a black hole is a remnant of an exploded sun much bigger than our own. The explosion is a rare celestial phenomenon called supernova, which happens when these developed suns use up all their nuclear fuel. Without fuel to maintain the huge pressure that is required to counter gravity, the star first implodes, and then the outer layers rebound against the sun's core and are violently ejected into space, in a process that is one of the most powerful explosions that occur in nature. Simultaneously, the massive core continues to cave in. It rapidly collapses into itself and forms a black hole.
The pull of this dark mass is so great that even light can't escape it, rendering it invisible. "Invisible - but not powerless," said Dr. Tal Alexander, a theoretical astrophysicist at the Weizmann Institute of Science's Physics Faculty. "The black hole's presence is felt by its immense gravitational pull. A star that happens to be close to a supermassive black hole will orbit very rapidly around a point of seemingly empty space." Another clue is the radiation emitted by gas that is heated up just before it is swallowed forever by the black hole.
Alexander and his colleagues at the Max Planck Institute for Astrophysics tracked the orbit of the closest known star to the black hole candidate Sagittarius A*, a dark mass 3,000,000 times the mass of the sun. Following the star for 10 years, they found that it does indeed orbit Sagittarius A*. Approaching the black hole's maw, the star reaches its highest velocity, whizzing past it at 5,000 kilometers per second.
Some astrophysicists have suggested in the past that perhaps the dark mass in the center of the Milky Way is not a black hole, but rather a dense cluster of compact stars, or even a giant blob of mysterious sub-atomic particles. It now appears that these are not viable alternatives. The new detailed analysis of the orbit, made possible by the techniques developed by the team, is fully consistent with the view that the dark mass is a supermassive black hole.
Their technique allowed precise observation of the center of the galaxy, overcoming the problem of interstellar dust permeating space. The observations were made with the new European Very Large Telescope in Chile whose detectors were developed by scientists from the Max Planck Institute for Extraterrestrial Physics, Observatoire de Paris, Office National d'Etudes et de Recherches Aerospatiales, and Observatoire de Grenoble.
Such observations could provide information on a point we know surprisingly little about: our own place in the universe. Alexander said: "We currently do not even know the earth's exact distance from the center of our own galaxy – understanding such stellar orbits might tell us where we are."
The Weizmann Institute of Science, in Rehovot, Israel, is one of the world's foremost centers of scientific research and graduate study. Its 2,500 scientists, students, technicians and engineers pursue basic research in the quest for knowledge and to enhance the quality of human life. New ways of fighting disease and hunger, protecting the environment, and harnessing alternative sources of energy are high priorities at Weizmann.
Editor's Note: The original news release can be found here
Send page by E-Mail Hubble Spots An Icy World Far Beyond Pluto
Posted: Tuesday, October 8, 2002
Source: Space Telescope Science Institute (http://www.stsci.edu)
NASA's Hubble Space Telescope has measured the largest object in the solar system ever seen since the discovery of Pluto 72 years ago.
Approximately half the size of Pluto, the icy world 2002 LM60, dubbed "Quaoar" (pronounced kwa-whar) by its discoverers, is the farthest object in the solar system ever to be resolved by a telescope. It was initially detected by a ground-based telescope, as simply a dot of light, until astronomers aimed the powerful Hubble telescope at it.
Quaoar is about 4 billion miles away from Earth, well over a billion miles farther away than Pluto. Unlike Pluto, its orbit around the Sun is very circular, even more so than most of the planetary-class bodies in the solar system.
Although smaller than Pluto, Quaoar is greater in volume than all the asteroids combined (though probably only one-third the mass of the asteroid belt, because it's icy rather than rocky). Quaoar's composition is theorized to be largely ices mixed with rock, not unlike that of a comet, though 100 million times greater in volume.
This finding yields important new insights into the origin and dynamics of the planets, and the mysterious population of bodies dwelling in the solar system's final frontier: the elusive, icy Kuiper belt beyond Neptune.
Michael Brown and Chadwick Trujillo of Caltech are reporting the findings today at the 34th annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Birmingham, Ala.
Earlier this year, Trujillo and Brown used the Palomar Oschin Schmidt telescope to discover Quaoar as an 18.5-magnitude object creeping across the summer constellation Ophiuchus (it's less than 1/10,000th the brightness of the faintest star seen by the human eye). Brown had to do follow-up observations using Hubble's new Advanced Camera for Surveys on July 5 and August 1, 2002, to measure the object's true angular size of 40 milliarcseconds, corresponding to a diameter of about 800 miles (1300 kilometers). Only Hubble has the sharpness needed to actually resolve the disk of the distant world, leading to the first-ever direct measurement of the true size of a Kuiper belt object (KBO).
Like Pluto, Quaoar dwells in the Kuiper belt, an icy debris field of comet-like bodies extending 7 billion miles beyond Neptune's orbit. Over the past decade more than 500 icy worlds have been found in the Kuiper belt. With a few exceptions all have been significantly smaller than Pluto.
Previous record holders are a KBO called Varuna, and an object called 2002 AW197, each approximately 540 miles across (900 kilometers). Unlike Hubble's direct observations, these diameters are deduced from measuring the objects' temperatures and calculating a size based on assumptions about the KBOs' reflectivity, so the uncertainty in true size is much greater.
This latest large KBO is too new to have been officially named by the International Astronomical Union. Trujillo and Brown have proposed naming it after a creation god of the Tongva native American tribe, the original inhabitants of the Los Angeles basin. According to legend, Quaoar, "came down from heaven; and, after reducing chaos to order, laid out the world on the back of seven giants. He then created the lower animals, and then mankind."
Quaoar's "icy dwarf" cousin, Pluto, was discovered in 1930 in the course of a 15-year search for trans-Neptunian planets. It wasn't realized until much later that Pluto actually was the largest of the known Kuiper belt objects. The Kuiper belt wasn't theorized until 1950, after comet orbits provided telltale evidence of a vast nesting ground for comets just beyond Neptune. The first recognized Kuiper belt objects were not discovered until the early 1990s. This new object is by far the "biggest fish" astronomers have snagged in KBO surveys. Brown predicts that within a few years even larger KBOs will be found, and Hubble will be invaluable for follow-up observations to pin down sizes.
Editor's Note: The original news release can be found at http://oposite.stsci.edu/pubinfo/PR/2002/17/pr.html
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