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Changes in Comet Rotation May Be Predicted With Greater Accuracy

September 6, 2013 Leave a comment

Credit: NASA / JPL-Calthech / UMD

Credit: NASA / JPL-Calthech / UMD

Planetary Science Institute researchers have discovered a way to predict the changes in the rotational states of comets that could help scientists learn more about the approaching Comet C/2012 S1 (ISON), which will pass by the Sun on Thanksgiving Day and has attracted worldwide interest because it may become sufficiently bright to be seen by the naked eye.

PSI Senior Scientists Nalin H. Samarasinha and Beatrice E.A. Mueller have determined such changes are a function of a comet’s size, period and solar energy it receives, but surprisingly not a function of the fraction of a comet’s surface that is active according to a paper published in the Astrophysical Journal Letters.

“You get more change if there is more solar energy and less change if it is spinning more rapidly to begin with or if it is a larger comet. Larger, rapidly rotating comets are not going to change their spin status very much,” Samarasinha said. “We expected that the fraction of the surface of the comet that is active would also be a controlling factor, but that proved not to be the case.”

Full Story: http://www.psi.edu/news/cometrotation.html

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IBEX Spacecraft Measures Changes In The Direction Of Interstellar Winds Buffeting Our Solar System

September 6, 2013 Leave a comment

Data from NASA’s Interstellar Boundary Explorer (IBEX) spacecraft reveal that neutral interstellar atoms are flowing into the solar system from a different direction than previously observed.

Interstellar atoms flow past the Earth as the solar system passes through the surrounding interstellar cloud at 23 kilometers per second (50,000 miles per hour). The latest IBEX measurements of the interstellar wind direction were discovered to differ from those made by the Ulysses spacecraft in the 1990s. That difference led the IBEX team to compare the IBEX measurements to data gathered by 11 spacecraft between 1972 and 2011. Statistical testing of the Earth-orbiting and interplanetary spacecraft data showed that, over the past 40 years, the longitude of the interstellar helium wind has changed by 6.8 ± 2.4 degrees.

“We concluded it’s highly likely that the direction of the interstellar wind has changed over the past 40 years. It’s also highly unlikely that the direction of the interstellar helium wind has remained constant,” says Dr. Priscilla Frisch, lead author of the study and a senior scientist in the Department of Astronomy and Astrophysics at the University of Chicago.

Full Story: http://www.swri.org/9what/releases/2013/ibex-wind.htm#.UilbyiywUV0

A&A Press Release – No Evidence Of Planetary Influence On Solar Activity

September 6, 2013 Leave a comment

Image Credit: Swedish Solar Telescope at the Roque de los Muchachos Observatory

Image Credit: Swedish Solar Telescope at the Roque de los Muchachos Observatory

In 2012, Astronomy & Astrophysics published a statistical study of the isotopic records of solar activity, in which Abreu et al. claimed that there is evidence of planetary influence on solar activity. A&A is publishing a new analysis of these isotopic data by Cameron and Schüssler. It corrects technical errors in the statistical tests performed by Abreu et al. They find no evidence of any planetary effect on solar activity.

The Sun is a magnetically active star. Its activity manifests itself as dark sunspots and bright faculae on its visible surface, as well as violent mass ejections and the acceleration of high-energy particles resulting from the release of magnetic energy in its outer atmosphere. The frequency with which these phenomena occur varies in a somewhat irregular activity cycle of about 11 years, during which the global magnetic field of the Sun reverses. The solar magnetic field and the activity cycle originate in a self-excited dynamo mechanism based upon convective flows and rotation in the outer third of the solar radius.

Systematic observations of sunspots since the beginning of the 17th century indicate that solar activity also varies on longer timescales, including periods of very low activity, such as the so-called Maunder minimum between 1640 and 1700.

Full Story: http://www.aanda.org/index.php?option=com_content&task=view&id=966&Itemid=277

Coldest Brown Dwarfs Blur Lines Between Stars And Planets

September 6, 2013 Leave a comment

Astronomers are constantly on the hunt for ever-colder star-like bodies, and two years ago a new class of objects was discovered by researchers using NASA’s WISE space telescope. However, until now no one has known exactly how cool their surfaces really are – some evidence suggested they could be room temperature.

A new study shows that while these brown dwarfs, sometimes called failed stars, are indeed the coldest known free-floating celestial bodies, they are warmer than previously thought with temperatures about 250-350 degrees Fahrenheit.

To reach such low surface temperatures after cooling for billions of years means that these objects can only have about 5 to 20 times the mass of Jupiter. Unlike the Sun, these objects’ only source of energy is from their gravitational contraction, which depends directly on their mass.

“If one of these objects was found orbiting a star, there is a good chance that it would be called a planet,” says Trent Dupuy, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics. But because they probably formed on their own and not in a proto-planetary disk, astronomers still call these objects brown dwarfs even if they are “planetary mass.”

Full Story: http://www.cfa.harvard.edu/news/2013/pr201323.html

Powerful Jets Blowing Material Out Of Galaxy

September 6, 2013 Leave a comment

Astronomers using a worldwide network of radio telescopes have found strong evidence that a powerful jet of material propelled to nearly light speed by a galaxy’s central black hole is blowing massive amounts of gas out of the galaxy. This process, they said, is limiting the growth of the black hole and the rate of star formation in the galaxy, and thus is a key to understanding how galaxies develop.

Astronomers have theorized that many galaxies should be more massive and have more stars than is actually the case. Scientists proposed two major mechanisms that would slow or halt the process of mass growth and star formation — violent stellar winds from bursts of star formation and pushback from the jets powered by the galaxy’s central, supermassive black hole.

“With the finely-detailed images provided by an intercontinental combination of radio telescopes, we have been able to see massive clumps of cold gas being pushed away from the galaxy’s center by the black-hole-powered jets,” said Raffaella Morganti, of the Netherlands Institute for Radio Astronomy and the University of Groningen.

Full Story: http://www.nrao.edu/pr/2013/jetblowout/