Mystery World Baffles Astronomers

Kepler-78b is a planet that shouldn't exist. This scorching lava world, shown here in an artist's conception, circles its star every eight and a half hours at a distance of less than one million miles. According to current theories of planet formation, it couldn't have formed so close to its star, nor could it have moved there. David A. Aguilar (CfA). High Resolution (jpg) - Low Resolution (jpg)

This illustration compares our Earth with the newly confirmed lava planet Kepler-78b. Kepler-78b is about 20 percent larger than Earth, with a diameter of 9,200 miles, and weighs roughly 1.8 times as much as Earth. David A. Aguilar (CfA). High Resolution (jpg) - Low Resolution (jpg)

 

This diagram illustrates the tight orbit of Kepler-78b, which orbits its star every 8.5 hours at a distance of less than a million miles. It is only 2.7 stellar radii from the center of the star, or 1.7 stellar radii from the star's surface. David A. Aguilar (CfA). High Resolution (jpg) -Low Resolution (jpg)

 

Cambridge, MA - Kepler-78b is a planet that shouldn't exist. This scorching lava world circles its star every eight and a half hours at a distance of less than one million miles - one of the tightest known orbits. According to current theories of planet formation, it couldn't have formed so close to its star, nor could it have moved there. 

 

"This planet is a complete mystery," says astronomer David Latham of the Harvard-Smithsonian Center for Astrophysics (CfA). "We don't know how it formed or how it got to where it is today. What we do know is that it's not going to last forever."

"Kepler-78b is going to end up in the star very soon, astronomically speaking," agrees CfA astronomer Dimitar Sasselov.

Not only is Kepler-78b a mystery world, it is the first known Earth-sized planet with an Earth-like density. Kepler-78b is about 20 percent larger than the Earth, with a diameter of 9,200 miles, and weighs almost twice as much. As a result it has a density similar to Earth's, which suggests an Earth-like composition of iron and rock.

The tight orbit of Kepler-78b poses a challenge to theorists. When this planetary system was forming, the young star was larger than it is now. As a result, the current orbit of Kepler-78b would have been inside the swollen star.

"It couldn't have formed in place because you can't form a planet inside a star. It couldn't have formed further out and migrated inward, because it would have migrated all the way into the star. This planet is an enigma," explains Sasselov.

According to Latham, Kepler-78b is a member of a new class of planets recently identified in data from NASA's Kepler spacecraft. These newfound worlds all orbit their stars with periods of less than 12 hours. They're also small, about the size of Earth. Kepler-78b is the first planet in the new class to have its mass measured.

"Kepler-78b is the poster child for this new class of planets," notes Latham.

The team studied Kepler-78b using a newly commissioned, high-precision spectrograph known as HARPS-North, at the Roque de los Muchachos Observatory on La Palma. They coordinated their work with a second, independent team using the HIRES spectrograph at the Keck Observatory. The teams' measurements agreed with each other, increasing their confidence in the result.

Kepler-78b is a doomed world. Gravitational tides will draw it even closer to its star. Eventually it will move so close that the star's gravity will rip the world apart. Theorists predict that Kepler-78b will vanish within three billion years.

Interestingly, our solar system could have held a planet like Kepler-78b. If it had, the planet would have been destroyed long ago leaving no signs for astronomers today.

Kepler-78b orbits a Sun-like G-type star located 400 light-years from Earth in the constellation Cygnus.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Source: Harvard-Smithsonian Center for Astrophysics (CfA)

Caltech Scientists Detects First Progenitor of Type Ib Supernova

Using data from the Keck II and Hubble Space Telescopes, this composite image shows the supernova iPTF13bvn (upper inset), and its possible progenitor star (lower inset), in the galaxy NGC 5806.

Kamuela, Hawaii — Powerful new survey telescopes led by the California Institute of Technology (Caltech) are being combined with the W. M. Keck Observatory to provide insight into rare, exotic cosmic explosions. Caltech's intermediate Palomar Transient Factory (iPTF) recently described the first direct detection of the progenitor of a rare type of supernova in a nearby galaxy. The findings were published n the September 20 issue of Astrophysical Journal Letters [http://dx.doi.org/10.1088/2041-8205/775/1/L7].

The paper describes the detection of a Type Ib supernova, a rare explosion in which the progenitor star lacks an outer layer of hydrogen, the most abundant element in the universe. It has proven difficult to pin down which kinds of stars give rise to Type Ib supernovae. One of the most promising ideas, according to graduate student and lead author Yi Cao, is they originate from Wolf-Rayet stars. These objects are 10 times more massive and thousands of times brighter than the Sun and have lost their hydrogen envelope by means of very strong stellar winds. Until recently, no solid evidence existed to support this theory. Cao and colleagues believe that the young supernova they discovered, iPTF13bvn, occurred at a location formerly occupied by a likely Wolf-Rayet star.

Supernova iPTF13bvn was spotted on June 16, less than a day after the onset of its explosion. With the aid of the world-leading adaptive optics system installed on the Keck II telescope, one of Keck Observatory's two 10-meter telescopes in Hawaii, the team obtained a high-resolution image of this supernova to determine its precise position. Then they compared the Keck Observatory image to a series of pictures of the same galaxy (NGC 5806) taken by the Hubble Space Telescope in 2005, and found one starlike source spatially coincident to the supernova. Its intrinsic brightness, color, and size — as well as its mass-loss history, inferred from supernova radio emissions — were characteristic of a Wolf-Rayet star.

“All evidence is consistent with the theoretical expectation that the progenitor of this Type Ib supernova is a Wolf-Rayet star,” said Cao. “Our next step is to check for the disappearance of this progenitor star after the supernova fades away. We expect that it will have been destroyed in the supernova explosion.”

Though Wolf-Rayet progenitors have long been predicted for Type Ib supernova, the new work represents the first time researchers have been able to fill the gap between theory and observation, according to study coauthor and Mansi Kasliwal from the Carnegie Institution for Science. “This is a big step in our understanding of the evolution of massive stars and their relation to supernovae,” she said.

The iPTF builds on the legacy of the Caltech-led Palomar Transient Factory (PTF), designed in 2008 to systematically chart the transient sky by using a robotic observing system mounted on the 48-inch Samuel Oschin Telescope on Palomar Mountain near San Diego, California. This state-of-the-art, robotic telescope scans the sky rapidly over a thousand square degrees each night to search for transients.

The W. M. Keck Observatory operates the largest and most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and world-leading laser guide star adaptive optics systems. The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

Source:  W. M. Keck Observatory

Five Years of Great Discoveries for NASA's IBEX

During its first five years, IBEX has made some astounding discoveries

Image Credit: NASA's Goddard Space Flight Center

IBEX discovered a giant ribbon at the edge of the solar system, an anomaly that has now been determined to be a reflection where solar wind particles heading out into interstellar space are reflected back into the solar system by a galactic magnetic field. Image Credit: NASA/IBEX. View larger

IBEX found that Energetic Neutral Atoms, or ENAs, are coming from a region just outside Earth's magnetopause where nearly stationary protons from the solar wind interact with the tenuous cloud of hydrogen atoms in Earth's exosphere.Image Credit: NASA's Goddard Space Flight Center. View larger

A recent mapping of the heliotail shows it has two lobes of slower particles on the sides, faster particles above and below, with the entire structure twisted, as it experiences the pushing and pulling of magnetic fields outside the solar system.Image Credit: NASA's Goddard Space Flight Center. View larger

IBEX has found that there's more oxygen in our solar system than there is in the nearby interstellar material. Image Credit: NASA's Goddard Space Flight Center. View larger

Launched on Oct. 19, 2008, the Interstellar Boundary Explorer, or IBEX, spacecraft, is unique to NASA's heliophysics fleet: it images the outer boundary of the heliosphere, a boundary at the furthest edges of the solar system, far past the planets, some 8 million miles away. There, the constant stream of solar particles flowing off the sun, the solar wind, pushes up against the interstellar material flowing in from the local galactic neighborhood.

IBEX is also different because it creates images from particles instead of light. IBEX, scientists create maps from the observed neutral atoms. Some are of non-solar origin, others were created by collisions of solar wind particles with other neutral atoms far from the sun. Observing where these energetic neutral atoms, or ENAs, come from describes what's going on in these distant regions. Over the course of six months and many orbits around Earth, IBEX can paint a picture of the entire sky in ENAs. 

During its first five years, IBEX has made some astounding discoveries.

Mapping the Boundaries

In its first year, IBEX scientists created the first-ever all-sky map of the heliosphere's boundary, where the influence of the solar wind diminishes and interacts with the interstellar medium. The most startling finding is that the map was not uniform or symmetrical, but shows a bright ribbon of energetic neutral atoms snaking through it.

During its second and third years, IBEX showed that the heliosphere's boundaries changed more rapidly than expected, with variations as short as six months. Additional sets of all-sky maps showed the evolution of the interstellar boundary region: the mysterious ribbon feature at the nose, of the heliosphere – in the front as it moves through space – evolved.  Also, a knot-like feature spread and diminished. This variation over time is challenging scientists to try to understand how the heliosphere can change so rapidly.

ENAs Near Earth

Because IBEX is orbiting Earth, it also can look back toward Earth's neutral-atom environment and so has provided the first ENA images of the magnetosphere from the outside.

Nearby, IBEX has scanned the moon, as well. The moon has no atmosphere or magnetosphere, so the solar wind slams unimpeded into its surface. IBEX observations showed that the moon creates a backscattered, neutral solar wind: about 10 percent of the impinging solar-wind protons bounce off the lunar surface, becoming ENAs as they do.

The Heliosphere: Looking Ahead and Looking Behind

Measurements by IBEX announced in 2012 show the influence of the heliosphere on the local interstellar medium is different than expected. Previous models showed a boundary ahead of the heliosphere, outside the influence of the sun: a shock formed by the entire heliosphere pushing through the interstellar material around it. IBEX data suggests that there is no bow shock preceding the heliosphere's movement through space.

IBEX also offered up the first observations of the heliotail. If our eyes could see particles and we looked straight down the tail we would see an unexpected shape a little like a four-leaf clover. The two side leaves are filled with slow moving particles and the upper and lower leaves with fast ones.

Into the Galaxy

Much further away, IBEX also provided information about the local galactic environment. It made the first direct measurements of neutral hydrogen, oxygen, and neon coming into the heliosphere from the interstellar medium. The measurements show that the composition of the current galactic neighborhood is different than that of the sun and the solar system. This puzzle may mean that the sun has moved out of the region where it formed, or that some of the oxygen has been captured by dust in interstellar space.

IBEX also found that the speed of the galactic wind registered around 52 thousand miles per hour. By comparing this wind to previous results from other missions over the last 40 years, scientists believe that the direction of the wind has changed by about 7 degrees in the last four decades. While the cause of this shift is unknown, it may be telling us something about changing conditions as we move through our region of the Milky Way.

IBEX is a NASA Heliophysics Small Explorer mission. The Southwest Research Institute in San Antonio, Texas, leads IBEX with teams of national and international partners. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the Explorers Program for the agency's Science Mission Directorate in Washington.

Related Links

• NASA's IBEX website

• High Resolution Media

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md. 

A Ghostly Trio from NASA's Spitzer Space Telescope

Death Beckons Three Aging Stars
This trio of ghostly images from NASA's Spitzer Space Telescope shows the disembodied remains of dying stars called planetary nebulas. Planetary nebulas are a late stage in a sun-like star's life, when its outer layers have sloughed off and are lit up by ultraviolet light from the central star. They come in a variety of shapes, as indicated by these three spooky structures.  In all of the images, infrared light at wavelengths of 3.6 microns is rendered in blue, 4.5 microns in green, and 8.0 microns in red. Credit: NASA/JPL-Caltech/J.

In the spirit of Halloween, scientists are releasing a trio of stellar ghosts caught in infrared light by NASA's Spitzer Space Telescope. All three spooky structures, called planetary nebulas, are in fact material ejected from dying stars. As death beckoned, the stars' wispy bits and pieces were blown into outer space. 

"Some might call the images haunting," said Joseph Hora of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., principal investigator of the Spitzer observing program. "We look to the pictures for a sense of the history of the stars' mass loss, and to learn how they evolved over time."

All stars about the mass of our sun will die similarly ethereal deaths. As sun-like stars grow old, billions of years after their inception, they run out of fuel in their cores and puff up into red, giant stars, aptly named "red giants." The stars eventually cast off their outer layers, which expand away from the star. When ultraviolet light from the core of a dying star energizes the ejected layers, the billowy material glows, bringing their beautiful shapes to light. 

These objects in their final death throes, the planetary nebulas, were named erroneously after their resemblance to planets by William Herschel in 1785. They come in an array of shapes, as illustrated by the three highlighted here in infrared images from Spitzer. The ghostly material will linger for only a few thousand years before ultimately fading into the dark night.

Exposed Cranium Nebula

The brain-like orb called PMR 1 has been nicknamed the "Exposed Cranium" nebula by Spitzer scientists. This planetary nebula, located roughly 5,000 light-years away in the Vela constellation, is host to a hot, massive dying star that is rapidly disintegrating, losing its mass. The nebula's insides, which appear mushy and red in this view, are made up primarily of ionized gas, while the outer green shell is cooler, consisting of glowing hydrogen molecules.

Ghost of Jupiter Nebula

The Ghost of Jupiter, also known as NGC 3242, is located roughly 1,400 light-years away in the constellation Hydra. Spitzer's infrared view shows off the cooler outer halo of the dying star, colored here in red. Also evident are concentric rings around the object, the result of material being tossed out periodically during the star's fitful death.

Little Dumbbell Nebula

This planetary nebula, known as NGC 650, or the Little Dumbbell, is about 2,500 light-years from Earth in the Perseus constellation. Unlike the other spherical nebulas, it has a bipolar or butterfly shape due to a "waist," or disk, of thick material, running from lower left to upper right. Fast winds blow material away from the star, above and below this dusty disk. The ghoulish green and red clouds are from glowing hydrogen molecules. The green area is hotter than the red.

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 in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

 Source: NASA's Spitzer Space Telescope

Chandra Archive Collection: Preserving the Legacy of the X-ray Universe

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Every year, October is designated as American Archive Month. While many people may think "archive" means only dusty books and letters, there are, in fact, many other types of important archives. This includes the use of archives for major telescopes and observatories like NASA's Chandra X-ray Observatory.

The Chandra Data Archive (CDA) plays a central role in the mission by enabling the astronomical community - as well as the general public - access to data collected by the observatory. The primary role of the CDA is to store and distribute data, which the CDA does with the help of powerful search engines. The CDA is one of the legacies of the Chandra mission that will serve both the scientific community and the public for decades to come.

To celebrate and support American Archive Month, we have selected images from a group of eight objects in the CDA to be released to the public for the first time. These images represent the observations of thousands of objects that are permanently available to the world thanks to Chandra's archive.

G266.2-1.2:
G266.2-1.2 was produced by the explosion of a massive star in the Milky Way galaxy. A Chandra observation of this supernova remnant reveals the presence of extremely high-energy particles produced as the shock wave from this explosion expands into interstellar space. In this image, the X-rays from Chandra (purple) have been combined with optical data from the Digitized Sky Survey (red, green, and blue).

3C353:
Jets generated by supermassive black holes at the centers of galaxies can transport huge amounts of energy across great distances. 3C353 is a wide, double-lobed source where the galaxy is the tiny point in the center and giant plumes of radiation can be seen in X-rays from Chandra (purple) and radio data from the Very Large Array (orange).

NGC 3576:
A region of glowing gas in the Sagittarius arm of the Milky Way galaxy, NGC 3576 is located about 9,000 light years from Earth. Such nebulas present a tableau of the drama of the evolution of massive stars, from the formation in vast dark clouds, their relatively brief (a few million years) lives, and the eventual destruction in supernova explosions. The diffuse X-ray data detected by Chandra (blue) are likely due to the winds from young, massive stars that are blowing throughout the nebula. Optical data from ESO are shown in orange and yellow.

NGC 4945:
This image provides a view into the central region of a galaxy that is similar in overall appearance to our own Milky Way, but contains a much more active supermassive black hole within the white area near the top. This galaxy, known as NGC 4945, is only about 13 million light years from Earth and is seen edge-on. X-rays from Chandra (blue), which have been overlaid on an optical image from the European Space Observatory, reveal the presence of the supermassive black hole at the center of this galaxy.

IC 1396A:
When radiation and winds from massive young stars impact clouds of cool gas, they can trigger new generations of stars to form. This is what may be happening in this object known as the Elephant Trunk Nebula (or its official name of IC 1396A). X-rays from Chandra (purple) have been combined with optical (red, green, and blue) and infrared (orange and cyan) to give a more complete picture of this source.

3C 397 (G41.1-0.3):
3C 397 (also known as G41.1-0.3) is a Galactic supernova remnant with an unusual shape. Researchers think its box-like appearance is produced as the heated remains of the exploded star -- detected by Chandra in X-rays (purple) -- runs into cooler gas surrounding it. This composite of the area around 3C 397 also contains infrared emission from Spitzer (yellow) and optical data from the Digitized Sky Survey (red, green, and blue).

SNR B0049-73.6:
The details of how massive stars explode remains one of the biggest questions in astrophysics. Located in the neighboring galaxy of the Small Magellanic Cloud, this supernova, SNR B0049-73.6, provides astronomers with another excellent example of such an explosion to study. Chandra observations of the dynamics and composition of the debris from the explosion support the view that the explosion was produced by the collapse of the central core of a star. In this image, X-rays from Chandra (purple) are combined with infrared data from the 2MASS survey (red, green, and blue).

NGC 6946:
NGC 6946 is a medium-sized, face-on spiral galaxy about 22 million light years away from Earth. In the past century, eight supernovas have been observed to explode in the arms of this galaxy. Chandra observations (purple) have, in fact, revealed three of the oldest supernovas ever detected in X-rays, giving more credence to its nickname of the "Fireworks Galaxy." This composite image also includes optical data from the Gemini Observatory in red, yellow, and cyan.

Source: Chandra X-Ray Observatory

 

Carbon Worlds May be Waterless, Finds NASA Study

This artist's concept illustrates the fate of two different planets: the one on the left is similar to Earth, made up largely of silicate-based rocks with oceans coating its surface. The one on the right is rich in carbon -- and dry. Chances are low that life as we know it, which requires liquid water, would thrive under such barren conditions. Image credit: NASA/JPL-Caltech.  › Full image and caption

Planets rich in carbon, including so-called diamond planets, may lack oceans, according to NASA-funded theoretical research.

Our sun is a carbon-poor star, and as result, our planet Earth is made up largely of silicates, not carbon. Stars with much more carbon than the sun, on the other hand, are predicted to make planets chock full of carbon, and perhaps even layers of diamond.

By modeling the ingredients in these carbon-based planetary systems, the scientists determined they lack icy water reservoirs thought to supply planets with oceans.

"The building blocks that went into making our oceans are the icy asteroids and comets," said Torrence Johnson of NASA's Jet Propulsion Laboratory in Pasadena, Calif, who presented the results Oct. 7 at the American Astronomical Society Division of Planetary Sciences meeting in Denver. Johnson, a team member of several NASA planetary missions, including Galileo, Voyager and Cassini, has spent decades studying the planets in our own solar system.

"If we keep track of these building blocks, we find that planets around carbon-rich stars come up dry," he said.

Johnson and his colleagues say the extra carbon in developing star systems would snag the oxygen, preventing it from forming water.

"It's ironic that if carbon, the main element of life, becomes too abundant, it will steal away the oxygen that would have made water, the solvent essential to life as we know it," said Jonathan Lunine of Cornell University, Ithaca, N.Y., a collaborator on the research.

One of the big questions in the study of planets beyond our solar system, called exoplanets, is whether or not they are habitable. Researchers identify such planets by first looking for those that are situated within the "habitable zone" around their parent stars, which is where temperatures are warm enough for water to pool on the surface. NASA's Kepler mission has found several planets within this zone, and researchers continue to scrutinize the Kepler data for candidates as small as Earth.

But even if a planet is found in this so-called "Goldilocks" zone, where oceans could, in theory, abound, is there actually enough water available to wet the surface? Johnson and his team addressed this question with planetary models based on measurements of our sun's carbon-to-oxygen ratio. Our sun, like other stars, inherited a soup of elements from the Big Bang and from previous generations of stars, including hydrogen, helium, nitrogen, silicon, carbon and oxygen.

"Our universe has its own top 10 list of elements," said Johnson, referring to the 10 most abundant elements in our universe.

These models accurately predict how much water was locked up in the form of ice early in the history of our solar system, billions of years ago, before making its way to Earth. Comets and/or the parent bodies of asteroids are thought to have been the main water suppliers, though researchers still debate their roles. Either way, the objects are said to have begun their journey from far beyond Earth, past a boundary called the "snow line," before impacting Earth and depositing water deep in the planet and on its surface.

When the researchers applied the planetary models to the carbon-rich stars, the water disappeared. "There's no snow beyond the snow line," said Johnson.

"All rocky planets aren't created equal," said Lunine. "So-called diamond planets the size of Earth, if they exist, will look totally alien to us: lifeless, ocean-less desert worlds."

The computer model results supporting these conclusions were published in the Astrophysical Journal last year (http://arxiv.org/abs/1208.3289). The implications for habitability in these systems were the focus of the Division of Planetary Sciences meeting.

The California Institute of Technology, Pasadena, manages JPL for NASA.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov  

ALMA Reveals Ghostly Shape of ‘Coldest Place in the Universe’

The Boomerang Nebula, called the “coldest place in the Universe,” reveals its true shape with ALMA. The background blue structure, as seen in visible light with the Hubble Space Telescope, shows a classic double-lobe shape with a very narrow central region. ALMA’s resolution and ability to see the cold molecular gas reveals the nebula’s more elongated shape, as seen in red.  Credit: Bill Saxton; NRAO/AUI/NSF; NASA/Hubble; Raghvendra Saha. Low-resolution JPEG image - High-resolution TIFF image

At a cosmologically crisp one degree Kelvin (minus 458 degrees Fahrenheit), the Boomerang Nebula is the coldest known object in the Universe – colder, in fact, than the faint afterglow of the Big Bang, which is the natural background temperature of space.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope have taken a new look at this intriguing object to learn more about its frigid properties and to determine its true shape, which has an eerily ghost-like appearance.

As originally observed with ground-based telescopes, this nebula appeared lopsided, which is how it got its name. Later observations with the Hubble Space Telescope revealed a bow-tie-like structure. The new ALMA data, however, reveal that the Hubble image tells only part of the story, and the twin lobes seen in that image may actually be a trick of the light as seen at visible wavelengths.

“This ultra-cold object is extremely intriguing and we’re learning much more about its true nature with ALMA,” said Raghvendra Sahai, a researcher and principal scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, and lead author of a paper published in the Astrophysical Journal. “What seemed like a double lobe, or ‘boomerang’ shape, from Earth-based optical telescopes, is actually a much broader structure that is expanding rapidly into space.”

The Boomerang Nebula, located about 5,000 light-years away in the constellation Centaurus, is a relatively young example of an object known as a planetary nebula. Planetary nebulae, contrary to their name, are actually the end-of-life phases of stars like our Sun that have sloughed off their outer layers. What remains at their centers are white dwarf stars, which emit intense ultraviolet radiation that causes the gas in the nebulae to glow and emit light in brilliant colors.

The Boomerang is a pre-planetary nebula, representing the stage in a star's life immediately preceding the planetary nebula phase, when the central star is not yet hot enough to emit enough ultraviolet radiation to produce the characteristic glow. At this stage, the nebula is seen by starlight reflecting off its dust grains.

The outflow of gas from this particular star is expanding rapidly and cooling itself in the process. This is similar in principle to the way refrigerators use expanding gas to produce cold temperatures. The researchers were able to take the temperature of the gas in the nebula by seeing how it absorbed the cosmic microwave background radiation, which has a very uniform temperature of 2.8 degrees Kelvin (minus 455 degrees Fahrenheit).

“When astronomers looked at this object in 2003 with Hubble, they saw a very classic ‘hourglass’ shape,” commented Sahai. “Many planetary nebulae have this same double-lobe appearance, which is the result of streams of high-speed gas being jettisoned from the star. The jets then excavate holes in a surrounding cloud of gas that was ejected by the star even earlier in its lifetime as a red giant.”

Observations with single-dish millimeter wavelength telescopes, however, did not detect the narrow waist seen by Hubble. Instead, they found a more uniform and nearly spherical outflow of material.

ALMA’s unprecedented resolution allowed the researchers to reconcile this discrepancy. By observing the distribution of carbon monoxide molecules, which glow brightly at millimeter wavelengths, the astronomers were able to detect the double-lobe structure that is seen in the Hubble image, but only in the inner regions of the nebula. Further out, they actually observed a more elongated cloud of cold gas that is roughly round.

The researchers also discovered a dense lane of millimeter-sized dust grains surrounding the star, which explains why this outer cloud has an hourglass shape in visible light. The dust grains have created a mask that shades a portion of the central star and allows its light to leak out only in narrow but opposite directions into the cloud, giving it an hourglass appearance.

“This is important for the understanding of how stars die and become planetary nebulae,” said Sahai. “Using ALMA, we were quite literally and figuratively able to shed new light on the death throes of a Sun-like star.”

The new research also indicated that the outer fringes of the nebula are beginning to warm, even though they are still slightly colder than the cosmic microwave background. This warming may be due to the photoelectric effect -- an effect first proposed by Einstein in which light is absorbed by solid material, which then re-emits electrons.

Additional authors on this paper include Wouter Vlemmings, Chalmers University of Technology, Onsala, Sweden; Patrick Huggins, New York University, New York; Lars-Ake Nyman, Joint ALMA Observatory, Santiago de Chile; and Yiannis Gonidakis, CSIRO, Australia Telescope National Facility.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Contact: 

Charles Blue
(434) 296-0314

Email: cblue@nrao.edu

Unique Chemical Composition Surrounding Supermassive Black Hole – A Step toward Development of New Black Hole Exploration Method

The Atacama Large Millimeter/submillimeter Array (ALMA) successfully captured a detailed image of high density molecular gas around an active galactic nucleus harboring a supermassive black hole. The observations at the highest ever achieved reveal a unique chemical composition characterized by enhancement of hydrogen cyanide (HCN) around the black hole. An research team thought a high temperature affected by the black hole caused this peculiar chemical properties. The team expect that this unique chemical properties can be used to find black holes hidden behind dust. 

Spiral galaxy NGC 1097 observed with European Southern Observatory’s Very large Telescope in optical wavelength (left) and the central 2100 light years observed with ALMA (right). The ALMA observations reveal intense emission from dust around the central black hole and in the circum-nuclear star burst ring. The star sign shows the location of the emission peak in near infrared, which reflects the star formation activity, whereas the central plus sign shows the location of the radio emission peak in the wavelength of 6 cm which comes from the active supermassive black hole. The emission peak position in the ALMA image agrees well with that of 6 cm emission. This ensures that ALMA detects the emission from the vicinity of the central black hole.

The research findings are presented in the article “Submillimeter ALMA Observation of the Dense Gas in the Low-Luminosity Type-1 Active Nucleus of NGC 1097” published in the Publication of the Astronomical Society of Japan, Vol. 65, of October 25, 2013.  

Link  

• Unique Chemical Composition Surrounding Supermassive Black Hole – A Step toward Development of New Black Hole Exploration Method

•  Graduate School of Science, the University of Tokyo

Source: NAOJ - National Astronomical Observatory of Japan

Fat Black Holes Grown up in Cities: “Observational” result using Virtual Observatory

An artist’s illustration of galaxy distribution, a host galaxy of an active galactic nucleus (AGN), and an active galactic nucleus. An AGN is a luminous compact region at the center of the galaxy, powered by the accretion of gas onto the massive black hole. This research reveals that the mass of a massive black hole at the galaxy center is related to the distribution of surrounding galaxies.

The research team investigated environment in which a galaxy with a massive black hole at its center exists. The team’s research extended over data for approximately 70 million galaxies, with approximately 10,000 massive black holes researched. This vast amount of data was collected through the Virtual Observatory; it connects a variety of astronomical databases around the world via the Internet, making it possible to comprehensively use the collected data.

The difference of galactic density according to black-hole mass (the vertical axis shows the size of regions with enhanced galactic density: the bigger the size, the higher the density). The heavier black holes are located in galaxies with higher density for black holes with mass larger than ~10^8 solar mass. While the less massive black holes show no correlation between the mass of black holes and the density of galaxies.

The scientific paper on which this article is based appears in the Astrophysical Journal. (Komiya et al. “A Cross-correlation Analysis of Active Galactic Nuclei and Galaxies Using Virtual Observatory: Dependence on Virial Mass of Supermassive Black Hole”, published in the Astrophysical Journal, vol.775, article id.43)

Link

• Fat Black Holes Grown up in Cities: “Observational” result using Virtual Observatory
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Source:  NAOJ - National Astronomical Observatory of Japan

NASA Releases Movie of Sun's Canyon of Fire

Images of a gigantic filament eruption on the sun were captured on Sept. 29-30, 2013, by NASA's Solar Dynamics Observatory, or SDO. Image Credit:NASA/SDO. › View Promo Image

A magnetic filament of solar material erupted on the sun in late September, breaking the quiet conditions in a spectacular fashion. The 200,000 mile long filament ripped through the sun's atmosphere, the corona, leaving behind what looks like a canyon of fire. The glowing canyon traces the channel where magnetic fields held the filament aloft before the explosion.  Visualizers at NASA's Goddard Space Flight Center in Greenbelt, Md. combined two days of satellite data to create a short movie of this gigantic event on the sun.

In reality, the sun is not made of fire, but of something called plasma: particles so hot that their electrons have boiled off, creating a charged gas that is interwoven with magnetic fields.

These images were captured on Sept. 29-30, 2013, by NASA's Solar Dynamics Observatory, or SDO, which constantly observes the sun in a variety of wavelengths.

Different wavelengths help capture different aspect of events in the corona. The red images shown in the movie help highlight plasma at temperatures of 90,000° F and are good for observing filaments as they form and erupt. The yellow images, showing temperatures at 1,000,000° F, are useful for observing material coursing along the sun's magnetic field lines, seen in the movie as an arcade of loops across the area of the eruption. The browner images at the beginning of the movie show material at temperatures of 1,800,000° F, and it is here where the canyon of fire imagery is most obvious.  By comparing this with the other colors, one sees that the two swirling ribbons moving farther away from each other are, in fact, the footprints of the giant magnetic field loops, which are growing and expanding as the filament pulls them upward.

The movie runs 2.3 minutes and is available for download in high resolution at: http://svs.gsfc.nasa.gov/goto?11379

Related Links

•   NASA's SDO website
•   Associated NASA news story
•   NASA's Solar Event archives

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md.

NASA's SDO Sees Sun Emit a Mid-level Solar Flare

NASA's Solar Dynamics Observatory or SDO, captured this image on the sun of an M9.4-class solar flare, which peaked at 8:30 pm EDT on Oct. 23, 2013. The image displays light in the wavelength of 131 Angstroms, which is good for viewing the intense heat of a solar flare and typically colored teal. Image Credit: NASA/SDO. › View full disk image

The sun emitted a mid-level solar flare that peaked at 8:30 pm EDT on Oct. 23, 2013. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however -- when intense enough -- they can disturb the atmosphere in the layer where GPS and communications signals travel. Such radiation can disrupt radio signals for as long as the flare is ongoing, anywhere from minutes to hours.

To see how this event may impact Earth, please visit NOAA's Space Weather Prediction Center at http://spaceweather.gov, the U.S. government's official source for space weather forecasts, alerts, watches and warnings.

This flare is classified as an M9.4 flare, on a scale from M1 to M9.9.  This rating puts it at the very top of the scale for M class flares, which are the weakest flares that can cause some space weather effects near Earth. In the past, they have caused brief radio blackouts at the poles.  The next highest level is X-class, which denotes the most intense flares.

Increased numbers of flares are quite common at the moment, since the sun is near solar maximum. Humans have tracked solar cycles continuously since they were discovered in 1843, and it is normal for there to be many flares a day during the sun's peak activity.

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md. 

Sagittarius A*: A Glimpse of the Violent Past of Milky Way's Giant Black Hole

Sagittarius A*

Credit: NASA/CXC/APC/Université Paris Diderot/M.Clavel et al

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Sagittarius A* Time-Lapse

More Animations

Researchers using NASA's Chandra X-ray Observatory have found evidence that the normally dim region very close to the supermassive black hole at the center of the Milky Way Galaxy flared up with at least two luminous outbursts in the past few hundred years.

This discovery comes from a new study of rapid variations in the X-ray emission from gas clouds surrounding the supermassive black hole, a.k.a. Sagittarius A*, or Sgr A* for short. The scientists show that the most probable interpretation of these variations is that they are caused by light echoes.

The echoes from Sgr A* were likely produced when large clumps of material, possibly from a disrupted star or planet, fell into the black hole. Some of the X-rays produced by these episodes then bounced off gas clouds about thirty to a hundred light years away from the black hole, similar to how the sound from a person's voice can bounce off canyon walls. Just as echoes of sound reverberate long after the original noise was created, so too do light echoes in space replay the original event.

While light echoes from Sgr A* have been seen before in X-rays by Chandra and other observatories, this is the first time that evidence for two distinct flares has been seen within a single set of data.

More than just a cosmic parlor trick, light echoes provide astronomers an opportunity to piece together what objects like Sgr A* were doing long before there were X-ray telescopes to observe them. The X-ray echoes suggest that the area very close to Sgr A* was at least a million times brighter within the past few hundred years. X-rays from the outbursts (as viewed in Earth's time frame) that followed a straight path would have arrived at Earth at that time. However, the reflected X-rays in the light echoes took a longer path as they bounced off the gas clouds and only reached Chandra in the last few years.

A new animation shows Chandra images that have been combined from data taken between 1999 and 2011. This sequence of images, where the position of Sgr A* is marked with a cross, show how the light echoes behave. As the sequence plays, the X-ray emission appears to be moving away from the black hole in some regions. In other regions it gets dimmer or brighter, as the X-rays pass into or away from reflecting material.

The X-ray emission shown here is from a process called fluorescence. Iron atoms in these clouds have been bombarded by X-rays, knocking out electrons close to the nucleus and causing electrons further out to fill the hole, emitting X-rays in the process. Other types of X-ray emission exist in this region but are not shown here, explaining the dark areas.

This is the first time that astronomers have seen both increasing and decreasing X-ray emission in the same structures. Because the change in X-rays lasts for only two years in one region and over ten years in others, this new study indicates that at least two separate flares were responsible for the light echoes observed from Sgr A*.

There are several possible causes of the flares: a short-lived jet produced by the partial disruption of a star by Sgr A*; the ripping apart of a planet by Sgr A*; the collection by Sgr A* of debris from close encounters between two stars; and an increase in the consumption of material by Sgr A* because of clumps in the gas ejected by massive stars orbiting Sgr A*. Further studies of the variations are needed to decide between these options.

The researchers also examined the possibility that a magnetar - a neutron star with a very strong magnetic field - recently discovered near Sgr A* might be responsible for these variations. However, this would require an outburst that is much brighter than the brightest magnetar flare ever observed.

A paper describing these results has been published in the October 2013 issue of the journal Astronomy and Astrophysics and is available online. The first author is Maïca Clavel from AstroParticule et Cosmologie (APC) in Paris, France. The co-authors are Régis Terrier and Andrea Goldwurm from APC; Mark Morris from University of California, Los Angeles, CA; Gabriele Ponti from Max-Planck Institute for Extraterrestrial Physics, Garching, Germany; Simona Soldi from APC and Guillaume Trap from Palais de la découverte - Universcience, Paris, France.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra Program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

Fast Facts for Sagittarius A*:


Scale Image: is about 18.5 arcmin across (about 140 light years)
Category: Black Holes, Milky Way Galaxy
Coordinates (J2000): RA 17h 45m 40s | Dec -29° 00' 28.00"
Constellation: Sagittarius
Observation Date: 54 pointings between 21 Sep 1999 and 29 Jul 2011
Observation Time: 477 hours 21 min (19 days 21 hours 21 min).
Obs. ID: 242, 945, 1561, 2273, 2276, 2282, 2284, 2943, 2951-2954, 3392, 3393, 3549, 3663, 3665, 4500, 4683, 4684, 5360, 5950-5954, 6113, 6363, 6639-6646, 7048, 7554-7559, 9169-9174, 10556, 11843, 12949, 13438, 13508
Instrument: ACIS
Also Known As: Galactic Center
References: Clavel, M. et al, 2013, A&A 558, A32; arXiv:1307.3954 
Color Code: X-ray (Blue) 
Distance Estimate: About 26,000 light years

NASA's Great Observatories Begin Deepest Ever Probe of the Universe

Abell 2744, Pandora's Cluster, MACS J0416.1-2403, MACS J0717.5+3745, MACS J1149.5+2223. Credit: NASA, ESA, and J. Lotz and M. Mountain (STScI).  Release Images

NASA's Great Observatories are teaming up to look deeper into the universe than ever before. With a boost from natural "zoom lenses" found in space, they should be able to uncover galaxies that are as much as 100 times fainter than what the Hubble, Spitzer, and Chandra space telescopes can typically see.

This ambitious collaborative program is called The Frontier Fields. Astronomers will spend the next three years peering at six massive clusters of galaxies. Researchers are interested not only as to what's inside the clusters, but also what's behind them. The gravitational fields of the clusters brighten and magnify distant background galaxies that are so faint they would otherwise be unobservable.

The clusters themselves are among the most massive assemblages of matter known.

Astronomers anticipate that these observations will reveal populations of never-before-seen galaxies that existed when the universe was only a few hundred million years old. The Hubble and Spitzer data will be combined to measure the galaxies' distances and masses more accurately than either observatory could measure alone, demonstrating the synergy of these Great Observatories for such studies. The Chandra X-ray Observatory will also peer deep into the fields, imaging them at X-ray wavelengths to help determine the masses and lensing power of the clusters, as well as identify background galaxies with massive black holes.

"The idea is to use nature's natural telescopes in combination with the Great Observatories to look much deeper than before and find the most distant and faint galaxies we can possibly see," said principal investigator Jennifer Lotz of the Space Telescope Science Institute (STScI) in Baltimore, Md.

"We want to understand when and how the first stars and galaxies formed in the universe, and each Great Observatory gives us a different piece of the puzzle. Hubble tells you which galaxies to look at and how many stars are being born in those systems. Spitzer tells you how old the galaxy is and how many stars have formed," said Peter Capak, the Spitzer principal investigator of the Frontier Fields program.

The high-resolution Hubble data from the Frontier Fields program will also be used to trace the distribution of dark matter within the foreground clusters. Accounting for the bulk of the universe's mass, dark matter is the underlying, invisible scaffolding attached to galaxies. "The apparent positions of those lensed galaxies then tell you what's happening with the cluster itself, where the dark matter is in that cluster," Lotz said. "We'll use that information to make a better model of the cluster to better understand its lensing power."

The Hubble and Spitzer observations will be much more challenging for researchers than previous deep fields that have been studied by this powerful pair of observatories with great success. "With a deep image, you've got a direct image — what you see is what you get. But when we use a gravitational lens, background galaxies appear distorted and brighter," Lotz said. "In order to understand the true properties of a background galaxy, you have to understand how it is distorted and how it is magnified. This depends on the distribution of dark matter in the gravitational lens — the foreground cluster."

What's more, the galaxies seen in previous ultra-deep fields are just the most massive at those epochs. "They are the tip of the iceberg. If you want to see the galaxies that will turn into ones like our Milky Way, you have to go much fainter," Lotz said. Without using the big natural telescopes in space, astronomers would have to wait for the James Webb Space Telescope. In fact, the Frontier Fields offer a sneak peek of what the Webb telescope will routinely see anywhere it points in space, when it is launched in 2018.

The Hubble Frontier Fields initiative grew out of high-level discussions at STScI concerning what important, forward-looking science Hubble should be doing in upcoming years. Despite several deep field surveys, astronomers realized that a lot was still to be learned about the distant universe. And, such knowledge would help in planning the observing strategy for the Webb telescope.

To get a better assessment of whether doing more deep field observations was scientifically interesting or urgent, STScI chartered a "Hubble Deep Field Initiative" working group, which included U.S. and European astronomers who were expert users of the Great Observatories. The astronomers also considered synergies with other observatories, such as Spitzer, Chandra, and the new Atacama Large Millimeter Array. STScI Director Matt Mountain allocated his director's discretionary time to the program.

The first object to be looked at this month is called Pandora's Cluster (Abell 2744), which has been previously observed by all three Great Observatories but not to the depth of the new observations. The giant galaxy cluster appears to be the result of a simultaneous pile-up of at least four separate, smaller galaxy clusters that took place over a span of 350 million years.

Join several members of the Frontier Fields collaboration during the live Hubble Hangout event at 4:00pm (EDT) on Thursday, October 24 to discuss more on what's to come from these observations, how the clusters were chosen, and what we hope to learn from them. Visit: https://plus.google.com/u/0/events/cpl8pr6rjvls7en3c9ltrgelc80 . 

CONTACT

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Jennifer Lotz
Space Telescope Science Institute, Baltimore, Md.
410-338-4467
lotz@stsci.edu

Cassini Gets New Views of Titan's Land of Lakes

This false-color mosaic, made from infrared data collected by NASA's Cassini spacecraft, reveals the differences in the composition of surface materials around hydrocarbon lakes at Titan, Saturn's largest moon. Image Credit: NASA/JPL-Caltech/University of Arizona/University of Idaho. Full image and caption

Almost all of the hydrocarbon seas and lakes on the surface of Saturn's moon Titan cluster around the north pole, as can be seen in this mosaic from NASA's Cassini mission. Image Credit: NASA/JPL-Caltech/SSI/JHUAPL/Univ. of Arizona. Full image and caption

Ultracold hydrocarbon lakes and seas (dark shapes) near the north pole of Saturn's moon Titan can be seen embedded in some kind of bright surface material in this infrared mosaic from NASA's Cassini mission. Image Credit: NASA/JPL-Caltech/SSI/JHUAPL/Univ. of Arizona. Full image and caption

The vast hydrocarbon seas and lakes (dark shapes) near the north pole of Saturn's moon Titan sprawl out beneath the watchful eye of NASA's Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI/JHUAPL/Univ. of Arizona. Full image and caption

PASADENA, Calif.-- With the sun now shining down over the north pole of Saturn's moon Titan, a little luck with the weather, and trajectories that put the spacecraft into optimal viewing positions, NASA's Cassini spacecraft has obtained new pictures of the liquid methane and ethane seas and lakes that reside near Titan's north pole. The images reveal new clues about how the lakes formed and about Titan's Earth-like "hydrologic" cycle, which involves hydrocarbons rather than water.

The new images are available online at: http://www.nasa.gov/mission_pages/cassini/multimedia/index.html.

While there is one large lake and a few smaller ones near Titan's south pole, almost all of Titan's lakes appear near the moon's north pole. Cassini scientists have been able to study much of the terrain with radar, which can penetrate beneath Titan's clouds and thick haze. And until now, Cassini's visual and infrared mapping spectrometer and imaging science subsystem had only been able to capture distant, oblique or partial views of this area.

Several factors combined recently to give these instruments great observing opportunities. Two recent flybys provided better viewing geometry. Sunlight has begun to pierce the winter darkness that shrouded Titan's north pole at Cassini's arrival in the Saturn system nine years ago. A thick cap of haze that once hung over the north pole has also dissipated as northern summer approaches. And Titan's beautiful, nearly cloudless, rain-free weather continued during Cassini's flybys this past summer.

The images are mosaics in infrared light based on data obtained during flybys of Titan on July 10, July 26, and Sept. 12, 2013. The colorized mosaic from the visual and infrared mapping spectrometer, which maps infrared colors onto the visible-color spectrum, reveals differences in the composition of material around the lakes. The data suggest parts of Titan's lakes and seas may have evaporated and left behind the Titan equivalent of Earth's salt flats. Only at Titan, the evaporated material is thought to be organic chemicals originally from Titan's haze particles that once dissolved in liquid methane. They appear orange in this image against the greenish backdrop of Titan's typical bedrock of water ice.

"The view from Cassini's visual and infrared mapping spectrometer gives us a holistic view of an area that we'd only seen in bits and pieces before and at a lower resolution," said Jason Barnes, a participating scientist for the instrument at the University of Idaho, Moscow. "It turns out that Titan's north pole is even more interesting than we thought, with a complex interplay of liquids in lakes and seas and deposits left from the evaporation of past lakes and seas."

The near-infrared images from Cassini's imaging cameras show a bright unit of terrain in the northern land of lakes that had not previously been visible in the data. The bright area suggests that the surface here is unique from the rest of Titan, which might explain why almost all of the lakes are found in this region. Titan's lakes have very distinctive shapes -- rounded cookie-cutter silhouettes and steep sides -- and a variety of formation mechanisms have been proposed. The explanations range from the collapse of land after a volcanic eruption to karst terrain, where liquids dissolve soluble bedrock. Karst terrains on Earth can create spectacular topography such as the Carlsbad Caverns in New Mexico.

"Ever since the lakes and seas were discovered, we've been wondering why they're concentrated at high northern latitudes," said Elizabeth (Zibi) Turtle, a Cassini imaging team associate based at the Johns Hopkins Applied Physics Laboratory, Laurel, Md. "So, seeing that there's something special about the surface in this region is a big clue to help narrow down the possible explanations."

Launched in 1997, Cassini has been exploring the Saturn system since 2004. A full Saturn year is 30 years, and Cassini has been able to observe nearly a third of a Saturn year. In that time, Saturn and its moons have seen the seasons change from northern winter to northern summer.

"Titan's northern lakes region is one of the most Earth-like and intriguing in the solar system," said Linda Spilker, Cassini project scientist, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We know lakes here change with the seasons, and Cassini's long mission at Saturn gives us the opportunity to watch the seasons change at Titan, too. Now that the sun is shining in the north and we have these wonderful views, we can begin to compare the different data sets and tease out what Titan's lakes are doing near the north pole."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate, Washington. The California Institute of Technology in Pasadena manages JPL for NASA. The VIMS team is based at the University of Arizona in Tucson. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini mission, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov