Series of bumps sent Uranus into its sideways spin, new research suggests

ScienceDaily (Oct. 10, 2011) — Uranus' highly tilted axis makes it something of an oddball in our Solar System. The accepted wisdom is that Uranus was knocked on its side by a single large impact, but new research being presented at the EPSC-DPS Joint Meeting in Nantes rewrites our theories of how Uranus became so tilted and also solves fresh mysteries about the position and orbits of its moons. By using simulations of planetary formation and collisions, it appears that early in its life Uranus experienced a succession of small punches instead of a single knock-out blow. This research has important ramifications on our theories of giant planet formation.

Uranus is unusual in that its spin axis is inclined by 98 degrees compared to its orbital plane around the Sun. This is far more pronounced than other planets, such as Jupiter (3 degrees), Earth (23 degrees), or Saturn and Neptune (29 degrees). Uranus is, in effect, spinning on its side.

The generally accepted theory is that in the past a body a few times more massive than Earth collided with Uranus, knocking the planet on its side. There is, however, one significant flaw in this notion: the moons of Uranus should have been left orbiting in their original angles, but they too lie at almost exactly 98 degrees.

This long-standing mystery has been solved by an international team of scientists led by Alessandro Morbidelli (Observatoire de la Cote d'Azur in Nice, France), who is presenting his group's research at the EPSC-DPS Joint Meeting in Nantes, France.

Morbidelli and his team used simulations to reproduce various impact scenarios in order to ascertain the most likely cause of Uranus' tilt. They discovered that if Uranus had been hit when still surrounded by a protoplanetary disk -- the material from which the moons would form -- then the disk would have reformed into a fat doughnut shape around the new, highly-tilted equatorial plane. Collisions within the disk would have flattened the doughnut, which would then go onto form the moons in the positions we see today.

However, the simulation threw up an unexpected result: in the above scenario, the moons displayed retrograde motion -- that is to say, they orbited in the opposite direction to that which we observe. Morbidelli's group tweaked their parameters in order to explain this. The surprising discovery was that if Uranus was not tilted in one go, as is commonly thought, but rather was bumped in at least two smaller collisions, then there is a much higher probability of seeing the moons orbit in the direction we observe.

This research is at odds with current theories of how planets form, which may now need adjusting. Morbidelli elaborates: "The standard planet formation theory assumes that Uranus, Neptune and the cores of Jupiter and Saturn formed by accreting only small objects in the protoplanetary disk. They should have suffered no giant collisions. The fact that Uranus was hit at least twice suggests that significant impacts were typical in the formation of giant planets. So, the standard theory has to be revised."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Europlanet Media Centre, via AlphaGalileo.

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Escaping gravity's clutches: Information could escape from black holes after all, study suggests

ScienceDaily (Aug. 11, 2011) — New research by scientists at the University of York gives a fresh perspective on the physics of black holes. Black holes are objects in space that are so massive and compact they were described by Einstein as "bending" space. Conventional thinking asserts that black holes swallow everything that gets too close and that nothing can escape, but the study by Prof. Samuel Braunstein and Dr. Manas Patra suggests that information could escape from black holes after all.

The implications could be revolutionary, suggesting that gravity may not be a fundamental force of nature.

Prof. Braunstein says: "Our results didn't need the details of a black hole's curved space geometry. That lends support to recent proposals that space, time and even gravity itself may be emergent properties within a deeper theory. Our work subtly changes those proposals, by identifying quantum information theory as the likely candidate for the source of an emergent theory of gravity."

But quantum mechanics is the theory of light and atoms, and many physicists are skeptical that it could be used to explain the slow evaporation of black holes without incorporating the effects of gravity.

The research, which appears in the latest issue of Physical Review Letters, uses the basic tenets of quantum mechanics to give a new description of information leaking from a black hole.

Prof. Braunstein says: "Our results actually extend the predictions made by well-established techniques that rely on a detailed knowledge of space time and black hole geometry."

Dr. Patra adds: "We cannot claim to have proven that escape from a black hole is truly possible, but that is the most straight-forward interpretation of our results. Indeed, our results suggest that quantum information theory will play a key role in a future theory combining quantum mechanics and gravity."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of York.

Journal Reference:

Samuel Braunstein, Manas Patra. Black Hole Evaporation Rates without Spacetime. Physical Review Letters, 2011; 107 (7) DOI: 10.1103/PhysRevLett.107.071302

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Sun and planets constructed differently, analysis from NASA mission suggests

ScienceDaily (June 30, 2011) — The sun and the solar system's rocky inner planets, including Earth, may have formed differently than previously thought, according to UCLA scientists and colleagues analyzing samples returned by NASA's Genesis mission.

The data from Genesis, which collected material from the solar wind blowing from the sun, reveal differences between the sun and planets with regard to oxygen and nitrogen, two of the most abundant elements in our solar system, the researchers report in two studies in the June 24 issue of the journal Science. And although the differences are slight, the research could help determine how our solar system evolved.

"We want to understand how rocky planets form, particularly our rocky planet," said Genesis co-investigator and UCLA professor of Earth and space sciences Kevin McKeegan, who was the lead author of the Science study on oxygen. "To understand that, we need to understand how the isotope composition of the most abundant element in the Earth came to be what it is."

On Earth, the air contains three kinds, or isotopes, of oxygen atoms, which differ in the number of neutrons they contain. All three have eight protons, and almost all have eight neutrons (O-16), but a small proportion of isotopes contain nine neutrons (O-17) or 10 neutrons (O-18). Although isotopes of an element behave similarly, there are subtle differences in reaction rates according to the isotopic mass, McKeegan said.

"We found that the Earth and moon, as well as Martian and other meteorites, which are samples of asteroids, have a lower concentration of the O-16 than does the sun," McKeegan said. "The implication is that we did not form out of the same solar nebula materials that created the sun. Just how and why remains to be discovered."

McKeegan and his colleagues measured, for the first time, the isotopic composition of oxygen in the solar wind. They found that the sun has about 6 percent more O-16 -- relative to both of the minor oxygen isotopes -- than Earth does. Because the sun represents the "starting composition of the entire solar system," these findings are surprising, McKeegan said.

"It's the most abundant element in the Earth, and it is isotopically anomalous," he said, adding that something chemically unusual happened to the material that eventually formed Earth and other rocky planets some 4.6 billion years ago, after the sun had already formed.

"The present composition of the rocky planets is quite different from the starting composition in a way we do not fully understand," he said, "but it must have involved interesting chemistry before the planets formed in the gaseous nebula that produced the sun and planets."

The data were obtained from an analysis of material ejected from the outer portion of the sun. That material can be thought of as a "fossil of our nebula" because scientific evidence suggests that the sun's outer layer has not changed measurably in billions of years. The sample of solar material collected by Genesis was small, but there was enough to be analyzed using UCLA's MegaSIMS (secondary ion mass spectrometer).

"This is the first time the heavy elements in the sun have had their isotope composition determined with precision, directly from solar material," McKeegan said. "The Genesis mission was a success. The mission has achieved its highest priority objectives. We are learning how planets form."

Analyses of meteorites from Mars indicate that oxygen on Mars is very similar to oxygen on Earth, but not identical, McKeegan said.

Genesis launched in August 2001. The spacecraft traveled to the L1 Lagrange Point, about 1 million miles from Earth, where it remained for 886 days between 2001 and 2004, passively collecting solar wind samples.

On Sept. 8, 2004, the spacecraft released a sample return capsule that entered Earth's atmosphere. Although the capsule made a hard landing -- the result of a failed parachute -- in the Utah Test and Training Range in Dugway, Utah, it marked NASA's first sample return since the final Apollo lunar mission in 1972 and the first material collected beyond the moon.

Co-authors of the oxygen study included Veronika Heber, a UCLA research scientist in the Department of Earth and Space Sciences; George Jarzebinski, senior electronics engineer at UCLA; Chris Coath, a former UCLA researcher who designed the ion optics of the MegaSIMS; Peter Mao, a former UCLA researcher who is currently an astrophysicist at the California Institute of Technology; Antti Kallio, a former UCLA postdoctoral scholar who acquired much of the solar wind data; Takaya Kunihiro, a former UCLA postdoctoral scholar currently at Japan's Okayama University; and Don Burnett, a professor at the California Institute of Technology, who was Genesis' principal investigator. A team from Los Alamos National Laboratory led by Roger Wiens built a device on the Genesis spacecraft for the analysis of oxygen and nitrogen from the solar wind. Wiens and his colleagues are also co-authors of the study. NASA funded the research.

"The sun houses more than 99 percent of the material currently in our solar system, so it's a good idea to get to know it better," Burnett said.

A second paper in Science by different researchers details differences between the sun and planets with regard to the element nitrogen. Like oxygen, nitrogen has one isotope (N-14) that makes up nearly 100 percent of the nitrogen atoms in the solar system, but there is also a tiny amount of N-15.

Researchers studying the same Genesis samples found that compared to Earth's atmosphere, nitrogen in the sun and Jupiter had slightly more N-14 -- but 40 percent less N-15. The sun and Jupiter appear to have the same nitrogen composition, but as with oxygen, the nitrogen composition of Earth and the rest of the inner solar system is very different.

"These findings show that all solar system objects, including the terrestrial planets, meteorites and comets, are anomalous compared to the initial composition of the nebula from which the solar system formed," said Bernard Marty, a Genesis co-investigator from the Centre de Recherches Pétrographiques et Géochimiques in France and lead author of the second Science study. "Understanding the cause of such a heterogeneity will impact our view on the formation of the solar system."

The Jet Propulsion Laboratory in Pasadena, Calif., managed the Genesis mission for NASA's Science Mission Directorate in Washington, D.C. Genesis was part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver developed and operated the spacecraft. Analysis at the Centre de Recherches Pétrographiques et Géochimiques was supported by the Centre National d'Etudes Spatiales and the Centre National de la Recherche Scientifique, both in Paris.

For more information on the Genesis mission, visit http://genesismission.jpl.nasa.gov.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Los Angeles. The original article was written by Stuart Wolpert.

Journal References:

K. D. McKeegan, A. P. A. Kallio, V. S. Heber, G. Jarzebinski, P. H. Mao, C. D. Coath, T. Kunihiro, R. C. Wiens, J. E. Nordholt, R. W. Moses, D. B. Reisenfeld, A. J. G. Jurewicz, D. S. Burnett. The Oxygen Isotopic Composition of the Sun Inferred from Captured Solar Wind. Science, 2011; 332 (6037): 1528 DOI: 10.1126/science.1204636B. Marty, M. Chaussidon, R. C. Wiens, A. J. G. Jurewicz, D. S. Burnett. A 15N-Poor Isotopic Composition for the Solar System As Shown by Genesis Solar Wind Samples. Science, 2011; 332 (6037): 1533 DOI: 10.1126/science.1204656

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Increasing the number of family physicians reduces hospital readmissions, study suggests

ScienceDaily (May 3, 2011) — Boston- Researchers from Boston University School of Medicine and Boston Medical Center have found that by adding one family physician per 1,000, or 100 per 100,000, could reduce hospital readmission costs by $579 million per year, or 83 percent of the Patient Protection and Affordable Care Act (ACA) target.

These findings currently appear on the website of the "Robert Graham Center," a primary care think tank.

Growth of family physicians has fallen over the last decade due to payment disparities and other strong incentives for subspecialization, and lack of accountability of teaching hospitals for producing the physicians the country needs.

The Patient Protection and Affordable Care Act (ACA) seeks to improve healthcare quality and reduce costs. One provision targets a decrease in hospital readmissions to save $710 million annually. It is believed that timely management of fragile patients in primary care after discharge may reduce readmission.

The researchers used data from the Hospital Compare database, which included readmission rates for pneumonia, heart attack and heart failure, for 4,459 hospitals as well as the Area Source File that contains data for physicians per population at the county level. Combined, readmissions for pneumonia, heart attack and heart failure in 2005 accounted for 15.7 percent of all readmissions and numbered 74,419, 20,866 and 90,273, respectively; corresponding Medicare expenditures were $533, $136 and $590 million, respectively.

"Using these data, we found that 30-day readmission rates for all three diagnoses decrease as the number of family physicians increases," said senior author Brian Jack, MD, an associate professor and vice chair for Academic Affairs in the Department of Family Medicine at Boston University School of Medicine/Boston Medical Center. "Conversely, increased numbers of physicians in all other major specialties, including general internal medicine, is associated with increased risk of readmission," he added.

According to Jack this work demonstrates tremendous cost savings from an adequate family physician work force.

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