Posted on by Fraser Cain

World’s Largest Telescope

An image of how one element of the SKA might look. Image credit: Chris Fluke. Click to enlarge
European funding has now been agreed to start designing the world’s biggest telescope. The “Square Kilometre Array” (SKA) will be an international radio telescope with a collecting area of one million square metres – equivalent to about 200 football pitches – making SKA 200 times bigger than the University of Manchester’s Lovell Telescope at Jodrell Bank and so the largest radio telescope ever constructed. Such a telescope would be so sensitive that it could detect TV Broadcasts coming from the nearest stars.

The four-year Square Kilometre Array Design Study (SKADS) will bring together European and international astronomers to formulate and agree the most effective design. The final design will enable the SKA to probe the cosmos in unprecedented detail, answering fundamental questions about the Universe, such as “what is dark energy?” and “how did the structure we see in galaxies today actually form?”.

The new telescope will test Einstein’s General Theory of Relativity to the limit – and perhaps prove it wrong. It is certain to add to the long list of fundamental discoveries already made by radio astronomers including quasars, pulsars and the radiation left over from the Big Bang. By the end of this decade the design will be complete and astronomers anticipate building SKA in stages, leading to completion and full operation in 2020.

The SKA concept was first proposed to observe the characteristic radio emission from hydrogen gas. Measurements of the hydrogen signature will enable astronomers to locate and weigh a billion galaxies.

As the University of Manchester’s Prof Peter Wilkinson points out, “Hydrogen is the most abundant element in the universe, but its signal is weak and so a huge collecting area is needed to be able to study it at the vast distances that take us back in time towards the Big Bang”. To which Prof Steve Rawlings, University of Oxford, adds,”The distribution of these galaxies in space tells us how the universe has evolved since the Big Bang and hence about the nature of the Dark Energy which is now making the universe expand faster with time”.

Another target for the SKA is pulsars – spinning remnants of stellar explosions which are the most accurate clocks in the universe. A million times the mass of the Earth but only the size of a large city, pulsars can spin around hundreds of times per second. Already these amazing objects have enabled astronomers to confirm Einstein’s prediction of gravitational waves, but University of Manchester’s Dr Michael Kramer is looking further ahead. “With the SKA we will find a pulsar orbiting a black hole and, by watching how the clock rate varies, we can tell if Einstein had the last word on gravity or not”, he says.

Prof Richard Schilizzi, the International SKA Project Director, stresses the scale of the instrument needed to fulfil these science goals. “Designing and then building, such an enormous technologically-advanced instrument is beyond the scope of individual nations. Only by harnessing the ideas and resources of countries around the world is such a project possible”. Astronomers in Australia, South Africa, Canada, India, China and the USA are collaborating closely with colleagues in Europe to develop the required technology which will include sophisticated electronics and powerful computers that will play a far bigger role than in the present generation of radio telescopes. The European effort is based on phased array receivers, similar to those in aircraft radar systems. When placed at the focus of conventional mass-produced radio ‘dishes’, these arrays operate like wide-angle radio cameras enabling huge areas of sky to be observed simultaneously. A separate, much larger, phased array at the centre of the SKA will act like a radio fish-eye lens, constantly scanning the sky.

Funding for this global design programme has been provided by the European Commission’s Framework 6 ‘Design Studies’ programme, which is contributing about 27% of the total ?38M funding over the next four years. Individual countries are contributing the remainder. The UK has invested ?5.6M (?8.3M) funding provided by PPARC.
When coupled with the UK’s share of the EC contribution, then the UK’s overall contribution to the SKA Design Study (SKADS) programme is about 30% of the total.

The ?38M European technology development programme is funded by the European Commission and governments in eight countries led by the Netherlands, the UK, France and Italy. The programme is being coordinated by Ir. Arnold van Ardenne, Head of Emerging Technologies at The Netherlands ASTRON Institute. In van Ardenne’s view “the critical task is to demonstrate that large numbers of electronic arrays can be built cost effectively – so that our dreams of radio cameras and radio fish-eye lenses can be turned into reality”.

In the UK, a group of universities currently including Manchester, Oxford, Cambridge, Leeds and Glasgow, funded by PPARC, is involved in all aspects of the design but is concentrating on sophisticated digital phased arrays and the distribution and analysis of the enormous volumes of data which the SKA will produce. University of Cambridge’s Dr Paul Alexander makes the point that “the electronics in the SKA makes it very flexible and allows for completely new ways of scanning the sky. But to make it work will require massive computing power”. Designers believe that by the time the SKA reaches full operation, 14 years from now, a new generation of computers will be up to the task.

The geographical location of SKA will be decided in the mid-term future and several nations have already expressed interest in hosting this state of the art astronomical facility.

Original Source: PPARC News Release

Posted on by Fraser Cain

New Horizons Blasts Off for Pluto

Liftoff of the Atlas V carrying NASA’s New Horizons spacecraft. Image credit: NASA/KSC Click to enlarge
The first mission to distant planet Pluto is under way after the successful launch today of NASA’s New Horizons spacecraft from Cape Canaveral Air Force Station, Fla.

New Horizons roared into the afternoon sky aboard a powerful Atlas V rocket at 2 p.m. EST. It separated from its solid-fuel kick motor 44 minutes, 53 seconds after launch, and mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., where the spacecraft was designed and built, received the first radio signals from New Horizons a little more than five minutes later. The radio communications, sent through NASA’s Deep Space Network antennas in Canberra, Australia, confirmed to controllers that the spacecraft was healthy and ready to begin initial operations.

“Today, NASA began an unprecedented journey of exploration to the ninth planet in the solar system,” says Dr. Colleen Hartman, deputy associate administrator for NASA’s Science Mission Directorate, Washington, D.C. “Right now, what we know about Pluto could be written on the back of a postage stamp. After this mission, we’ll be able to fill textbooks with new information.”

The 1,054-pound, piano-sized spacecraft is the fastest ever launched, speeding away from Earth at approximately 36,000 miles per hour, on a trajectory that will take it more than 3 billion miles toward its primary science target. New Horizons will zip past Jupiter for a gravity assist and science studies in February 2007, and conduct the first close-up, in-depth study of Pluto and its moons in summer 2015. As part of a potential extended mission, the spacecraft would then examine one or more additional objects in the Kuiper Belt, the region of ancient, icy, rocky bodies (including Pluto) far beyond Neptune?s orbit.

“The United States of America has just made history by launching the first spacecraft to explore Pluto and the Kuiper Belt beyond,” says Dr. Alan Stern, New Horizons principal investigator, from Southwest Research Institute in Boulder, Colo. No other nation has this capability. This is the kind of exploration that forefathers like Lewis and Clark, 200 years ago this year, made a trademark of our nation.”

Over the next several weeks, mission operators at APL will place the spacecraft in flight mode, check out its critical operating systems and perform small propulsive maneuvers to refine its path toward Jupiter. Following that, among other operations, the team will begin checking and commissioning most of the seven science instruments.

“This is the gateway to a long, exciting journey,” says Glen Fountain, New Horizons project manager from APL. “The team has worked hard for the past four years to get the spacecraft ready for the voyage to Pluto and beyond, to places we’ve never seen up close. This is a once-in-a-lifetime opportunity, in the tradition of the Mariner, Pioneer, and Voyager missions to set out for first looks in our solar system.”

After the Jupiter encounter ? during which New Horizons will train its science instruments on the large planet and its moons ?? the spacecraft will “sleep” in electronic hibernation for much of the cruise to Pluto. Operators will turn off all but the most critical electronic systems and check in with the spacecraft once a year to check out the critical systems, calibrate the instruments and perform course corrections, if necessary.

Between the in-depth checkouts, New Horizons will send back a beacon signal each week to give operators an instant read on spacecraft health. The entire spacecraft, drawing electricity from a single radioisotope thermoelectric generator, operates on less power than a pair of 100-watt household light bulbs.

New Horizons is the first mission in NASA’s New Frontiers Program of medium-class spacecraft exploration projects. Stern leads the mission and science team as principal investigator. APL manages the mission for NASA’s Science Mission Directorate and is operating the spacecraft in flight. The mission team also includes Ball Aerospace Corporation, the Boeing Company, NASA Goddard Space Flight Center, NASA Jet Propulsion Laboratory, Stanford University, KinetX, Inc., Lockheed Martin Corporation, University of Colorado, the U.S. Department of Energy, and a number of other firms, NASA centers, and university partners.

Original Source: APL News Release

Posted on by Fraser Cain

Self-Repairing Spacecraft

A time lapse sequence of self-repair taking place. Image credit: ESA Click to enlarge
Building spacecraft is a tough job. They are precision pieces of engineering that have to survive in the airless environment of space, where temperatures can swing from hundreds of degrees Celsius to hundreds of degree below zero in moments. Once a spacecraft is in orbit, engineers have virtually no chance of repairing anything that breaks. But what if a spacecraft could fix itself?

Thanks to a new study funded by ESA’s General Studies Programme, and carried out by the Department of Aerospace Engineering, University of Bristol, UK, engineers have taken a step towards that amazing possibility. They took their inspiration from nature.

“When we cut ourselves we don’t have to glue ourselves back together, instead we have a self-healing mechanism. Our blood hardens to form a protective seal for new skin to form underneath,” says Dr Christopher Semprimoschnig, a materials scientist at ESA’s European Space Technology Research Centre (ESTEC) in the Netherlands, who oversaw the study.

He imagined such cuts as analogous to the ‘wear-and-tear’ suffered by spacecraft. Extremes of temperature can cause small cracks to open in the superstructure, as can impacts by micrometeroids – small dust grains travelling at remarkable speeds of several kilometres per second. Over the lifetime of a mission the cracks build up, weakening the spacecraft until a catastrophic failure becomes inevitable.

The challenge for Semprimoschnig was to replicate the human process of healing small cracks before they can open up into anything more serious. He and the team at Bristol did it by replacing a few percent of the fibres running through a resinous composite material, similar to that used to make spacecraft components, with hollow fibres containing adhesive materials. Ironically, to make the material self-repairable, the hollow fibres had to be made of an easily breakable substance: glass. “When damage occurs, the fibres must break easily otherwise they cannot release the liquids to fill the cracks and perform the repair,” says Semprimoschnig.

In humans, the air chemically reacts with the blood, hardening it. In the airless environment of space, alternate mechanical veins have to be filled with liquid resin and a special hardener that leak out and mix when the fibres are broken. Both must be runny enough to fill the cracks quickly and harden before it evaporates.

“We have taken the first step but there is at least a decade to go before this technology finds its way onto a spacecraft,” says Semprimoschnig, who believes that larger scale tests are now needed.

The promise of self-healing spacecraft opens up the possibility of longer duration missions. The benefits are two-fold. Firstly, doubling the lifetime of a spacecraft in orbit around Earth would roughly halve the cost of the mission. Secondly, doubling spacecraft lifetimes means that mission planners could contemplate missions to far-away destinations in the Solar System that are currently too risky.

In short, self-healing spacecraft promise a new era of more reliable spacecraft, meaning more data for scientists and more reliable telecommunication possibilities for us all.

Original Source: ESA Portal

Posted on by Fraser Cain

Saturnian Storms About to Merge

Saturnian storms swirling in the region “storm alley”. Image credit: NASA/JPL/SSI Click to enlarge
Two Saturnian storms swirl in the region informally dubbed “storm alley” by scientists. This mid-latitude region has been active with storms since Cassini scientists began monitoring Saturn in early 2004.

The large storm at left is at least 2,500 kilometers (1,600 miles) across from north to south. This is bigger than typical storms in the region, which are the size of large Earth hurricanes, or about 1,000 kilometers (600 miles) across. To the left, the smaller storm is about 700 kilometers (400 miles) across.

The two storms are interacting. Their threadlike arms are intertwined, and they might have merged a few days after this image was taken. See PIA06082 and PIA06083 for movies of storm activity in this region.

The image was taken with the Cassini spacecraft narrow-angle camera on Dec. 9, 2005, at a distance of approximately 3.2 million kilometers (2 million miles) from Saturn. The image was obtained using a filter sensitive to wavelengths of infrared light centered at 727 nanometers. The image scale is 38 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 Nancy Atkinson

Satellites on a Budget – High Altitude Balloons

Balloon photograph taken from 25km. Image credit: Paul Verhage. Click to enlarge.
Paul Verhage has some pictures that you’d swear were taken from space. And they were. But Verhage is not an astronaut, nor does he work for NASA or any company that has satellites orbiting Earth. He is a teacher in the Boise, Idaho school district. His hobby, however, is out of this world.

Verhage is one of about 200 people across the United States who launch and recover what have been called a “poor man’s satellite.” Amateur Radio High Altitude Ballooning (ARHAB) allows individuals to launch functioning satellites to “near space,” at a fraction of the cost of traditional rocket launch vehicles.

Usually, the cost to launch anything into space on regular rockets is quite high, reaching thousands of dollars per pound. Additionally, the waiting period for payloads to be put on a manifest and then launched can be several years.

Verhage says that the total cost for building, launching and recovering these Near Spacecraft is less than $1,000. “Our launch vehicles and fuel are latex weather balloons and helium,” he said.

Plus, once an individual or small group begins designing a Near Spacecraft, it could be ready for launch within six to twelve months.

Verhage has launched about 50 balloons since 1996. Payloads on his Near Spacecraft include mini-weather stations, Geiger counters and cameras.

Near space lies begins between 60,000 and 75,000 feet (~ 18 to 23 km) and continues to 62.5 miles (100km), where space begins.

“At these altitudes, air pressure is only 1% of that at ground level, and air temperatures are approximately -60 degrees F,” he said. “These conditions are closer to the surface of Mars than to the surface of Earth.”

Verhage also said that because of the low air pressure, the air is too thin to refract or scatter sunlight. Therefore, the sky is black rather than blue. So, what is seen at these altitudes is very close to what the shuttle astronauts see from orbit.

Verhage said his highest flight reached an altitude of 114,600 feet (35 km), and his lowest went only 8 feet (2.4 meters) off the ground.

The main parts of a Near Spacecraft are flight computers, an airframe, and a recovery system. All these components are reusable for multiple flights. “Think of building this Near Spacecraft as building your own reusable Space Shuttle,” said Verhage.

The avionics operates experiments, collects data, and determines the status of the spacecraft, and Verhage makes his own flight computers. The airframe is usually the most inexpensive part of the spacecraft and can be made from materials such as Styrofoam and Ripstop Nylon, put together with hot glue.

The recovery system consists of a GPS, a radio receiver such as a ham radio, and a laptop with GPS software. Additionally, and probably most important is the Chase Crew. “It’s like a road rally,” says Verhage, “but no one in the Chase Crew knows quite for sure where they are going to end up!”

The process of launching a Near Spacecraft involves getting the capsule ready, filling the balloon with helium and releasing it. Ascent rates for the balloons vary for each flight but are typically between 1000 and 1200 feet per minute, with the flights taking 2-3 hours to reach apogee. A filled balloon is about 7 feet tall and 6 feet wide. They expand in size as the balloon ascends, and at maximum altitude can be over 20 feet wide.

The flight ends when the balloon bursts from the reduced atmospheric pressure. To ensure a good landing, a parachute is pre-deployed before launch. A Near Spacecraft will free fall, with speeds of over 6,000 feet per minute until about 50,000 feet in altitude, where the air is dense enough to slow the capsule.

The GPS receiver that Verhage uses signals its position every 60 seconds, so after the spacecraft lands, Verhage and his team usually know where the spacecraft is, but recovering it is mostly a matter of being able to get to where it lies. Verhage has lost only one capsule. The batteries died during the flight, so the GPS wasn’t functioning. Another capsule was recovered 815 days after launch, found by the Air National Guard near a bombing range.

Some balloons are recovered only 10 miles from the launch site, while others have traveled over 150 miles away.

“Some of the recoveries are easy,” said Verhage. “In one flight, one of my chase crew, Dan Miller, caught the balloon as it landed. But some recoveries in Idaho are tough. We’ve spent hours climbing a mountain in some cases.”

Other experiments that Verhage has flown include a Visible Light Photometer, Medium Bandwidth Photometers, an Infrared Radiometer, a Glider Drop, Insect Survival, and Bacteria Exposure.

One of Verhage’s most interesting experiments involved using a Geiger counter to measure cosmic radiation. On the ground, a Geiger counter detects about 4 cosmic rays a minute. At 62,000 the count goes to 800 counts per minute, but Verhage discovered that above that altitude the count does down. “I learned about primary cosmic rays from that discovery,” he said.

Flying the experiments are a great experience, Verhage said, but launching a camera and getting pictures from Near Space provides an irreplaceable “wow” factor. “To have an image of the Earth showing its curvature is pretty amazing,” Verhage said.

“For cameras,” he continued, “the dumber they are the better. Too many of the newer cameras have a power save feature, so they shut off when they’re not used in so many minutes. When they turn off at 50,000 feet, there’s nothing I can do to turn them back on.”

While digital cameras are easy to interface with the flight computer, Verhage said, they require some inventive wiring too keep the camera from shutting off. He said that so far, his best photos have come from film cameras.

Verhage is writing an e-book that details how to build, launch and recover a Near Spacecraft, and the first 8 chapters are available free, online. The e-book will have 15 chapters when finished, totaling about 800 pages in length.
Parallax, the company that manufactures a microcontroller is sponsoring the e-book’s publication.

Verhage teaches electronics at the Dehryl A. Dennis Professional Technical Center in Boise. He writes a bimonthly column about his adventures with ARHAB for Nuts and Volts magazine, and also shares his enthusiasm for space exploration through the NASA/JPL Solar System Ambassador program.

Verhage said his hobby incorporates everything he is interested in: GPS, microcontrollers and space exploration, and he encourages anyone to experience the thrill of sending a spacecraft to Near Space.

By Nancy Atkinson

Posted on by Fraser Cain

Asteroid Broke Up 8.2 Million Years Ago

The Earth. Image credit: NASA Click to enlarge
In a new study that provides a novel way of looking at our solar system’s past, a group of planetary scientists and geochemists announce that they have found evidence on Earth of an asteroid breakup or collision that occurred 8.2 million years ago.

Reporting in the January 19 issue of the journal Nature, scientists from the California Institute of Technology, the Southwest Research Institute (SwRI), and Charles University in the Czech Republic show that core samples from oceanic sediment are consistent with computer simulations of the breakup of a 100-mile-wide body in the asteroid belt between Mars and Jupiter. The larger fragments of this asteroid are still orbiting the asteroid belt, and their hypothetical source has been known for years as the asteroid “Veritas.”

Ken Farley of Caltech discovered a spike in a rare isotope known as helium 3 that began 8.2 million years ago and gradually decreased over the next 1.5 million years. This information suggests that Earth must have been dusted with an extraterrestrial source.

“The helium 3 spike found in these sediments is the smoking gun that something quite dramatic happened to the interplanetary dust population 8.2 million years ago,” says Farley, the Keck Foundation Professor of Geochemistry at Caltech and chair of the Division of Geological and Planetary Sciences. “It’s one of the biggest dust events of the last 80 million years.”

Interplanetary dust is composed of bits of rock from a few to several hundred microns in diameter produced by asteroid collisions or ejected from comets. Interplanetary dust migrates toward the sun, and en route some of this dust is captured by the Earth’s gravitational field and deposited on its surface.

Presently, more than 20,000 tons of this material accumulates on Earth each year, but the accretion rate should fluctuate with the level of asteroid collisions and changes in the number of active comets. By looking at ancient sediments that include both interplanetary dust and ordinary terrestrial sediment, the researchers for the first time have been able to detect major dust-producing solar system events of the past.

Because interplanetary dust particles are so small and rare in sediment-significantly less than a part per million-they are difficult to detect using direct measurements. However, these particles are extremely rich in helium 3, in comparison with terrestrial materials. Over the last decade, Ken Farley has measured helium 3 concentrations in sediments formed over the last 80 million years to create a record of the interplanetary dust flux.

To assure that the peak was not a fluke present at only one site on the seafloor, Farley studied two different localities: one in the Indian Ocean and one in the Atlantic. The event is recorded clearly at both sites.

To find the source of these particles, William F. Bottke and David Nesvorny of the SwRI Space Studies Department in Boulder, Colorado, along with David Vokrouhlicky of Charles University, studied clusters of asteroid orbits that are likely the consequence of ancient asteroidal collisions.

“While asteroids are constantly crashing into one another in the main asteroid belt,” says Bottke, “only once in a great while does an extremely large one shatter.”

The scientists identified one cluster of asteroid fragments whose size, age, and remarkably similar orbits made it a likely candidate for the Earth-dusting event. Tracking the orbits of the cluster backwards in time using computer models, they found that, 8.2 million years ago, all of its fragments shared the same orbital orientation in space. This event defines when the 100-mile-wide asteroid called Veritas was blown apart by impact and coincides with the spike in the interplanetary seafloor sediments Farley had found.

“The Veritas disruption was extraordinary,” says Nesvorny. “It was the largest asteroid collision to take place in the last 100 million years.”

As a final check, the SwRI-Czech team used computer simulations to follow the evolution of dust particles produced by the 100-mile-wide Veritas breakup event. Their work shows that the Veritas event could produce the spike in extraterrestrial dust raining on the Earth 8.2 million years ago as well as a gradual decline in the dust flux.

“The match between our model results and the helium 3 deposits is very compelling,” Vokrouhlicky says. “It makes us wonder whether other helium 3 peaks in oceanic cores can also be traced back to asteroid breakups.”

This research was funded by NASA’s Planetary Geology and Geophysics program and received additional financial support from Czech Republic grant agency and the National Science Foundation’s COBASE program. The Nature paper is titled “A late Miocene dust shower from the breakup of an asteroid in the main belt.”

Original Source: caltech News Release

Posted on by Fraser Cain

Juventae Chasma on Mars

The depression of Juventae Chasma taken by HRSC. Image credit: ESA Click to enlarge
These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, show the depression of Juventae Chasma, cut into the plains of Lunae Planum on Mars.

The HRSC obtained these images during orbit 243 with a ground resolution of approximately 23.4 metres per pixel. The scenes show the region of Lunae Planum, at approximately 5? South and 297? East.

The depression of Juventae Chasma, located north of Valles Marineris, cuts more than 5000 metres into the plains of Lunae Planum. The floor of Juventae Chasma is partly covered by dunes.

In the valley, to the north-east, there is a mountain composed of bright, layered material. This mountain is approximately 2500 metres high, it has a length of 59 kilometres and a width of up to 23 kilometres.

The OMEGA spectrometer on board Mars Express will be able to confirm that this mountain is indeed composed of sulphate deposits. The colour scenes have been derived from the three HRSC-colour channels and the nadir channel.

***image4:left***The perspective views have been calculated from the digital terrain model derived from the stereo channels. The 3D anaglyph image was calculated from the nadir and one stereo channel. Image resolution has been decreased for use on the internet.

Original Source: ESA Mars Express

Posted on by Fraser Cain

Kuiper Belt-Like Disks Around Two Nearby Stars

Two debris disks resemble the Kuiper Belt. Image credit: UC Berkeley Click to enlarge
A survey by NASA’s Hubble Space Telescope of 22 nearby stars has turned up two with bright debris disks that appear to be the equivalent of our own solar system’s Kuiper Belt, a ring of icy rocks outside the orbit of Neptune and the source of short-period comets.

The debris disks encircling these stars fall into two categories – wide and narrow belts – that appear to describe all nine stars, including the sun, which are known to have debris disks linked to planet formation. In fact, the sharp outer edges of the narrow belts, such as the Kuiper Belt in our solar system, may be a tip-off to the existence of a star-like companion that continually grooms the edge, in the same way that shepherding moons trim the edges of debris rings around Saturn and Uranus.

Research astronomer Paul Kalas, professor of astronomy James Graham and graduate student Michael Fitzgerald of the University of California, Berkeley, along with Mark C. Clampin of Goddard Space Flight Center in Greenbelt, Md., will report their discovery and conclusions in the Jan. 20 issue of Astrophysical Journal Letters.

The newfound stellar disks, each about 60 light years from Earth, bring to nine the number of stars with dusty debris disks observable at visible wavelengths. The new ones are different, however, in that they are old enough – more than 300 million years – to have settled into stable configurations akin to the stable planet and debris orbits in our own solar system, which is 4.6 billion years old. The other seven, except for the sun, range from tens of millions to 200 million years old – young by solar standards.

In addition, the masses of the stars are closer to that of the sun.

“These are the oldest debris disks seen in reflected light, and are important because they show what the Kuiper Belt might look like from the outside,” said Kalas, the lead researcher. “These are the types of stars around which you would expect to find habitable zones and planets that could develop life.”

Most debris disks are lost in the glare of the central star, but the high resolution and sensitivity of the Hubble Space Telescope’s Advanced Camera for Surveys has made it possible to look for these disks after blocking the light from the star. Kalas has discovered debris disks around two other stars (AU Microscopii and Fomalhaut) in the past two years, one of them with the Hubble telescope, and has studied details of most of the other known stars with disks.

“We know of 100-plus stars that have infrared emission in excess of that emitted from the star, and that excess thermal emission comes from circumstellar dust,” Kalas said. “The hard part is obtaining resolved images that give spatial information. Now, two decades after they were first discovered, we are finally beginning to see the dust disks. These recent detections are really a tribute to all the hard work that went into upgrading Hubble’s instruments during the last servicing mission.”

The small sampling already shows that such disks fall into two categories: those with a broad belt, wider than about 50 astronomical units; and narrow ones with a width of between 20 and 30 AU and a sharp outer boundary, probably like our own Kuiper Belt. An astronomical unit, or AU, is the average distance between the Earth and sun, about 93 million miles. Our Kuiper Belt is thought to be narrow, extending from the orbit of Neptune at 30 AU to about 50 AU.

Most of the known debris disks seem to have a central area cleared of debris, perhaps by planets, which are likely responsible for the sharp inner edges of many of these belts.

Kalas and Graham speculate that stars also having sharp outer edges to their debris disks have a companion – a star or brown dwarf, perhaps – that keeps the disk from spreading outward, similar to the way that Saturn’s moons shape the edges of many of the planet’s rings.

“The story of how you make a ring around a planet could be the same as the story of making rings around a star,” Kalas said. Only one of the nine stars is known to have a companion, but then, he said, no one has yet looked at most of these stars to see if they have faint companions at large distances from the primary star.

He suggests that a stray star passing by may have ripped off the edges of the original planetary disk, but a star-sized companion would be necessary to keep the remaining disk material, such as asteroids, comets and dust, from spreading outward.

If true, that would mean that the sun also has a companion keeping the Kuiper Belt confined within a sharp boundary. Though a companion star has been proposed before – most recently by UC Berkeley physics professor Richard Muller, who dubbed the companion Nemesis – no evidence has been found for such a companion.

A key uncertainty, Kalas said, is that while we can see many of the large planetesimals in our Kuiper Belt, we can barely detect the dust.

“Ironically, our own debris disk is the closest, yet we know the least about it,” he said. “We would really like to know if dust in our Kuiper Belt extends significantly beyond the 50 AU edge of the larger objects. When we acquire this information, only then will we be able to place our sun correctly in the wide or narrow disk categories.”

The star survey by Kalas, Graham, Fitzgerald and Clampin was one of the first projects of the Advanced Camera for Surveys aboard the Hubble, which was installed in 2002. The 22 stars were observed over a two year period ending in September 2004. The stars with debris disks detectable in visible light were HD 53143, a K star slightly smaller than the sun but about 1 billion years old, and HD 139664, an F star slightly larger than the sun but only 300 million years old.

“One is a K star and the other is an F star, therefore they are more likely to form planetary systems with life than the massive and short-lived stars such as beta-Pictoris and Fomalhaut,” he noted. “When we look at HD 53143 and HD 139664, we may be looking at astrophysical mirrors to our Kuiper Belt.”

The disk around the oldest of the two stars, HD 53143, is wide like that of beta-Pictoris (beta-Pic), which was the first debris disk ever observed, about 20 years ago, and AU Microscopii (AU Mic), which Kalas discovered last year. Both beta-Pic and AU Mic are about 10 million years old.

The disk around HD 139664, however, is a narrow belt, similar to the disk around the star Fomalhaut, which Kalas imaged for the first time early last year. HD 139664 has a very sharp outer edge at 109 AU, similar to the sharp outer edge of our Kuiper Belt at 50 AU. The belt around HD 139664 starts about 60 AU from the star and peaks in density at 83 AU.

“If we can understand the origin of the sharp outer edge around HD 139664, we might better understand the history of our solar system,” Kalas said.

The research was supported by grants from NASA through the Space Telescope Science Institute.

Original Source: UC Berkeley News Release

Posted on by Fraser Cain

Natural Particle Accelerator Discovered

A graphic representing NASA’s ACE and Wind and ESA’s Cluster spacecraft encountering solar particle jets. Image credit: UC Berkeley Click to enlarge
A fleet of NASA and European Space Agency space-weather probes observed an immense jet of electrically charged particles in the solar wind between the Sun and Earth. The jet, at least 200 times as wide as the Earth, was powered by clashing magnetic fields in a process called “magnetic reconnection”.
magnetic reconnection in the solar wind

These jets are the result of natural particle accelerators dwarfing anything built on Earth. Scientists build miles-long particle accelerators on Earth to smash atoms together in an effort to understand the fundamental laws of physics.

Similar reconnection-powered jets occur in Earth’s magnetic shield, producing effects that can disable orbiting spacecraft and cause severe magnetic storms on our planet, sometimes disrupting power stations.

The newly discovered interplanetary jets are far larger than those occurring within Earth’s magnetic shield. The new observation is the first direct measurement indicating magnetic reconnection can happen on immense scales.

Understanding magnetic reconnection is fundamental to comprehending explosive phenomena throughout the Universe, such as solar flares (billion-megaton explosions in the Sun’s atmosphere), gamma-ray bursts (intense bursts of radiation from exotic stars), and laboratory nuclear fusion. Just as a rubber band can suddenly snap when twisted too far, magnetic reconnection is a natural process by which the energy in a stressed magnetic field is suddenly released when it changes shape, accelerating particles (ions and electrons).

“Only with coordinated measurements by Sun-Earth connection spacecraft like ACE, Wind, and Cluster can we explore the space environment with unprecedented detail and in three dimensions,” says Dr. Tai Phan, lead author of the results, from the University of California, Berkeley. “The near-Earth space environment is the only natural laboratory where we can make direct measurements of the physics of explosive magnetic phenomena occurring throughout the Universe.” Phan’s article appears as the cover article in Nature on January 12.

The solar wind is a dilute stream of electrically charged (ionized) gas that blows continually from the Sun. Because the solar wind is electrically charged, it carries solar magnetic fields with it. The solar wind arising from different places on the Sun carries magnetic fields pointing in different directions. Magnetic reconnection in the solar wind takes place when “sheets” of oppositely directed magnetic fields get pressed together. In doing so, the sheets connect to form an X-shaped cross-section that is then annihilated, or broken, to form a new magnetic line geometry. The creation of a different magnetic geometry produces extensive jets of particles streaming away from the reconnection site.

Until recently, magnetic reconnection was mostly reported in Earth’s “magnetosphere”, the natural magnetic shield surrounding Earth. It is composed of magnetic field lines generated by our planet, and defends us from the continuous flow of charged particles that make up the solar wind by deflecting them. However, when the interplanetary magnetic field lines carried by the solar wind happen to be in the opposite orientation to the Earth?s magnetic field lines, reconnection is triggered and solar material can break through Earth’s shield.

Some previous reconnection events measured in Earth?s magnetosphere suggested that the phenomenon was intrinsically random and patchy in nature, extending not more than a few tens of thousands of kilometers (miles). However, “This discovery settles a long-standing debate concerning whether reconnection is intrinsically patchy, or whether instead it can operate across vast regions in space,” said Dr. Jack Gosling of the University of Colorado, a co-author on the paper and a pioneer in research on reconnection in space.

The broader picture of magnetic reconnection emerged when six spacecraft ? the four European Space Agency Cluster spacecraft and NASA’s Advanced Composition Explorer (ACE) and Wind probes ? were flying in the solar wind outside Earth?s magnetosphere on 2 February 2002 and made a chance discovery. During a time span of about two and a half hours, all spacecraft observed in sequence a single huge stream of jetting particles, at least 2.5 million kilometers wide (about 1.5 million miles or nearly 200 Earth diameters), caused by the largest reconnection event ever measured directly.

“If the observed reconnection were patchy, one or more spacecraft most likely would have not encountered an accelerated flow of particles,” said Phan. “Furthermore, patchy and random reconnection events would have resulted in different spacecraft detecting jets directed in different directions, which was not the case.”

Since the spacecraft detected the jet for more than two hours, the reconnection must have been almost steady over at least that timespan. Another 27 large-scale reconnection events ? with the associated jets – were identified by ACE and Wind, four of which extended more than 50 Earth diameters, or 650,000 kilometers (about 400,000 miles). Thanks to these additional data, the team could conclude that reconnection in the solar wind is to be looked at as an extended and steady phenomenon.

The 2 February 2002 event could have been considerably larger, but the spacecraft were separated by no more than 200 Earth diameters, so its true extent is unknown. Two new NASA missions will help gauge the actual size of these events and examine them in more detail. The Solar Terrestrial Relations Observatory (STEREO) mission, scheduled for launch in May or June of 2006, will consist of two spacecraft orbiting the Sun on opposite sides of the Earth, separated by as much as 186 million miles (almost 300 million kilometers). Their primary mission is to observe Coronal Mass Ejections, billion-ton eruptions of electrically charged gas from the Sun, in three dimensions. However, the spacecraft will also be able to detect magnetic reconnection events occurring in the solar wind with instruments that measure magnetic fields and charged particles. The Magnetospheric Multi-Scale mission (MMS), planned for launch in 2013, will use four identical spacecraft in various Earth orbits to perform detailed studies of the cause of magnetic reconnection in the Earth’s magnetosphere.

Original Source: NASA News Release

Posted on by Fraser Cain

Fossil Galaxy in the Early Universe

Haro 11 galaxy closeup view. Image credit: Hubble. Click to enlarge
A tiny galaxy has given astronomers a glimpse of a time when the first bright objects in the universe formed, ending the dark ages that followed the birth of the universe.

Astronomers from Sweden, Spain and the Johns Hopkins University used NASA’s Far Ultraviolet Spectroscopic Explorer (FUSE) satellite to make the first direct measurement of ionizing radiation leaking from a dwarf galaxy undergoing a burst of star formation. The result, which has ramifications for understanding how the early universe evolved, will help astronomers determine whether the first stars ? or some other type of object ? ended the cosmic dark age.

The team will present its results Jan. 12 at the American Astronomical Society’s 207th meeting in Washington, D.C.

Considered by many astronomers to be relics from an early stage of the universe, dwarf galaxies are small, very faint galaxies containing a large fraction of gas and relatively few stars. According to one model of galaxy formation, many of these smaller galaxies merged to build up today’s larger ones. If that is true, any dwarf galaxies observed now can be thought of as “fossils” that managed to survive ? without significant changes ? from an earlier period.

Led by Nils Bergvall of the Astronomical Observatory in Uppsala, Sweden, the team observed a small galaxy, known as Haro 11, which is located about 281 million light years away in the southern constellation of Sculptor. The team’s analysis of FUSE data produced an important result: between 4 percent and 10 percent of the ionizing radiation produced by the hot stars in Haro 11 is able to escape into intergalactic space.

Ionization is the process by which atoms and molecules are stripped of electrons and converted to positively charged ions. The history of the ionization level is important to understanding the evolution of structures in the early universe, because it determines how easily stars and galaxies can form, according to B-G Andersson, a research scientist in the Henry A. Rowland Department of Physics and Astronomy at Johns Hopkins, and a member of the FUSE team.

“The more ionized a gas becomes, the less efficiently it can cool. The cooling rate in turn controls the ability of the gas to form denser structures, such as stars and galaxies,” Andersson said. The hotter the gas, the less likely it is for structures to form, he said.

The ionization history of the universe therefore reveals when the first luminous objects formed, and when the first stars began to shine.

The Big Bang occurred about 13.7 billion years ago. At that time, the infant universe was too hot for light to shine. Matter was completely ionized: atoms were broken up into electrons and atomic nuclei, which scatter light like fog. As it expanded and then cooled, matter combined into neutral atoms of some of the lightest elements. The imprint of this transition today is seen as cosmic microwave background radiation.

The present universe is, however, predominantly ionized; astronomers generally agree that this reionization occurred between 12.5 and 13 billion years ago, when the first large-scale galaxies and galaxy clusters were forming. The details of this ionization are still unclear, but are of intense interest to astronomers studying these so-called “dark ages” of the universe.

Astronomers are unsure if the first stars or some other type of object ended those dark ages, but FUSE observations of “Haro 11” provide a clue.

The observations also help increase understanding of how the universe became reionized. According to the team, likely contributors include the intense radiation generated as matter fell into black holes that formed what we now see as quasars and the leakage of radiation from regions of early star formation. But until now, direct evidence for the viability of the latter mechanism has not been available.

“This is the latest example where the FUSE observation of a relatively nearby object holds important ramifications for cosmological questions,” said Dr. George Sonneborn, NASA/FUSE Project Scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md.

This result has been accepted for publication by the European journal Astronomy and Astrophysics.

Original Source: JHU News Release