Posted on by Fraser Cain

Update on the Mars Rovers

Image credit: NASA/JPL

In case you’d forgotten about them, NASA’s twin Mars Exploration spacecraft, Spirit and Opportunity, are still on their way to the Red Planet. Spirit made its third trajectory correction last week to fine-tune its flight path as it gets closer. Both rovers have rebooted their computers in the past two weeks to remove any data errors that could have caused by the recent powerful solar storms. Spirit should arrive at the Gusev Crater on January 4, 2004, while Opportunity will land Meridiani Planum on January 25.

NASA’s Spirit spacecraft made its third trajectory correction maneuver on Friday, Nov. 14, fine tuning its flight path toward Mars with an engine-firing operation planned into the seven-month trip.

The trajectory adjustment was designed to alter Spirit’s velocity by 0.6 meters per second (1.3 miles per hour), moving the arrival point by 770 kilometers (478 miles) and arrival time by 16.5 minutes closer to the planned target location and time, said Louis D’Amario, the project’s navigation team chief. To accomplish that adjustment, the flight team commanded Spirit to fire its engines for 132 seconds in the direction of the spacecraft’s rotation axis and for short pulses totaling 27 seconds in a direction roughly perpendicular to the rotation axis.

Spirit has three more scheduled dates for additional trajectory corrections before reaching Mars less than seven weeks from now. The spacecraft is carrying the first of two Mars Exploration Rovers equipped to examine the geology around their landing sites for evidence about past environmental conditions.

Both Spirit and its twin, Opportunity, have rebooted their computers in the past two weeks. Mission controllers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., sent commands for that procedure on each spacecraft to correct possible corruption of computer memory registers by radiation from powerful solar flares in late October and early November. The flares were among the most intense ever recorded.

“We had no evidence of memory problems, but we considered it prudent to reboot both spacecraft to assure memory integrity, using the sleep-wake cycle that we plan to do each night after the rovers are on the surface of Mars,” said JPL’s Peter Theisinger, project manager for the Mars Exploration Rover Project.

High-energy protons ejected by the stormy Sun appeared on Oct. 28 as bursts of bright spots in star-tracking instruments used by both Spirit and Opportunity to sense the spacecrafts’ orientation. The instruments interpreted the proton hits as stars, so the bursts overwhelmed their ability to recognize star patterns and determine spacecraft attitude. Both spacecraft temporarily switched to a backup method of attitude sensing, using the Sun. They resumed use of the star trackers last week.

Spirit’s target is arrival at Mars’ Gusev Crater at 04:35 Jan. 4, 2004, Universal Time (8:35 p.m. Jan. 3, Pacific Standard Time and 11:35 p.m. Jan. 3, Eastern Standard Time). These are “Earth received times,” meaning they reflect the delay necessary for a speed-of-light signal from Mars to reach Earth; on Mars, the landing will have happened nearly 10 minutes earlier. Three weeks later, at 05:05 Jan. 25, Universal Time, Opportunity will arrive at a level plain called Meridiani Planum on the opposite side of Mars from Gusev. Each rover will examine its landing area for geological evidence about the history of water there, key information for assessing whether the site ever could have been hospitable to life.

As of 6 a.m. PST on Nov. 19, Spirit had traveled 396.5 million kilometers (246.4 million miles) since its June 10 launch, with 91.5 million kilometers (56.2 million miles) to go before reaching Mars. Opportunity, launched on July 7, had traveled 326 million kilometers (202 million miles) and has 130 million kilometers (81 million miles) yet to go.

JPL, a division of the California Institute of Technology, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Additional information about the project is available from JPL at http://mars.jpl.nasa.gov/mer and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Station in Orbit for Five Years

Image credit: NASA

The International Space Station has been in orbit for five years as of November 20, 2003. The first element of the station, the Russian Zarya control module, was launched on November 20, 1998, and then quickly followed up by the US-built Unity module. Since then, the station has orbited the Earth 29,000 times and has been inhabited since November 2, 2000. Eight successive crews, 22 people, have staffed the station and performed research in bioastronautics, physical sciences, fundamental space biology, space product development and space flight disciplines. Happy birthday ISS.

The International Space Station reaches the historic five years in space milestone on November 20, 2003. The unique orbiting laboratory complex has grown from a lone, uninhabited module into a permanently staffed, house-sized research facility.

The Station remains the largest and most complex international space research project in history. The Station will eventually triple scientific capacity with components awaiting the Space Shuttle’s return to flight.

The first Space Station element, the Russian Zarya control module, was launched from Baikonur, Kazakhstan, Nov. 20, 1998. Two weeks later, the Space Shuttle Endeavour delivered the second element, the U.S. connecting module called Unity. The challenges, triumphs and tragedy shared by the international partnership since then have solidified cooperation on the Station among the United States, Russia, Canada, Japan and Europe.

“Together with our international partners we have learned how to build, operate and maintain a very complex spacecraft, through the good times and the bad,” said Bill Gerstenmaier, NASA Space Station Program Manager. “With this experience to guide us, we look forward to the future, with a vast expansion of the Station on the horizon.”

At five years old, the Station is still growing. More than 80 tons of equipment and hardware are in the Space Station Processing Facility at NASA’s Kennedy Space Center (KSC), Fla. being prepared for launch.

The Space Station has orbited the Earth more than 29,000 times. It is visible in the night sky as it flies more than 210 miles overhead. The living and working area inside the Station has a volume of about 15,000 cubic feet, larger than a three-bedroom house.

The orbiting complex has been inhabited since Nov. 2, 2000. Eight successive crews, 22 people, have staffed the Station. Residents have conducted research in bioastronautics, physical sciences, fundamental space biology, space product development and space flight disciplines. In the U.S. Destiny Lab alone, astronauts have worked on over 70 different science experiments.

Hundreds of people on Earth support Station operations from the Station Mission Control Center at NASA’s Johnson Space Center in Houston. Round-the-clock science operations are handled by the Payload Operations Center team at NASA’s Marshall Space Flight Center in Huntsville, Ala. Hundreds of other scientists and engineers perform important jobs, such as training Station crews and building new hardware that will become part of the orbiting laboratory.

Additional research facilities are being readied for launch on future Shuttle missions. They will enhance Destiny’s capabilities in the areas of fundamental space biology; glass and porous ceramics materials processing research; human physiology research; combustion research; research on the behavior of fluids; Earth observations; and experiment refrigerator/freezer conditioned sample storage.

Also awaiting launch at KSC are solar arrays and support structures that will triple the sunlight-gathering, solar cell area, thereby increasing the power dedicated to research by 84 percent.

The Node 2 module that will serve as a connector between the U.S., European and Japanese research labs is at KSC undergoing pre-launch processing. The Kibo Japanese Experiment Module, including a pressurized lab already at KSC, will also be added to the Station. The European Columbus Laboratory, under construction in Bremen, Germany, will expand the Station’s volume to almost that of a five-bedroom house.

For information about NASA, human spaceflight, astronauts, and the International Space Station on the Internet, visit:

http://www.nasa.gov

Original Source: NASA News Release

Posted on by Fraser Cain

1,000 People Have Joined the Forum!

The Universe Today forums reached a pretty big milestone this week with the addition of our 1,000th member – not bad for only four months. There’s lots to talk about, so if you’re interested in connecting with other space enthusiasts, come take a look, sign up, and join the conversations – it’s totally free.

I’d like make a special thanks to all the moderators. They’ve been working furiously behind the scenes to make sure everyone plays nice.

Click here to access the Universe Today forums.

I know it can be a little confusing to get going in the beginning, so if you have any questions, please drop me an email at [email protected].

Thanks!

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

NASA Reforms Safety Panel

Image credit: NASA

NASA has set up a new safety advisory panel to replace the previous group that resigned back in September following the Columbia accident investigation report. The new ten members make up the NASA Aerospace Safety Advisory Panel, and will be an independent group responsible for safety oversight of NASA operations. This new safety board will play a key role in helping to ensure the space shuttles are safe to return to flight later in 2004.

NASA Administrator Sean O’Keefe today announced the new NASA Aerospace Safety Advisory Panel (ASAP), which includes nine distinguished members and a new charter. The initial meeting of the new panel is expected soon.

“The Columbia Accident Investigation Board report clearly indicated we need to get back to basics with our safety assessment,” said Administrator O’Keefe. “By recommitting ourselves to the original concept for the ASAP, we believe a stronger, more focused advisory panel will benefit the entire agency well beyond our Return to Flight efforts.”

The ASAP was originally chartered by Congress in 1967 after the tragic Apollo One fire, to act as an independent body to advise the NASA Administrator on safety issues regarding operations, missions and other agency initiatives. The new charter calls for the ASAP to be composed of recognized safety, management and engineering experts from industry, academia and other government agencies.

Over the years, administrative procedures were added to govern the conduct of the panel. These procedures have been revoked, and the new panel will have the opportunity to develop its agenda in concert with the oversight findings of the Columbia Accident Investigation Board.

“By drawing on and tasking the technical support of the NASA Engineering and Safety Center, the panel will have a deep capacity to conduct comprehensive, independent, external oversight of our safety systems, operations and culture. We welcome the members’ active participation in our efforts to emerge from the Columbia tragedy a smarter, stronger and safer agency dedicated to exploration,” said Administrator O’Keefe.

In late September 2003, 11 ASAP members and consultants resigned in the wake of the Columbia accident.

The new ASAP members are:

Rear Admiral Walt Cantrell, USN (Ret)

Former Commander, Space and Naval Warfare Systems Command
Member, NASA Stafford-Covey Return to Flight Task Group
Former NASA Aerospace Safety Advisory Panel member

Vice Admiral Joe Dyer, USN (Ret)

Former Commander, Naval Air Systems Command
General Manager, Military Systems Division, iRobot Corporation

Augustine Esogbue, Ph.D.

Professor and Director, Intelligent Systems & Controls Laboratory, School of
Industrial and Systems Engineering, Georgia Institute of Technology
Fellow, American Association for the Advancement of Science

Major General Rusty Gideon, USAF (Ret)

Former Commander, U.S. Air Force Safety Center, and USAF Chief of Safety
Former Director of Operations, Headquarters Air Force Materiel Command
Former Commander, Foreign Aerospace Science and Technology Center

Deborah Grubbe

DuPont Corporate Director — Safety and Health
Member, National Academy of Sciences
Former consultant, Columbia Accident Investigation Board

Rosemary O?Leary, J.D., Ph.D.

Professor of Public Administration and Political Science, Maxwell School of
Citizenship and Public Affairs at Syracuse University, New York
Member, NASA Stafford-Covey Return to Flight Task Group

John Marshall

Delta Airlines, Vice President Corporate Safety and Compliance, Atlanta
Co-chair, Commercial Aviation Safety Team
Board member, National Defense Transportation Association

Steve Wallace

Director, Office of Accident Investigation, Federal Aviation Administration
FAA representative to National Transportation Safety Board
Former Columbia Accident Investigation Board member

Rick Williams

Corporate Safety Director, Alcoa, New York
Former Director, Human Resources, Alcoa Primary Metals, Knoxville, Tenn.

Brigadier General Joseph Smith, USA — Ex-Officio Member

Director, U.S. Army Safety Center, Fort Rucker, Ala.

The new ASAP will begin with the original charter, signed by then-NASA Administrator James E. Webb. New provisions help assure an independent, long-term oversight of the agency’s safety policies and programs. Some of the revisions include:

* The new ASAP will report quarterly instead of annually
* The term for new members is two years, extendable to a maximum of six years in order to stagger terms of service and ensure a fresh perspective at regular intervals
* The new ASAP focuses on NASA’s safety and quality systems. ASAP will focus on industrial and systems safety, risk management, trend analysis and the management of these activities

“We’ve taken extra steps to ensure the independence of this panel,” said Associate Administrator for Safety and Mission Assurance Bryan O’Connor. “While the original law and the new charter allow for NASA members, none of the new members is a current or former agency employee or contractor.”

The new ASAP is also expected to play an important role in the ongoing safety assessment and review of the Space Shuttle program after Return to Flight. “We intend for the ASAP to oversee our implementation of the Columbia Accident Investigation Board’s recommendations long after the work of the Stafford-Covey Return to Flight Task Group is completed,” added Administrator O’Keefe. “Our intent is to institutionalize a renewed commitment to safety, and the panel will help us assure that we follow through on that objective.”

The new Aerospace Safety Advisory Panel charter and member biographies are available on the Internet, at:

http://www.nasa.gov/news/highlights/returntoflight.html

Original Source: NASA News Release

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.