Distant Planetary System Is a Super-Sized Solar System

Artist’s rendering of the planetary system HR 8799 at an early stage in its evolution, showing the planet HR 8799c, as well as a disk of gas and dust, and interior planets. (Credit: Dunlap Institute for Astronomy & Astrophysics; Mediafarm)

A team of astronomers, including Quinn Konopacky of the Dunlap Institute for Astronomy & Astrophysics, University of Toronto, has made the most detailed examination yet of the atmosphere of a Jupiter-like planet beyond our Solar System.

According to Konopacky, "We have been able to observe this planet in unprecedented detail because of the advanced instrumentation we are using on the Keck II telescope, our ground-breaking observing and data-processing techniques, and because of the nature of the planetary system."

Konopacky is lead author of the paper describing the team's findings, to be published March 14th in Science Express, and March 22nd in the journal Science.

The team, using a high-resolution imaging spectrograph called OSIRIS, uncovered the chemical fingerprints of specific molecules, revealing a cloudy atmosphere containing carbon monoxide and water vapour. "With this level of detail," says Travis Barman, a Lowell Observatory astronomer and co-author of the paper, "we can compare the amount of carbon to the amount of oxygen present in the planet's atmosphere, and this chemical mix provides clues as to how the entire planetary system formed."

There has been considerable uncertainty about how systems of planets form, with two leading models, called core accretion and gravitational instability. Planetary properties, such as the composition of a planet's atmosphere, are clues as to whether a system formed according to one model or the other.

"This is the sharpest spectrum ever obtained of an extrasolar planet," according to co-author Bruce Macintosh of the Lawrence Livermore National Laboratory. "This shows the power of directly imaging a planetary system. It is the exquisite resolution afforded by these new observations that has allowed us to really begin to probe planet formation."

The spectrum reveals that the carbon to oxygen ratio is consistent with the core accretion scenario, the model thought to explain the formation of our Solar System.

The planet, designated HR 8799c, is one of four gas giants known to orbit a star 130 light-years from Earth. The authors and their collaborators previously discovered HR 8799c and its three companions back in 2008 and 2010. All the planets are larger than any in our Solar System, with masses three to seven times that of Jupiter. Their orbits are similarly large when compared to our system. HR 8799c orbits 40 times farther from its parent star than Earth orbits from the Sun; in our Solar System, that would put it well beyond the realm of Neptune.

According to the core accretion model, the star HR 8799 was originally surrounded by nothing but a huge disk of gas and dust. As the gas cooled, ice formed; this process depleted the disk of oxygen atoms. Ice and dust collected into planetary cores which, once they were large enough, attracted surrounding gas to form large atmospheres. The gas was depleted of oxygen, and this is reflected in the planet's atmosphere today as an enhanced carbon to oxygen ratio.

The core accretion model also predicts that large gas giant planets form at great distances from the central star, and smaller rocky planets closer in, as in our Solar System. It is rocky planets, not too far, nor close to the star, that are prime candidates for supporting life.

"The results suggest the HR 8799 system is like a scaled-up Solar System," says Konopacky. "And so, in addition to the gas giants far from their parent star, it would not come as a surprise to find Earth-like planets closer in."

The observations of HR 8799c were made with the Keck II 10-metre telescope in Hawaii, one of the two largest optical telescopes in the world. The telescope's adaptive optics system corrects for distortion caused by Earth's atmosphere, making the view through Keck II sharper than through the Hubble Space Telescope.

Astronomers refer to this as spatial resolution. Seeing exoplanets around stars is like trying to see a firefly next to a spotlight. Keck's adaptive optics and high spatial resolution, combined with advanced data-processing techniques, allow astronomers to more clearly see both the stellar "spotlight" and planetary "firefly."

"We can directly image the planets around HR 8799 because they are all large, young, and very far from their parent star. This makes the system an excellent laboratory for studying exoplanet atmospheres," says coauthor Christian Marois of the National Research Council of Canada. "Since its discovery, this system just keeps surprising us."

Konopacky and her team will continue to study the super-sized planets to learn more details about their nature and their atmospheres. Future observations will be made using the recently upgraded OSIRIS instrument which utilizes a new diffraction grating -- the key component of the spectrograph that separates light according to wavelength, just like a prism. The new grating was developed at the Dunlap Institute and installed in the spectrograph in December 2012.

"These future observations will tell us much more about the planets in this system," says Dunlap Fellow Konopacky. "And the more we learn about this distant planetary system, the more we learn about our own."

Source:

http://www.sciencedaily.com/releases/2013/03/130314144211.htm

Magnetic fields in astrophysics: an electronic 'textbooklet'

Fig. 1: Field lines in the head of a magnetic jet. (Rainer Moll, MPA)

Magnetic fields play an important role in many objects in the universe, from the Sun with its spots and the magnetically heated corona visible during a solar eclipse, to pulsars and the spectacular 'jets' from black holes and protostars. The behaviour of the magnetic field in these objects, however, is very different from experience at home or in physics class, since in astrophysical objects magnetic field lines are 'tied' to an ionized gas. The theory for such magnetic fields, called magnetohydrodynamics (MHD), is explained in a concise textbook published online. It emphasizes understanding of MHD by visualization of the flows and forces as they take place in a magnetized fluid. To this end, the text also includes a number of small video clips of basic MHD flows. 

In physical processes where magnetic fields are present, one generally also has electric fields, currents and charge densities. Mathematically speaking, one has to deal with the full set of Maxwell's equations plus the equations of motion for the particles making up the plasma - the domain of plasma physics. Luckily, for most flows seen in astronomical objects, however, this complexity is rarely necessary. The electrical conductivity of an ionized gas makes MHD an extremely accurate approximation. Compared with ordinary fluid mechanics, only the magnetic field needs to be included explicitly in the theory. The other electromagnetic quantities can be evaluated afterwards; they are neither needed for a proper description, nor of much use for physical understanding. Thanks to this simplification it has become possible to include magnetic fields realistically in numerical simulations, for example of extragalactic jets (Fig. 1). 

The price to be paid is that we have to give up some of our intuitions about the way electric and magnetic fields work. Our experience is dominated by processes taking place in the Earth's electrically insulating atmosphere (in copper wires, batteries, induction coils etc.). Most astrophysical processes on the other hand happen in an ionised gas, such as in a star, the solar wind, or the intergalactic medium. 

Because of the strong coupling between the magnetic field and the electrically conducting gas, MHD flows behave more or less like visco-elastic but otherwise ordinary fluids. This makes MHD an eminently visualizable theory (for an example see the video clip inFig. 2), which also motivates the approach used in the textbooklet. The first chapter (only 36 pages) is a concise introduction including exercises. The exercises are important as illustrations of the points made in the text (especially the less intuitive ones). Almost all are mathematically unchallenging, though some do require a background in undergraduate physics. This is the 'essential' part. The supplement in chapter 2 contains further explanations, more specialized topics and occasional connections to topics somewhat outside the scope of MHD.

Fig. 2: A fluid flow stretching a bundle of field lines (mp4 movie) (Merel van 't Hoff, MPA)

Essential magnetohydrodynamics for_astrophysics from Sergio Sancevero

Source:

http://www.mpa-garching.mpg.de/mpa/institute/news_archives/news1302_aaa/news1302_aaa-en.html

Elliptical Galaxy Reveals a Spectacular "Ruins" of Black Holes and Neutron Stars

The Chandra X-Ray Observatory image of the elliptical galaxy NGC 4261 revealed dozens of black holes and neutron stars strung out across tens of thousands of light years like beads on a necklace. The spectacular structure, which is not apparent from the optical image of the galaxy, is thought to be the remains of a collision between galaxies a few billion years ago, when a smaller galaxy was captured and pulled apart by the gravitational tidal forces of NGC 4261. As the doomed galaxy fell into the larger galaxy, large streams of gas were pulled out into long tidal tails. Shock waves in these tidal tails triggered the formation of many massive stars.

Over the course of a few million years, these stars evolved into neutron stars or black holes. A few of these collapsed stars had companion stars, and became bright X-ray sources as gas from the companions was captured by their intense gravitational fields.

The currently favored view is that elliptical galaxies are produced by collisions between spiral galaxies. Computer simulations of galaxy collisions support this idea, and optical evidence of tails, shells, ripples, arcs and other structures have been interpreted as evidence for this theory.

However as the image above shows, the optical evidence rather quickly fades into the starry background of the galaxy, whereas the X-ray signature lingers for hundreds of millions of years. Chandra's image of NGC 4261 shows that X-ray observations may be the best way to identify the ancient remains of mergers between galaxies.

The Hubble Space Telescope picture below of the center of NGC 4261 tells a dramatic tale. The gas and dust in this disk are swirling into what is almost certainly a super, perhaps super-super massive black hole. The disk is probably what remains of the smaller galaxy that fell in hundreds of millions of years ago. Collisions like this may be a common way of creating such active galactic nuclei as quasars. Strangely, the center of this fiery whirlpool is offset from the exact center of the galaxy - for a reason that for now remains an astronomical mystery.

Source:

http://www.dailygalaxy.com/my_weblog/2013/03/elliptical-galaxy-reveals-spectacular-ruins-of-black-holes-and-neutron-stars.html

NASA's Aquarius Sees Salty Shifts

NASA has released the first full year of validated ocean surface salinity data from the agency's Aquarius instrument aboard the Aquarius/SAC-D spacecraft. The data cover the period from Dec. 2011 through Dec. 2012. Red colors represent areas of high salinity, while blue shades represent areas of low salinity. Among the prominent salinity features visible in this view are the large area of highly saline water across the North Atlantic. This area, the saltiest anywhere in the open ocean, is analogous to deserts on land, where little rainfall and much evaporation occur. Aquarius is a focused effort to measure ocean surface salinity and will provide the global view of salinity variability needed for climate studies. The mission is a collaboration between NASA and the Space Agency of Argentina (Comision Nacional de Actividades Espaciales). Image credit: NASA/GSFC/JPL-Caltech

The colorful images chronicle the seasonal stirrings of our salty world: Pulses of freshwater gush from the Amazon River's mouth; an invisible seam divides the salty Arabian Sea from the fresher waters of the Bay of Bengal; a large patch of freshwater appears in the eastern tropical Pacific in the winter. These and other changes in ocean salinity patterns are revealed by the first full year of surface salinity data captured by NASA's Aquarius instrument. 

"With a bit more than a year of data, we are seeing some surprising patterns, especially in the tropics," said Aquarius Principal Investigator Gary Lagerloef, of Earth & Space Research in Seattle. "We see features evolve rapidly over time." 

Launched June 10, 2011, aboard the Argentine spacecraft Aquarius/Satelite de Aplicaciones Cientificas (SAC)-D, Aquarius is NASA's first satellite instrument specifically built to study the salt content of ocean surface waters. Salinity variations, one of the main drivers of ocean circulation, are closely connected with the cycling of freshwater around the planet and provide scientists with valuable information on how the changing global climate is altering global rainfall patterns. 

The salinity sensor detects the microwave emissivity of the top approximately 1 inch (1 to 2 centimeters) of ocean water - a physical property that varies depending on temperature and saltiness. The instrument collects data in 240-mile-wide (386 kilometers) swaths in an orbit designed to obtain a complete survey of global salinity of ice-free oceans every seven days. 

The Changing Ocean 

The animated version of Aquarius' first year of data unveils a world of varying salinity patterns. The Arabian Sea, nestled up against the dry Middle East, appears much saltier than the neighboring Bay of Bengal, which gets showered by intense monsoon rains and receives freshwater discharges from the Ganges and other large rivers. Another mighty river, the Amazon, releases a large freshwater plume that heads east toward Africa or bends up north to the Caribbean, depending on the prevailing seasonal currents. Pools of freshwater carried by ocean currents from the central Pacific Ocean's regions of heavy rainfall pile up next to Panama's coast, while the Mediterranean Sea sticks out in the Aquarius maps as a very salty sea. 

One of the features that stand out most clearly is a large patch of highly saline water across the North Atlantic. This area, the saltiest anywhere in the open ocean, is analogous to deserts on land, where little rainfall and a lot of evaporation occur. A NASA-funded expedition, the Salinity Processes in the Upper Ocean Regional Study (SPURS), traveled to the North Atlantic's saltiest spot last fall to analyze the causes behind this high salt concentration and to validate Aquarius measurements. 

"My conclusion after five weeks out at sea and analyzing five weekly maps of salinity from Aquarius while we were there was that indeed, the patterns of salinity variation seen from Aquarius and by the ship were similar," said Eric Lindstrom, NASA's physical oceanography program scientist, NASA Headquarters, Washington, and a participant of the SPURS research cruise. 

Future Goals 

"The Aquarius prime mission is scheduled to run for three years but there is no reason to think that the instrument could not be able to provide valuable data for much longer than that," said Gene Carl Feldman, Aquarius project manager at NASA's Goddard Space Flight Center in Greenbelt, Md. "The instrument has been performing flawlessly and our colleagues in Argentina are doing a fantastic job running the spacecraft, providing us a nice, stable ride." 

In future years, one of the main goals of the Aquarius team is to figure out ways to fine-tune the readings and retrieve data closer to the coasts and the poles. Land and ice emit very bright microwave emissions that swamp the signal read by the satellite. At the poles, there's the added complication that cold polar waters require very large changes in their salt concentration to modify their microwave signal. 

Still, the Aquarius team was surprised by how close to the coast the instrument is already able to collect salinity measurements. 

"The fact that we're getting areas, particularly around islands in the Pacific, that are not obviously badly contaminated is pretty remarkable. It says that our ability to screen out land contamination seems to be working quite well," Feldman said. 

Another factor that affects salinity readings is intense rainfall. Heavy rain can affect salinity readings by attenuating the microwave signal Aquarius reads off the ocean surface as it travels through the soaked atmosphere. Rainfall can also create roughness and shallow pools of freshwater on the ocean surface. In the future, the Aquarius team wants to use another instrument aboard Aquarius/SAC-D, the Argentine-built Microwave Radiometer, to gauge the presence of intense rain simultaneously to salinity readings, so that scientists can flag data collected during heavy rainfall. 

An ultimate goal is combining the Aquarius measurements with those of its European counterpart, the Soil Moisture and Ocean Salinity satellite (SMOS) to produce more accurate and finer maps of ocean salinity. In addition, the Aquarius team, in collaboration with researchers at the U.S. Department of Agriculture, is about to release its first global soil moisture dataset, which will complement SMOS' soil moisture measurements. 

"The first year of the Aquarius mission has mostly been about understanding how the instruments and algorithms are performing," Feldman said. "Now that we have overcome the major hurdles, we can really begin to focus on understanding what the data are telling us about how the ocean works, how it affects weather and climate, and what new insights we can gain by having these remarkable salinity measurements." 

Aquarius was built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.; and NASA Goddard. JPL managed Aquarius through its commissioning phase and is archiving mission data. Goddard now manages Aquarius mission operations and processes science data. Argentina's space agency, Comision Nacional de Actividades Espaciales (CONAE), provided the SAC-D spacecraft, optical camera, thermal camera with Canada, microwave radiometer, sensors from various Argentine institutions and the mission operations center. France and Italy also contributed instruments. For more information about NASA's Aquarius mission, visit: http://www.nasa.gov/aquarius . 

For a narrated global tour of Aquarius ocean surface salinity measurements, see: http://www.youtube.com/watch?v=5xQP_B18vMw . A visualization showing changes in global ocean surface salinity as measured by Aquarius from Dec. 2011 through Dec. 2012 can be seen at: http://www.youtube.com/watch?v=RJVnZnZUUYc . - See more at: http://www.jpl.nasa.gov/news/news.php?release=2013-074&cid=release_2013-074#sthash.B43H9PQd.dpuf

Source:

http://www.jpl.nasa.gov/news/news.php?release=2013-074&cid=release_2013-074

White Dwarf Stars Offer Best Potential to Identify Twin Earths

"In the quest for extraterrestrial biological signatures, the first stars we study should be white dwarfs," said Avi Loeb, theorist at the Harvard-Smithsonian Center for Astrophysics (CfA) and director of the Institute for Theory and Computation. Even dying stars could host planets with life - and if such life exists, we might be able to detect it within the next decade. This encouraging result comes from a new theoretical study of Earth-like planets orbiting white dwarf stars. Researchers found that we could detect oxygen in the atmosphere of a white dwarf's planet much more easily than for an Earth-like planet orbiting a Sun-like star.

When a star like the Sun dies, it puffs off its outer layers, leaving behind a hot core called a white dwarf. A typical white dwarf is about the size of Earth. It slowly cools and fades over time, but it can retain heat long enough to warm a nearby world for billions of years. Since a white dwarf is much smaller and fainter than the Sun, a planet would have to be much closer in to be habitable with liquid water on its surface. A habitable planet would circle the white dwarf once every 10 hours at a distance of about a million miles.* Before a star becomes a white dwarf it swells into a red giant, engulfing and destroying any nearby planets. Therefore, a planet would have to arrive in the habitable zone after the star evolved into a white dwarf. A planet could form from leftover dust and gas (making it a second-generation world), or migrate inward from a larger distance.

If planets exist in the habitable zones of white dwarfs, we would need to find them before we could study them. The abundance of heavy elements on the surface of white dwarfs suggests that a significant fraction of them have rocky planets. Loeb and his colleague Dan Maoz (Tel Aviv University) estimate that a survey of the 500 closest white dwarfs could spot one or more habitable Earths.

The best method for finding such planets is a transit search - looking for a star that dims as an orbiting planet crosses in front of it. Since a white dwarf is about the same size as Earth, an Earth-sized planet would block a large fraction of its light and create an obvious signal.

More importantly, we can only study the atmospheres of transiting planets. When the white dwarf's light shines through the ring of air that surrounds the planet's silhouetted disk, the atmosphere absorbs some starlight. This leaves chemical fingerprints showing whether that air contains water vapor, or even signatures of life, such as oxygen.

Astronomers are particularly interested in finding oxygen because the oxygen in the Earth's atmosphere is continuously replenished, through photosynthesis, by plant life. Were all life to cease on Earth, our atmosphere would quickly become devoid of oxygen, which would dissolve in the oceans and oxidize the surface. Thus, the presence of large quantities of oxygen in the atmosphere of a distant planet would signal the likely presence of life there.

NASA's James Webb Space Telescope (JWST), scheduled for launch by the end of this decade, promises to sniff out the gases of these alien worlds. Loeb and Maoz created a synthetic spectrum, replicating what JWST would see if it examined a habitable planet orbiting a white dwarf. They found that both oxygen and water vapor would be detectable with only a few hours of total observation time.

"JWST offers the best hope of finding an inhabited planet in the near future," said Maoz.* Recent research by CfA astronomers Courtney Dressing and David Charbonneau showed that the closest habitable planet is likely to orbit a red dwarf star (a cool, low-mass star undergoing nuclear fusion). Since a red dwarf, although smaller and fainter than the Sun, is much larger and brighter than a white dwarf, its glare would overwhelm the faint signal from an orbiting planet's atmosphere. JWST would have to observe hundreds of hours of transits to have any hope of analyzing the atmosphere's composition.

"Although the closest habitable planet might orbit a red dwarf star, the closest one we can easily prove to be life-bearing might orbit a white dwarf," said Loeb. *Their paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society and is available online.

Source:

http://www.dailygalaxy.com/my_weblog/2013/02/-white-dwarf-stars-offer-best-potential-to-identify-habitable-planets.html