On October 6, Numerous observatories detected the object and captured images of it. Computations correctly predicted impact would occur 19 hours after discovery in the Nubian Desert of northern Sudan. Analyses were performed while the asteroid was en route and its surviving pieces were located on October 7 by meteorite hunters in an intense search.
The event tested the ability of society to respond very quickly to a predicted impact, as well as predict the arrival time and location on Earth of the asteroid's surviving parts.
From the article: Reports by scientists of meteorites striking Earth in the past have resembled police reports of so many muggings -- the offenders came out of nowhere and then disappeared into the crowd, making it difficult to get more than very basic facts.
Now an international research team has been able to identify an asteroid in space before it entered Earth's atmosphere, enabling computers to determine its area of origin in the solar system as well as predict the arrival time and location on Earth of its shattered surviving parts. "I would say that this work demonstrates, for the first time, the ability of astronomers to discover and predict the impact of a space object," says Sandia National Laboratories researcher Mark Boslough, a member of the research team.
Perhaps more importantly, the event tested the ability of society to respond very quickly to a predicted impact, says Boslough. "In this case, it was never a threat, so the response was scientific. Had it been deemed a threat -- a larger asteroid that would explode over a populated area -- an alert could have been issued in time that could potentially save lives by evacuating the danger zone or instructing people to take cover."
The profusion of information in this case also helps meteoriticists learn the orbits of parent bodies that yield various types of meteorites.
Such knowledge could help future space missions explore or even mine the asteroids in Earth-crossing orbits, Boslough says.
The four-meter-diameter asteroid, called 2008 TC3, was initially sighted by the automated Catalina Sky Survey telescope at Mount Lemmon, Ariz., on Oct. 6. Numerous observatories, alerted to the invader, then imaged the object. Computations correctly predicted impact would occur 19 hours after discovery in the Nubian Desert of northern Sudan.
According to NASA's Near Earth Object program, "A spectacular fireball lit up the predawn sky above Northern Sudan on October 7, 2008."
A wide variety of analyses were performed while the asteroid was en route and after its surviving pieces were located by meteorite hunters in an intense search.
Researchers, listed in the paper describing this work in the March 26 issue of the journal Nature, range from the SETI Institute, the University of Khartoum, Juba University (Sudan), Sandia, Caltech, NASA Johnson Space Center and NASA Ames, to other universities in the U.S., Canada, Ireland, England, Czech Republic and the Netherlands.
Sandia researcher Dick Spalding interpreted recorded data about the atmospheric fireball, and Boslough estimated the aerodynamic pressure and strength of the asteroid based on the estimated burst altitude of 36 kilometers.
Searchers have recovered 47 meteorites so far -- offshoots from the disintegrating asteroid, mostly immolated by its encounter with atmospheric friction -- with a total mass of 3.95 kilograms.
The analyzed material showed carbon-rich materials not yet represented in meteorite collections, indicating that fragile materials still unknown may account for some asteroid classes. Such meteorites are less likely to survive due to destruction upon entry and weathering once they land on Earth's surface.
"Chunks of iron and hard rock last longer and are easier to find than clumps of soft carbonaceous materials," says Boslough.
"We knew that locating an incoming object while still in space could be done, but it had never actually been demonstrated until now," says Boslough. "In this post-rational age where scientific explanations and computer models are often derided as 'only theories,' it is nice to have a demonstration like this."
Friday, March 27, 2009
Most Popular: We Saw It Coming: Asteroid Monitored from Space to Impact
Tuesday, March 3, 2009
Brown Dwarfs Do Not Hang Out With Stars
Brown dwarfs, objects that are less massive than stars but larger than planets, just got more elusive, based on a study of 233 nearby multiple-star systems by NASA's Hubble Space Telescope. Hubble found only two brown dwarfs as companions to normal stars. This means the so-called "brown dwarf desert" (the absence of brown dwarfs around solar-type stars) extends to the smallest stars in the universe.
Sergio Dieterich of Georgia State University in Atlanta and team leader of the study is reporting the results today at the 213th meeting of the American Astronomical Society (AAS) in Long Beach, Calif.
"We still did not find brown dwarfs around small red stars whose mass is only slightly above the hydrogen burning limit. Especially when we consider the fact that brown dwarfs binaries do exist, the fact that there are very few binaries whose components lie on different sides of the hydrogen burning limit is significant," says Dieterich.
The 233 stars surveyed are part of the RECONS (Research Consortium on Nearby Stars) survey meant to understand the nature of the sun's nearest stellar neighbors, both individually and as a population. The current primary goals are to discover and characterize "missing" members of the sample of stars within 32.6 light-years (10 parsecs) of Earth.
RECONS searches for nearby stars through analyzing existing all-sky surveys, combined with observations by a variety of telescopes in both hemispheres. A total of 12 brown dwarfs are currently known within 32.6 light-years of Earth, as compared to 239 red dwarf stars (stars that are largely 20 percent the mass of our sun and are roughly half its diameter and temperature).
In fact, the number of known brown dwarfs is close to that of known extrasolar planets. However, the number of exoplanets known in this region so far is very likely only a lower limit as smaller mass exoplanets are not within our capability of detection at present.
The Hubble survey, taken with Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS), provides strong statistics pointing to the fact that brown dwarfs do not exist around even the least massive stars. "If mass ratio was the driving factor we would expect to find more brown dwarfs around small red stars than around solar type stars," says Dieterich.
These results are complementary to another study also being reported at the AAS meeting by Micaela Stumpf of the Max Planck Institute for Astronomy in Heidelberg, Germany. The results imply that brown dwarfs tend to hang out with their own kind.
Nearly ten years' worth of NICMOS observations, combined with recent ground-based adaptive optics results, have provided a first estimate of the orbit of the double brown dwarf system Kelu-1 AB. The eccentric orbit is tilted nearly edge-on to Earth and the dwarfs complete an orbit every 38 years.
Based on the orbital dynamics, the total mass of the system is estimated to be 184 Jupiter masses. But, based on spectroscopic and photometric measurements, the two brown dwarfs are no larger than 61 and 50 Jupiter masses, respectively (a star is no smaller than 75 Jupiter masses). Stumpf is reporting that there may in fact be a third member of the system to account for the "missing mass." This would make it potentially the first ever confirmed triple brown dwarf system.
All-sky surveys planned for the next decade, with advanced telescopes like the Large Synoptic Survey Telescope, promise to ultimately solve the puzzle of the "brown dwarf desert" by doing deep infrared searches for the underlying brown dwarf population.
Hubble Views Galactic Core in Unprecedented New Detail
This composite color infrared image of the center of our Milky Way galaxy reveals a new population of massive stars and new details in complex structures in the hot ionized gas swirling around the central 300 light-years. This sweeping panorama is the sharpest infrared picture ever made of the Galactic core. It offers a nearby laboratory for how massive stars form and influence their environment in the often violent nuclear regions of other galaxies.
The spatial resolution of NICMOS corresponds to 0.025 light-years at the distance of the Galactic core of 26,000 light-years. Hubble reveals details in objects as small as 20 times the size of our own solar system.
The NICMOS mosaic image represents the largest piece of sky ever mapped for one NICMOS observing program. It was combined with a full-color Spitzer image to yield a color composite of the nuclear region. The picture measures 300 x 115 light-years. Outside the boundary of the NICMOS survey, the IRAC exposures (which are 1/10th as sharp) can be seen at wavelengths of 3.6 microns (shown as blue), 4.5 microns (shown as green), 5.8 microns (shown as orange), and 8.0 microns (shown as red).
The new NICMOS data show the glow from ionized hydrogen gas as well as a multitude of stars. Hubble reveals an important population of stars with strong stellar winds, signified by excess emission from ionized gas at one infrared wavelength (1.87 microns) compared to another slightly different wavelength (1.90 microns).
NICMOS shows a large number of these massive stars distributed throughout the region. A new finding is that astronomers now see that the massive stars are not confined to one of the three known clusters of massive stars in the Galactic Center, known as the Central cluster, the Arches cluster, and the Quintuplet cluster. These three clusters are easily seen as tight concentrations of bright, massive stars in the NICMOS image. The distributed stars may have formed in isolation, or they may have originated in clusters that have been disrupted by strong gravitational tidal forces.
The winds and radiation from these stars form the complex structures seen in the core, and in some cases, they may be triggering new generations of stars. At upper left, large arcs of ionized gas are resolved into arrays of intriguingly organized linear filaments indicating perhaps a critical role of the influence of locally strong magnetic fields.
The lower left region shows pillars of gas sculpted by winds from hot massive stars in the Quintuplet cluster. At the center of the image, ionized gas surrounding the supermassive black hole at the center of the galaxy is confined to a bright spiral embedded within a circum-nuclear dusty inner-tube-shaped torus.
Monday, February 23, 2009
Star Light, Star Bright, Its Explanation is Out of Sight
A mysterious flash of light from somewhere near or far in the universe is still keeping astronomers in the dark long after it was first detected by NASA's Hubble Space Telescope in 2006. It might represent an entirely new class of stellar phenomena that has previously gone undetected in the universe, say researchers.
Astronomers commonly observe intense flashes of light from a variety of stellar explosions and outbursts, such as novae and supernovae. Hubble discovered the cosmic flash on February 21, 2006. It steadily rose in brightness for 100 days, and then dimmed back to oblivion after another 100 days.
The rise and fall in brightness has a signature that simply has never been recorded for any other type of celestial event. Supernovae peak after no more than 70 days, and gravitational lensing events are much shorter. Therefore, this observation defies a simple explanation, reports Kyle Barbary of the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, Calif. He is describing the bizarre Hubble observation at the 213th meeting of the American Astronomical Society in Long Beach, Calif. "We have never seen anything like it," he concludes.
The spectral fingerprints of light coming from the object, cataloged as SCP 06F6, also have eluded identification as being due to any specific element. One guess is that the features are redshifted molecular carbon absorption lines in a star roughly one billion light-years away.
But searches through various astronomical survey catalogs for the source of the light have not uncovered any evidence for a star or galaxy at the location of the flash. The Supernova Cosmology Project at LBNL discovered it serendipitously in a search for supernovae.
Hubble was aimed at a cluster of galaxies 8 billion light-years away in the spring constellation Bootes. But the mystery object could be anywhere in between, even in the halo of our own Milky Way galaxy.
Papers published by other researchers since the event was reported in June 2006, have suggested a bizarre zoo of possibilities: the core collapse and explosion of a carbon rich star, a collision between a white dwarf and an asteroid, or the collision of a white dwarf with a black hole.
But Barbary does not believe that any model offered so far fully explains the observations. "I don't think we really know what the discovery means until we can observe similar objects in the future."
All-sky surveys for variable phenomena, such as those to be conducted with the planned Large Synoptic Survey Telescope, may ultimately find similar transient events in the universe.
Hubble Finds Stars that Go Ballistic
Even some stars go ballistic, racing through interstellar space like bullets and tearing through clouds of gas.
Images from NASA's Hubble Space Telescope reveal 14 young, runaway stars plowing through regions of dense interstellar gas, creating brilliant arrowhead structures and trailing tails of glowing gas. These arrowheads, or bow shocks, form when the stars' powerful stellar winds, streams of matter flowing from the stars, slam into surrounding dense gas. The phenomenon is similar to that seen when a speeding boat pushes through water on a lake.
"We think we have found a new class of bright, high-velocity stellar interlopers," says astronomer Raghvendra Sahai of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and leader of the Hubble study. "Finding these stars is a complete surprise because we were not looking for them. When I first saw the images, I said 'Wow. This is like a bullet speeding through the interstellar medium.' Hubble's sharp 'eye' reveals the structure and shape of these bow shocks."
The astronomers can only estimate the ages, masses, and velocities of these renegade stars. The stars appear to be young - just millions of years old. Their ages are based partly on their strong stellar winds.
Most stars produce powerful winds either when they are very young or very old. Only very massive stars greater than 10 times the Sun's mass have stellar winds throughout their lifetimes. But the objects observed by Hubble are not very massive, because they do not have glowing clouds of ionized gas around them. They are medium-sized stars that are a few to eight times more massive than the Sun. The stars are not old because the shapes of the nebulae around aging, dying stars are very different, and old stars are almost never found near dense interstellar clouds.
Depending on their distance from Earth, the bullet-nosed bow shocks could be 100 billion to a trillion miles wide (the equivalent of 17 to 170 solar system diameters, measured out to Neptune's orbit). The bow shocks indicate that the stars are traveling fast, more than 112,000 miles an hour (more than 180,000 kilometers an hour) with respect to the dense gas they are plowing through, which is roughly five times faster than typical young stars.
"The high-speed stars were likely kicked out of their homes, which were probably massive star clusters," Sahai says.
There are two possible ways this stellar expulsion could have happened. One way is if one star in a binary system exploded as a supernova and the partner got kicked out. Another scenario is a collision between two binary star systems or a binary system and a third star. One or more of these stars could have picked up energy from the interaction and escaped the cluster.
Assuming their youthful phase lasts only a million years and they are moving at roughly 112,000 miles an hour, the stars have traveled about 160 light-years.
Runaway stars have been seen before. The Infrared Astronomical Satellite (IRAS), which performed an all-sky infrared survey in 1983, spied a few similar-looking objects. The first observation of these objects was in the late 1980s. But those stars produced much larger bow shocks than the stars in the Hubble study, suggesting that they are more massive stars with more powerful stellar winds.
"The stars in our study are likely the lower-mass and/or lower-speed counterparts to the massive stars with bow shocks detected by IRAS," Sahai explains. "We think the massive runaway stars observed before were just the tip of the iceberg. The stars seen with Hubble may represent the bulk of the population, both because many more lower-mass stars inhabit the universe than higher-mass stars, and because a much larger number are subject to modest speed kicks."
Astronomers have not spotted many of these stellar interlopers before because they are hard to find. "You don't know where to look for them because you cannot predict where they will be," Sahai says. "So all of them have been found serendipitously, including the 14 stars we found with Hubble."
Sahai and his team used Hubble's Advanced Camera for Surveys to examine 35 objects that appeared as bright infrared sources in the IRAS archive. They were looking for long-lived pre-planetary nebulae, puffed-up aging stars on the verge of shedding most of their outer layers to become glowing planetary nebulae. Instead, the astronomers stumbled upon the runaway stars.
The team is planning follow-up studies to search for more interlopers, as well as study selected objects from this Hubble survey in greater detail to understand their effects on their environment.
"One of the questions that these very showy encounters raise is what effect they have on the clouds," says team member Mark Morris of the University of California, Los Angeles. "Is it an insignificant flash in the pan, or do the strong winds from these stars stir up the clouds and thereby slow down their evolution toward forming another generation of stars?"
Tuesday, December 30, 2008
PS3s Help Astrophysicists Solve Black Hole Mystery
Newswise — Using only the computing power of 16 Sony Playstation 3 gaming consoles, scientists at The University of Alabama in Huntsville and the University of Massachusetts, Dartmouth, have solved a mystery about the speed at which vibrating black holes stop vibrating.
It may be the first time this kind of research has been conducted exclusively on a PS3 cluster: A related 2007 UMass Dartmouth/UAHuntsville project using a smaller PS3 cluster also used a "traditional" supercomputer to run its simulations.
The biggest advantage of the console cluster — the PS3 Gravity Grid — at UMass Dartmouth was the cost saving, said Dr. Lior Burko, an assistant physics professor at UAHuntsville. "If we had rented computing time from a supercomputer center it would have cost us about $5,000 to run our simulation one time. For this project we ran our simulation several dozens of times to test different parameters and circumstances, so you can see how much that would have cost us."
"You can build a cluster like this for perhaps $6,000, and then you can run the simulation as many times as you like at no additional cost."
"Science budgets have been significantly dropping over the last decade," said UMass Dartmount Physics Professor Gaurav Khanna, who built the PS3 cluster. "Here's a way that people can do science projects less expensively."
Khanna recently launched a website which includes step-by-step instructions for building a supercomputing PS3 cluster.
The PS3 cluster was well suited to this type of astrophysical research, which requires a large number of mathematical calculations but has low demands for RAM memory, Burko said. "Not every kind of job would be suitable for that system, but it is exactly the kind of computation that we did."
The current price for supercomputing time through a center like the National Science Foundation's TeraGrid or the Alabama Supercomputing Center is about $1 per CPU hour. Each PS3 has a powerful Cell processor. The 16-unit PS3 grid can complete a 5,000-CPU-hour (and $5,000) simulation run in about a day. That is a speed comparable to a rented supercomputer.
Published in the journal, "Classical and Quantum Gravity," the new research resolved a dispute over the speed at which black holes stop vibrating after they first form or are perturbed by something like swallowing some matter.
"Think of a bell," said Burko. "A bell rings, but eventually it gets quiet. The energy that goes out with the sound waves is energy that the bell is losing. A black hole does exactly that in gravitational waves instead of sound waves. A black hole that is wobbling is emitting gravitational waves. When those vibrations die down you get a quiet black hole."
(Most black holes are "quiet," which means the only things astronomers can measure are their mass and how fast they spin.)
Khanna and Burko used a high resolution computer simulation to "perturb" a simulated spinning black hole, then watched as it returned to its quiet state. They found that the speed at which black holes go quiet was the faster of the two competing theories.
Monday, October 6, 2008
Microwaves Can Extract Water from Moon, Mars
"A lot of people think that water doesn't exist on the Moon," said Bill Kaukler, an Associate Research Professor in the Center for Materials Research at The University of Alabama in Huntsville. "However, in the polar regions, exploratory satellites have found huge amounts of hydrogen, which is evidence that water exists."
Kaukler has performed research with NASA, and for the past three years has been investigating the use of microwaves to extract water from the Moon.
When astronauts land on the Moon in the not too distant future, it's possible they will be visiting an outpost where they can pick up some fuel and a refreshing container of liquid.
That outpost won't be offering the 64-ounce Big Gulp soft drinks that you find at many of the convenience stores across the country, but it will be offering a critical commodity water.
Research conducted by material scientists may lead to the ability to extract water from the Moon and possibly Mars by shooting microwave beams into their surface, according to Bill Kaukler, an Associate Research Professor in the Center for Materials Research at The University of Alabama in Huntsville.
³A lot of people think that water doesn¹t exist on the Moon,² said Kaukler. ³It¹s true that not all parts of the Moon have water. Where the Apollo missions landed, there isn¹t much water because it is exposed to the sun half of the time. However, in the polar regions, exploratory satellites have found huge amounts of hydrogen, which is evidence that water exists.²
Kaukler has performed research with NASA for more than 25 years and for the past three years has been investigating the use of microwaves to replenish water on space missions or as a rocket fuel supply.
The Moon¹s surface is covered with over two meters deep of regolith (like soil), a layer of loose, powdery, heterogeneous material created by hundreds of millions of years of meteorite and comet bombardment. Below that covering lies bedrock. ³Ice is just inches below the surface of the moon in craters at the poles (where solar heating doesn¹t occur),² he said.
Kaukler and Marshall Space Flight Center scientist Edwin Ethridge have been conducting research on the use of microwaves to warm the lunar regolith to draw the water up to the surface.
³Using microwaves to heat the soil offers several advantages,² Kaukler said. ³Microwaves are not strongly absorbed by the regolith (soil) so it can penetrate several feet into the soil and heat it.² Heating is possible because the Moon¹s soil has about 5 percent iron, similar to volcanic rock on Earth, according to Kaukler. Microwave absorption is the most efficient method to heat large volumes of regolith or rock.
He said research shows that if the regolith can be warmed from a minus 150 degrees Celsius to minus 50 degrees, the vapor pressure of the water mixed in with the regolith particles is much higher than the Moon¹s atmospheric pressure. Kaukler said the moon¹s vacuum environment literally percolates the water vapor to the surface through the regolith particles. The water vapor collects on a cold (below minus 50 C) plate where it forms as ice and is scraped off for human consumption or where it can be converted by electrolysis to hydrogen and oxygen to be used as a fuel and oxidizer that can be used in space travel, like going to Mars.
The scientists have been confident of their research, but were encouraged by findings this summer when the Phoenix Mars lander confirmed the presence of water ice on the Martian surface. The lander scratched just two inches below the surface of Mars to expose the ice.
Kaukler, Ethridge and other materials scientists have developed a prototype and have used simulated lunar regolith to test their ideas. Their prototype has the power of one kilowatt, about the same as a typical home microwave oven.
What their experiments show is that they are able to remove 99 percent of water-ice through sublimation, or converting the frozen water directly into a gas, and could capture 95 percent of the liberated water.
While the one-kilowatt device may prove the concept, Kaukler said a 10-kilowatt unit would speed up the process of collecting water and make it more effective on the Moon¹s surface. He envisions a robotic, roving device powered by a nuclear generator to roam the Moon¹s surface in search of water sources.
Kaukler believes the concept of shooting microwave beams into the surface of the Moon or Mars to extract water offers several distinct advantages: not having to dig the regolith and put it into a furnace is a big advantage since heavy equipment won¹t be needed; leaving the Moon essentially undisturbed is important; not worrying about the underlying geology is practical since hidden or buried rocks (that have no water) could damage digging equipment.
Perhaps the most important factor of this project is not carrying water on a journey, thus saving space and weight on long-distance trips. ³This is the essence of the concept of In Situ Resource Utilization or ISRU, ³ Kaukler said. ³The philosophy is to use what is on the Moon (or Mars) to make habitats without having to bring the material from Earth.²
Another crucial factor is safety. The microwave process penetrates into the surface at least two meters deep, thus eliminating the need to dig into the surface to get to the ice, according to the scientists. Kaukler said the idea of kicking up dust by digging on the Moon poses a problem for equipment and astronauts if the abrasive dust finds its way into the wrong places, as it did for the Apollo astronauts.
Research continues, according to Kaukler. More investigation is necessary to learn about the electromagnetic properties of regolith in the various microwave frequencies. Altering those frequencies could allow the device to penetrate deeper into the surface if necessary to reach additional water.
Kaukler and Ethridge are also exploring the use of microwaves for melting or sintering the regolith to make structures on the Moon.
An important concept they developed was the use of microwave melting of the regolith surface to make a dust-free crust. Such surfaces have uses as a landing pad (no dust kicked around the landing site by rockets), working surfaces to stabilize equipment and floors or roadways for astronauts to live and travel on. Conventional bricks, blocks or walls can also be prepared this way without bringing adhesives or special cements to Moon.
