Avoiding An Asteroid Collision

Illustration only.

by Staff Writers
Tel Aviv, Israel (SPX) Sep 14, 2010
Though it was once believed that allasteroids are giant pieces of solid rock, later hypotheses have it that some are actually a collection of small gravel-sized rocks, held together by gravity. If one of these "rubble piles" spins fast enough, it's speculated that pieces could separate from it through centrifugal force and form a second collection - in effect, a second asteroid.

Now researchers at Tel Aviv University, in collaboration with an international group of scientists, have proved the existence of these theoretical "separated asteroid" pairs.

Ph.D. student David Polishook of Tel Aviv University's Department of Geophysics and Planetary Sciences and his supervisor Dr. Noah Brosch of the university's School of Physics and Astronomy say the research has not only verified a theory, but could have greater implications if an asteroid passes close to earth.

Instead of a solid mountain colliding with earth's surface, says Dr. Brosch, the planet would be pelted with the innumerable pebbles and rocks that comprise it, like a shotgun blast instead of a single cannonball. This knowledge could guide the defensive tactics to be taken if an asteroid were on track to collide with the Earth.

A large part of the research for the study, recently published in the journal Nature, was done at Tel Aviv University's Wise Observatory, located deep in the Negev Desert - the first and only modern astronomical observatory in the Middle East.

Spinning out in space
According to Dr. Brosch, separated asteroids are composed of small pebbles glued together by gravitational attraction. Their paths are affected by the gravitational pull of major planets, but the radiation of the sun, he says, can also have an immense impact. Once the sun's light is absorbed by the asteroid, rotation speeds up. When it reaches a certain speed, a piece will break off to form a separate asteroid.

The phenomenon can be compared to a figure skater on the ice. "The faster they spin, the harder it is for them to keep their arms close to their bodies," explains Dr. Brosch.

As a result, asteroid pairs are formed, characterized by the trajectory of their rotation around the sun. Though they may be millions of miles apart, the two asteroids share the same orbit. Dr. Brosch says this demonstrates that they come from the same original asteroid source.

Looking into the light
During the course of the study, Polishook and an international group ofastronomers studied 35 asteroid pairs. Traditionally, measuring bodies in the solar system involves studying photographic images. But the small size and extreme distance of the asteroids forced researchers to measure these pairs in an innovative way.

Instead, researchers measured the light reflected from each member of the asteroid pairs. The results proved that in each asteroid pair, one body was formed from the other.

The smaller asteroid, he explains, was always less than forty percent of the size of the bigger asteroid. These findings fit precisely into a theory developed at the University of Colorado at Boulder, which concluded that no more than forty percent of the original asteroid can split off.

With this study, says Dr. Brosch, researchers have been able to prove the connection between two separate spinning asteroids and demonstrate the existence of asteroids that exist in paired relationships.

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New Results On Dwarf Galaxy Evolution

File image: dwarf galaxy.

by Staff Writers
Lisbon, Portugal (SPX) Sep 13, 2010
The 'Local Cosmology from Isolated Dwarfs (LCID)' team showed their most recent results that suggest that reionization alone is not able to stop star formation in Dwarf Galaxies, as had been expected. The results were presented during the European Week of Astronomy and Space Sciences.

The Big Bang model predicts that the universe started out as completely ionized plasma, which later cooled and allowed all of the atoms to recombine into neutral atoms.

The first generation of stars and galaxies formed from this neutral material and produced high energy radiation which then "reionized" the universe. This period of reionization ended approximately 1 billion years after the Big Bang.

The 'Local Cosmology from Isolated Dwarfs (LCID)' project, led by Carme Gallart of the Instituto de Astrofisica de Canarias (Tenerife, Spain), has used over 100 orbits of the Hubble Space Telescope (HST) observing time with the ACS camera in order to obtain detailed star formation histories for six Local Group dwarf galaxies, which include details about early star formation.

"All the galaxies in the sample, including those that ended star formation very early on, such as the Cetus dSph galaxy, formed most of their stars after reionization was complete. This demonstrates that reionization alone is not able to stop star formation in the smallest galaxies, as had been expected" says Gallart, who has been working with a team of about a dozen people for 5 years on this project.

The smallest galaxies represent important probes of the conditions of the early Universe, since their early star formation can be strongly influenced by cosmic reionization.

The most common prediction of models of dwarf galaxy evolution is that the early ionization of the gas in these galaxies by the cosmic UV background should have halted and prevented any subsequent star formation in them after about 12.5 Gyr ago.

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Deadly Tides Mean Early Exit For Hot Jupiters

An artist's depiction of an early stage in the destruction of a hot Jupiter by its star. Credit: NASA/GSFC/Frank Reddy

by Elizabeth Zubritsky
Greenbelt MD (SPX) Sep 10, 2010
Bad news for planet hunters: most of the "hot Jupiters" that astronomers have been searching for in starclusters were likely destroyed long ago by their stars.

In a paper accepted for publication by the Astrophysical Journal, John Debes and Brian Jackson of NASA's Goddard Space Flight Center in Greenbelt, Md., offer this new explanation for why no transiting planets (planets that pass in front of their stars and temporarily block some of the light) have been found yet in star clusters.

The researchers also predict that the planet hunting being done by the Kepler mission is more likely to succeed in younger star clusters than older ones.

"Planets are elusive creatures," says Jackson, a NASA Postdoctoral Program fellow at Goddard, "and we found another reason that they're elusive."

When astronomers began to search for planets in star-packed globular clusters about 10 years ago, they hoped to find many new worlds. One survey of the cluster called 47 Tucanae (47 Tuc), for example, was expected to find at least a dozen planets among the roughly 34,000 candidate stars.

"They looked at so many stars, people thought for sure they would find some planets," says Debes, a NASA Postdoctoral Program fellow at Goddard. "But they didn't."

More than 450 exoplanets (short for "extrasolar planets," or planets outside our solar system) have been found, but "most of them have been detected around single stars," Debes notes.

"Globular clusters turn out to be rough neighborhoods for planets," explains Jackson, "because there are lots of stars around to beat up on them and not much for them to eat."

The high density of stars in these clusters means that planets can be kicked out of their solar systems by nearby stars. In addition, the globular clusters surveyed so far have been rather poor in metals (elements heavier than hydrogen and helium), which are the raw materials for making planets; this is known as low metallicity.

Debes and Jackson propose that hot Jupiters-large planets that are at least 3 to 4 times closer to their host stars than Mercury is to our sun-are quickly destroyed. In these cramped orbits, the gravitational pull of the planet on the star can create a tide-that is, a bulge-on the star.

As the planet orbits, the bulge on the star points a little bit behind the planet and essentially pulls against it; this drag reduces the energy of the planet's orbit, and the planet moves a little closer to the star. Then the bulge on the star gets bigger and saps even more energy from the planet's orbit.

This continues for billions of years until the planet crashes into the star or is torn apart by the star's gravity, according to Jackson's model of tidal orbital decay.

"The last moments for these planets can be pretty dramatic, as their atmospheres are ripped away by their stars' gravity," says Jackson.

"It has even been suggested recently the hot Jupiter called WASP-12B is close enough to its star that it is currently being destroyed."

Debes and Jackson modeled what would have happened in 47 Tuc if the tidal effect were unleashed on hot Jupiters. They recreated the range of masses and sizes of the stars in that cluster and simulated a likely arrangement of planets. Then they let the stars' tides go to work on the close-in planets.

The model predicted that so many of these planets would be destroyed, the survey would come up empty-handed. "Our model shows that you don't need to consider metallicity to explain the survey results," says Debes, "though this and other effects will also reduce the number of planets."

Ron Gilliland, who is at the Space Telescope Science Institute in Baltimore and participated in the 47 Tuc survey, says, "This analysis of tidal interactions of planets and their host stars provides another potentially good explanation-in addition to the strong correlation between metallicity and the presence of planets-of why we failed to detect exoplanets in 47 Tuc."

In general, Debes and Jackson's model predicts that one-third of the hot Jupiters will be destroyed by the time a cluster is a billion years old, which is still juvenile compared to our solar system (about 4-1/2 billion years old). 47 Tuc has recently been estimated to be more than 11 billion years old. At that age, the researchers expect more than 96% of the hot Jupiters to be gone.

The Kepler mission, which is searching for hot Jupiters and smaller, Earth-like planets, gives Debes and Jackson a good chance to test their model.

Kepler will survey four open clusters-groups of stars that are not as dense as globular clusters-ranging from less than half a billion to nearly 8 billion years old, and all of the clusters have enough raw materials to form significant numbers of planets, Debes notes.

If tidal orbital decay is occurring, Debes and Jackson predict, Kepler could find up to three times more Jupiter-sized planets in the youngest cluster than in the oldest one. (An exact number depends on the brightness of the stars, the planets' distance from the stars, and other conditions.)

"If we do find planets in those clusters with Kepler," says Gilliland, a Kepler co-investigator, "looking at the correlations with age and metallicity will be interesting for shaping our understanding of the formation of planets, as well as their continued existence after they are formed."

If the tidal orbital decay model proves right, Debes adds, planet hunting in clusters may become even harder. "The big, obvious planets may be gone, so we'll have to look for smaller, more distant planets," he explains. "That means we will have to look for a much longer time at large numbers of stars and use instruments that are sensitive enough to detect these fainter planets."

The Kepler mission is managed by NASA's Ames Research Center, Moffett Field, Calif., for the Science Mission Directorate at NASA Headquarters in Washington.

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Universe Chaotic From Very Beginning

The work has direct implications for cosmology and shows in particular that the erratic changes between red- and blue-shift directions in the early universe were in fact chaotic.

by Staff Writers

Evanston IL (SPX) Sep 08, 2010

Seven years ago Northwestern University physicist Adilson E. Motter conjectured that the expansion of the universe at the time of the big bang was highly chaotic. Now he and a colleague have proven it using rigorous mathematical arguments.

The study, published by the journal Communications in Mathematical Physics, reports not only that chaos is absolute but also the mathematical tools that can be used to detect it. When applied to the most accepted model for the evolution of the universe, these tools demonstrate that the early universewas chaotic.

Certain things are absolute. The speed of light, for example, is the same with respect to any observer in the empty space. Others are relative.

Think of the pitch of a siren on an ambulance, which goes from high to low as it passes the observer. A longstanding problem in physics has been to determine whether chaos - the phenomenon by which tiny events lead to very large changes in the time evolution of a system, such as the universe - is absolute or relative in systems governed by general relativity, where the time itself is relative.

A concrete aspect of this conundrum concerns one's ability to determine unambiguously whether the universe as a whole has ever behaved chaotically. If chaos is relative, as suggested by some previous studies, this question simply cannot be answered because different observers, moving with respect to each other, could reach opposite conclusions based on the ticks of their own clocks.

"A competing interpretation has been that chaos could be a property of the observer rather than a property of the system being observed," said Motter, an author of the paper and an assistant professor of physics andastronomy at Northwestern's Weinberg College of Arts and Sciences. "Our study shows that different physical observers will necessarily agree on the chaotic nature of the system."

The work has direct implications for cosmology and shows in particular that the erratic changes between red- and blue-shift directions in the early universe were in fact chaotic.

Motter worked with colleague Katrin Gelfert, a mathematician from the Federal University of Rio de Janeiro, Brazil, and a former visiting faculty member at Northwestern, who says that the mathematical aspects of the problem are inspiring and likely to lead to other mathematical developments.

An important open question in cosmology is to explain why distant parts of the visible universe - including those that are too distant to have ever interacted with each other - are so similar.

"One might suggest 'Because the large-scale universe was created uniform,'" Motter said, "but this is not the type of answer physicists would take for granted."

Fifty years ago, physicists believed that the true answer could be in what happened a fraction of a second after the big bang. Though the initial studies failed to show that an arbitrary initial state of the universe would eventually converge to its current form, researchers found something potentially even more interesting: the possibility that the universe as a whole was born inherently chaotic.

The present-day universe is expanding and does so in all directions, Motter explained, leading to red shift of distant light sources in all three dimensions - the optical analog of the low pitch in a moving siren. The early universe, on the other hand, expanded in only two dimensions and contracted in the third dimension.

This led to red shift in two directions and blue shift in one. The contracting direction, however, was not always the same in this system. Instead, it alternated erratically between x, y and z.

"According to the classical theory of general relativity, the early universe experienced infinitely many oscillations between contracting and expanding directions," Motter said.

"This could mean that the early evolution of the universe, though not necessarily its current state, depended very sensitively on the initial conditions set by the big bang."

This problem gained a new dimension 22 years ago when two other researchers, Gerson Francisco and George Matsas, found that different descriptions of the same events were leading to different conclusions about the chaotic nature of the early universe. Because different descriptions can represent the perspectives of different observers, this challenged the hypothesis that there would be an agreement among different observers. Within the theory of general relativity, such an agreement goes by the name of a "relativistic invariant."

"Technically, we have established the conditions under which the indicators of chaos are relativistic invariants," Motter said. "Our mathematical characterization also explains existing controversial results. They were generated by singularities induced by the choice of the time coordinate, which are not present for physically admissible observables."

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China Launches Satellite Sinosat-6 For TV, Radio Live Broadcast

China launches the "SinoSat-6" satellite for radio and television live broadcast from the Xichang Satellite Launch Center in southwest China's Sichuan Province on Sept. 5, 2010. Photo courtesy Xinhua.

by Staff Writers
Xichang, China (XNA) Sep 06, 2010
China successfully launched the "SinoSat-6" satellite for radio and television live broadcast at 12:14 a.m.Sunday from the Xichang Satellite Launch Center in southwest China's Sichuan Province.

The satellite was carried on the Long March 3B rocket which took the SinoSat-6 into a geostationary transfer orbit 26 minutes after the launch.

In the following days, Xi'an Satellite Control Center and Yuanwang tracking ship will manipulate the satellite's position and transfer it to enter the geostationary orbit.

SinoSat-6 has a designed lifespan of 15 years and will eventually work at longitude 126.4 degrees east about 35,700 kilometers above the equator, said the China Aerospace Science and Technology Corporation (CASTC), the satellite's researcher and producer.

It will mainly serve for relaying TV and radio live broadcast signals and will greatly improve cultural life for people living in remote and mountainous regions, according to China Satellite Communications Corporation which will operate the satellite.

China has launched the first SinoSat series satellite, SinoSat-1, in 1998. The SinoSat-2 was launched in 2006 but malfuctioned for it failed to deploy its solar panels and communication antennae.

SinoSat-6 will serve as a substitute for SinoSat-3 which was launched on June 1, 2007, according to the China Aerospace Science and Technology Corporation.

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God did not create Universe: Hawking

by Staff Writers
London (AFP) Sept 2, 2010
God no longer has any place in theories on the creation of the Universe due to a series of developments in physics, British scientist Stephen Hawking said in extracts published Thursday from a new book.

In a hardening of the more accommodating position on religion that he took in his 1988 international best-seller "A Brief History of Time", Hawking said the Big Bang was merely the consequence of the law of gravity.

"Because there is a law such as gravity, the Universe can and will create itself from nothing. Spontaneous creation is the reason there is something rather than nothing, why the Universe exists, why we exist," he writes in "The Grand Design", which is being serialised by The Times newspaper.

"It is not necessary to invoke God to light the blue touch paper and set the Universe going," added the wheelchair-bound expert.

Hawking has achieved worldwide fame for his research, writing and television documentaries despite suffering since the age of 21 motor neurone disease that has left him disabled and dependent on a voice synthesiser.

In "A Brief History of Time", Hawking had suggested that the idea of God or a divine being was not necessarily incompatible with a scientific understanding of the Universe.

But in his latest work, Hawking cites the 1992 discovery of a planet orbiting a star outside our own Solar System as a turning point against Isaac Newton's belief that the Universe could not have arisen out of chaos.

"That makes the coincidences of our planetary conditions -- the single Sun, the lucky combination of Earth-Sun distance and solar mass -- far less remarkable, and far less compelling as evidence that the Earth was carefully designed just to please us human beings," he wrote.

Hawking argued earlier this year that mankind's only chance of long-term survival lies in colonising space, as humans drain Earth of resources and face a terrifying array of new threats.

He also warned in a recent television series that mankind should avoid contact with aliens at all costs, as the consequences could be devastating.

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Sunlight Spawns Many Binary And 'Divorced' Binary Asteroids

The conclusion fits a theory of binary asteroid formation originated by co-author Daniel Scheeres, a professor of aerospace engineering sciences at the University of Colorado, Boulder. His theory predicts that if a binary asteroid forms by rotational fission, the two can only escape from each other if the smaller one is less than 60 percent the size of the larger asteroid.

by Staff Writers
The asteroid beltbetween Mars and Jupiter is often depicted as a dull zone of dead rocks with an occasional wayward speedster smashing through on its way toward the sun.

A new study appearing in the journal Nature paints a different picture, one of slow but steady change, where sunlight gradually drives asteroids to split in two and move far apart to become independent asteroids among the millions orbiting the sun.

"This shows that asteroids are not inert, dead bodies of no interest," said study co-author Franck Marchis, a research astronomer at the University of California, Berkeley, and the SETI Institute in Mountain View, Calif. "In fact, small asteroids very slowly evolve into binaries and, eventually, divorced binaries."

Marchis, who studies double- and triple-asteroid systems, teamed up with former UC Berkeley undergraduate Brent Macomber to analyze two pairs of former or "divorced" binaries, which are asteroid pairs that have drifted apart and are no longer gravitationally bound to one another. Macomber, now a graduate student at Texas A and M University, participated through UC Berkeley's Undergraduate Research Apprentice Program (URAP), which matches students with researchers in need of assistance.

Marchis and Macomber contributed their findings to a group of astronomers in the Czech Republic, who analyzed the evolution of 35 pairs of divorced binaries.

The leader of that group, Petr Pravec of the Astronomical Institute in the Czech Republic, and 25 colleagues from 15 other institutions published the results this week, showing that all of the asteroid pairs have similar relative masses and relative velocities that point to a similar origin by fission.

The conclusion fits a theory of binary asteroid formation originated by co-author Daniel Scheeres, a professor of aerospace engineering sciences at the University of Colorado, Boulder. His theory predicts that if a binary asteroid forms by rotational fission, the two can only escape from each other if the smaller one is less than 60 percent the size of the larger asteroid.

Of all the asteroid pairs in the study, the smallest of each pair was always less than 60 percent of the mass of its companion asteroid.

Of the estimated one million asteroids 1 kilometer or more in diameter orbiting the sun, many are thought to be rubble piles of smaller rocks gravitationally bound together.

Previous research has shown that asteroid rubble piles less than 10 kilometers in diameter can start rotating faster because of the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect: the imbalance between sunlight absorbed on one side of an out-of-round asteroid and heatradiated on the other makes it spin.

"Sunlight striking an asteroid less than 10 kilometers across can change its rotation over millions of years, a slow motion version of how a windmill reacts to the wind," Scheeres said.

As an asteroid spins up, the equator bulges and the rocks at the extreme edge eventually reach escape velocity and detach. The detached rocks coalesce into a moonlet and, over millions of years, the primary and secondary asteroids "separate gently from each other at relatively low velocities," Scheeres said.

"This slow process, rather than catastrophic demolition, replenishes the population of binary asteroids, and accounts for the many binaries and ex-binaries that we see," Marchis said, noting that 10-15 percent of all small asteroids could be a binary system.

The researchers focused on so-called "asteroid pairs": independent asteroids in the same orbit around the sun that have come close to each other - usually within a few miles - at very low relative speeds at some point in the past million years. Asteroid pairs were first discovered in 2008 by co-author David Vokrouhlicky of Charles University in Prague, Czech Republic, but their formation process remained a mystery prior to the new study.

Suspecting that asteroid pairs were at one point binary asteroid systems, Pravec asked collaborators to measure two characteristics of each of the 35 asteroid pairs: the relative brightness of each asteroid - which correlates to its size - and the spin rates of the asteroid pairs using a technique known as photometry.

The 35 asteroids in the study ranged from about 1 to 10 kilometers (0.6 - 6 miles) in diameter. Observations were contributed by co-authors from institutions in North Carolina, California, Massachusetts, Chile, Israel, Slovakia, the Ukraine, Spain and France.

Macomber's contributions to research are not unusual for a UC Berkeley undergraduate. More than 1,400 students were involved in research last year in all fields of science, social science and the humanities.

"In the three years that I worked with Dr. Marchis, I got more experience than I could have possibly imagined in all aspects of observationalastronomy, everything from planning a night of observations, to collecting data with advanced adaptive optics imagers, to processing the data after the observations are completed," said Macomber, who obtained his bachelor's in physics and astronomy in December 2008, worked for a semester with Marchis at the SETI Institute and is now a Bradley Fellow in the Department of Aerospace Engineering at Texas A and M.

"The most important thing I learned was how real science works, the process of collaborating with a team around the world to collect observations, analyze them and publish scientific results."

"When students work with us, they can be involved in state-of-the-art research and make a real contribution to science," Marchis said.

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