Rare Radio Supernova In Nearby Galaxy Is Nearest Supernova In Five Years

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ScienceDaily (June 11, 2009) — The chance discovery last month of a rare radio supernova -- an exploding star seen only at radio wavelengths and undetected by optical or X-ray telescopes -- underscores the promise of new, more sensitive radio surveys to find supernovas hidden by gas and dust.

"This supernova is the nearest supernova in five years, yet is completely obscured in optical, ultraviolet and X-rays due to the dense medium of the galaxy," said Geoffrey Bower, assistant professor of astronomy at the University of California, Berkeley, and coauthor of a paper describing the discovery in the June issue of the journal Astronomy & Astrophysics. "This just popped out; in the future, we want to go from discovery of radio supernovas by accident to specifically looking for them."
Sky surveys like the one just launched by the Allen Telescope Array, which will look for bright but short-lived radio bursts from supernovas, will provide better estimates of the rate of star formation in nearby galaxies, Bower said. Radio emissions from supernovas also can help astronomers understand how stars explode and what happens before their cores collapse, since radio emissions are caused when debris from the explosion collides with the stellar wind previously shed by the stars.
Bower's colleagues are Andreas Bunthaler, Karl M. Menten and Christian Henkel of the Max Planck Institute for Radioastronomy in Bonn, Germany; Mark J. Reid of Harvard University's Center for Astrophysics; and Heino Falcke of the University of Nijmegen in the Netherlands.
The radio supernova was discovered on April 8 in M82, a small irregular galaxy located nearly 12 million light years from Earth in the M81 galaxy group, by the Very Large Array, a New Mexico facility operated by the National Radio Astronomy Observatory (NRAO). It was subsequently confirmed by NRAO's Very Long Baseline Array (VLBA), a 10-telescope array whose baseline stretches from Hawaii to the Virgin Islands, providing the sharpest vision of any telescope on Earth.
The Allen Telescope Array, comprising 42 of a planned 350 radio dishes and supported by UC Berkeley and the SETI Institute of Mountain View, Calif., last week began a major survey of the radio sky that should turn up many more such radio supernovas, Bower said. While the VLA and VLBA have very narrow fields of view unsuited to all-sky surveys, the ATA's wide-angle view is ideal for scanning the full sky once a day, which is necessary to find sources that brighten and dim over several days.
"The ATA can detect objects at least 10 times fainter than this radio supernova, which pushes our survey an order of magnitude deeper than other radio surveys with more attention to transient and variable sources. Radio supernovas are a really strong aspect of that survey," he said. "This ( new radio supernova) is the kind of discovery that we would like to make with the Allen Telescope Array."
The ATA will compile an updated catalog of radio sources much as the Sloan Digital Sky Survey updated the older Palomar Observatory Sky Survey of visible and infrared objects. At the same time, it will look for radio signals indicative of intelligent life around other stars.
Not all supernovas produce radio emissions, Bower said. If the star has not sloughed off much of its envelope before collapsing inward to form a neutron star or black hole – a classic Type II supernova – then few radio emissions are produced from gas collisions.
On the other hand, supernovas in very active star-forming regions, like the center of M82, should produce copious radio emissions because of the density of gas and dust in the interstellar medium. That same gas and dust blocks optical, ultraviolet and X-rays, however, making radio surveys one of the few options to find and observe such supernovas.
Bower and his colleagues were studying the motion of M82 with the VLBA, which links the VLA and nine other radio telescopes into a very high resolution instrument, when they noticed a very bright radio source – five times brighter than anything else in the galaxy – in the VLA data. The team looked at earlier observations and found the same source, but almost twice as bright, in data taken May 3, 2008. Data from March 24, 2008, showed an even brighter source – 10 times brighter than in April 2009 – while Oct. 29, 2007, data showed no bright radio source.
Extrapolating backward in time, the research team estimates that the star exploded sometime in January 2008, apparently near the very center of the galaxy. The team rejected alternative explanations for the dimming radio source, such as a flare created by a star falling into a supermassive black hole.
The newly discovered supernova is thus the brightest in radio wavelengths in the past 20 years, Bower said, and is one of only a few dozen radio supernovas observed to date.
The team also looked at the complete data from the VLBA and detected a ring structure indicative of a shock wave plunging through the interstellar medium, bolstering its conclusion that it is a supernova. The ring is about 2,000 astronomical units across, consistent with a year-old supernova. (An astronomical unit 93 million miles, the average distance between Earth and the sun.)
The research was funded through National Science Foundation support of NRAO.
Adapted from materials provided by University of California - Berkeley. Original article written by Robert Sanders.

Baby Stars Finally Found In Jumbled Galactic Center

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ScienceDaily (June 12, 2009) — Astronomers have at last uncovered newborn stars at the frenzied center of our Milky Way galaxy. The discovery was made using the infrared vision of NASA's Spitzer Space Telescope.

The heart of our spiral galaxy is cluttered with stars, dust and gas, and at its very center, a supermassive black hole. Conditions there are harsh, with fierce stellar winds, powerful shock waves and other factors that make it difficult for stars to form. Astronomers have known that stars can form in this chaotic place, but they're baffled as to how this occurs. Confounding the problem is all the dust standing between us and the center of our galaxy. Until now, nobody had been able to definitively locate any baby stars.
"These stars are like needles in a haystack," said Solange Ramirez, the principal investigator of the research program at NASA's Exoplanet Science Institute at the California Institute of Technology, Pasadena. "There's no way to find them using optical light, because dust gets in the way. We needed Spitzer's infrared instruments to cut through the dust and narrow in on the objects."
The team plans to look for additional baby stars in the future, and ultimately to piece together what types of conditions allow stars to form in such an inhospitable environment as our galaxy's core.
"By studying individual stars in the galactic center, we can better understand how stars are formed in different interstellar environments," said Deokkeun An of the Infrared Processing and Analysis Center at Caltech, lead author of a paper submitted for publication in the Astrophysical Journal. "The Milky Way galaxy is just one of more than hundreds of billions of galaxies in the visible universe. However, our galaxy is so special because we can take a closer look at its individual stellar components." An started working on this program while a graduate student at Ohio State University, Columbus, under the leadership of Ohio State astronomer Kris Sellgren, the co-investigator on the project.
The core of the Milky Way is a mysterious place about 600 light-years across (light would take 600 years to travel from one end to the other). While this is just a fraction of the size of the entire Milky Way, which is about 100,000 light-years across, the core is stuffed with 10 percent of all the gas in the galaxy -- and loads and loads of stars.
Before now, there were only a few clues that stars can form in the galaxy's core. Astronomers had found clusters of massive adolescent stars, in addition to clouds of charged gas -- a sign that new stars are beginning to ignite and ionize surrounding gas. Past attempts had been unsuccessful in finding newborn stars, or as astronomers call them, young stellar objects.
Ramirez and colleagues began their search by scanning large Spitzer mosaics of our galactic center. They narrowed in on more than 100 candidates, but needed more detailed data to confirm the stars' identities. Young stellar objects, when viewed from far away, can look a lot like much older stars. Both types of stars are very dusty, and the dust lying between us and them obscures the view even further.
To sort through the confusion, the astronomers looked at their candidate stars with Spitzer's spectrograph – an instrument that breaks light apart to reveal its rainbow-like array of infrared colors. Molecules around stars leave imprints in their light, which the spectrograph can detect.
The results revealed three stars with clear signs of youth, for example, certain warm, dense gases. These youthful features are found in other places in the galaxy where stars are being formed.
"It is amazing to me that we have found these stars," said Ramirez. "The galactic center is a very interesting place. It has young stars, old stars, black holes, everything. We started mining a catalog of about 1 million sources and managed to find three young stars -- stars that will help reveal the secrets at the core of the Milky Way."
The young stellar objects are all less than about 1 million years old. They are embedded in cocoons of gas and dust, which will eventually flatten to disks that, according to theory, later lump together to form planets.
Other collaborators include Richard Arendt of NASA's Goddard Space Flight Center, Greenbelt, Md.; A. C. Adwin Boogert of NASA's Herschel Science Center, Caltech in Pasadena; Mathias Schultheis of the Besancon Observatory in France; Susan Stolovy of NASA's Spitzer Science Center, Caltech in Pasadena; Angela Cotera of SETI Institute, Mountain View, Calif.; and Thomas Robitaille and Howard Smith of Harvard Smithsonian Center for Astrophysics, Cambridge, Mass.
Adapted from materials provided by NASA/Jet Propulsion Laboratory.

Planet-forming Disk Discovered Orbiting Twin Suns

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ScienceDaily (June 11, 2009) — Astronomers have announced that a sequence of images collected with the Smithsonian's Submillimeter Array (SMA) clearly reveals the presence of a rotating molecular disk orbiting the young binary star system V4046 Sagittarii. The SMA images provide an unusually vivid snapshot of the process of formation of giant planets, comets, and Pluto-like bodies. The results also confirm that such objects may just as easily form around double stars as around single stars like our Sun.

These findings are being presented by UCLA graduate student David Rodriguez in a press conference at the American Astronomical Society meeting in Pasadena, Calif.
"It's a case of seeing is believing," says Joel Kastner of the Rochester (NY) Institute of Technology, the lead scientist on the study. "We had the first evidence for this rotating disk in radio telescope observations of V4046 Sagittarii that we made last summer. But at that point, all we had were molecular spectra, and there are different ways to interpret the spectra. Once we saw the image data from the SMA, there was no doubt that we have a rotating disk here."
Co-author David Wilner of the Harvard-Smithsonian Center for Astrophysics (CfA) adds, "This is strong evidence that planets can form around binary stars, which expands the number of places we can look for extrasolar planets. Somewhere in our galaxy, an alien world may enjoy double sunrises and double sunsets."
Wilner is one of the world's experts on radiointerferometry, the technique used in this study to form images with the SMA's multiple radio antennas. The other contributor to the SMA study of V4046 Sagittarii led by RIT's Kastner and UCLA's Rodriguez is Ben Zuckerman of UCLA.
According to Rodriguez, the images clearly demonstrate that the molecular disk orbiting the V4046 Sagittarii binary system extends from within the approximate radius of Neptune's orbit out to about 10 times that orbit. This region corresponds to the zone where the solar system's giant planets, as well as its Pluto-like Kuiper Belt objects, may have formed.
"We believe that V4046 Sagittarii provides one of the clearest examples yet discovered of a Keplerian, planet-forming disk orbiting a young star system," Wilner says. "This particular system is made that much more remarkable by the fact that it consists of a pair of solar-mass stars that are approximately 12 million years old and are separated by a mere 5 solar diameters."
"This could be the oldest known orbiting protoplanetary molecular disk. It shows that, at least for some stars, formation of Jovian-mass planets may continue well after a few million years, which astronomers have deduced is characteristic of the formation time for most such planets," Zuckerman says.
Findings of this study build on previous work published in the December 2008 issue of Astronomy and Astrophysics in which Kastner and his team first suggested that the case of V4046 Sagittarii illustrates well how planets may form easily around certain types of binary stars.
"We thought the molecular gas around these two stars almost literally represented 'smoking gun' evidence of recent or possibly ongoing 'giant' Jupiter-like planet formation around the binary star system," Kastner says. "The SMA images showing an orbiting disk certainly support that idea."
The evidence for a molecular disk orbiting these twin young suns in the constellation Sagittarius suggested to the scientists that many such binary systems should also host as-yet-undetected planets.
"The most successful technique used so far for the discovery of extrasolar planets - that of measurement of precision radial velocities - is exceedingly difficult for close binary stars such as V4046 Sagittarii. So these radio observations are probing a new region of discovery space for extrasolar planets," says Rodriguez.
"At a distance of only 240 light-years from the solar system, the V4046 Sagittarii binary is at least two times closer to Earth than almost all known planet-forming star systems, which gives us a good shot at imaging any planets that have already formed and are now orbiting the stars," he continues.
Kastner and collaborators had previously used the 30-meter radiotelescope operated by the Institut de Radio Astronomie Millimetrique (IRAM) to study radio molecular spectra emitted from the vicinity of the twin stars. The scientists used these data to identify the raw materials for planet formation around V4046 Sagittarii - carbon monoxide and hydrogen cyanide - in the noxious circumstellar gas cloud.
"In this case the stars are so close together, and the profile of the gas - in terms of the types of molecules that are there - is so much like the types of gaseous disks that we see around single stars, that we now have a direct link between planets forming around single stars and planets forming around double stars," Kastner says.
Adapted from materials provided by Harvard-Smithsonian Center for Astrophysics.

Search For ET Just Got Easier: Effective Way To Search Atmospheres Of Planets For Signs Of Life

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ScienceDaily (June 12, 2009) — Astronomers using the Science and Technology Facilities Council's (STFC) William Herschel Telescope (WHT) on La Palma have confirmed an effective way to search the atmospheres of planets for signs of life, vastly improving our chances of finding alien life outside our solar system.

The team from the Instituto de Astrofisica de Canarias (IAC) used the WHT and the Nordic Optical Telescope (NOT) to gather information about the chemical composition of the Earth's atmosphere from sunlight that has passed through it. The research is published June11 in Nature.
When a planet passes in front of its parent star, part of the starlight passes through the planet's atmosphere and contains information about the constituents of the atmosphere, providing vital information about the planet itself. This is called a transmission spectrum and even though astronomers can't use exactly the same method to look at the Earth's atmosphere, they were able to gain a spectrum of our planet by observing light reflected from the Moon towards the Earth during a lunar eclipse. This is the first time the transmission spectrum of the Earth has been measured.
The spectrum not only contained signs of life but these signs were unmistakably strong. It also contained unexpected molecular bands and the signature of the earth ionosphere.
Enric Palle, lead author of the paper, from the Instituto de Astrofisica de Canarias, said, "Now we know what the transmission spectrum of a inhabited planet looks like, we have a much better idea of how to find and recognize Earth like planets outside our solar system where life may be thriving. The information in this spectrum shows us that this is a very effective way to gather information about the biological processes that may be taking place on a planet."
Pilar Montañes-Rodriguez, from the Instituto de Astrofisica de Canarias, added, "Many discoveries of Earth-size planets are expected in the next decades and some will orbit in the habitable zone of their parent stars. Obtaining their atmospheric properties will be highly challenging; the greatest reward will happen when one of those planets shows a spectrum like that of our Earth."
The past two decades have witnessed the discovery of hundreds of exoplanets (planets beyond our solar system). Ambitious missions, ground and space based, are already being planned for the next decades, and the discovery of Earth-like planets is only a matter of time. Once these planets are found, techniques like transmission spectra will be invaluable to their further exploration.
Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council (STFC), said, "This new transmission spectrum is good news for future upcoming ground and space based missions dedicated to the search for life in the Universe. The UK is committed to cutting edge science and UK owned facilities like the WHT are helping to make many groundbreaking discoveries and expand our knowledge of the Universe. Not only do these results improve our knowledge of our own planet but we now have an effective way to search for life on the increasing number of exoplanets being found by astronomers."
The results on the WHT were achieved using LIRIS, a very efficient near-IR imager/spectrograph built and developed at IAC. LIRIS became a common-user instrument at the WHT as a result of the agreement signed by IAC to become a partner at ING in 2003.
Journal reference:
Enric Pallé, María Rosa Zapatero Osorio, Rafael Barrena, Pilar Montañés-Rodríguez & Eduardo L. Martín. Earth's transmission spectrum from lunar eclipse observations. Nature, 2009; 459 (7248): 814 DOI: 10.1038/nature08050
Adapted from materials provided by Science and Technology Facilities Council.

Heaviest Stellar Black Hole Discovered In Nearby Galaxy

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http://www.sciencedaily.com/releases/2007/10/071017145225.htm

Science Daily — Astronomers have located an exceptionally massive black hole in orbit around a huge companion star. This result has intriguing implications for the evolution and ultimate fate of massive stars.

The black hole is part of a binary system in M33, a nearby galaxy about 3 million light years from Earth. By combining data from NASA's Chandra X-ray Observatory and the Gemini telescope on Mauna Kea, Hawaii, the mass of the black hole, known as M33 X-7, was determined to be 15.7 times that of the Sun. This makes M33 X-7 the most massive stellar black hole known. A stellar black hole is formed from the collapse of the core of a massive star at the end of its life.
"This discovery raises all sorts of questions about how such a big black hole could have been formed," said Jerome Orosz of San Diego State University, lead author of the paper appearing in the October 18th issue of the journal Nature.
M33 X-7 orbits a companion star that eclipses the black hole every three and a half days. The companion star also has an unusually large mass, 70 times that of the Sun. This makes it the most massive companion star in a binary system containing a black hole.
"This is a huge star that is partnered with a huge black hole," said coauthor Jeffrey McClintock of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "Eventually, the companion will also go supernova and then we'll have a pair of black holes."
The properties of the M33 X-7 binary system - a massive black hole in a close orbit around a massive companion star - are difficult to explain using conventional models for the evolution of massive stars. The parent star for the black hole must have had a mass greater than the existing companion in order to have formed a black hole before the companion star.
Such a massive star would have had a radius larger than the present separation between the stars, so the stars must have been brought closer while sharing a common outer atmosphere. This process typically results in a large amount of mass being lost from the system, so much that the parent star should not have been able to form a 15.7 solar-mass black hole.
The black hole's progenitor must have shed gas at a rate about 10 times less than predicted by models before it exploded. If even more massive stars also lose very little material, it could explain the incredibly luminous supernova seen recently as SN 2006gy. The progenitor for SN 2006gy is thought to have been about 150 times the mass of the Sun when it exploded.
"Massive stars can be much less extravagant than people think by hanging onto a lot more of their mass toward the end of their lives," said Orosz. "This can have a big effect on the black holes that these stellar time-bombs make."
Coauthor Wolfgang Pietsch was also the lead author of an article in the Astrophysical Journal that used Chandra observations to report that M33 X-7 is the first black hole in a binary system observed to undergo eclipses. The eclipsing nature enables unusually accurate estimates for the mass of the black hole and its companion.
"Because it's eclipsing and because it has such extreme properties, this black hole is an incredible test-bed for studying astrophysics," said Pietsch.
The length of the eclipse seen by Chandra gives information about the size of the companion. The scale of the companion's motion, as inferred from the Gemini observations, gives information about the mass of the black hole and its companion. Other observed properties of the binary were used to constrain the mass estimates.
NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. Gemini is an international partnership managed by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation.
Note: This story has been adapted from material provided by Chandra X-ray Center.

Fausto Intilla

www.oloscience.com

New Isotope Molecule May Add To Venus' Greenhouse Effect

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http://www.sciencedaily.com/releases/2007/10/071010130150.htm

Science Daily — Planetary scientists on both sides of the Atlantic have tracked down a rare molecule in the atmospheres of both Mars and Venus. The molecule, an exotic form of carbon dioxide, could affect the way the greenhouse mechanism works on Venus.

The discovery is being announced at the annual meeting of the American Astronomical Society's Division of Planetary Sciences in Orlando, Florida. Its presence could affect the way the greenhouse mechanism works on Venus. The mystery began back in April 2006, soon after ESA's Venus Express arrived at the second planet in the Solar System.
A European team including members from France, Belgium and Russia lead by Jean-Loup Bertaux, Service d'Aeronomie du CNRS, France and Ann-Carine Vandaele, Institut d'Aeronomie Spatiale de Belgique, were using their Infrared Atmospheric Spectrometer (SOIR) instrument to measure solar occultations.
To do this, the instrument watches the Sun set behind Venus, allowing the scientists to study the way specific wavelengths of light are absorbed by the planet's atmosphere. These wavelengths and the level of absorption then give away the identity and amount of gases in the atmosphere.
The team saw an unidentified signature at 3.3 micrometres in the mid-infrared region of the spectrum. "It was conspicuous and systematic, increasing with depth in the atmosphere during the occultation, so we knew it was real," says Bertaux.
The team kept their discovery confidential as they attempted to identify the molecule responsible. They thought at first that it must be an organic molecule. These molecules contain carbon and hydrogen. However, none of the known organic molecules fitted well with the observations.
Then, in December 2006, Mike Mumma of NASA's Goddard Space Flight Center, Maryland, enquired whether the SOIR team was seeing anything special on Venus at 3.3 microns. He had discovered an unidentified spectral signature at that wavelength using telescopes on Hawaii pointing at Mars. The two teams compared the absorption signatures: they were identical.
This was a big clue. Both the atmospheres of Mars and Venus are composed of 95% carbon dioxide, although Venus's atmosphere is much thicker than the one at Mars. The American team suggested that the signature could be coming from an isotope of carbon dioxide, where one oxygen atom is 'normal', with eight protons and eight neutrons, while the other has eight protons and ten neutrons. Such an isotope makes up about 1% of carbon dioxide on Earth; the rest contains two normal oxygen atoms.
However, no one had previously seen the molecule absorb at 3.3 micrometres. An investigation by three independent groups, one led by Mumma in America; Sergei Tashkun and Valery Perevalov at Tomsk State University, Russia; and Richard Dahoo at Service d'Aéronomie du CNRS, France, all came to the same conclusion. The signature could be caused by a rare transition only possible in the isotope.
The different weights of the oxygen atoms allow the molecule to alter its vibration in two ways simultaneously, whereas normal molecules can only change one state at a time.
This rare transition allows it to absorb even more energy and so contribute even more to the greenhouse effect on Venus. On Earth, however, there is 250 000 times less carbon dioxide so its additional contribution to our greenhouse effect will be small.
Note: This story has been adapted from material provided by European Space Agency.

Fausto Intilla

www.oloscience.com

Earth-like Planet Forming In Nearby Star System, Astronomers Believe

Source:

http://www.sciencedaily.com/releases/2007/10/071003130744.htm

Science Daily — An Earth-like planet is likely forming 424 light-years away in a star system called HD 113766, say astronomers using NASA's Spitzer Space Telescope.

Scientists have discovered a huge belt of warm dust – enough to build a Mars-size planet or larger – swirling around a distant star that is just slightly more massive than our sun.
The dust belt, which they suspect is clumping together into planets, is located in the middle of the system's terrestrial habitable zone. This is the region around a star where liquid water could exist on any rocky planets that might form. Earth is located in the middle of our sun's terrestrial habitable zone.
At approximately 10 million years old, the star is also at just the right age for forming rocky planets.
"The timing for this system to be building an Earth is very good," says Dr. Carey Lisse, of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. "If the system was too young, its planet-forming disk would be full of gas, and it would be making gas-giant planets like Jupiter instead. If the system was too old, then dust aggregation or clumping would have already occurred and all the system's rocky planets would have already formed."
According to Lisse, the conditions for forming an Earth-like planet are more than just being in the right place at the right time and around the right star – it's also about the right mix of dusty materials.
Using Spitzer's infrared spectrometer instrument, he determined that the material in HD 113766 is more processed than the snowball-like stuff that makes up infant solar systems and comets, which are considered cosmic "refrigerators" because they contain pristine ingredients from the early solar system. However, it is also not as processed as the stuff found in mature planets and the largest asteroids. This means the dust belt must be in a transitional phase, when rocky planets are just beginning to form.
How do scientists know the material is more processed than that of comets? From missions like NASA's Deep Impact – in which an 820-pound impactor spacecraft collided with comet Tempel 1 – scientists know that early star systems contain a lot of fragile organic material. That material includes polycyclic aromatic hydrocarbons (carbon-based molecules found on charred barbeque grills and automobile exhaust on Earth), water ice, and carbonates (chalk). Lisse says that HD 113766 does not contain any water ice, carbonates or fragile organic materials.
From meteorite studies on Earth, scientists also have a good idea of what makes up asteroids – the more processed rocky leftovers of planet formation. These studies tell us that metals began separating from rocks in Earth's early days, when the planet's body was completely molten. During this time, almost all the heavy metals fell to Earth's center in a process called "differentiation." Lisse says that, unlike planets and asteroids, the metals in HD 113766 have not totally separated from the rocky material, suggesting that rocky planets have not yet formed.
"The material mix in this belt is most reminiscent of the stuff found in lava flows on Earth. I thought of Mauna Kea material when I first saw the dust composition in this system – it contains raw rock and is abundant in iron sulfides, which are similar to fool's gold," says Lisse, referring to a well-known Hawaiian volcano.
"It is fantastic to think we are able to detect the process of terrestrial planet formation. Stay tuned — I expect lots more fireworks as the planet in HD113766 grows," he adds.
Lisse's article, Circumstellar Dust Created by Terrestrial Planet Formation in HD 113766, will be published in an upcoming issue of Astrophysical Journal. He will also present his findings at the upcoming meeting of the American Astronomical Society Division for Planetary Sciences in Orlando, Fla. Lisse's research was funded through a Johns Hopkins Applied Physics Laboratory Stuart S. Janney Fellowship and a Spitzer Space Telescope guest observer grant.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.
The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL.
Note: This story has been adapted from material provided by Johns Hopkins University.

Fausto Intilla

www.oloscience.com

Disc Of Silicates Found In Heart Of Magnificent Ant Nebula

Source:

http://www.sciencedaily.com/releases/2007/09/070927113205.htm

Science Daily — Using ESO's Very Large Telescope Interferometer and its unique ability to see small details, astronomers have uncovered a flat, nearly edge-on disc of silicates in the heart of the magnificent Ant Nebula. The disc seems, however, too 'skinny' to explain how the nebula got its intriguing ant-like shape.
The Ant Nebula is one of the most striking planetary nebulae known. Planetary nebulae - whose name arises because most are spherical and looked like planets when they were first discovered through older, less powerful telescopes - are glowing structures of gas cast off by solar-like stars at the ends of their lives. The morphology of the Ant Nebula - a bright core, three nested pairs of bipolar lobes and a ring-like outflow - is so unique that it was nicknamed the 'Chamber of Horrors' of planetary nebulae in the late 1950s.
But how can a spherical star produce such complex structures? The answer, many astronomers think, requires understanding of the discs surrounding the central star. By their nature, these discs bear witness to the phenomena that lead to the asymmetrical structures of planetary nebulae.
"The challenge is to actually detect these discs," explains team leader Olivier Chesneau, from the Observatoire de la Côte d'Azur, France. "Most astronomical instruments do not have a sharp enough view to find, let alone study them. The Very Large Telescope Interferometer however, with its exceptionally high spatial resolution, is a powerful disc-hunter."
The disc of the Ant Nebula, which cannot be detected with a single 8.2-m VLT Unit Telescope, was uncovered in the interferometric mode where two 8.2-m Unit Telescopes were used to combine light, through the MID-infrared Interferometric instrument (MIDI). The observations reveal a flat, nearly edge-on disc whose major axis is perpendicular to the axis of the bipolar lobes.
The disc extends from about 9 times the mean distance between the Earth and the Sun (9 Astronomical Units or 9 AU) to more than 500 AU. At the distance of the Ant Nebula, this corresponds to having detected structures that subtend an angle of only 6 milli-arcseconds. This is similar to distinguishing a two-storey building on the Moon.
The dust mass stored in the disc appears to be only one hundred thousandth the mass of the Sun and is a hundred times smaller than the mass found in the bipolar lobes.
"We must therefore conclude that the disc is too light to have a significant impact on the outflowing material and cannot explain the shape of the Ant Nebula", says Chesneau. "Instead, it looks more like this disc is some remnant of the material expelled by the star."
The observations also provide unquestionable evidence that the disc is primarily composed of amorphous silicate. "This," says Chesneau, "most likely indicates that the disc is young, perhaps as young as the planetary nebula itself."
The astronomers favour the possibility that the large quantity of material in the lobes was propelled by several large-scale events, triggered with the help of a cool stellar companion. The solution of the mystery thus resides in the core of the system, and requires better characterisation of the hot central star and its putative companion, currently hidden from our view by the dusty disc.
The results are presented in a Letter to the Editor published by the research journal Astronomy and Astrophysics ("A silicate disk in the heart of the Ant" by O. Chesneau et al.).
The team is composed of O. Chesneau and A. Spang (Observatoire de la Côte d'Azur, France), F. Lykou, E. Lagadec, and A.A. Zijlstra (University of Manchester, UK), B. Balick (University of Washington, Seattle, USA), M. Matsuura (NAOJ, Tokyo, Japan), N. Smith (University of California, USA), and S. Wolf (Max-Planck-Institute for Astronomy, Heidelberg, Germany).
Note: This story has been adapted from material provided by ESO.

Fausto Intilla
www.oloscience.com

Into The Chrysalis: VLT Interferometer Detects Disc Around Aged Star

Source:

http://www.sciencedaily.com/releases/2007/09/070927113202.htm

Science Daily — A team of European astronomers has used ESO's Very Large Telescope Interferometer and its razor-sharp eyes to discover a reservoir of dust trapped in a disc that surrounds an elderly star. The discovery provides additional clues about the shaping of planetary nebulae.

In the last phases of their life, stars such as our Sun evolve from a red giant which would engulf the orbit of Mars to a white dwarf, an object that is barely larger than the Earth. The transition is accomplished by the shedding of a huge envelope of gas and dust that sparkles in many colours, producing a most spectacular object: a planetary nebula. The celestial chrysalis becomes a cosmic butterfly.
This metamorphosis, rapid in terms of the star's lifetime, is rather complex and poorly understood. In particular, astronomers want to understand how a spherical star can produce a great variety of planetary nebulae, some with very asymmetrical shapes.
A team of scientists therefore embarked upon the study of a star which is presently on its way to becoming a cosmic butterfly. The star, V390 Velorum, is 5000 times as bright as our Sun and is located 2,600 light-years away. It is also known to have a companion that accomplishes its ballet in 500 days.
Astronomers postulate that elderly stars with companions possess a reservoir of dust that is thought to play a lead role in the final chapters of their lives. The shape and structure of these reservoirs remain, however, largely unknown.
To scrutinize the object with great precision, the astronomers linked observations taken with ESO's powerful interferometric instruments, AMBER and MIDI, at the Very Large Telescope Interferometer. In particular, they combined, using AMBER, the near-infrared light of three of VLT's 8.2-m Unit Telescopes. "Only this triple combination of powerful telescopes allows us to pinpoint the position and the shape of the dusty reservoir on a milli-arcsecond scale," explains Pieter Deroo, lead-author of the paper that presents these results in the research journal Astronomy and Astrophysics.
These observations clearly demonstrate that the dust present around the star cannot be distributed in a spherical shell. "This shows that whatever mechanism is shaping asymmetric planetary nebulae is already present prior to the metamorphosis taking place," says Hans Van Winckel, member of the team.
The astronomers found indeed evidence for a disc extending from 9 Astronomical Units* to several hundreds of AU. "This disc is found around a star that is in a very brief phase of its life - just a blink of an eye over the star's lifespan of billions of years - but this phase is very important," says Deroo. "It is in this period that a huge morphological change occurs, leading to the creation of a planetary nebula," he adds.
The very high spatial resolution measurements allowed the astronomers to decouple the unresolved contribution of the central star from the resolved disc emission. Even the very inner structure of the disc as well as its orientation and inclination could be determined. The observations probe the physical nature of the disc and reveal that the dust in the inner rim is extremely hot and puffed up. The disc is circumbinary as it surrounds both stars.
Dust processing (coagulation, crystallisation) is found to be very efficient in this circumbinary disc, despite the rather short evolutionary timescales involved. The disc around this evolved object is very similar to those around young stellar objects, in which planets are formed.
"The combination of MIDI and AMBER on ESO's VLTI is an extremely powerful and perhaps unique tool to study the geometry of the material around stars," concludes Van Winckel.
It looks like it is the season for disc 'hunting': the detection of a dusty disc in the notable Ant Nebula was also just announced (see ESO 42/07).
The results presented here are reported in a Letter to the Editor to appear in the research journal Astronomy and Astrophysics ("AMBER and MIDI interferometric observations of the post-AGB binary IRAS 08544-4431: the circumbinary disc resolved", by P. Deroo et al.).
The team includes Pieter Deroo, Bram Acke, Tijl Verhoelst, and Hans Van Winckel (K. U. Leuven, Belgium), Carsten Dominik (University of Amsterdam, the Netherlands), and Eric Tatulli (INAF-Observatorio di Arcetri, Firenze, Italy).
*One Astronomical Unit (AU) is the mean distance between the Earth and the Sun. It corresponds to 149.6 million kilometres. For comparison, Saturn is 10 AU away from the Sun.
Note: This story has been adapted from material provided by European Organisation For Astronomical Research In The Southern Hemisphere.

Fausto Intilla

www.oloscience.com

Cornucopia Of Earth-sized Planets Modeled By NASA

Source:

http://www.sciencedaily.com/releases/2007/09/070924132510.htm

Science Daily — In the Star Wars movies fictional planets are covered with forests, oceans, deserts, and volcanoes. But new models from a team of MIT, NASA, and Carnegie scientists begin to describe an even wider range of Earth-size planets that astronomers might actually be able to find in the near future.

Sara Seager, Massachusetts Institute of Technology, Cambridge, Mass.; Marc Kuchner, NASA Goddard Space Flight Center, Greenbelt, Md.; Catherine Hier-Majumder, Carnegie Institution of Washington, (deceased); and Burkhard Militzer, Carnegie, have created models for 14 different types of solid planets that might exist in our galaxy.
The 14 types have various compositions, and the team calculated how large each planet would be for a given mass. Some are pure water ice, carbon, iron, silicate, carbon monoxide, and silicon carbide; others are mixtures of these various compounds.
"We’re thinking seriously about the different kinds of roughly Earth-size planets that might be out there, like George Lucas, but for real," says Kuchner.
The team took a different approach from previous studies. Rather than assume that planets around other stars are scaled-up or scaled-down versions of the planets in our solar system, they considered all types of planets that might be possible, given what astronomers know about the composition of protoplanetary disks around young stars.
"We have learned that extrasolar giant planets often differ tremendously from the worlds in our solar system, so we let our imaginations run wild and tried to cover all the bases with our models of smaller planets," says Kuchner. "We can make educated guesses about where these different kinds of planets might be found. For example, carbon planets and carbon-monoxide planets might favor evolved stars such as white dwarfs and pulsars, or they might form in carbon-rich disks like the one around the star Beta Pictoris. But ultimately, we need observations to give us the answers."
The team calculated how gravity would compress planets of varying compositions. The resulting computer models predict a planet’s diameter for a given composition and mass. For example, a 1-Earth-mass planet made of pure water will be about 9,500 miles across, whereas an iron planet with the same mass will be only about 3,000 miles in diameter. For comparison, Earth, which is made mostly of silicates, is 7,926 miles across at its equator.
Some of the results were expected, such as the fact that pure water planets (similar to the moons of the outer planets in our solar system, which consist mostly of water ice) were the least dense of the solid planets, and pure iron planets are the most dense. But there were some surprises. The team discovered that no matter what material a planet is made of, the mass/diameter relationship follows a similar pattern.
"All materials compress in a similar way because of the structure of solids," explains Seager. "If you squeeze a rock, nothing much happens until you reach some critical pressure, then it crushes. Planets behave the same way, but they react at different pressures depending on the composition. This is a big step forward in our fundamental understanding of planets."
The team hopes that these models will yield insights into planet compositions when astronomers start finding Earth-sized planets around other stars. Missions such as the French Corot satellite, which launched on December 27, 2006, and NASA’s Kepler spacecraft, scheduled to launch in 2009, can find planets not much larger than Earth by watching them pass in front of their host stars, events known as transits. The transits yield the planet’s size, and follow-up studies can measure the mass. By comparing a planet's size and mass, astronomers might be able to determine whether it is mostly water ice or mostly iron, for example.
But astronomers using the transit method will find it difficult at best to distinguish a silicate planet from a carbon planet, because they’re about the same size for a given mass. "To make this finer distinction, we will need some help from NASA’s James Webb Space Telescope or Terrestrial Planet Finder," says Kuchner. "With these instruments, we could take spectra of Earth-mass planets, which will tell us about their chemistries."
The team’s paper is currently scheduled to appear in the October 20 issue of the Astrophysical Journal.
Note: This story has been adapted from a news release issued by NASA Goddard Space Flight Center.

Fausto Intilla

www.oloscience.com

A Warm South Pole? Yes, On Neptune!

Source:

http://www.sciencedaily.com/releases/2007/09/070918100600.htm

Science Daily — An international team of astronomers using ESO's Very Large Telescope has discovered that the south pole of Neptune is much hotter than the rest of the planet. This is consistent with the fact that it is late southern summer and this region has been in sunlight for about 40 years.

The scientists are publishing the first temperature maps of the lowest portion of Neptune's atmosphere, showing that this warm south pole is providing an avenue for methane to escape out of the deep atmosphere.
"The temperatures are so high that methane gas, which should be frozen out in the upper part of Neptune's atmosphere (the stratosphere), can leak out through this region," said Glenn Orton, lead author of the paper reporting the results. "This solves a long-standing problem of identifying the source of Neptune's high stratospheric methane abundances."
The temperature at the south pole is higher than anywhere else on the planet by about 10 degrees Celsius. The average temperature on Neptune is about minus 200 degrees Celsius.
Neptune, the farthest planet of our solar system, is located about 30 times farther away from the Sun than Earth is. Only about 1/900th as much sunlight reaches Neptune as our planet. Yet, the small amount of sunlight it receives significantly affects the planet's atmosphere.
The astronomers found that these temperature variations are consistent with seasonal changes. A Neptunian year lasts about 165 Earth years. It has been summer in the south pole of Neptune for about 40 years now, and they predict that as winter turns to summer in the north pole, an abundance of methane will leak out of a warm north pole in about 80 years.
"Neptune's south pole is currently tilted toward the Sun, just like the Earth's south pole is tilted toward the Sun during summer in the Southern Hemisphere," explains Orton. "But on Neptune the antarctic summer lasts 40 years instead of a few months, and a lot of solar energy input during that time can make big temperature differences between the regions in continual sunlight and those with day-night variations."
"Neptune has the strongest winds of any planet in the Solar System; sometimes, the wind blows there at more than 2000 kilometres per hour. It is certainly not the place you would like to go on a holiday," he adds.
The new observations also reveal mysterious high-latitude 'hot spots' in the stratosphere that have no immediate analogue in other planetary atmospheres. The astronomers think that these hot spots are generated by upwelling gas from much deeper in the atmosphere.
Methane is not the primary constituent of Neptune's atmosphere, which, as a giant planet, is mostly composed of the light gases, hydrogen and helium. But it is the methane in Neptune's upper atmosphere that absorbs the red light from the Sun and reflects the blue light back into space, making Neptune appear blue.
The new results were obtained with the mid-infrared camera/spectrometer VISIR on ESO's VLT 8.2-m Unit Telescope 3 (Melipal).
Reference: "Evidence for Methane Escape and Strong Seasonal and Dynamical Perturbations of Neptune's Atmospheric Temperatures", by Glenn S. Orton et al., is published by the research journal Astronomy and Astrophysics.
The team of astronomers includes Glenn S. Orton, Cédric Leyrat, and A. James Friedson (Jet Propulsion Laboratory, California Institute of Technology, USA), Thérèse Encrenaz (LESIA, Observatoire de Paris, France), and Richard Puetter (Center for Astrophysics & Space Sciences, University of California, USA).
Note: This story has been adapted from a news release issued by ESO.

Fausto Intilla

www.oloscience.com

Exoplanet Offers Clues To Earth's Future

Source:

http://www.sciencedaily.com/releases/2007/09/070912130828.htm

Science Daily — An international team of astronomers that includes Steve Kawaler of Iowa State University has announced the first discovery of a planet orbiting a star near the end of its life.

The news provides a preliminary picture of what could be the Earth's destiny in four to five billion years. That's when the sun will exhaust its hydrogen fuel, expand enormously as a red giant and expel its outer layers in an explosive helium flash.
The planet discovered by the researchers, "V 391 Pegasi b," has survived all those changes to its sun.
The international research team was led by Roberto Silvotti from the INAF-Osservatorio Astronomico di Capodimonte in Naples, Italy. They discovered the planet orbiting "V 391 Pegasi," a faint star in the constellation of Pegasus.
"The exciting thing about finding a planet around this star is that it indicates that planetary systems can survive the giant phase and the helium flash of their parent star," said Kawaler, an Iowa State professor of physics and astronomy. "It bodes well for the survival of our own Earth in the distant future. Before V 391 Pegasi lost its outer regions at the helium flash, the planet orbited the star at about the same distance that the Earth orbits our sun."
But, Kawaler said, "We shouldn't take too much heart in this -- this planet is larger than Jupiter, so a smaller planet like the Earth could still be vulnerable."
Kawaler helped the 23-member research team make its discovery by coordinating observations during a 2003 run of the Whole Earth Telescope. Iowa State is a lead institution in the Whole Earth Telescope, a worldwide network of cooperating observatories that allow astronomers to take uninterrupted measurements of variable stars that change in brightness. The discovery of V 391 Pegasi b was made by detailed measurements of the clocklike variation of the star caused by the planet tugging on it.
Kawaler also advanced the project by doing theoretical calculations to make sure irregularities of the star's orbital motion were caused by the orbiting planet.
The astronomers found that at the present time, V 391 Pegasi b has an orbital distance 1.7 times the medium distance between the Earth and the sun. As stars age and reach their red giant phase, they undergo an enormous expansion (with their volume increasing by a factor of millions) that can easily reach and engulf their inner planets.
"The same will happen to the sun," Silvotti said. "As far as our planets are concerned, we expect Mercury and Venus to disappear in the sun's envelope, whereas Mars should survive. The fate of the Earth is less clear because its position is really at the limit: it appears more likely that the Earth will not survive the red giant expansion of the sun either, but it is not for sure."
As is the case for almost all planets beyond our solar system, V 391 Pegasi b cannot be seen directly. Silvotti said it took seven years of observations and calculations to confirm the existence of the planet.
The announcement, culminating seven years of research, will be published in the Sept. 13 issue of the journal Nature.
Note: This story has been adapted from a news release issued by Iowa State University.

Fausto Intilla

www.oloscience.com

NASA Astronomers Find Bizarre Planet-mass Object Orbiting Neutron Star

Source:

http://www.sciencedaily.com/releases/2007/09/070912154610.htm

Science Daily — Using NASA’s Swift and Rossi X-ray Timing Explorer (RXTE) satellites, astronomers have discovered one of the most bizarre planet-mass objects ever found.

The object’s minimum mass is only about 7 times the mass of Jupiter. But instead of orbiting a normal star, this low-mass body orbits a rapidly spinning pulsar. It orbits the pulsar every 54.7 minutes at an average distance of only about 230,000 miles (slightly less than the Earth-Moon distance).
"This object is merely the skeleton of a star," says co-discoverer Craig Markwardt of NASA’s Goddard Space Flight Center in Greenbelt, Md. "The pulsar has eaten away the star’s outer envelope, and all the remains is its helium-rich core."
Hans Krimm of NASA Goddard discovered the system on June 7, when Swift’s Burst Alert Telescope picked up an outburst of X rays and gamma rays in the direction of the galactic center. The source was named SWIFT J1756.9-2508 for its sky coordinates in the constellation Sagittarius.
RXTE began observing SWIFT J1756.9 on June 13 with its Proportional Counter Array (PCA). After analyzing the PCA data, Markwardt realized that the object was pulsing in X rays 182.07 times per second, which told him that it was a rapidly spinning pulsar. These so-called millisecond pulsars are neutron stars that spin hundreds of times per second, faster than a kitchen blender. Normally, the spin rate of neutron stars slows down as they age, but much like we can pull a string to “spin up” a top, gas spiraling onto a neutron star from its companion can maintain or even increase its fast spin.
In the case of SWIFT J1756.9-2508, Markwardt detected subtle modulations in the X-ray timing data that revealed a low-mass companion tugging the pulsar toward and away from Earth. His calculations show that the companion has a minimum mass about 7 times that of Jupiter. Because we don’t know the orbital inclination of the system, the companion’s actual mass is unknown, but it is extremely unlikely to exceed 30 Jupiters.
MIT astronomers led by Deepto Chakrabarty also observed the system with RXTE, before it faded to invisibility on June 21. Chakrabarty’s group reached identical conclusions, and the two teams have coauthored a paper that has been accepted for publication in the Astrophysical Journal Letters.
The system is only the eighth millisecond pulsar that is observed to be accreting mass from a companion. Only one other such system has a pulsar companion with such a low mass. The companion in this system, XTE J1807-294, also has a minimum mass of about 7 Jupiters. "Given that we don’t know the exact mass of either companion, ours could be the smallest," says Krimm.
The system probably formed several billion years ago, when it consisted of a very massive star and a smaller star with perhaps 1 to 3 solar masses. The more massive star evolved quickly and exploded as a supernova, leaving behind the neutron star. The smaller star eventually started to puff up en route to becoming a red giant, and the two objects became embedded in the extended stellar envelope. This drained orbital energy, causing the two stars to draw ever nearer, while simultaneously ejecting the envelope.
Today, the two objects are so close to each other than the neutron star’s powerful gravity produces a tidal bulge on its companion, siphoning off gas that flows into a disk that surrounds the neutron star. The flow eventually becomes unstable and dumps large quantities of gas onto the neutron star, causing an outburst like the one observed in June.
Evolution models by Christopher Deloye of Northwestern University suggest that the low-mass companion is helium dominated. "Despite its extremely low mass, the companion isn’t considered a planet because of its formation," says Deloye. "It’s essentially a white dwarf that has been whittled down to a planetary mass."
After billions of years, little remains of the companion star, and it remains unclear whether it will survive. "It’s been taking a beating, but that’s part of nature," adds Krimm.
With an estimated distance of roughly 25,000 light-years, the system is normally too faint to be detected at any wavelength, and is only visible during an outburst. SWIFT J1756.9 has never been seen to erupt until this June, so as Markwardt points out, "We don't know how long it will slumber before it wakes up again."
Note: This story has been adapted from a news release issued by NASA Goddard Space Flight Center.

Fausto Intilla

www.oloscience.com

Amateur Astronomers Help Professionals Unveil The Atmosphere Of Venus

Source:

http://www.sciencedaily.com/releases/2007/08/070824120456.htm

Science Daily — Results from an ongoing collaboration between amateur astronomers and the European Space Agency to support the Venus Express mission will be presented at the European Planetary Science Congress in Potsdam on Wednesday 22nd August.

Silvia Kowollik, from the Zollern-Alb Observatory in Germany and one of the participants in the project, said, "This is the first time there’s been a European collaboration between amateur astronomers and scientists. In the United States, they have a long tradition and a lot of experience in this kind of work. In Europe we are just starting."
Since its launch in 2006, ESA’s Venus Amateur Observing Project (VAOP) has invited amateur astronomers to submit scientifically useful images and data to support scientists working on the Venus Express mission. The amateur images, taken in the infrared, visible and ultraviolet bands, give a different, global perspective on features observed by the spacecraft, show a comparative view of the planet in various parts of the spectrum covered by instruments aboard Venus Express, and can also capture views of Venus that are hidden to the spacecraft in its orbit. The highly elliptical orbit of Venus Express means that the spacecraft moves slowly around the planet’s south pole but whips over the northern latitudes, so the ground-based images are especially important for observing features north of the equator.
Dr Thomas Widemann, who is participating in a parallel professional campaign of ground-based observations to support Venus Express said, "There have been huge advances in relatively cheaply available equipment, which means that amateurs can take images in wavelengths from infrared through to ultraviolet with impressive accuracy and content. These amateur observations are the last link in a chain that starts with Venus Express and continues with the professional ground-based activities. When joined together, all these observations will all help to peel back the atmosphere of Venus and reveal her mysteries."
Developments in video astronomy have meant that amateurs can select and combine thousands of rapidly exposed video frames in order to cancel out the distorting effects of atmospheric turbulence.
Ms Kowollik said, "This has been a great experience for amateurs. Several observers in Germany have taken part and have gained considerable expertise in image processing. We are now looking forward to future Venus observation campaigns."
The ultraviolet observations are of particular interest because scientists still do not know the chemical constituent of Venus’s atmosphere that causes the planet’s yellowish tinge. Dr Widemann said, "Something is absorbing the blue end of the visible spectrum. There are many theories – it could be material derived from meteorites that contains iron, it could be molecules of carbon monoxide dissolved in sulphuric acid droplets, or molecules made of several sulphur atoms. Perhaps it’s a combination of all of these. The amateur ultraviolet observations may assist in this investigation. To know for sure, we need measurements taken within the Venusian atmosphere, perhaps by instruments carried by a balloon."
"The next ground-based observing campaign will begin in September, when Venus increases its angular distance to the Sun in the morning sky", Dr Widemann said, "By participating in the VAOP, amateurs can receive proper recognition for their skill from the professional community. It should be a great boost for amateurs across Europe and will give them a just reward for their enthusiasm.
Note: This story has been adapted from a news release issued by European Planetology Network.

Fausto Intilla

www.oloscience.com

Jupiter: Friend Or Foe?

Source:

http://www.sciencedaily.com/releases/2007/08/070824133636.htm

Science Daily — The traditional belief that Jupiter acts as a celestial shield, deflecting asteroids and comets away from the inner Solar System, has been challenged by the first in a series of studies evaluating the impact risk to the Earth posed by different groups of object.

On Friday 24th August at the European Planetary Science Congress in Potsdam, Dr Jonathan Horner presented a study of the impact hazard posed to Earth by the Centaurs, the parent population of the Jupiter Family of comets (JFCs). The results show that the presence of a Jupiter-like planet in the Solar System does not necessarily lead to a lower impact rate at the Earth.
Dr Horner, from the UK's Open University (OU), said, "The idea that a Jupiter-like planet plays an important role in lessening the impact risk on potentially habitable planets is a common belief but there has only really been one study done on this in the past, which looked at the hazard due to the Long Period Comets. We are carrying out an ongoing series of studies of the impact risks in planetary systems, starting off by looking at our own Solar System, since we know the most about it!"
The team at the OU developed a computer model that could track the paths of 100,000 Centaurs around the Solar System over 10 million years. The simulation was run five times: once with Jupiter at its current mass, once without a Jupiter, and then with planets of three-quarters, a half and a quarter the mass of Jupiter (for comparison, Saturn is about a third of the mass of Jupiter). The team found that the impact rate in a Solar System with a planet like our Jupiter is about comparable to the case where there is no Jupiter at all. However, when the mass of Jupiter was between these two extremes, the Earth suffered an increased number of impacts from the JFCs.
Dr Horner said, "We've found that if a planet about the mass of Saturn or a bit larger occupied Jupiter's place, then the number of impacts on Earth would increase. However if nothing was there at all, there wouldn't be any difference from our current impact rate. Rather than it being a clear cut case that Jupiter acts as a shield, it seems that Jupiter almost gives with one hand and takes away with the other!"
The study shows that if there is no giant planet present, the JFCs will not be diverted onto Earth-crossing orbits, so the impact rate at the Earth is low. A Saturn-mass planet would have the gravitational pull to inject objects onto Earth-crossing orbits, but would not be massive enough to easily eject objects from the Solar System. This means that there would be more objects on Earth-crossing orbits at any given time, and therefore more impacts.
However, a planet with Jupiter's vast mass can give objects the gravitational boost to eject them from the Solar System. Therefore, if Jupiter deflects JFCs to an Earth-crossing orbit, it may well later sweep them right out of the Solar System and off the collision course with the Earth.
The group is now assessing the impact risk posed to the Earth by the Asteroids and will go on to study the Long Period Comets, before examining the role of the position of Jupiter within our system.
Jupiter family of comets
The Jupiter Family of Comets (JFCs) are short period comets with an orbital period of less than 20 years. Their orbits are controlled by Jupiter and they are believed to originate from the Kuiper Belt, a vast population of small icy bodies that orbit just beyond Neptune. Famous JFCs include Comet 81P/Wild 2, which was encountered by the Stardust spacecraft in January 2004 and Comet Shoemaker Levy-9, which broke up and collided with Jupiter in July 1994.
Note: This story has been adapted from a news release issued by European Planetology Network.

Fausto Intilla

www.oloscience.com

Speeding Star: Johnny Appleseed Of The Cosmos

Source:

http://www.sciencedaily.com/releases/2007/08/070815174450.htm

Science Daily — A new ultraviolet mosaic from NASA's Galaxy Evolution Explorer shows a speeding star that is leaving an enormous trail of "seeds" for new solar systems. The star, named Mira (pronounced my-rah) after the latin word for "wonderful," is shedding material that will be recycled into new stars, planets and possibly even life as it hurls through our galaxy. Mira appears as a small white dot in the bulb-shaped structure at right, and is moving from left to right in this view. The shed material can be seen in light blue. The dots in the picture are stars and distant galaxies.The Galaxy Evolution Explorer discovered Mira's strange comet-like tail during part of its routine survey of the entire sky at ultraviolet wavelengths. When astronomers first saw the picture, they were shocked because Mira has been studied for over 400 years yet nothing like this has ever been documented before. Mira's comet-like tail stretches a startling 13 light-years across the sky. For comparison, the nearest star to our sun, Proxima Centauri, is only about 4 light-years away. Mira's tail also tells a tale of its history – the material making it up has been slowly blown off over time, with the oldest material at the end of the tail having been released about 30,000 years ago. Mira is a highly evolved, "red giant" star near the end of its life. Technically, it is called an asymptotic giant branch star. It is red in color and bloated; for example, if a red giant were to replace our sun, it would engulf everything out to the orbit of Mars. Our sun will mature into a red giant in about 5 billion years. Like other red giants, Mira will lose a large fraction of its mass in the form of gas and dust. In fact, Mira ejects the equivalent of the Earth's mass every 10 years. It has released enough material over the past 30,000 years to seed at least 3,000 Earth-sized planets or 9 Jupiter-sized ones. While most stars travel along together around the disk of our Milky Way, Mira is charging through it. Because Mira is not moving with the "pack," it is moving much faster relative to the ambient gas in our section of the Milky Way. It is zipping along at 130 kilometers per second, or 291,000 miles per hour, relative to this gas. Mira's breakneck speed together with its outflow of material are responsible for its unique glowing tail. Images from the Galaxy Evolution Explorer show a large build-up of gas, or bow shock, in front of the star, similar to water piling up in front of a speeding boat. Scientists now know that hot gas in this bow shock mixes with the cooler, hydrogen gas being shed from Mira, causing it to heat up as it swirls back into a turbulent wake. As the hydrogen gas loses energy, it fluoresces with ultraviolet light, which the Galaxy Evolution Explorer can detect. Mira, also known as Mira A, is not alone in its travels through space. It has a distant companion star called Mira B that is thought to be the burnt-out, dead core of a star, called a white dwarf. Mira A and B circle around each other slowly, making one orbit about every 500 years. Astronomers believe that Mira B has no effect on Mira's tail. Mira is also what's called a pulsating variable star. It dims and brightens by a factor of 1,500 every 332 days, and will become bright enough to see with the naked eye in mid-November 2007. Because it was the first variable star with a regular period ever discovered, other stars of this type are often referred to as "Miras." Mira is located 350 light-years from Earth in the constellation Cetus, otherwise known as the whale. Coincidentally, Mira and its "whale of a tail" can be found in the tail of the whale constellation.

Note: This story has been adapted from a news release issued by National Aeronautics and Space Administration.

Fausto Intilla

www.oloscience.com

Largest Transiting Extrasolar Planet Found Around A Distant

Source:

http://www.sciencedaily.com/releases/2007/08/070806121128.htm

Science Daily — An international team of astronomers with the Trans-atlantic Exoplanet Survey just announced the discovery of TrES-4, a new extrasolar planet in the constellation of Hercules. The new planet was identified by astronomers looking for transiting planets -- that is, planets that pass in front of their home star -- using a network of small automated telescopes in Arizona, California, and the Canary Islands.

TrES-4 was discovered less than half a degree (about the size of the full Moon) from the team's third planet, TrES-3."TrES-4 is the largest known exoplanet," said Georgi Mandushev, Lowell Observatory astronomer and the lead author of the paper announcing the discovery. "It is about 70 percent bigger than Jupiter, the Solar System's largest planet, but less massive, making it a planet of extremely low density. Its mean density is only about 0.2 grams per cubic centimeter, or about the density of balsa wood! And because of the planet's relatively weak pull on its upper atmosphere, some of the atmosphere probably escapes in a comet-like tail." The new planet TrES-4 was first noticed by Lowell Observatory's Planet Search Survey Telescope (PSST), set up and operated by Edward Dunham and Georgi Mandushev. The Sleuth telescope, maintained by David Charbonneau (CfA) and Francis O'Donovan (Caltech), at Caltech's Palomar Observatory also observed transits of TrES-4, confirming the initial detections. TrES-4 is about 1400 light years away and orbits its host star in three and a half days. Being only about 4.5 million miles from its home star, the planet is also very hot, about 1,600 Kelvin or 2,300 degrees Fahrenheit."TrES-4 appears to be something of a theoretical problem," said Edward Dunham, Lowell Observatory Instrument Scientist. "It is larger relative to its mass than current models of superheated giant planets can presently explain. Problems are good, though, since we learn new things by solving them." "We continue to be surprised by how relatively large these giant planets can be," adds Francis O'Donovan, a graduate student in astronomy at the California Institute of Technology who operates one of the TrES telescopes. "But if we can explain the sizes of these bloated planets in their harsh environments, it may help us understand better our own Solar System planets and their formation."By definition, a transiting planet passes directly between the Earth and the star, blocking some of the star's light and causing a slight drop in its brightness. To look for transits, the small telescopes are automated to take wide-field timed exposures of the clear skies on as many nights as possible. When observations are completed for a particular field -- usually over an approximate two-month period -- astronomers measure very precisely the light from every star in the field in order to detect the possible signature of a transiting planet. "TrES-4 blocks off about one percent of the light of the star as it passes in front of it," said Mandushev. "With our telescopes and observing techniques, we can measure this tiny drop in the star's brightness and deduce the presence of a planet there." Not only is the planet TrES-4 mysterious and intriguing, but so is its host star cataloged as GSC 02620-00648. Georgi Mandushev explains: "The host star of TrES-4 appears to be about the same age as our Sun, but because it is more massive, it has evolved much faster. It has become what astronomers call a 'subgiant', or a star that has exhausted all of its hydrogen fuel in the core and is on its way of becoming a 'red giant', a huge, cool red star like Arcturus or Aldebaran."In order to help confirm they had found a planet, Gáspár Bakos of the Hungarian Automated Telescope Network (HATNet) and Harvard's Guillermo Torres switched from the 10-centimeter TrES telescopes to one of the 10-meter telescopes at the W. M. Keck Observatory on the summit of Mauna Kea, Hawaii. Using this giant telescope, they confirmed that the TrES team had indeed found a new planet. In order to measure accurately the size and other properties of TrES-4, astronomers also made follow up observations with bigger telescopes at Lowell Observatory and Fred L. Whipple Observatory in Arizona. The authors of the paper "TrES-4: A Transiting Hot Jupiter of Very Low Density", accepted for publication in the Astrophysical Journal, are: Georgi Mandushev and Edward Dunham of Lowell Observatory; Francis T. O'Donovan and Lynne Hillenbrand of the California Institute of Technology; David Charbonneau, Guillermo Torres, David Latham, Gáspár Bakos, Alessandro Sozzetti, and José Fernández of the Harvard-Smithsonian Center for Astrophysics; Mark Everett and Gilbert Esquerdo of the Planetary Science Institute; Markus Rabus and Juan Belmonte of Instituto de Astrofísica de Canarias in Tenerife, Spain; and Timothy Brown of the Las Cumbres Observatory Global Telescope.This research is funded by NASA through the Origins of Solar Systems Program.

Note: This story has been adapted from a news release issued by Lowell Observatory.

Fausto Intilla

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