Posted on by Fraser Cain

Gravity Probe B Launch Delayed

Image credit: NASA

NASA has decided to push back the launch of its mission to test Einstein’s theory of general relativity, Gravity Probe B, until December 6. During recent tests, engineers noticed electronic noise coming from the sensor attached to one of the spacecraft’s gyros, so they’ve extended the launch date to find time to fix it. Once it does launch, Gravity Probe B will detect any distortions on its four spinning gyroscopes to detect the Earth’s distortion of spacetime around it – as predicted by Einstein.

After a review of test data, a decision has been made to reschedule the launch of Gravity Probe B (GP-B). The launch had been scheduled for Dec. 6 from Vandenberg Air Force Base in California.

Data obtained during spacecraft prelaunch testing shows electronic noise on an output channel associated with the No. 1 experiment gyro. This could compromise the quality of data received from it. The problem has been isolated to a component in the spacecraft?s experiment control unit (ECU). While there is a second available output channel for this gyro, a postponement of the launch will allow time for a repair. This precaution will restore full redundancy to the experiment and provide the greatest chance for success over the planned 16-month life of the mission.

At Space Launch Complex 2, the rocket has successfully completed the scheduled prelaunch preparations up to this time, and there are no issues or concerns with the Delta II. The current plans are for it to remain at the pad enclosed within the gantry-like mobile service tower until the spacecraft arrives.

The length of the postponement will not be known for about a week until a course of action has been developed to address the GP-B problem.

Original Source: NASA News Release

Posted on by Fraser Cain

Chandra Sees the Most Distant X-Ray Jet

Image credit: Chandra

The most distant jet ever seen was recently photographed by the Chandra X-Ray Observatory. The jet is huge, blasting 100,000 light years out of a quasar 12 billion light years away – astronomers are seeing it when the Universe was only 1.4 billion years old. This gives astronomers an opportunity to study the intensity of the cosmic microwave background radiation, as light from the jet needs to move through the sea of particles left over from the Big Bang.

The most distant jet ever observed was discovered in an image of a quasar made by NASA’s Chandra X-ray Observatory. Extending more than 100,000 light years from the supermassive black hole powering the quasar, the jet of high-energy particles provides astronomers with information about the intensity of the cosmic microwave background radiation 12 billion years ago.

The discovery of this jet was a surprise to the astronomers, according to team members. Astronomers had previously known the distant quasar GB1508+5714 to be a powerful X-ray source, but there had been no indication of any complex structure or a jet.

“This jet is especially significant because it allows us to probe the cosmic background radiation 1.4 billion years after the Big Bang,” said Aneta Siemiginowska of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., lead author of a report on this research in the November 20th Astrophysical Journal Letters. Prior to this discovery, the most distant confirmed X-ray jet corresponded to a time about 3 billion years after the Big Bang.

Quasars are thought to be galaxies that harbor an active central supermassive black hole fueled by infalling gas and stars. This accretion process is often observed to be accompanied by the generation of powerful high-energy jets.

Radio Image of GB1508
As the electrons in the jet fly away from the quasar at near the speed of light, they move through the sea of cosmic background radiation left over from the hot early phase of the universe. When a fast-moving electron collides with one of these background photons, it can boost the photon’s energy up into the X-ray band. The X-ray brightness of the jet depends on the power in the electron beam and the intensity of the background radiation.

“Everyone assumes that the background radiation will change in a predictable way with time, but it is important to have this check on the predictions,” said Siemiginowska. “This jet is hopefully just the first in a large sample of these distant objects that can be used to tell us how the intensity of the cosmic microwave background changed over time.”

“In fact, if this interpretation is correct, then discovery of this jet is consistent with our previous prediction that X-ray jets can be detected at arbitrarily large distances!” said team member Dan Schwartz, also of the Harvard-Smithsonian Center for Astrophysics.

Chandra originally observed GB1508+5714 with the purpose of studying the X-ray emission from the dust located between the Earth and the far-flung quasar. The jet was found by Siemiginowska and her colleagues when they examined the data once it became available publicly in the Chandra archive.

This led another astronomer to then carefully look at radio observations of the object. Indeed, archived Very Large Array data confirmed the existence of the jet associated with the quasar GB1508+5714. A paper on the radio observations of GB1508+5714 has been accepted by Astrophysical Journal Letters from Teddy Cheung of Brandeis University in Waltham, Mass.

Another group of astronomers led by Weimen Yuan of the University of Cambridge, UK independently reported the discovery of the extended emission in GB1508+5714 in X-rays. In a paper to be published in an upcoming issue of the Monthly Notices of the Royal Astronomical Society, the authors note that significant energy is being deposited in the outer regions of the host galaxy at a very early stage. This energy input could have a profound effect on the evolution of the galaxy by triggering the formation of stars, or inhibiting the growth of the galaxy through accretion of matter from intergalactic space.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Original Source: Chandra News Release

Posted on by Fraser Cain

Bringing Back a Piece of Mars

Image credit: ESA

The European Space Agency is planning a mission to study the surface of Mars by picking up material from the surface and returning it to the Earth. The Mars Sample Return mission will consist of two parts: the return capsule will launch in 2011 and go into orbit around Mars; the lander and ascent module will launch two years later and land on the planet to collect a sample from a depth of 2 metres. It will then launch into Mars’ orbit, link up with the return capsule, and bring the sample back to the Earth.

What is the next best thing to humans landing on Mars and exploring the wonders of the Red Planet? The answer: touching, imaging and analysing carefully preserved samples of Martian rock in a state-of-the-art laboratory on Earth.

If all goes according to plan, this is exactly what ESA?s long-term Aurora Programme of solar system exploration will achieve a decade from now, when the first samples of Mars material will be sealed in a special capsule and returned to Earth for analysis.

The first step towards making this great leap in human knowledge a reality was taken at the end of October with the announcement of the winners of competitive contracts for the Mars Sample Return (MSR) mission, the second Flagship robotic mission to be proposed as part of Aurora.

The parallel contracts for the Phase A studies that will carry out a full mission design iteration for the MSR have been placed with two industrial teams.

One team, headed by Alenia Spazio (Italy), includes Alcatel (France), Dutch Space (Netherlands), ELV (Italy) and MDR (Canada). The other team, headed by EADS Astrium (UK), also includes Astrium SAS (France), EADS ST (France), Galileo Avionica (Italy), RAL (UK), SAS (Belgium), SENER (Spain) and Utopia Consultancies (Germany).

?The industrial proposals received were of outstanding quality, reflecting the enthusiasm and the commitment of the industrial teams who prepared them,? said Bruno Gardini, Aurora Project Manager.

Bringing Mars back to Earth
As currently envisaged, the MSR will be a two-stage endeavour. First, a spacecraft that includes a return capsule will be launched in 2011 and inserted into orbit around Mars. Then, two years later, a second spacecraft carrying a descent module and a Mars ascent vehicle (MAV) will be launched on a similar trajectory.

During its final approach to Mars, the descent module/MAV will be released and make a controlled landing on the planet. A robotic drill will then collect a soil sample from a depth of 1? to 2 metres and seal it inside a small canister on the ascent vehicle. Other samples of Martian soil and air may also be gathered and stored inside the canister.

Carrying its precious samples, the MAV will lift off from the surface, then rendezvous and dock with the spacecraft in Martian orbit. After receiving the canister loaded with Martian rocks, the spacecraft will return to Earth with the re-entry capsule containing the samples and send it plummeting into the atmosphere.

Slowed by a parachute or inflatable device, the capsule will make a fairly gentle touchdown before recovery teams retrieve the container from the landing site and deliver it to a planetary protection facility where the samples will be removed to await analysis by eager scientists. The design of the capsule will ensure that the structural integrity of the sample container remains intact, even if the parachute fails to open and a crash landing occurs.

?The Mars Sample Return mission is one of the most challenging missions ever considered by ESA,? said Gardini. ?Not only does it include many new technologies and four or five different spacecraft, but it is also a mission of tremendous scientific importance and the first robotic mission with a similar profile to a possible human expedition to Mars.?

A number of the critical technologies required for the success of this ambitious endeavour have yet to be developed in Europe, e.g. re-entry of spacecraft arriving from deep space at a high velocity. As a preliminary stage in developing a vehicle capable of bringing back samples from Mars, it was considered necessary to develop this re-entry capability and to demonstrate its maturity as part of the Aurora Programme. Feasibility studies for a dedicated Arrow mission, known as the Earth re-entry Vehicle Demonstrator (EVD), were recently announced.

In the same way, testing of the complex rendezvous and docking techniques will be carried out as an experiment on the ExoMars mission, the first Flagship mission of the Aurora Programme. The Phase A industrial study contracts for the ExoMars mission began in September.

Original Source: ESA News Release

Posted on by Fraser Cain

True Colour Picture of Mars

Image credit: NASA/JPL

The NASA/ASU THEMIS imaging team has released a photo of Mars which has been corrected as close as possible to realistic colour. This image of cliffs and basalt sand dunes in the southern Melas Chasma region of Mars was taken by NASA’s Mars Odyssey spacecraft. Astronomer and space artist Don Davis used photographs from the Hubble Space Telescope and his own experience to modify the colours in the picture until they looked natural.

This spectacular view of the sunlit cliffs and basaltic sand dunes in southern Melas Chasma shows Mars in a way rarely seen: in full, realistic color. The colorization is the result of a collaboration between THEMIS team members at Cornell University and space artist Don Davis, who is an expert on true-color renderings of planetary and astronomical objects. Davis began with calibrated and co-registered THEMIS VIS multi-band radiance files produced by the Cornell group. Using as a guide true-color imaging from the Hubble Space Telescope and his own personal experience at Mt. Wilson and other observatories, he performed a manual color balance to match more closely the colors of previous visual Mars observations. He also did some manual smoothing and other image processing to mimimize the effects of residual scattered light in the images. The result is a view of Mars that invites comparisons to Earth; a scene that one might observe out the window on a flight over the southwest United States, but not quite. The basaltic dunes are commonplace on Mars but a rare feature on Earth. The rounded knobs and elongated mesas on the canyon floor show an erosional style as exotic as Utah’s Bryce Canyon but wholly familiar on Mars. Although the inhospitable Martian atmosphere cannot be seen, the magnificent Martian landscape on display in this image beckons space-suited human explorers and the sightseers who will follow.

Initial image processing and calibration by THEMIS team members J. Bell, T. McConnochie, and D. Savransky at Cornell University; additional processing and final color balance by space artist Don Davis.

Original Source: NASA/ASU News Release

Posted on by Fraser Cain

ESO Watches Burst Afterglow for Five Weeks

Image credit: ESO

Gamma-ray bursts are some of the largest explosions in the Universe; one can generate more energy in a few seconds than the Sun creates in 10 billion years. It’s believed they’re caused when a super-massive star collapses, called a hypernova. Astronomers from the European Southern Observatory tracked the afterglow of a recent burst by using a technique called polarimetry, which lets them track the shape of the explosion. If it was a spherical explosion, the light would have random polarity, but they found that gas is flowing out in jets which are widening over time.

“Gamma-ray bursts (GRBs)” are certainly amongst the most dramatic events known in astrophysics. These short flashes of energetic gamma-rays, first detected in the late 1960’s by military satellites, last from less than one second to several minutes.

GRBs have been found to be situated at extremely large (“cosmological”) distances. The energy released in a few seconds during such an event is larger than that of the Sun during its entire lifetime of more than 10,000 million years. The GRBs are indeed the most powerful events since the Big Bang known in the Universe, cf. ESO PR 08/99 and ESO PR 20/00.

During the past years circumstantial evidence has mounted that GRBs signal the collapse of extremely massive stars, the so-called hypernovae. This was finally demonstrated some months ago when astronomers, using the FORS instrument on ESO’s Very Large Telescope (VLT), documented in unprecedented detail the changes in the spectrum of the light source (“the optical afterglow”) of the gamma-ray burst GRB 030329 (cf. ESO PR 16/03). A conclusive and direct link between cosmological gamma-ray bursts and explosions of very massive stars was provided on this occasion.

Gamma-Ray Burst GRB 030329 was discovered on March 29, 2003 by NASA’s High Energy Transient Explorer spacecraft. Follow-up observations with the UVES spectrograph at the 8.2-m VLT KUEYEN telescope at the Paranal Observatory (Chile) showed the burst to have a redshift of 0.1685 [1]. This corresponds to a distance of about 2,650 million light-years, making GRB 030329 the second-nearest long-duration GRB ever detected. The proximity of GRB 030329 resulted in very bright afterglow emission, permitting the most extensive follow-up observations of any afterglow to date.

A team of astronomers [2] led by Jochen Greiner of the Max-Planck-Institut f?r extraterrestrische Physik (Germany) decided to make use of this unique opportunity to study the polarisation properties of the afterglow of GRB 030329 as it developed after the explosion.

Hypernovae, the source of GRBs, are indeed so far away that they can only be seen as unresolved points of light. To probe their spatial structure, astronomers have thus to rely on a trick: polarimetry (see ESO PR 23/03).

Polarimetry works as follows: light is composed of electromagnetic waves which oscillate in certain directions (planes). Reflection or scattering of light favours certain orientations of the electric and magnetic fields over others. This is why polarising sunglasses can filter out the glint of sunlight reflecting off a pond.

The radiation in a gamma-ray burst is generated in an ordered magnetic field, as so-called synchrotron radiation [3]. If the hypernova is spherically symmetric, all orientations of the electromagnetic waves will be present equally and will average out, so there will be no net polarisation. If, however, the gas is not ejected symmetrically, but into a jet, a slight net polarisation will be imprinted on the light. This net polarisation will change with time since the opening angle of the jet widens with time, and we see a different fraction of the emission cone.

Studying the polarisation properties of the afterglow of a gamma-ray burst thus allows to gain knowledge about the underlying spatial structures and the strength and orientation of the magnetic field in the region where the radiation is generated. “And doing this over a long period of time, as the afterglow fades and evolves, provides us with a unique diagnostic tool for gamma-ray burst studies”, says Jochen Greiner.

Although previous single measurements of the polarisation of GRB’s optical afterglow exist, no detailed study has ever been done of the evolution of polarisation with time. This is indeed a very demanding task, only possible with an extremely stable instrument on the largest telescope… and a sufficient bright optical afterglow.

As soon as GRB 030329 was detected, the team of astronomers therefore turned to the powerful multi-mode FORS1 instrument on the VLT ANTU telescope. They obtained 31 polarimetric observations over a period of 38 days, enabling them to measure, for the first time, the changes of the polarisation of an optical gamma-ray burst afterglow with time. This unique set of observational data documents the physical changes in the remote object in unsurpassed detail.

Their data show the presence of polarisation at the level of 0.3 to 2.5 % throughout the 38-day period with significant variability in strength and orientation on timescales down to hours. This particular behaviour has not been predicted by any of the major theories.

Unfortunately, the very complex light curve of this GRB afterglow, in itself not understood, prevents a straightforward application of existing polarisation models. “It turns out that deriving the direction of the jet and the magnetic field structure is not as simple as we thought originally”, notes Olaf Reimer, another member of the team. “But the rapid changes of the polarisation properties, even during smooth phases of the afterglow light curve, provide a challenge to afterglow theory”.

“Possibly”, adds Jochen Greiner, “the overall low level of polarisation indicates that the strength of the magnetic field in the parallel and perpendicular directions do not differ by more than 10%, thus suggesting a field strongly coupled with the moving material. This is different from the large-scale field which is left-over from the exploding star and which is thought to produce the high-level of polarisation in the gamma-rays.”

Original Source: ESO News Release

Posted on by Fraser Cain

Nozomi is on a Collision Course with Mars

The Mars-bound Japanese spacecraft Nozomi, which has been plagued with problems since its launch in 1998, could be on a collision course with the Red Planet, and might crash into it if engineers can’t change its trajectory. Officials from the Japanese space agency will attempt to fire the spacecraft’s engines on December 8 to kick it into a safer orbit. But before that, they need to fix the spacecraft’s malfunctioning electrical. One worry is that Nozomi was never intended to enter Mars’ atmosphere, so it wasn’t carefully decontaminated – it could deliver Earth-based microbes to the Martian surface.

Posted on by Fraser Cain

Ancient Rivers Lasted a While on Mars

Image credit: NASA/JPL

NASA’s Mars Global Surveyor spacecraft has revealed new features on Mars that look like ancient river deltas. This discovery might help answer the mystery of how long water flowed on the surface of the Red Planet. The shape of this formation suggests that a river flowed into a body of water for quite a while, changing its course and building up layers of sediment over time. The area is about 13 km long and 11 km wide, and located in a crater in the southern hemisphere.

Newly seen details in a fan-shaped apron of debris on Mars may help settle a decades-long debate about whether the planet had long-lasting rivers instead of just brief, intense floods.

Pictures from NASA’s Mars Global Surveyor orbiter show eroded ancient deposits of transported sediment long since hardened into interweaving, curved ridges of layered rock. Scientists interpret some of the curves as traces of ancient meanders made in a sedimentary fan as flowing water changed its course over time.

“Meanders are key, unequivocal evidence that some valleys on early Mars held persistent flows of water over considerable periods of time,” said Dr. Michael Malin of Malin Space Science Systems, San Diego, which supplied and operates the spacecraft’s Mars Orbiter Camera.

“The shape of the fan and the pattern of inverted channels in it suggest it may have been a real delta, a deposit made where a river enters a body of water,” he said. “If so, it would be the strongest indicator yet Mars once had lakes.”

Malin and Dr. Ken Edgett, also of Malin Space Science Systems, have published pictures and analysis of the landform in today’s online edition of Science Express. The images with captions are available online from the Mars Orbiter Camera team, at http://www.msss.com/mars_images/moc/2003/11/13/ and from NASA’s Jet Propulsion Laboratory, Pasadena, Calif., at http://photojournal.jpl.nasa.gov/catalog/PIA04869.

The fan covers an area about 13 kilometers (8 miles) long and 11 kilometers (7 miles) wide in an unnamed southern hemisphere crater downslope from a large network of channels that apparently drained into it billions of years ago.

“This latest discovery by the intrepid Mars Global Surveyor is our first definitive evidence of persistent surface water,” commented Dr. Jim Garvin, NASA’s Lead Scientist for Mars Exploration, NASA Headquarters, Washington, D.C. “It reaffirms we are on the right pathway for searching the record of martian landscapes and eventually rocks for the record of habitats. Such localities may serve as key landing sites for future missions, such as the Mars Science Laboratory in 2009,” continued Garvin. “These astounding findings suggest that “following the water” with Mars Global Surveyor, Mars Odyssey, and soon with the Mars Exploration Rovers, is a powerful approach that will ultimately allow us to understand the history of habitats on the red planet.”

No liquid water has been detected on Mars, although one of the previous major discoveries from Mars Global Surveyor pictures suggests that some gullies have been cut in geologically recent times by the flow of ephemeral liquid water. Another NASA orbiter, Mars Odyssey, has discovered extensive deposits of near-surface ice at high latitudes. Mars’ atmosphere is now so thin that, over most of the planet, any liquid water at the surface would rapidly evaporate or freeze, so evidence of persistent surface water in the past is also evidence for a more clement past climate.

Malin and Edgett estimate that the volume of material in the delta-like fan is about one-fourth the volume of what was removed by the cutting of the upstream channels. Their analysis draws on information from Mars Global Surveyor’s laser altimeter and from cameras on Mars Odyssey and NASA’s Viking Orbiter, as well as images from the Mars Orbiter Camera.

“Because the debris in this fan is now cemented, it shows that some sedimentary rocks on Mars were deposited by water,” Edgett said. “This has been suspected, but never so clearly demonstrated before.”

The camera on Mars Global Surveyor has returned more than 155,000 pictures since the spacecraft began orbiting Mars on Sept. 12, 1997. Still, its high-resolution images cover only about three percent of the planet’s surface. Information about Mars Global Surveyor is available on the Internet at http://mars.jpl.nasa.gov/mgs.

JPL, a division of the California Institute of Technology, Pasadena, manages Mars Global Surveyor for NASA’s Office of Space Science in Washington. JPL’s industrial partner is Lockheed Martin Space Systems, Denver, which developed and operates the spacecraft. Malin Space Science Systems and the California Institute of Technology built the Mars Orbiter Camera. Malin Space Science Systems operates the camera from facilities in San Diego.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

New Cassini Image of Jupiter Released

Image credit: NASA/JPL

The team responsible for the Cassini spacecraft’s imaging system have produced the most detailed mosaic image of Jupiter ever created – the whole planet is visible down to a resolution of 60 km. The spacecraft took a series of 27 images over the course of an hour on December 29, 2000. The separate photos were then blended together on a computer to account for Jupiter’s rotation and the movement of the spacecraft.

This true color mosaic of Jupiter was constructed from images taken by the narrow angle camera onboard NASA’s Cassini spacecraft starting at 5:31 Universal time on December 29, 2000, as the spacecraft neared Jupiter during its flyby of the giant planet. It is the most detailed global color portrait of Jupiter ever produced; the smallest visible features are ~ 60 km (37 miles) across. The mosaic is composed of 27 images: nine images were required to cover the entire planet in a tic-tac-toe pattern, and each of those locations was imaged in red, green, and blue to provide true color. Although Cassini’s camera can see more colors than humans can, Jupiter here looks the way that the human eye would see it.

Cassini’s camera is digital, much like today’s popular cameras, and it takes images in each color separately as different spectral filters are rotated in front of its light-sensitive detector. Over an hour was required for this portrait. Jupiter rotated during this time, so the face it presented to the camera, and the lighting on its moving clouds, were constantly changing. In order to assemble a seamless mosaic, each image was first digitally re-positioned to reflect the planet’s appearance at the instant the first exposure was taken. Then, the lighting variation across each image was removed, and the mosaic was re-illuminated by a computer-generated ‘Sun’ from a direction that allowed all imaged portions to appear in sunlight at once. The result, which was slightly contrast-enhanced to bring out subtleties in the Jupiter atmosphere, is a view that the spacecraft would have had at the same distance from the planet but ~ 80 degrees solar phase.

Everything visible on the planet is a cloud. The parallel reddish-brown and white bands, the white ovals, and the large Great Red Spot persist over many years despite the intense turbulence visible in the atmosphere. The most energetic features are the small, bright clouds to the left of the Great Red Spot and in similar locations in the northern half of the planet. These clouds grow and disappear over a few days and generate lightning. Streaks form as clouds are sheared apart by Jupiter’s intense jet streams that run parallel to the colored bands. The prominent dark band in the northern half of the planet is the location of Jupiter’s fastest jet stream, with eastward winds of 480 km (300 miles) per hour. Jupiter’s diameter is eleven times that of Earth, so the smallest storms on this mosaic are comparable in size to the largest hurricanes on Earth.

Unlike Earth, where only water condenses to form clouds, Jupiter’s clouds are made of ammonia, hydrogen sulfide, and water. The updrafts and downdrafts bring different mixtures of these substances up from below, leading to clouds at different heights. The brown and orange colors may be due to trace chemicals dredged up from deeper levels of the atmosphere, or they may be byproducts of chemical reactions driven by ultraviolet light from the Sun. Bluish areas, such as the small features just north and south of the equator, are areas of reduced cloud cover, where one can see deeper.

Original Source: Arizona University News Release

Posted on by Fraser Cain

Three Kinds of Explosions Could Be the Same Thing

Image credit: Hubble

Three of the Universe’s largest explosions: gamma-ray bursts, X-ray flashes, and supernovae could actually come from the same event – the collapse of a supermassive star. An astronomer from Caltech has found that the different kinds of explosions seem to contain the same amount of energy, they’re just divided up differently between low and high-energy jets. NASA is going to launch a new gamma-ray detecting spacecraft, called SWIFT, which should be able to detect 100 gamma-ray busts a year. This should give scientists new targets to study.

For the past several decades, astrophysicists have been puzzling over the origin of powerful but seemingly different explosions that light up the cosmos several times a day. A new study this week demonstrates that all three flavors of these cosmic explosions–gamma-ray bursts, X-ray flashes, and certain supernovae of type Ic–are in fact connected by their common explosive energy, suggesting that a single type of phenomenon, the explosion of a massive star, is the culprit. The main difference between them is the “escape route” used by the energy as it flees from the dying star and its newly born black hole.

In the November 13 issue of the journal Nature, Caltech graduate student Edo Berger and an international group of colleagues report that cosmic explosions have pretty much the same total energy, but this energy is divided up differently between fast and slow jets in each explosion. This insight was made possible by radio observations, carried out at the National Radio Astronomy Observatory’s Very Large Array (VLA), and Caltech’s Owens Valley Radio Observatory, of a gamma-ray burst that was localized by NASA’s High Energy Transient Explorer (HETE) satellite on March 29 of this year.

The burst, which at 2.6 billion light-years is the closest classical gamma-ray burst ever detected, allowed Berger and the other team members to obtain unprecedented detail about the jets shooting out from the dying star. The burst was in the constellation Leo.

“By monitoring all the escape routes, we realized that the gamma rays were just a small part of the story for this burst,” Berger says, referring to the nested jet of the burst of March 29, which had a thin core of weak gamma rays surrounded by a slow and massive envelope that produced copious radio waves.

“This stumped me,” Berger adds, “because gamma-ray bursts are supposed to produce mainly gamma rays, not radio waves!”

Gamma-ray bursts, first detected accidentally decades ago by military satellites watching for nuclear tests on Earth and in space, occur about once a day. Until now it was generally assumed that the explosions are so titanic that the accelerated particles rushing out in antipodal jets always give off prodigious amounts of gamma radiation, sometimes for hundreds of seconds. On the other hand, the more numerous supernovae of type Ic in our local part of the universe seem to be weaker explosions that produce only slow particles. X-ray flashes were thought to occupy the middle ground.

“The insight gained from the burst of March 29 prompted us to examine previously studied cosmic explosions,” says Berger. “In all cases we found that the total energy of the explosion is the same. This means that cosmic explosions are beasts with different faces but the same body.”

According to Shri Kulkarni, MacArthur Professor of Astronomy and Planetary Science at Caltech and Berger’s thesis supervisor, these findings are significant because they suggest that many more explosions may go undetected. “By relying on gamma rays or X rays to tell us when an explosion is taking place, we may be exposing only the tip of the cosmic explosion iceberg.”

The mystery we need to confront at this point, Kulkarni adds, is why the energy in some explosions chooses a different escape route than in others.

At any rate, adds Dale Frail, an astronomer at the VLA and coauthor of the Nature manuscript, astrophysicists will almost certainly make progress in the near future. In a few months NASA will launch a gamma-ray detecting satellite known as Swift, which is expected to localize about 100 gamma-ray bursts each year. Even more importantly, the new satellite will relay very accurate positions of the bursts within one or two minutes of initial detection.

The article appearing in Nature is titled “A Common Origin for Cosmic Explosions Inferred from Calorimetry of GRB 030329.” In addition to Berger, the lead author, and Kulkarni and Frail, the other authors are Guy Pooley, of Cambridge University’s Mullard Radio Astronomy Observatory; Vince McIntyre and Robin Wark, both of the Australia Telescope National Facility; Re’em Sari, associate professor of astrophysics and planetary science at Caltech; Derek Fox, a postdoctoral scholar in astronomy at Caltech; Alicia Soderberg, a graduate student in astrophysics at Caltech; Sarah Yost, a postdoctoral scholar in physics at Caltech; and Paul Price, a postdoctoral scholar at the University of Hawaii’s Institute for Astronomy.

Original Source: Caltech News Release

Posted on by Fraser Cain

There Might Not Be Ice at the Moon’s Pole

Image credit: Cornell University

At the South Pole of the Moon, there is a region that is always in the shadow of craters which scientists have long believed could have deposits of water ice. Despite the fact that ice was detected by two spacecraft that orbited the moon, a new survey of the area by the giant Arecibo radio observatory has failed to find any surface deposits of ice. This doesn’t mean that the ice isn’t there, but it might be trapped in a large area under the surface, like lunar permafrost. Arecibo is a good instrument for detecting ice because it gives a very specific echo signature in the radio spectrum.

Despite evidence from two space probes in the 1990s, radar astronomers say they can find no signs of thick ice at the moon’s poles. If there is water at the lunar poles, the researchers say, it is widely scattered and permanently frozen inside the dust layers, something akin to terrestrial permafrost.

Using the 70-centimeter (cm)-wavelength radar system at the National Science Foundation’s (NSF) Arecibo Observatory, Puerto Rico, the research group sent signals deeper into the lunar polar surface — more than five meters (about 5.5 yards) — than ever before at this spatial resolution. “If there is ice at the poles, the only way left to test it is to go there directly and melt a small volume around the dust and look for water with a mass spectrometer,” says Bruce Campbell of the Center for Earth and Planetary Studies at the Smithsonian Institution.

Campbell is the lead author of an article, “Long-Wavelength Radar Probing of the Lunar Poles,” in the Nov. 13, 2003, issue of the journal Nature . His collaborators on the latest radar probe of the moon were Donald Campbell, professor of astronomy at Cornell University; J.F. Chandler of Smithsonian Astrophysical Observatory; and Alice Hine, Mike Nolan and Phil Perillat of the Arecibo Observatory, which is managed by the National Astronomy and Ionosphere Center at Cornell for the NSF.

Suggestions of lunar ice first came in 1996 when radio data from the Clementine spacecraft gave some indications of the presence of ice on the wall of a crater at the moon’s south pole. Then, neutron spectrometer data from the Lunar Prospector spacecraft, launched in 1998, indicated the presence of hydrogen, and by inference, water, at a depth of about a meter at the lunar poles. But radar probes by the 12-cm-wavelength radar at Arecibo showed no evidence of thick ice at depths of up to a meter. “Lunar Prospector had found significant concentrations of hydrogen at the lunar poles equivalent to water ice at concentrations of a few percent of the lunar soil,” says Donald Campbell. “There have been suggestions that it may be in the form of thick deposits of ice at some depth, but this new data from Arecibo makes that unlikely.”

Says Bruce Campbell, “There are no places that we have looked at with any of these wavelengths where you see that kind of signature.”

The Nature paper notes that if ice does exist at the lunar poles it would be considerably different from “the thick, coherent layers of ice observed in shadowed craters on Mercury,” found in Arecibo radar imaging. “On Mercury what you see are quite thick deposits on the order of a meter or more buried by, at most, a shallow layer of dust. That’s the scenario we were trying to nail down for the moon,” says Bruce Campbell. The difference between Mercury and the moon, the researchers say, could be due to the lower average rate of comets striking the lunar surface, to recent comet impacts on Mercury or to a more rapid loss of ice on the moon.

What makes the lunar poles good cold traps for water is a temperature of minus 173 degrees Celsius (minus 280 degrees Fahrenheit). The limb of the sun rises only about two degrees above the horizon at the lunar poles so that sunlight never penetrates into deep craters, and a person standing on the crater floor would never see the sun. The Arecibo radar probed the floors of two craters in permanent shadow at the lunar south pole, Shoemaker and Faustini, and, at the north pole, the floors of Hermite and several small craters within the large crater Peary. In contrast, Clementine focused on the sloping walls of Shackleton crater, whose floor can’t be “seen” from Earth. “There is a debate on how to interpret data from a rough, tilted surface,” says Bruce Campbell.

The Arecibo radar probe is a particularly good detector of thick ice because it takes advantage of a phenomenon known as “coherent backscatter.” Radar waves can travel long distances without being absorbed in ice at temperatures well below freezing. Reflections from irregularities inside the ice produce a very strong radar echo. In contrast, lunar soil is much more absorptive and does not give as strong a radar echo.

Original Source: Cornell News Release