Interesting Science

Astronomy: NASA's New Horizons spacecraft is on the doorstep of Jupiter - the solar system's largest planet. The spacecraft will study and swing past Jupiter (video animation), increasing speed on its voyage toward Pluto, the Kuiper Belt and beyond.

The fastest spacecraft ever launched, New Horizons will make its closest pass to Jupiter on Febuary 28, 2007. Jupiter's gravity will accelerate New Horizons away from the sun by an additional 9,000 miles per hour, pushing it past 52,000 mph and hurling it toward a pass through the Pluto system in July 2015.

"Our highest priority is to get the spacecraft safely through the gravity assist and on its way to Pluto," says New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, Boulder, Colo. "We also have an incredible opportunity to conduct a real-world encounter stress test to wring out our procedures and techniques, and to collect some valuable science data."

The New Horizons mission team will use the flyby to put the probe's systems and seven science instruments through the paces of more than 700 observations of Jupiter and its four largest moons. The planned observations from January through June include scans of Jupiter's turbulent, stormy atmosphere; a detailed survey of its ring system; and a detailed study of Jupiter's moons.

The spacecraft also will take the first-ever trip down the long "tail" of Jupiter's magnetosphere, a wide stream of charged particles that extends tens of millions of miles beyond the planet, and the first close-up look at the "Little Red Spot," a nascent storm south of Jupiter's famous Great Red Spot.

Much of the data from the Jupiter flyby will not be sent back to Earth until after the spacecraft's closest approach to the planet. New Horizons' main priority during the Jupiter close approach phase is to observe the planet and store data on its recorders before orienting its main antenna to transmit information home beginning in early March.

"Since launch, New Horizons will reach Jupiter faster than any of NASA's previous spacecraft and begin a year of extraordinary planetary science to complement future exploration activities," says Jim Green acting director, Planetary Science Division, NASA headquarters, Washington.

New Horizons has undergone a full range of system and instrument checkouts, instrument calibrations, flight software enhancements, and three propulsive maneuvers to adjust its trajectory.

After an eight-year cruise from Jupiter across the expanse of the outer solar system, New Horizons will conduct a five-month-long study of Pluto and its three moons in 2015. Scientific research will include studying the global geology, mapping surface compositions and temperatures, and examining Pluto's atmospheric composition and structure. A potential extended mission would conduct similar studies of one or more smaller worlds in the Kuiper Belt, the region of ancient, rocky, icy planetary building blocks far beyond Neptune's orbit.

New Horizons is the first mission in NASA's New Frontiers Program of medium-class spacecraft exploration projects. The Applied Physics Laboratory, Laurel, Md., manages the mission for NASA's Science Mission Directorate, Washington. The mission team also includes NASA's Goddard Space Flight Center, Greenbelt, Md.; NASA's Jet Propulsion Laboratory, Pasadena, Calif.; the U.S. Department of Energy, Washington; Southwest Research Institute, Boulder, Colo.; and several corporations and university partners.

[Click here to download a high-resolution TIFF of the poster image above]

Source: NASA 07-012

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Background info from NASA's 'Mission Timeline':

Launch (video):
January 19, 2006

Launch Vehicle:
Atlas V 551 first stage; Centaur second stage; STAR 48B solid rocket third stage

Location:
Cape Canaveral Air Force Station, Florida

Trajectory:
*To Pluto via Jupiter Gravity Assist

The Voyage

Early Cruise: The first 13 months include spacecraft and instrument checkouts, instrument calibrations, trajectory correction maneuvers, and rehearsals for the Jupiter encounter.

Jupiter Encounter: Closest approach will occur Feb. 28, 2007. Moving about 47,000 miles per hour (about 21 kilometers per second), New Horizons would fly 3 to 4 times closer to Jupiter than the Cassini spacecraft, coming within 32 Jupiter radii of the large planet.

Interplanetary Cruise: activities during the approximately 8-year cruise to Pluto include annual spacecraft and instrument checkouts, trajectory corrections, instrument calibrations and Pluto encounter rehearsals.

Pluto-Charon Encounter

* Close approach: July 14, 2015
* Current 1st graders will see New Horizons arrive at Pluto during the summer before 11th grade!

Into the Kuiper Belt

Plans for an extended mission include one to two encounters of Kuiper Belt Objects, ranging from about 25 to 55 miles (40 to 90 kilometers) in diameter. New Horizons would acquire the same data it collected at Pluto-Charon - where applicable - and follow a timeline similar to the Pluto-Charon encounter:

* Closest Approach - 4 weeks: object observations
* Closest Approach + 2 weeks: post-encounter studies
* Closest Approach + 2 months: all data returned to Earth

Other Projected Orbit Crossing Dates

Saturn: June 8, 2008
Uranus: March 18, 2011
Neptune: August 24, 2014
Pluto: July 14, 2015

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Recent Posts:

"Astrophysics: Gas giants form quickly"

"NASA Study Finds New Kind of Organics in Stardust Mission (Video)"

"Hubble: NIST Math Technique Opens Clearer Window on Universe"

Technorati: nasa, new horizons, spacecraft, jupiter, video, animation, voyage, pluto, kuiper belt, sun, research, gravity, assist, moons, atmosphere, great, red, spot, little, neptune, orbit, cape, canaveral, cassini, charon, uranus, astrophysics, astronomy, stardust, hubble, mission, universe, solar system

Permanent Link posted by John Latter @ 7:21 PM 0 comments

In a study of nonhuman primates infected with the influenza virus that killed 50 million people in 1918, an international team of scientists has found a critical clue to how the virus killed so quickly and efficiently.

Writing this week (January 18) in the journal Nature (see below), a team led by University of Wisconsin-Madison virologist Yoshihiro Kawaoka reveals how the 1918 virus - modern history's most savage influenza strain - unleashes an immune response that destroys the lungs in a matter of days, leading to death.

The finding is important because it provides insight into how the virus that swept the world in the closing days of World War I was so efficiently deadly, claiming many of its victims in the prime of life. The work suggests that it may be possible in future outbreaks of highly pathogenic flu to stem the tide of death through early intervention.

The study "proves the 1918 virus was indeed different from all of the other flu viruses we know of," says Kawaoka, a professor in the UW-Madison School of Veterinary Medicine and at the University of Tokyo.

The new study, conducted at the Public Health Agency of Canada's National Microbiology Laboratory in Winnipeg, Manitoba, utilized the 1918 flu virus, which has been reconstructed by researchers using genes obtained from the tissues of victims of the great pandemic in a reverse genetics process that enables scientists to make fully functioning viruses.

"In 1918, the existence of viruses had barely been recognized. In fact, the influenza virus wasn't identified until 1933. Thanks to recent technological advancements, we are now able to study this virus and how it wreaked havoc around the globe," explains Darwyn Kobasa, research scientist with the Public Health Agency of Canada and lead author of the new study. "This research provides an important piece in the puzzle of the 1918 virus, helping us to better understand influenza viruses and their potential to cause pandemics."

By infecting monkeys with the virus, the team was able to show that the 1918 virus prompted a deadly respiratory infection that echoed historical accounts of how the disease claimed its victims.

Importantly, the new work shows that infection with the virus prompted an immune response that seems to derail the body's typical reaction to viral infection and instead unleashes an attack by the immune system on the lungs. As immune cells attack the respiratory system, the lungs fill with fluid and victims, in essence, drown.

The mechanisms that contribute to the lethality of the virus were uncovered by University of Washington researchers using functional genomics, a technique in which researchers analyze the gene functions and interactions. Learning more about the virulence mechanisms of the 1918 flu virus may help researchers understand how to keep the virus from causing such a severe immune response.

"This study in macaques, combined with our earlier research showing the host response in mice infected with the 1918 flu, suggests that the host immune response is out of control in animals infected with the virus," says Michael G. Katze*, professor of microbiology at the University of Washington in Seattle, who led the functional genomics portion of the new study and led the previous mouse-based study. "Our analysis revealed potential mechanisms of virulence, which we hope will help us develop novel antiviral strategies to both outwit the virus and moderate the host immune response."

The same excessive immune reaction is characteristic of the deadly complications of H5N1 avian influenza, the strain of bird flu present in Asia and which has claimed nearly 150 human lives, but has not yet shown a capacity to spread easily among people.

"What we see with the 1918 virus in infected monkeys is also what we see with H5N1 viruses," Kawaoka says, suggesting that the ability to modulate immune response may be a shared feature of the most virulent influenza viruses.

In the new study, conducted in a high-level biosafety laboratory (BSL 4) at the Public Health Agency of Canada's National Microbiology Laboratory, seven primates were infected with the reconstructed 1918 virus. Clinical signs of disease were apparent within 24 hours of infection, and within eight days, euthanization was necessary. The rapid course of the disease mirrors how quickly the disease ran its course in its human victims in 1918.

Upon infection, the virus grew rapidly in the infected animals, suggesting the agent somehow sets the stage for virulent infection. "Somehow, early in infection, this virus does something to the host that allows it to grow really well," says Kawaoka. "But we don't know what that is."

Knowing that the virus does something early in infection to trigger such a devastating immune response may provide biomedical researchers with clues about how to intervene and stop or mitigate the virus' potentially lethal effects, Kawaoka says.

"Things may be happening at an early time point (in infection), but we may be able to step in and stop that reaction."

[Source: University of Wisconsin-Madison (adapted)]

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Based on the Letter to Nature:

Aberrant innate immune response in lethal infection of macaques with the 1918 influenza virus

Kobasa D et al.

Nature 2007 Jan 18; 445:319-23.

Opening Paragraph

The 1918 influenza pandemic was unusually severe, resulting in about 50 million deaths worldwide. The 1918 virus is also highly pathogenic in mice, and studies have identified a multigenic origin of this virulent phenotype in mice. However, these initial characterizations of the 1918 virus did not address the question of its pathogenic potential in primates. Here we demonstrate that the 1918 virus caused a highly pathogenic respiratory infection in a cynomolgus macaque model that culminated in acute respiratory distress and a fatal outcome. Furthermore, infected animals mounted an immune response, characterized by dysregulation of the antiviral response, that was insufficient for protection, indicating that atypical host innate immune responses may contribute to lethality. The ability of influenza viruses to modulate host immune responses, such as that demonstrated for the avian H5N1 influenza viruses, may be a feature shared by the virulent influenza viruses.

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*Michael G. Katze is co-author of the following 2006 paper from the Journal of Virology:

An Integrated Molecular Signature of Disease: Analysis of Influenza Virus-Infected Macaques through Functional Genomics and Proteomics

T Baas et al.

J. Virol. doi:10.1128/JVI.00851-06

Abstract

Recent outbreaks of avian influenza in humans have stressed the need for an improved non-human primate model of influenza pathogenesis. In order to further develop a macaque model, we expanded our previous in vivo genomics experiments in influenza virus infected macaques by focusing on the innate immune response at day 2 post-inoculation and on gene expression in affected lung tissue with viral genetic material present. Finally, we sought to identify signature genes for early infection in whole blood. For these purposes, we infected six pigtailed macaques (Macaca nemestrina) with reconstructed influenza A/Texas/36/91 virus and three control animals with a sham inoculate. We sacrificed one control and two experimental animals at days 2, 4, and 7 post infection (PI). Lung tissue was harvested for pathology, gene expression profiling, and proteomics. Blood was collected for genomics every other day from each animal until experimental endpoint. Gross and microscopic pathology, immunohistochemistry, viral gene expression by arrays and/or quantitative real-time RT-PCR confirmed successful yet mild infection in all experimental animals. Genomic experiments were performed using macaque-specific oligonucleotide arrays and high-throughput proteomics revealed the host response to infection at the mRNA and protein levels. Our data showed dramatic differences in gene expression within regions in influenza virus-induced lesions based on the presence or absence of viral mRNA. We also identified genes tightly co-regulated in peripheral white blood cells and in lung tissue at day 2 post-inoculation. This latter finding opens the possibility of using gene expression arrays on whole blood to detect infection after exposure but prior to onset of symptoms or shedding.

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Related post: "Molecular Anatomy of Influenza Virus Detailed"

Technorati: study, nonhuman, primates, influenza, virus, 1918, journal, nature, strain, immune, response, history, world, war, I, death, new, monkeys, infecting, pandemic, genetics, viral, system, respiratory, infection, cells, lungs, gene, avian, virulent, innate, origin, viruses, macaques, anatomy, molecular

Permanent Link posted by John Latter @ 9:00 PM 0 comments

Archaeology: From The New York Times:

Archaeologists digging in Syria, in the upper reaches of what was ancient Mesopotamia, have found new evidence of how one of the world's earliest cities met a violent end by fire, collapsing walls and roofs, and a fierce rain of clay bullets. The battle left some of the oldest known ruins of organized warfare.

The excavations at the city, Tell Hamoukar, which was destroyed in about 3500 B.C., have also exposed remains suggesting its origins as a manufacturing center for obsidian tools and blades, perhaps as early as 4500 B.C.

The two discoveries were made in September and October and announced yesterday by the Oriental Institute of the University of Chicago and the Syrian Department of Antiquities. The site is in northeastern Syria, less than five miles from the Iraqi border.

Continued at "Ruins in Northern Syria Bear the Scars of a City's Final Battle"

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Based on a University of Chicago press release dated January 16, 2007:

New details in the tragic end of one of the world's earliest cities as well as clues about how urban life may have begun there were revealed in a recent excavation in northeastern Syria that was conducted by the University of Chicago and the Syrian Department of Antiquities.

"The attack must have been swift and intense. Buildings collapsed, burning out of control, burying everything in them under vast pile of rubble," said Clemens Reichel, the American co-director of the Syrian-American Archaeological Expedition to Hamoukar. Reichel, a Research Associate at the University's Oriental Institute, added that the assault probably left the residents destitute as they buried their dead in the ruins of the city.

Reichel made that assessment of the battle that destroyed Hamoukar about 3500 B.C. after an excavation was conducted in September and October at the site near the Iraqi border. The team uncovered further evidence of the accomplishments of the inhabitants among the remains of the walled city dating to the fourth millennium B.C.

In addition to the wall, the team has uncovered quasi-industrial installations and two large administrative buildings that had been destroyed by an intense fire. It was at the site that, mixed in with the debris from the collapsed wall, that over 1,000 egg-shaped sling bullets were found in 2005, leading the excavators to conclude that an early act of warfare had caused the end of the settlement.

Work in this past season may explain how powerful the early weapons were. "We literally have them at all stages of use, from manufacture to impact," Reichel said, pointing out that the team found a sling bullet that had pierced the plaster of a mud brick wall. The team also found 12 graves in the debris, very likely of people killed in the battle.

The team discovered several rooms with walls up to six feet high in which more than 1,100 sling bullets were found mixed in with collapsed walls and roofs. They also found a shallow pit into which a water jar had been buried to its rim in the floor of one of the rooms. This pit, ordinarily used to soak discarded clay sealings to recycle them into fresh sealing clay, was used to make sling bullets during the city's final hours. This was indicated by two dozen sling bullets than were lined up neatly along its edge.

"It looks as if they were - quite literally - throwing everything they could find against the aggressors," Reichel said.

Hamoukar was on a key trade route that led from Anatolia (modern-day Turkey) across Northern Syria and the river Tigris into Southern Mesopotamia. Some evidence of this long-lasting trade was found in an area to the south of Hamoukar's main site - a large mound. The team found obsidian fragments in an area of over 700 acres (280 hectares), which they dated to 4,500 - 4,000 B.C. using pottery fragments found with the obsidian. In addition to tools and blades, the team found large amounts of production debris such as cores, a discovery that is even more significant than finding actual tools.

"Finding cores and other production debris tells us that they are not just using these tools here, they are making them here," Salam al-Kuntar, the Syrian co-director of the expedition, explained. Obsidian does not occur around Hamoukar but had to be brought in from Turkey with the nearest sources being over 70 miles away.

The discovery of an obsidian processing center is significant, Reichel added, for it could explain the emergence of a city in this location at such an early time. A large-scale export of tools to Southern Mesopotamia would have resulted in significant revenue and accumulation of wealth. "This could have been the incentive that pulled people off their fields. People specialized instead of ploughing their own fields they bought their food supplies from surrounding villages. And once people accumulated a fortune they want a walled enclosure to protect it - your first city." Unlike in southern Mesopotamia, therefore, the prime mover towards urbanism appears to have been economic incentive, not coercion.

The obsidian workshops were located off the main mound and predate the destroyed city by several hundred years, but numerous older levels have already been noted below the destroyed buildings in small test trenches. "We have no clear idea how far the first city at Hamoukar goes back in time," Reichel said. "It could be much earlier than 3,500 B.C."

By the time the city was destroyed, he added, copper had started to replace obsidian as key raw material for tools. The discovery of numerous copper tools in the ruins of Hamoukar might indicate that Hamoukar had followed developed from an obsidian into a copper processing center, possibly also exporting copper tools to the south.

The discovery could lead the way to providing an additional explanation for how civilization developed in the Fertile Crescent. In the south, urban society emerged in the Uruk [Biblical Erech] culture in response to the needs of providing organization to an economy supported by an irrigation-based agriculture.

The latest findings from Hamoukar suggest that the specialized mass-production of goods for trade could have been a similar driving force in the North.

Images/Photos: Tell-Hamoukar

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Also of interest by Jason Ur:

Ur, J. A. 2002. Settlement and Landscape in Northern Mesopotamia: The Tell Hamoukar Survey 2000-2001. Akkadica 123:57-88.

Abstract

Since its inception in 1999, the Syrian-American Hamoukar Expedition has attempted to place on-site excavations into a larger context both on the site itself and within its region. The Tell Hamoukar Survey (THS) has conducted site-based surface collection and documentation of off-site traces of land use such as ancient roads and field scatters. Our ultimate goal is to understand the history of human settlement and land use in the eastern Upper Khabur basin through the synthesis of intensive problem-oriented excavation and extensive site survey and landscape studies.

This report summarizes the preliminary results of the 2000-2001 Tell Hamoukar Survey; discussed at length are the history of settlement in the region, the articulation of settlements via ancient roads (hollow ways), and the intensification of agriculture at the end of the 3rd millennium.

And the Oriental Institute Annual Report 2003-2004

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Two recent posts on Archaeology:

"Antikythera: Enigma of Ancient Computer Resolved At Last"

"Great Pyramids Of Giza - Building Blocks Made Of Concrete?"

Technorati: archaeology, syria, ancient, mesopotamia, clay, bullets, fire, oldest, known, ruins, city, tell, hamoukar, obsidian, tools, attack, rubble, dead, buried, fourth, millenium, b.c., new, evidence, excavation, sling, graves, killed, battle, tigris, mound, pottery, fragments, turkey, discovery, copper, uruk, erech

Permanent Link posted by John Latter @ 6:29 PM 0 comments

Using powerful computers to model the intricate dance of atoms and molecules, researchers at Rensselaer Polytechnic Institute have revealed the mechanism behind an important biological reaction. In collaboration with scientists from the Wadsworth Center of the New York State Department of Health, the team is working to harness the reaction to develop a "nanoswitch" for a variety of applications, from targeted drug delivery to genomics and proteomics to sensors.

The research is part of a burgeoning discipline called "quantum biology," (See "Quantum Biology" and "Quantum bio-physics in living organisms") which taps the skyrocketing power of today's high-performance computers to precisely model complex biological processes. The secret is quantum mechanics - the much-touted theory from physics that explains the inherent "weirdness" of the atomic realm.

Reporting in the February 2007 issue of Biophysical Journal (*see below), the researchers describe a mechanism to explain how an intein - a type of protein found in single-celled organisms and bacteria - cuts itself out of the host protein and reconnects the two remaining strands. The intein breaks a protein sequence at two points: first the N-terminal, and then the C-terminal. This aspect of the project, which is led by Saroj Nayak, associate professor of physics, applied physics, and astronomy at Rensselaer, focuses on the C-terminal reaction.

Another Rensselaer team previously found that the reaction at the C-terminal speeds up in acidic environments. But to control the reaction and use it as a nanoswitch, a better understanding of the mechanism behind this reaction is needed, according to Philip Shemella, a doctoral student in physics at Rensselaer and corresponding author of the current paper.

"You can use this protein that cuts itself and joins the pieces together in a predictable way," he said. "It already has a function that would be nice to harness for nanotechnology purposes." And because the reaction may be sensitive to light and other environmental stimuli, the process could become more than just a two-way switch between "on" and "off".

The researchers revealed the details of the reaction mechanism by applying the principles of quantum mechanics - a mathematical framework that describes the seemingly strange behavior of the smallest known particles. For example, quantum mechanics predicts that an electron can be in two different places at the same time; or that an imaginary cat can be simultaneously dead and alive, as suggested by one famous thought experiment (see "Schrodinger's cat").

Until recently, scientists could not apply quantum mechanics to biological systems because of the large numbers of atoms involved. But the latest generation of supercomputers, along with the development of efficient mathematical tools to solve quantum mechanical equations, is making these calculations possible, according to Shemella.

"Typically, quantum mechanics has been applied to solid-state problems because the symmetry makes the calculation smaller and easier, but there's really nothing different physically between a carbon atom in a protein and a carbon atom in a nanotube," he said. "Even though a protein is such an asymmetric, complex system, when you really zoom into the quantum mechanical level, they are just atoms. It doesn't matter if strange things are happening; it's still just carbon, nitrogen, hydrogen, and oxygen."

Quantum mechanics allows researchers to do things that can't be done with classical physics, such as modeling the way chemical bonds break and form, or including the effect of proton "tunneling" - allowing protons to move through energy barriers that normal logic would deem impossible.

For this project, the researchers used computing facilities at Rensselaer's Scientific Computation Research Center (SCOREC) and the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign. In the future, they hope to take advantage of Rensselaer's new Computational Center for Nanotechnology Innovations - a 100 million dollar partnership between Rensselaer, IBM, and New York state to create one of the world’s most powerful university-based supercomputing centers.

The additional computing power will allow them to model complex biological systems with even greater accuracy: "The more atoms you include, the more accurate your system," Shemella said.

The paper's other authors from Rensselaer were Georges Belfort, principal investigator for the project and the Russell Sage Professor of Chemical Engineering; Shekhar Garde, the Elaine and Jack S. Parker Career Development Professor of Chemical and Biological Engineering; Brian Pereira, a graduate student in chemical engineering; and Yiming Zhang, a graduate student in physics. Patrick Van Roey, a research scientist at the Wadsworth Center, also contributed to the project.

The research was funded by a grant from the National Science Foundation to Georges Belfort at Rensselaer, and a grant from the National Institutes of Health to Marlene Belfort at the Wadsworth Center.

[Source: Rensselaer Polytechnic Institute (RPI)]

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*Based on the paper:

Mechanism for Intein C-Terminal Cleavage: A Proposal from Quantum Mechanical Calculations

Abstract

Inteins are autocatalytic protein cleavage and splicing elements. A cysteine to alanine mutation at the N-terminal of inteins inhibits splicing and isolates the C-terminal cleavage reaction. Experiments indicate an enhanced C-terminal cleavage reaction rate upon decreasing the solution pH for the cleavage mutant, which cannot be explained by the existing mechanistic framework. We use intein crystal structure data and the information about conserved amino acids to perform semiempirical PM3 calculations followed by high-level density functional theory calculations in both gas phase and implicit solvent environments. Based on these calculations, we propose a detailed "low pH" mechanism for intein C-terminal cleavage. Water plays an important role in the proposed reaction mechanism, acting as an acid as well as a base. The protonation of the scissile peptide bond nitrogen by a hydronium ion is an important first step in the reaction. That step is followed by the attack of the C-terminal asparagine side chain on its carbonyl carbon, causing succinimide formation and simultaneous peptide bond cleavage. The computed reaction energy barrier in the gas phase is approx 33 kcal/mol and reduces to approx 25 kcal/mol in solution, close to the 21 kcal/mol experimentally observed at pH 6.0. This mechanism is consistent with the observed increase in C-terminal cleavage activity at low pH for the cleavage mutant of the Mycobacterium tuberculosis RecA mini-intein.

Technorati: model, atoms, mechanism, biological, reaction, nanoswitch, proteomics, genomics, quantum, biology, bio, physics, living, organisms, computers, mechanics, atomic, intein, protein, bacteria, astronomy, nanotechnology, electron, schrodinger, cat, symmetry, carbon, atom, nanotude, nitrogen, hydrogen, oxygen, supercomputers, ph, peptide, bond

Permanent Link posted by John Latter @ 8:04 PM 0 comments

Gas-giant planets like Jupiter and Saturn form soon after their stars do, according to new research.

Observations from NASA's Spitzer Space Telescope show that gas giants either form within the first 10 million years of a sun-like star's life, or not at all. The study offers new evidence that gas-giant planets must form early in a star's history. The lifespan of sun-like stars is about 10 billion years.

Ilaria Pascucci of the University of Arizona Steward Observatory in Tucson led a team of astronomers who conducted the most comprehensive search for gas around 15 different sun-like stars, most with ages ranging from 3 million to 30 million years.

The scientists used Spitzer's heat-seeking infrared eyes to search for warm gas in the inner portions of star systems, an area comparable to the zone between Earth and Jupiter in our own solar system.

In addition, Pascucci, team member Michael Meyer of the UA Steward Observatory and their colleagues probed for cold gas in the outer regions of these star systems with the Arizona Radio Observatory's 10-meter Submillimeter Telescope (SMT) on Mount Graham, Ariz. The outer zones of these star systems are analogous to the region around Saturn's orbit and beyond in our own solar system.

UA astronomers and their colleagues used the Arizona Radio Observatory's 10-meter Submillimeter Telescope on Mount Graham, Ariz., to probe cold gas in outer regions of other solar systems. For more about the SMT, visit the Website, http://aro.as.arizona.edu/(Photo: Dave Harvey)

All of the stars in the study – including those as young as a few million years – have less than 10 percent of Jupiter's mass in gas swirling around them, Pascucci said.

"This indicates that gas giant planets like Jupiter and Saturn have already formed in these young solar system analogs, or they never will," Meyer said.

Astronomers suspect that gas around a star may also be important for sending terrestrial, or rocky, planets like Earth into relatively circular orbits as they form. If Earth had a highly elliptical orbit rather than relatively circular one, its temperature swings would be so extreme that humans and other complex organisms might not have evolved.

Many of the sun-like star systems in the study don't currently contain enough gas to send developing rocky planets into circular orbit, Pascucci said. One possibility is that terrestrial planets around these stars have highly elliptical orbits that hinder the development of complex life. Another possibility is that some mechanism other than gas moves the terrestrial planets into circular orbits once they are fully formed. "Our observations tested only the effect of gas," Pascucci said.

Pascucci's paper was published in The Astrophysical Journal in November 2006 (see below). The astronomers are presenting a poster of their findings at the 209th meeting of the American Astronomical Society in Seattle, Washington. The observations were part of the Spitzer Legacy Science Program "Formation and Evolution of Planetary Systems" (FEPS).

Meyer, a co-author of the paper, is the principal investigator of the FEPS program.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. JPL is a division of Caltech. Spitzer's infrared spectrograph was built by Cornell University, Ithaca, N.Y., its development was led by Jim Houck.

The Arizona Radio Observatory offices are centrally located in the Steward Observatory building on The University of Arizona campus in Tucson.

Source: University of Arizona January 8 2007

[Astronomy, Astrophysics] [Image Credit: NASA/JPL-Caltech/T. Pyle (SSC)]

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Based on the paper:

Formation and Evolution of Planetary Systems: Upper Limits to the Gas Mass in Disks around Sun-like Stars

Abstract

We have carried out a sensitive search for gas emission lines at IR and millimeter wavelengths for a sample of 15 young Sun-like stars selected from our dust disk survey with Spitzer. We have used mid-IR lines to trace the warm (300-100 K) gas in the inner disk and millimeter transitions of CO to probe the cold (approx 20 K) outer disk. We report no gas line detections from our sample. Line flux upper limits are first converted to warm and cold gas mass limits using simple approximations allowing a direct comparison with values from the literature. We also present results from more sophisticated models following Gorti and Hollenbach that confirm and extend our simple analysis. These models show that the [S I] 25.23 micro-m line can set constraining limits on the gas surface density at the disk inner radius and traces disk regions up to a few AU. We find that none of the 15 systems have more than 0.04MJ of gas within a few AU from the disk inner radius for disk radii from 1 to approx 40 AU. These gas mass upper limits even in the eight systems younger than approx 30 Myr suggest that most of the gas is dispersed early. The gas mass upper limits in the 10-40 AU region, which is mainly traced by our CO data, are less than 2 M?. If these systems are analogs of the solar system, they either have already formed Uranus- and Neptune-like planets or will not form them beyond 100 Myr. Finally, the gas surface density upper limits at 1 AU are smaller than 0.01% of the minimum mass solar nebula for most of the sources. If terrestrial planets form frequently and their orbits are circularized by gas, then circularization occurs early.

Also see:

The Formation and Evolution of Planetary Systems: Placing Our Solar System in Context with Spitzer

Full Text (PDF)

We provide an overview of the Spitzer Legacy Program "Formation and Evolution of Planetary Systems" (FEPS) which was proposed in 2000, begun in 2001, and executed aboard the Spitzer Space Telescope between 2003 and 2006. This program exploits the sensitivity of Spitzer to carry out mid-infrared spectrophotometric observations of solar-type stars. With a sample of approx 328 stars ranging in age from approx 3 Myr to approx 3 Gyr, we trace the evolution of circumstellar gas and dust from primordial planet-building stages in young circumstellar disks through to older collisionally generated debris disks. When completed, our program will help define the time scales over which terrestrial and gas giant planets are built, constrain the frequency of planetesimal collisions as a function of time, and establish the diversity of mature planetary architectures.

In addition to the observational program, we have coordinated a concomitant theoretical effort aimed at understanding the dynamics of circumstellar dust with and without the effects of embedded planets, dust spectral energy distributions, and atomic and molecular gas line emission. Together with the observations, these efforts will provide astronomical context for understanding whether our Solar System - and its habitable planet - is a common or a rare circumstance. Additional information about the FEPS project can be found on the team website: feps.as.arizona.edu

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*About the Spitzer Space Telescope:

The Spitzer Space Telescope (formerly SIRTF, the Space Infrared Telescope Facility) was launched into space by a Delta rocket from Cape Canaveral, Florida on 25 August 2003. During its 2.5-year mission, Spitzer will obtain images and spectra by detecting the infrared energy, or heat, radiated by objects in space between wavelengths of 3 and 180 microns (1 micron is one-millionth of a meter). Most of this infrared radiation is blocked by the Earth's atmosphere and cannot be observed from the ground.

Consisting of a 0.85-meter telescope and three cryogenically-cooled science instruments, Spitzer is the largest infrared telescope ever launched into space. Its highly sensitive instruments give us a unique view of the Universe and allow us to peer into regions of space which are hidden from optical telescopes. Many areas of space are filled with vast, dense clouds of gas and dust which block our view. Infrared light, however can penetrate these clouds, allowing us to peer into regions of star formation, the centers of galaxies, and into newly forming planetary systems. Infrared also brings us information about the cooler objects in space, such as smaller stars which are too dim to be detected by their visible light, extrasolar planets, and giant molecular clouds. Also, many molecules in space, including organic molecules, have their unique signatures in the infrared.

Because infrared is primarily heat radiation, the telescope must be cooled to near absolute zero (-459 degrees Fahrenheit or -273 degrees Celsius) so that it can observe infrared signals from space without interference from the telescope's own heat. Also, the telescope must be protected from the heat of the Sun and the infrared radiation put out by the Earth. To do this, Spitzer carries a solar shield and will be launched into an Earth-trailing solar orbit. This unique orbit places Spitzer far enough away from the Earth to allow the telescope to cool rapidy without having to carry large amounts of cryogen (coolant). This innovative approach has significantly reduced the cost of the mission.

Spitzer will be the final mission in NASA's Great Observatories Program - a family of four orbiting observatories, each observing the Universe in a different kind of light (visible, gamma rays, X-rays, and infrared). Other missions in this program include the Hubble Space Telescope (HST), Compton Gamma-Ray Observatory (CGRO), and the Chandra X-Ray Observatory(CXO). Spitzer is also a part of NASA's Astronomical Search for Origins Program, designed to provide information which will help us understand our cosmic roots, and how galaxies, stars and planets develop and form. [Source: NASA]

Technorati: gas, giant, planets, jupiter, saturn, form, stars, new, research, nasa, spitzer, space, telescope, giants, sun, evidence, lifespan, observatory, search, infrared, star, systems, astrophysics, astronomy, mass, ir, au, uranus, neptune, solar, evolution, system, earth, clouds, x-rays, hubble

Permanent Link posted by John Latter @ 8:18 PM 0 comments

UPDATE: February 24 2007: The BBC video 'Time Travel' is no longer available and has been replaced by:

"The 2003 BBC documentary "The World's First Time Machine", directed by Ben Bowie and featuring Ronald Mallett (Professor of Physics, University of Connecticut), premiered in the USA on The Learning Channel on December 3, 2003." - see below.

Original post:

"BBC Horizon's Time Trip (originally broadcast on BBC Two, Thursday 18 December 2003 at 9pm) is a thrilling journey deep into the strangeness of cutting-edge physics - a place where beautiful, baffling ideas are sometimes indistinguishable from the utterly crazy.

On this journey, we meet a time-travelling pizza, a brilliant mathematician in a ski mask and even God. The journey ends with a strange and dark conclusion - one which calls into question our very existence.

Ever since Einstein showed it was theoretically possible, the quest to travel through time has drawn eccentric amateurs and brilliant scientists in almost equal numbers. The amateurs include Aage Nost, who demonstrates his time machine in front of the cameras. The professionals include the likes of Professor Frank Tipler of Tulane University. His time machine sounds good - but it would weigh half the mass of the galaxy.

There is, however, one way that time travel to the past could be possible..."

From 'Time Trip - questions and answers'

How widely accepted is the theory that we can travel in time?

The Future
According to Professor Paul Davies "Scientists have no doubt whatever that it is possible to build a time machine to visit the future". Since the publication of Einstein's Special Theory of Relativity in 1905, few, if any, scientists would dispute that time travel to the future is perfectly possible.

According to this theory, time runs slower for a moving person than for someone who is stationary. This has been proven by experiments using very accurate atomic clocks. In theory, a traveller on a super high-speed rocket ship could fly far out into the Universe and then come back to Earth at a time hundreds or thousands of years in its future.

Another consequence of special relativity is that gravity slows time down. So, another way of time travelling to the future would be to go and sit next to a black hole or a neutron star, both of which are very massive and have huge gravitational fields. When you went back to Earth, it would have aged more than you.

The Past
Time travel to the past is more problematic, but there is nothing in the known laws of physics to prevent it. It is accepted that if you could travel faster than light, you could travel to the past. However, it is impossible to accelerate anything to a speed faster than light because you would need an infinite amount of energy.

But hope for prospective time travellers comes from Einstein's General Theory of Relativity, considered to be the best theory of time and space that we have.

In 1948 Kurt Godel (info/profile) worked with general relativity to produce equations suggesting the possibility of time travel to the past. He showed that a rotating universe, consistent with Einstein's theory, would allow you travel back in time. Godel knew that his model was unlike the real universe we inhabit and also that even if we did live in such a universe, time travel would be practically unachievable because you would need a hugely powerful rocket in which to cover astronomical distances. Despite this, Godel's work was firm evidence that time travel to the past is, at least in theory, possible.

Since then, numerous other scientists have come up with other solutions of general relativity that allow time travel to the past. Most rely on the prediction of the existence of 'closed time-like curves'. According to these scientists, there are ways of distorting space-time to make it curved in such a way that shortcuts through space-time exist allowing you to effectively travel faster than light and journey back into the past.

Not all scientists like this idea and there are some scientists, like Professor Stephen Hawking, who insist that there must be something that prevents it. In 1990, Hawking proposed a Chronology Protection Conjecture* which says that the laws of physics disallow time machines. Basically, such scientists argue that nature will conspire to prevent the building of a time machine - one possibility is that runaway surges in quantum energy would generate massive gravitational fields and turn any time machine into mush. There are no clear answers to the issue because quantum physics and gravity do not sit well together and there is not yet a unified theory of quantum gravity.

Hawking and others have serious problems with the fact that time travel to the past would violate causality and this would have serious implications for our understanding of how the Universe works. A final answer to whether we really can travel back in time may have to wait until scientists find a way to bring quantum mechanics and general relativity together.

*See Stephen Hawking's Space and Time Warps:

"In science fiction, space and time warps are a commonplace. They are used for rapid journeys around the galaxy, or for travel through time. But today's science fiction, is often tomorrow's science fact. So what are the chances for space and time warps. The idea that space and time can be curved, or warped, is fairly recent. For more than two thousand years, the axioms of Euclidean geometry, were considered to be self evident. As those of you that were forced to learn Euclidean geometry at school may remember, one of the consequences of these axioms is, that the angles of a triangle, add up to a hundred and 80 degrees. However, in the last century, people began to realize that other forms of geometry were possible..."

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Also see "Professor Predicts Human Time Travel This Century":

With a brilliant idea and equations based on Einstein's relativity theories, Ronald Mallett from the University of Connecticut has devised an experiment to observe a time traveling neutron in a circulating light beam. While his team still needs funding for the project, Mallett calculates that the possibility of time travel using this method could be verified within a decade.

..."Einstein showed that mass and energy are the same thing," said Mallett, who published his first research on time travel in 2000 in Physics Letters**. "The time machine we’ve designed uses light in the form of circulating lasers to warp or loop time instead of using massive objects."

**See "Weak gravitational field of the electromagnetic radiation in a ring laser":

Abstract

The gravitational field due to the circulating flow of electromagnetic radiation of a unidirectional ring laser is found by solving the linearized Einstein field equations at any interior point of the laser ring. The general relativistic spin equations are then used to study the behavior of a massive spinning neutral particle at the center of the ring laser. It is found that the particle exhibits the phenomenon known as inertial frame-dragging.

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Permanent Link posted by John Latter @ 12:07 PM 0 comments