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June 1, 2006, 7:24 PM CT

The Case of the Neutron Star

The Case of the Neutron Star
A long observation with NASA's Chandra X-ray Observatory revealed important new details of a neutron star that is spewing out a wake of high-energy particles as it races through space. The deduced location of the neutron star on the edge of a supernova remnant, and the peculiar orientation of the neutron star wake, pose mysteries that remain unresolved.

"Like a kite flying in the wind, the behavior of this neutron star and its wake tell us what sort of gas it must be plowing through," said Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and lead author of a paper submitted to The Astrophysical Journal. "Yet we're still not sure how the neutron star got to its present location".

The neutron star, known as CXOU J061705.3+222127, or J0617 for short, appears to lie near the outer edge of an expanding bubble of hot gas associated with the supernova remnant IC 443. Presumably, J0617 was created at the time of the supernova -- approximately 30,000 years ago -- and propelled away from the site of the explosion at about 500,000 miles per hour.

However, the neutron star's wake is oriented almost perpendicularly to the direction expected if the neutron star were moving away from the center of the supernova remnant. This apparent misalignment had previously raised doubts about the association of the speeding neutron star with the supernova remnant.........

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June 1, 2006, 6:39 PM CT

From Dark To Bright And Red To White

From Dark To Bright And Red To White
Cassini's landmark investigation of Saturn's yin-yang moon Iapetus, with its bright and dark hemispheres, continues to provide insights into the nature of this intriguing body.

These two views of Iapetus primarily show terrain in the southern part of the moon's dark leading hemisphere -- the side of Iapetus that is coated with dark material. The bright south pole of Iapetus is visible, along with some terrain (at the bottom) that lies on the bright trailing hemisphere.

The dark terrain known as Cassini Regio is uniformly dark between the equator and about 30 degrees south latitude. From there down to about 50 to 60 degrees south latitude, the dark material looks "patchy" because south-facing crater walls are bright (being largely devoid of the dark material). South of this region, only some northward-facing crater walls are still dark, while the bright terrain has a somewhat reddish color.

See Dark-stained Iapetus for an up-close view of this transition in the northern hemisphere.

Beyond 90 degrees south (i.e., on the trailing side), the reddish color becomes white. The region at the bottom of the color view presented here shows this "color boundary" in the bright terrain, which also marks the boundary between the leading and trailing hemispheres.........

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May 30, 2006, 11:28 PM CT

Interiors Of Extrasolar Planets

Interiors Of Extrasolar Planets
Up to now, astronomers have discovered 188 extrasolar planets, among which 10 are known as "transiting planets". These planets pass between their star and us at each orbit (Figure 1). Given the current technical limitations, the only transiting planets that can be detected are giant planets orbiting close to their parent star known as "hot Jupiters" or Pegasids. The ten transiting planets known thus far have masses between 110 and 430 Earth masses (for comparison, Jupiter, with 318 Earth masses, is the most massive planet in our Solar System).

Eventhough rare, transiting planets are the key to understanding planetary formation because they are the only ones for which both the mass and radius can be determined. In principle, the obtained mean density can constrain their global composition. However, translating a mean density into a global composition needs accurate models of the internal structure and evolution of planets. The situation is made difficult by our relatively poor knowledge of the behaviour of matter at high pressures (the pressure in the interiors of giant planets is more than a million times the atmospheric pressure on Earth). Of the nine transiting planets known up to April 2006, only the least massive one could have its global composition determined satisfactorily. It was shown to possess a massive core of heavy elements, about 70 times the mass of the Earth, with a 40 Earth-mass envelope of hydrogen and helium. Of the remaining eight planets, six were found to be mostly made up of hydrogen and helium, like Jupiter and Saturn, but their core mass could not be determined. The last two were found to be too large to be explained by simple models.........

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May 27, 2006, 10:34 AM CT

Hubble's Gravitational Lens

Hubble's Gravitational Lens
NASA's Hubble Space Telescope has captured the first-ever picture of a group of five star-like images of a single distant quasar.

The multiple-image effect seen in the Hubble picture is produced by a process called gravitational lensing, in which the gravitational field of a massive object - in this case, a cluster of galaxies - bends and amplifies light from an object - in this case, a quasar - farther behind it.

Eventhough a number of examples of gravitational lensing have been observed, this "quintuple quasar" is the only case so far in which multiple quasar images are produced by an entire galaxy cluster acting as a gravitational lens.

The background quasar is the brilliant core of a galaxy. It is powered by a black hole, which is devouring gas and dust and creating a gusher of light in the process. When the quasar's light passes through the gravity field of the galaxy cluster that lies between us and the quasar, the light is bent by the space-warping gravity field in such a way that five separate images of the object are produced surrounding the cluster's center. The fifth quasar image is embedded to the right of the core of the central galaxy in the cluster. The cluster also creates a cobweb of images of other distant galaxies gravitationally lensed into arcs.........

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May 24, 2006, 7:04 PM CT

Our Milky Way Galaxy

Our Milky Way Galaxy

Modeler's view of our Milky Way Galaxy in a lumpy halo with a number of satellites.

Photo: NASA. Simulation: Stefan Gottlober/AIP.........

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May 22, 2006, 2:05 PM CT

Storms Roll Past Saturn

Storms Roll Past Saturn
Three large and impressive vortices, including two that appear to be interacting, are captured here as they swirl through Saturn's active southern latitudes.

This view shows latitudes slightly to the north of those seen in Round and Round They Go and was taken a few minutes previous to the left side image in that release.

The image was taken with the Cassini spacecraft narrow-angle camera using a spectral filter sensitive to wavelengths of infrared light centered at 750 nanometers. The image was acquired on April 15, 2006, at a distance of approximately 3.9 million kilometers (2.4 million miles) from Saturn. The image scale is 23 kilometers (14 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.........

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May 21, 2006, 9:46 AM CT

Cluster Flies Through Earth's Electrical Switch

Cluster Flies Through Earth's Electrical Switch
ESA's Cluster satellites have flown through regions of the Earth's magnetic field that accelerate electrons to approximately one hundredth the speed of light. The observations present Cluster scientists with their first detection of these events and give them a look at the details of a universal process known as magnetic reconnection.

On 25 January 2005, the four Cluster spacecraft found themselves in the right place at the right time: a region of space known as an electron diffusion region. It is a boundary just a few kilometres thick that occurs at an altitude of approximately 60 000 kilometres above the Earth's surface. It marks the frontier between the Earth's magnetic field and that of the Sun. The Sun's magnetic field is carried to the Earth by a wind of electrically charged particles, known as the solar wind.

An electron diffusion region is like an electrical switch. When it is flipped, it uses energy stored in the Sun's and Earth's magnetic fields to heat the electrically charged particles in its vicinity to large speeds. In this way, it initiates a process that can result in the creation of the aurora on Earth, where fast-moving charged particles collide with atmospheric atoms and make them glow.

There is also a more sinister side to the electron diffusion regions. The accelerated particles can damage satellites by colliding with them and causing electrical charges to build up. These short circuit and destroy sensitive equipment.........

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May 18, 2006, 9:31 PM CT

Searching For Crater Chains

Searching For Crater Chains
As the fragments of shattered comet 73P/Schwassmann Wachmann 3 glide harmlessly past Earth this month in full view of backyard telescopes, onlookers can't help but wonder, what if a comet like that didn't miss, but actually hit our planet?

For the answer to that question, we look to the Sahara desert.

In a remote windswept area named Aorounga, in Chad, there are three craters in a row, each about 10 km in diameter. "We believe this is a 'crater chain' formed by the impact of a fragmented comet or asteroid about 400 million years ago in the Late Devonian period," explains Adriana Ocampo of NASA headquarters.

Right: A space-based radar image of Aorounga South. [More].

Ocampo and his colleagues discovered the chain in 1996. The main crater "Aorounga South" had been known for a number of years-it sticks out of the sand and can be seen from airplanes and satellites. But a second and possibly third crater were buried. They lay hidden until radar onboard the space shuttle (SIR-C) penetrated the sandy ground, revealing their ragged outlines.

"Here on Earth, crater chains are rare," says Ocampo, but they are common in other parts of the solar system.

The first crater chains were discovered by NASA's Voyager 1 spacecraft. In 1979 when the probe flew past Jupiter's moon Callisto, cameras recorded a line of craters, at least fifteen long, evenly spaced as if someone had strafed the moon with a Gatling gun. Eventually, eight chains were found on Callisto and three more on Ganymede.........

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May 18, 2006, 9:24 PM CT

How Big is Big?

How Big is Big?
A team of scientists, which includes a Penn State astronomer, is announcing the construction of a new map of the sky containing more than 600,000 galaxies that covers distances of well over a billion light-years. "The map was created with data from several years of observations by the Sloan Digital Sky Survey," said Penn State Professor of Astronomy and Astrophysics Donald Schneider, a coauthor of the investigation. "The extremely large luminosities of the galaxies allow us to detect them at great distances, and the large-scale distribution of the sources carries information about the conditions present in the very early universe." Schneider is the Chairman of the Sloan Digital Sky Survey (SDSS) Quasar Science Group and the SDSS Scientific Publications Coordinator.

Since the 1970s, astronomers have discovered structures in the three-dimensional distribution of galaxies on ever larger scales, up to hundreds of millions of light years. Researchers from the Sloan Digital Sky Survey (SDSS-II) announced the first measurements of galactic structures more than a billion light years across.

The three-dimensional map of more than 600,000 galaxies covers over one-tenth of the sky. "The volume probed here is the same as a cube 5.3 billion light years on a side," said principal author Nikhil Padmanabhan of Princeton University. "It reaches one-third of the way to the edge of the observable Universe, and we measure structures that extend over a significant fraction of that distance".........

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May 14, 2006, 11:25 AM CT

Trail of Comet Crumbs

Trail of Comet Crumbs

NASA's Spitzer Space Telescope has snapped a picture of the bits and pieces making up Comet 73P/Schwassman-Wachmann 3, which is continuing to break apart on its periodic journey around the sun. The new infrared view shows several chunks of the comet riding along its own dusty trail of crumbs.

"Spitzer has revealed a trail of meteor-sized debris filling the comet's orbit," said Dr. William T. Reach of NASA's Spitzer Science Center at the California Institute of Technology, Pasadena. Reach and his team recently observed the comet using Spitzer.

Comet 73P/Schwassman-Wachmann 3 consists of a collection of fragments that file along like ducks in a row around the sun every 5.4 years. This year, the bunch will pass by Earth beginning on May 12 before swinging by the sun on June 6. The fragments won't get too close to Earth, about 7.3 million miles, or 30 times the distance between Earth and the moon, but they should be visible through binoculars in the countryside night skies.

The icy comet began falling apart in 1995 during one of its tropical trips to the sun. Astronomers believe that its crusty outer layer cracked due to the heat, allowing fresh ice to evaporate and split the comet apart.

During the past six weeks, amateur and professional astronomers have been watching the comet fall apart before their telescopes' eyes. Spitzer viewed the broken comet from its quiet perch up in space May 4 to May 6, covering a portion of the sky that allowed it to spot 45 of the 58 known fragments.........

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