Posted on by Fraser Cain

Rings from the Unlit Side

Saturn’s rings from their unlit side. Image credit: NASA/JPL/SSI Click to enlarge
This magnificent view looks down upon, and partially through, Saturn’s rings from their unlit side.
The densest part of the rings occults the bright globe of Saturn. Scientists can use observations like this to determine precisely the concentration of ring particles.

When the bright source is the signals coming from the spacecraft, the technique is called a ‘radio occultation.’ In a radio occultation measurement, a signal is beamed toward Earth from Cassini’s 4-meter-wide (13-foot) high-gain antenna. Researchers on Earth receive the signal as the spacecraft passes behind the rings. The reduction in Cassini’s radio signal tells researchers how densely packed the ring particles are. Scientists can also learn about the size distributions of the particles from occultations.

As an added (but tiny) bonus, Saturn’s moon Atlas (32 kilometers, or 20 miles across) is visible as a dark speck against the planet, just outside the A ring.

The image was taken in visible red light with the Cassini spacecraft wide-angle camera on Aug. 2, 2005, at a distance of approximately 617,000 kilometers (383,000 miles) from Saturn. The image scale is 37 kilometers (23 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.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Spirit’s Mountaintop View

Mini-panorama taken by Spirit. Image credit: NASA/JPL Click to enlarge
Working atop a range of Martian hills, NASA’s Spirit rover is rewarding researchers with tempting scenes filled with evidence of past planet environments.

“When the images came down and we could see horizon all the way around, that was every bit as exhilarating as getting to the top of any mountain I’ve climbed on Earth,” said Chris Leger, a rover planner at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

The summit sits 82 meters (269 feet) above the edge of the surrounding plains. It is 106 meters (348 feet) higher than the site where Spirit landed nearly 20 months ago. Spirit and twin rover, Opportunity, successfully completed their three-month prime missions in April 2004. They have inspected dozens of rocks and soil targets since then, continuing their pursuit of geological evidence about formerly wet conditions on Mars.

“Spirit has climbed to the hilltop and looked over the other side, but NASA did not do this just to say we can do it. The Mars rovers are addressing fundamental questions about Martian history and planetary environments,” said NASA’s Mars Exploration Program Director Doug McCuistion.

The crest of “Husband Hill” offers Spirit’s views of possible routes into a basin to the south with apparently layered outcrops. Shortly after Spirit landed, it observed a cluster of seven hills about 3 kilometers (2 miles) east of its landing site. NASA proposed naming the range “Columbia Hills” in tribute to the last crew of Space Shuttle Columbia. The tallest of the hills commemorates Rick Husband, Columbia’s commander.

Volcanic rocks covering the plain Spirit crossed on its way to the hills bore evidence of only slight alteration by water. When Spirit reached the base of the hills five months after landing, it immediately began finding rocks with wetter histories.

“This climb was motivated by science,” said Steve Squyres of Cornell University, Ithaca, N.Y. Squyres is principal investigator for the rovers’ science instruments. “Every time Spirit has gained altitude, we’ve found different rock types. Also, we’re doing what any field geologist would do in an area like this: climbing to a good vantage point for plotting a route.”

Researchers are viewing possible routes south to apparently layered ledges and to a feature dubbed “home plate,” which might be a plateau of older rock or a filled-in crater.

The landing site and the Columbia Hills are within Gusev Crater, a bowl about 150 kilometers (95 miles) in diameter. The crater was selected as the landing site for the Spirit rover because the shape of the terrain suggests the crater once held a lake. Volcanic deposits appear to have covered any sign of ancient lakebed geology out on the plain, but scientists say the hills expose older layers that have been lifted and tipped by a meteorite impact or other event.

“We’re finding abundant evidence for alteration of rocks in a water environment,” said Ray Arvidson of Washington University, St. Louis, Mo. Arvidson is deputy principal investigator for the rovers’ science instruments. “What we want to do is figure out which layers were on top of which other layers. To do that it has been helpful to keep climbing for good views of how the layers are tilted to varying degrees. Understanding the sequence of layers is equivalent to having a deep drill core from drilling beneath the plains.”

Both Spirit and Opportunity have been extremely successful. Their solar panels are generating plenty of energy thanks to repeated dust-cleaning events. Spirit has driven 4,827 meters (3.00 miles), and Opportunity 5,737 meters (3.56 miles).

JPL manages the Mars Exploration Rover project for NASA’s Science Mission Directorate. For images and information about the rovers and their discoveries on the Web, visit: http://www.nasa.gov/vision/universe/solarsystem/mer_main.html or http://marsrovers.jpl.nasa.gov.

Original Source: NASA News Release

Posted on by Fraser Cain

Probing the Formation of Galaxy Clusters

XMM-Newton image of galaxy cluster. Image credit: ESA Click to enlarge
ESA?s X-ray observatory, XMM-Newton, has for the first time allowed scientists to study in detail the formation history of galaxy clusters, not only with single arbitrarily selected objects, but with a complete representative sample of clusters.

Knowing how these massive objects formed is a key to understanding the past and future of the Universe.
Scientists currently base their well-founded picture of cosmic evolution on a model of structure formation where small structures form first and these then make up larger astronomical objects.

Galaxy clusters are the largest and most recently formed objects in the known Universe, and they have many properties that make them great astrophysical ?laboratories?. For example, they are important witnesses of the structure formation process and important ?probes? to test cosmological models.

To successfully test such cosmological models, we must have a good observational understanding of the dynamical structure of the individual galaxy clusters from representative cluster samples.

For example, we need to know how many clusters are well evolved. We also need to know which clusters have experienced a recent substantial gravitational accretion of mass, and which clusters are in a stage of collision and merging. In addition, a precise cluster mass measurement, performed with the same XMM-Newton data, is also a necessary prerequisite for quantitative cosmological studies.

The most easily visible part of galaxy clusters, i.e. the stars in all the galaxies, make up only a small fraction of the total of what makes up the cluster. Most of the observable matter of the cluster is composed of a hot gas (10-100 million degrees) trapped by the gravitational potential force of the cluster. This gas is completely invisible to human eyes, but because of its temperature, it is visible by its X-ray emission.

This is where XMM-Newton comes in. With its unprecedented photon-collecting power and capability of spatially resolved spectroscopy, XMM-Newton has enabled scientists to perform these studies so effectively that not only single objects, but also whole representative samples can be studied routinely.

XMM-Newton produces a combination of X-ray images (in different X-ray energy bands, which can be thought of as different X-ray ?colours?), and makes spectroscopic measurements of different regions in the cluster.

While the image brightness gives information on the gas density in the cluster, the colours and spectra provide an indication of the cluster?s internal gas temperature. From the temperature and density distribution, the physically very important parameters of pressure and ?entropy? can be also derived. Entropy is a measure of the heating and cooling history of a physical system.

The accompanying three images illustrate the use of entropy distribution in the ?X-ray luminous? gas as a way of identifying various physical processes. Entropy has the unique property of decreasing with radiative cooling, increasing due to heating processes, but staying constant with compression or expansion under energy conservation.

The latter ensures that a ?fossil record? of any heating or cooling is kept even if the gas subsequently changes its pressure adiabatically (under energy conservation).

These examples are drawn from the REFLEX-DXL sample, a statistically complete sample of some of the most X-ray luminous clusters found in the ROSAT All-Sky Survey. ROSAT was an X-ray observatory developed in the 1990s in co-operation between Germany, USA and UK.

The images provide views of the entropy distribution coded in colour where the values increase from blue, green, yellow to red and white.

Original Source: ESA Portal

Posted on by Fraser Cain

The Lure of Europa

Europa. Image credit: NASA Click to enlarge
The discovery that Jupiter’s moon Europa most likely has a cold, salty ocean beneath its frozen icy crust has put Europa on the short list of objects in our solar system that astrobiologists would like to study further. At the Earth System Processes II conference in Calgary, Canada, Ron Greeley, planetary geologist and professor of geology at Arizona State University in Phoenix, Arizona, gave a talk summing up what is known about Jupiter and its moons, and what remains to be discovered.

There have been six spacecraft that have explored the Jupiter system. The first two were Pioneer spacecraft in the 1970s that flew by the Jupiter system and made some brief observations. Those were followed by the Voyager I and II spacecraft, which gave us our first detailed views of the Galilean satellites. But most of the information we have has come from the Galileo mission. More recently, there was a flyby of the Cassini spacecraft, that went by Jupiter and made observations on its way to Saturn, where it is currently in operation. But nearly everything we know about the geology of the Jupiter system, and in particular the Galilean satellites (Io, Europa, Ganymede and Callisto), came from the Galileo mission. Galileo gave us an incredible wealth of information that we’re still in the process of analyzing today.

There are four Galilean satellites. Io, the innermost, is volcanically the most active object in the solar system. It derives its internal energy from tidal stressing in the interior, as it is being pushed-pulled between Europa and Jupiter. The explosive volcanism we see there is very impressive. There are plumes that are ejected some 200 kilometers (124 miles) above the surface. We also see effusive volcanism in the form of lava flows erupting onto the surface. These are very high-temperature, very fluid flows. On Io we see these flows extending for hundreds of kilometers across the surface.

All of the Galilean satellites are in elliptical orbits, which means that sometimes they’re closer to Jupiter, other times they’re farther away, and they’re being pushed-pulled by their neighbors. That generates internal friction to sufficient levels, in the case of Io, to melt the interior and “drive” the volcanoes. The same processes are taking place on Europa. And there is a possibility of silicate volcanism taking place beneath the icy crust on Europa.

Ganymede is the largest satellite in the solar system. It has an outer icy shell. We think that it has a sub-ice ocean of liquid water over a silicate core and perhaps a small internal metallic core. Ganymede has been subjected to geologic processes since its formation. It has a complex history, dominated by tectonic processes. We see a combination of very old features and very young features. We can see complex facture patterns on its surface that crosscut older fracture patterns. The surface is fractured into blocks that have been shifted about on the overriding, apparently liquid, interior. We also see the impact history dating from the period of early bombardment. Unscrambling the tectonic history of Ganymede is a work in process.

Callisto is the outermost of the Galilean satellites. It, too, has been subjected to impact bombardment, reflecting the early accretion history of the solar system in general, and the Jupiter system in particular. The surface is dominated by craters of all sizes. But we were surprised by the apparent lack of very tiny impact craters. We see very tiny impact craters on its neighbor, Ganymede; we don’t see them on Callisto. There is some process, we think, that is erasing the small craters – but only in selected areas on the moon. This is a mystery that has not been resolved: What is the process that is removing the tiny craters in some areas, or alternatively, might they not have formed there for some reason to begin with? Again, this is a topic of ongoing research.

What I want to talk about primarily, though, is Europa. Europa is about the size of Earth’s moon. It is primarily a silicate object, but it has an outer shell of H2O, the surface of which is frozen. The total volume of water that covers its silicate interior exceeds all of the water on Earth. The surface of that water is frozen. The question is: What’s beneath that frozen shell? Is there solid ice all the way to the bottom, or is there a liquid ocean? We think there is liquid water beneath the icy crust, but we don’t really know that for sure. Our ideas are based on models, and like all models, they are subject to further study.

The reason we think that there is a liquid ocean on Europa is from the behavior of the induced magnetic field around Europa that was measured by the magnetometer on Galileo. Jupiter has an enormous magnetic field. It, in turn, induces a magnetic field, not only on Europa, but also on Ganymede and Callisto. The way that induced magnetic field behaves is consistent with the presence of a subsurface salty liquid ocean, not just on Europa, but also on Ganymede and Callisto.

We do know that the surface is water ice. We know that there are non-ice components present, which includes various salts. And we know that the surface has been geologically processed: it has been fractured, healed, broken up repeatedly. We also see relatively few impact craters on the surface. That indicates that the surface is geologically young. Europa could even be geologically active today. Images of one region, in particular, show a surface that has been severely broken up. The icy plates have been broken apart and shifted into new positions. Material has oozed between the cracks, then apparently frozen, and we think that this could be one of the places where there was upwelling material, perhaps driven by the tidal heating I talked about earlier.

We tend to forget the scale of things in the planetary sciences. But these icy blocks are huge. When we think about future exploration, we would like to get down on the surface and make certain key measurements. So we have to think about spacecraft systems that could land in this kind of terrain. Because it is these places that might have material derived from below the ice, they are the highest priority for exploration. And yet, as is often the case in planetary exploration, the most interesting places are the most difficult to get to.

So what would we like to know? First and most fundamental is the “ocean notion.” Does liquid water exist or not? Is the ice shell thick or thin? If there is an ocean there, how thick is that icy crust? This is very important to know when we think about exploring a possible liquid ocean on Europa: If we want to get into the ocean, how deep must we go through the ice? What is the age of the surface? We say “young,” but that’s only a relative term. Is it thousands, hundreds of thousands, millions, or even billions of years old? The models allow for quite a spread in ages, based on the impact crater frequency. What are the environments there today that are favorable for astrobiology? And what were the environments in the past? Were they the same, or have they changed through time? The answers to these questions require new data.

Another thing that drives our interest in exploring the Galilean satellites is trying to understand their geological histories. To some extent, the diversity that we see, from Io to Europa to Ganymede and Callisto, can be linked to the amount of tidal energy that’s driving the system. Maximum tidal energy drives the volcanism that is so dominant on Io. At the other extreme, very little tidal energy on Callisto results in the preservation of the impact-cratering record. Europa and Ganymede are in between these two extreme cases.

The total surface area of the three icy moons of Jupiter (Europa, Ganymede and Callisto) is greater than the surface area of Mars, and, in fact, is about equivalent to the entire land surface of Earth. So when we discuss the exploration of the icy Galilean satellites, there is a lot of terrain to cover.

As for future exploration, let me share a little history. Three years ago, NASA established the Prometheus project. The Prometheus project involves the development of nuclear power and nuclear propulsion, something that had not been considered seriously for quite some time. The first mission to be flown in the Prometheus project was the Jupiter Icy Moons Orbiter, or JIMO. The goal was to explore the three icy moons within the context of the Jupiter system. It was a very ambitious project. Well, earlier this year JIMO was cancelled. But it looks as though this coming year there will be approval for a geophysical orbiter for Europa. The initial steps for getting that spacecraft underway are being considered now. Europa is a very high priority for exploration, and in recognition of that priority, this mission is likely to happen.

Why are we so interested in Europa? When we talk about astrobiology, we consider the three ingredients for life: water, the right chemistry, and energy. Their presence doesn’t mean that the magic spark of life ever happened, but those are the things that we think are required for life. And so, as I outlined, all three of Jupiter’s icy moons are potential targets. But Europa is the highest priority, because it seems to have the maximum internal energy.

So, of course, first we would like to know: Is there an ocean, yes or no?

Then, what’s the three-dimensional configuration of the icy crust? We know that organisms can live in fractures and cracks in Arctic ice. Such cracks are likely to be present on Europa, too, and could be niches that are of high interest for astrobiology.

Then we want to map the organic and inorganic surface compositions. We see in the data that exist today that the surface is heterogeneous. It’s not just pure ice on the surface. There are some areas that seem to be richer in non-ice components than other places. We want to map that material.

We also want to map interesting surface features and identify the places that are most important for future exploration, including landers.

Then we want to understand Europa in the context of the Jupiter environment. For example, how does the radiation environment imposed by Jupiter affect surface chemistry on Europa?

Ultimately, we want to get down on the surface, because there are a number of things that we can do only from the surface. We have a great wealth of data from the Galileo mission, and hope to have even more from the potential Europa mission, but it’s remote-sensing data. Next, we want to get a lander onto the surface that could make some critical ground-truth measurements, to place the remote-sensing data into context. And so within the scientific community, we feel that the next mission to Europa and the Jupiter system ought to have a landed package of some kind. But whether this will actually happen or not, stay tuned!

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Escaping Pulsar Breaks Speed Records

Pulsar path over about 2.5 million years. Image credit: Bill Saxton, NRAO/AUI/NSF Click to enlarge
A speeding, superdense neutron star somehow got a powerful “kick” that is propelling it completely out of our Milky Way Galaxy into the cold vastness of intergalactic space. Its discovery is puzzling astronomers who used the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope to directly measure the fastest speed yet found in a neutron star.

The neutron star is the remnant of a massive star born in the constellation Cygnus that exploded about two and a half million years ago in a titanic explosion known as a supernova. Ultra-precise VLBA measurements of its distance and motion show that it is on course to inevitably leave our Galaxy.

“We know that supernova explosions can give a kick to the resulting neutron star, but the tremendous speed of this object pushes the limits of our current understanding,” said Shami Chatterjee, of the National Radio Astronomy Observatory (NRAO) and the Harvard-Smithsonian Center for Astrophysics. “This discovery is very difficult for the latest models of supernova core collapse to explain,” he added.

Chatterjee and his colleagues used the VLBA to study the pulsar B1508+55, about 7700 light-years from Earth. With the ultrasharp radio “vision” of the continent-wide VLBA, they were able to precisely measure both the distance and the speed of the pulsar, a spinning neutron star emitting powerful beams of radio waves. Plotting its motion backward pointed to a birthplace among groups of giant stars in the constellation Cygnus — stars so massive that they inevitably explode as supernovae.

“This is the first direct measurement of a neutron star’s speed that exceeds 1,000 kilometers per second,” said Walter Brisken, an NRAO astronomer. “Most earlier estimates of neutron-star speeds depended on educated guesses about their distances. With this one, we have a precise, direct measurement of the distance, so we can measure the speed directly,” Brisken said. The VLBA measurements show the pulsar moving at nearly 1100 kilometers (more than 670 miles) per second — about 150 times faster than an orbiting Space Shuttle. At this speed, it could travel from London to New York in five seconds.

In order to measure the pulsar’s distance, the astronomers had to detect a “wobble” in its position caused by the Earth’s motion around the Sun. That “wobble” was roughly the length of a baseball bat as seen from the Moon. Then, with the distance determined, the scientists could calculate the pulsar’s speed by measuring its motion across the sky.

“The motion we measured with the VLBA was about equal to watching a home run ball in Boston’s Fenway Park from a seat on the Moon,” Chatterjee explained. “However, the pulsar took nearly 22 months to show that much apparent motion. The VLBA is the best possible telescope for tracking such tiny apparent motions.”

The star’s presumed birthplace among giant stars in the constellation Cygnus lies within the plane of the Milky Way, a spiral galaxy. The new VLBA observations indicate that the neutron star now is headed away from the Milky Way’s plane with enough speed to take it completely out of the Galaxy. Since the supernova explosion nearly 2 and a half million years ago, the pulsar has moved across about a third of the night sky as seen from Earth.

“We’ve thought for some time that supernova explosions can give a kick to the resulting neutron star, but the latest computer models of this process have not produced speeds anywhere near what we see in this object,” Chatterjee said. “This means that the models need to be checked, and possibly corrected, to account for our observations,” he said.

“There also are some other processes that may be able to add to the speed produced by the supernova kick, but we’ll have to investigate more thoroughly to draw any firm conclusions,” said Wouter Vlemmings of the Jodrell Bank Observatory in the UK and Cornell University in the U.S.

The observations of B1508+55 were part of a larger project to use the VLBA to measure the distances and motions of numerous pulsars. “This is the first result of this long-term project, and it’s pretty exciting to have something so spectacular come this early,” Brisken said. The VLBA observations were made at radio frequencies between 1.4 and 1.7 GigaHertz.

Chatterjee, Vlemmings and Brisken worked with Joseph Lazio of the Naval Research Laboratory, James Cordes of Cornell University, Miller Goss of NRAO, Stephen Thorsett of the University of California, Santa Cruz, Edward Fomalont of NRAO, Andrew Lyne and Michael Kramer, both of Jodrell Bank Observatory. The scientists presented their findings in the September 1 issue of the Astrophysical Journal Letters.

The VLBA is a system of ten radio-telescope antennas, each with a dish 25 meters (82 feet) in diameter and weighing 240 tons. From Mauna Kea on the Big Island of Hawaii to St. Croix in the U.S. Virgin Islands, the VLBA spans more than 5,000 miles, providing astronomers with the sharpest vision of any telescope on Earth or in space.

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

Headquartered in Cambridge, Massachusetts, 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 seven research divisions study the origin, evolution, and ultimate fate of the universe.

Original Source: CfA News Release

Posted on by Fraser Cain

Bright Young Stars in Trumpler 14

Trumpler 14. Image credit: NASA/CXC/PSU Click to enlarge
Chandra’s image of the star cluster Trumpler 14 shows about 1,600 stars and a diffuse glow from hot multimillion degree X-ray producing gas. The cluster has one of the highest concentrations of massive, luminous stars in the Galaxy. Located on the edge of a giant molecular cloud, it is part of the Carina Complex which contains at least 8 star clusters.

The bright stars in Trumpler 14 are young (about 1 million years old), and much more massive than the Sun. They will shine brightly, exhaust their prodigious energy, and explode spectacularly as supernovas in a few million years.

In the meantime, the young, massive stars have a profound influence on their environment through the ionizing effects of their light, and the high-speed winds of particles that are pushed away from their surfaces by the intense radiation. Shock waves that develop in these winds can heat gas to millions of degrees Celsius and produce intense X-ray sources. In the accompanying image (below, right), the bright white source in the center of the image has been resolved to reveal several massive stars.

On a larger scale, stellar winds can carve out cavities in the clouds of gas and dust that surround the stars, and trigger the formation of new stars. These cavities are filled with million-degree gas that produce the diffuse X-ray glow in the image.

The glow in the lower, rectangular part of the image (the gap between the upper and lower portions of the image is an instrumental artifact) is from a gas cloud that has been enriched with oxygen, neon, silicon and iron. This probably marks the final contribution of a once-bright star that exploded as a supernova thousands of years ago, and in the process dispersed these heavy elements into the interstellar medium.

Original Source: Chandra X-ray Observatory

Posted on by Fraser Cain

Massive Stars Have Protoplanetary Disks Too

An artist’s illustration of a circumstellar disk around a massive star. Image credit: NAOJ Click to enlarge
An international group of astronomers has used the Coronagraphic Imager for Adaptive Optics (CIAO) on the Subaru telescope in Hawai’i to obtain very sharp near-infrared polarized-light images of the birthplace of a massive proto-star known as the Becklin-Neugebauer (BN) object at a distance of 1500 light years from the Sun. The group’s images led to the discovery of a disk surrounding this newly forming star. This finding, described in detail in the September 1 issue of Nature, deepens our understanding of how massive stars form.

The research group, which includes astronomers from the Purple Mountain Observatory, China, National Astronomical Observatories of Japan, and University of Hertfordshire, UK, explored the region close to the Becklin-Neugebauer object and analyzed how infrared light is affected by dust. To do this, they took a polarized-light image of the object at a wavelength of 1.6 micrometers (the H band of infrared light). Images of the brightness of the object just show a circular distribution of light. However, an image of the light’s polarization shows a butterfly shape that reveals details that are undetectable by looking at the brightness distribution alone. To understand the environment around the star and what the butterfly shape implies, the astronomers created a computer model for comparison, along with a schematic of star formation. These models show that the butterfly shape is the signature of a disk and an outflow structure near the newborn star.

This discovery is the most concrete evidence for a disk around a massive young star and shows that massive stars like the BN object (which is about seven times the mass of the Sun) form the same way as lower-mass stars like the Sun.

There are two main theories to explain the formation of massive stars. The first states that massive stars are the results of the mergers of several low-mass stars. The second says that they are formed through gravitational collapse and mass accretion within circumstellar disks. Lower-mass stars like the Sun are most likely to have formed through the second method. The collapse-accretion theory assumes that a system has a star associated with a bipolar outflow, a circumstellar disk and an envelope, while the merger theory does not. The presence or absence of such structures can distinguish between the two formation scenarios.

Until recently, there has been little direct observational evidence in support of either theory of massive star formation. This is because, unlike lower-mass stars, newly forming massive stars are so rare and so far away from us that they have been difficult to observe. Large telescopes and adaptive optics, which greatly improve image sharpness, now make it possible to observe these objects with unprecedented clarity. High-resolution infrared polarimetry is an especially powerful tool for probing the environment hidden behind the bright glow of a massive star.

Polarization-the direction that light waves oscillate in as they stream away from an object-is an important characteristic of radiation. Sun light doesn?t have a preferred direction of oscillation, but can become polarized when scattered by Earth?s atmosphere, or after reflecting off the surface of water. A similar action occurs in a circumstellar cloud around a newborn star. The star lights up its surroundings-the circumstellar disk, the envelope and the cavity walls formed by the outflow streams. The light can travel freely within the cavity and then reflect off its walls. This reflected light becomes highly polarized. By contrast, the disk and the envelope are relatively opaque to light. This reduces the polarization of light coming from those regions.

The group?s success in detecting evidence for a disk and outflow around the BN object through high-resolution infrared polarimetry suggests that the same technique can be applied to other forming stars. This would allow astronomers to obtain a comprehensive observational description of the formation of massive stars greater than ten times the mass of the Sun.

Original Source: NAOJ News Release

Posted on by Fraser Cain

Hubble Working on Only Two Gyros Now

Hubble Space Telescope. Image credit: NASA/STScI Click to enlarge
NASA’s Hubble Space Telescope entered a new era of science operations this week, when engineers shut down one of the three operational gyroscopes aboard the observatory. The two-gyro mode is expected to preserve the operating life of the third gyro and extend Hubble’s science observations through mid-2008, an eight-month extension.

This conclusion followed detailed analysis by engineers and scientists at NASA’s Goddard Space Flight Center, Greenbelt, Md., and the Space Telescope Science Institute (STScI) in Baltimore. Thorough testing of the two-gyro mode was completed prior to implementation.

The gyros are an integral part of Hubble’s complex pointing control system. The system maintains precise pointing of the telescope during science observations. The system was originally designed to operate on three gyros, with another three in reserve. Two of the six are no longer functional.

“Hubble science on two gyros will be indistinguishable from the superb science we have become accustomed to over the years,” said senior Hubble scientist David Leckrone at Goddard.

Gyros are the heart, though not the sole component, of Hubble’s pointing control system. When only two gyros are available, the observatory experiences an “unsensed” direction. Using Hubble’s Fine Guidance Sensors, engineers were able to “fill in” the missing data normally generated by the third gyro.

Hubble also needs to know its location as it completes one observation and slews across the sky to acquire its next target. This information, previously supplied by the observatory’s three gyros, is provided by onboard magnetometers and Fixed Head Star Trackers.

Many Hubble astronomers were consulted and were part of the overall decision process about two-gyro science operations. Switching off one gyro can preserve it for future use and extended two-gyro operational time for Hubble.

NASA has stated a Space Shuttle servicing mission to Hubble will be considered after two successful return-to-flight missions. The servicing mission would include installing new gyros, batteries, and science instruments to provide several more years of observations.

For more information about Hubble on the Web, visit:

http://hubble.nasa.gov/index.php http://hubblesite.org/news/2005/24

For information about NASA and agency programs on the Web, visit:

http://www.nasa.gov/home

Original Source: Hubble News Release

Posted on by Fraser Cain

Podcast: Interview with Simon Singh

My guest today is Simon Singh, author of many science-related books including Fermat’s Enigma, and The Code Book. His latest book, Big Bang, investigates the origins of the search for our place in an ever expanding Universe. Simon speaks to me from his home in London, England. I just want to apologize in advance for the murky audio quality – that’s what you get when you call London from Canada through Skype. I’ve got an audio transcript that you can refer to if you’re have trouble making out what Simon said.
Continue reading “Podcast: Interview with Simon Singh”