Rosetta's goal is to learn the primordial story a comet tells as it gloriously falls to pieces.

Comets are primitive leftovers from our solar system's 'construction' about 4.5 billion years ago. Because they spend much of their time in the deep freeze of the outer solar system, comets are well preserved-a gold mine for astronomers who want to know what conditions were like back "in the beginning."

As their elongated orbits swing them closer to the sun, comets transform into the most breathtaking bodies in the night sky. A European Space Agency mission launched in 2004 with U.S. instruments on board, Rosetta will have a front-row seat for the metamorphosis.

What we know of comets so far comes from a handful of flyby missions.

"In some ways, a flyby is just a tantalizing glimpse of a comet at one stage in its evolution," says Claudia Alexander, project scientist for the U.S. Rosetta Project at JPL. "Rosetta is different. It will orbit 67P for 17 months. We'll see this comet evolve right before our eyesas we accompany it toward the sun and back out again."

Fierce solar heat will have a profound effect on Rosetta's target. "We'll watch the comet start as just a little nugget in space and then become something poetic and beautiful, trailing a vast tail."

At the moment, Rosetta is "resting up" for the challenges ahead. It's hibernating, engaged in its high-speed chase while fast asleep.

Reveille is on or around New Year's Day 2014, when the spacecraft begins a months-long program of self-checkups.

If all goes well, in August of the same year, Rosetta will enter orbit around 67P's nucleus and begin scanning its surface for a landing site. Once a site is chosen, the spacecraft will descend as low as 1 km to deploy the lander.

The lander's name is "Philae" after an island in the Nile, the site of an obelisk that helped decipher-you guessed it-the Rosetta Stone.

Touchdown is scheduled for November 2014, when Philae will make the first ever controlled landing on a comet's nucleus.

"When we land, the comet could already be active!" says Alexander. Because a comet has little gravity, the lander will anchor itself with harpoons. "The feet may drill into something crunchy like permafrost, or maybe into something rock solid," she speculates.

Once it is fastened, the lander will commence an unprecedented first-hand study of a comet's nucleus. Among other things, it will gather samples for examination by automatic onboard microscopes and take panoramic images of the comet's terrain from ground level.

Meanwhile, orbiting overhead, the Rosetta spacecraft will be busy, too. Onboard sensors will map the comet's surface and magnetic field, monitor the comet's erupting jets and geysers, measure outflow rates, and much more. Together, the orbiter and lander will build up the first 3D picture of the layers and pockets under the surface of a comet.

The results should tell quite a story indeed.

]]> Thu, 09 FEB 2012 08:59:14 AEST Munich, Germany (SPX) Feb 07, 2012 - It is not entirely clear when exactly the last major asteroid impact on Earth occurred. But there are plenty of examples of impact craters, such as the Nordlinger Ries in Bavaria. That there will be other collisions in the future is something of which Alan Harris, asteroid researcher at the German Aerospace Center, is certain.

Over the next three and a half years, he will be heading the NEOShield (Near Earth Object Shield) international collaboration, established in January 2012.

In total, 13 partners from research institutions and industry will jointly investigate the prevention of impacts by asteroids and comets. The investigations will include the impact of a space probe with the asteroids to deflect them from their threatening courses. The European Union is supporting the project with four million Euros. The partners are contributing another 1.8 million Euros.

When asteroids approach the Earth, they typically do so at a speed of between five and 30 kilometres per second. "In order to modify their orbit and prevent a collision with Earth, a force must be exerted on them," explains Alan Harris. "And at the precise time, as well."

Existing examples of asteroids that have followed their natural course towards Earth include the Barringer Crater in Arizona, with a diameter of 1200 metres, or the Tunguska Region in Siberia, where an asteroid explosion in 1908 uprooted millions of trees. Smaller asteroids or comets could also cause this sort of damage.

"The crater in Arizona was caused by an object about 50 metres in diameter." There are numerous near Earth objects, or NEOs. Thousands have been discovered in the last 20 years.

"This means that a dangerous collision with Earth is likely every couple of hundred years," the asteroid researcher estimates.

NEOs in sight
A prerequisite to investigate possible methods for preventing an asteroid impact on Earth is the precise understanding of the physical properties of NEOs. "We want to find out as much as we can about the enemy that might be on course for Earth," says Harris. In this international project, the DLR planetary researchers are pooling their knowledge of the composition, structure and surface texture of asteroids and comets. ' Project leader Alan Harris's team is also analysing observational data from the past two decades: "So far, the data has not been adequately investigated from the perspective of asteroid defence."

To date, over 8000 NEOs have been discovered, and another 70 are found every month. By the end of the project we should have answers to a number of questions - for example, the asteroid researchers want to determine ways to observe threatening asteroids from the ground, and which space missions can be used to determine their properties.

Various methods, which the scientists are investigating in detail, can then come into play, depending on the time between the discovery and the potential entry into Earth's atmosphere, and on the size of the asteroid.

Impacts on asteroids
One method that the NEOShield consortium will be investigating in more detail involves using a spacecraft to deflect an asteroid from its course by impacting it. "In my opinion, this is a very practical method."

However, there are still many unanswered questions with this method that need investigating. How does such a space probe need to be controlled to reach its target reliably and at the correct angle? How can we minimise the effect that movements of fuel inside the space probe have on its impact?

In addition, laboratory experiments in which projectiles will be fired at materials that correspond to those in an asteroid, will be carried out. This, in turn, will enable the scientists to draw conclusions on the behaviour of asteroids in such a collision.

Using gravity to change course
Scientists will also study a method to deflect asteroids on course for Earth without physically contacting them, if they are discovered years before their potential collision.

If a spacecraft is guided into the direct vicinity of a potentially dangerous NEO, the added gravity might have an effect on the asteroid and, as if hauling it in on a rope, gradually drag it off course. But a period of several years would be required to achieve a significant change in the asteroid's orbit.

"To date, this method only exists on paper, but it could work." The research to be conducted over the next three and a half years should show how realistic it is to drag threatening asteroids off track using gravity tractors.

Explosive power in space
Alan Harris would only consider this alternative method if time is pressing: "If a very large, dangerous object with a diameter of one kilometre or more is discovered, the two methods described above would probably not solve the problem," explains Harris.

"The greatest force we would be able to use to divert the asteroid from its path would be a nuclear explosion." Though there are no actual plans for a mission of this kind, this is a solution that the scientists want to investigate as part of their project. However, they want to know the effects that an explosion in the direct vicinity of an asteroid or on its surface would have in the vacuum of space. "This technique is regarded as a very controversial."

Proposals for space missions
Data from asteroid observations and the results of laboratory experiments, extrapolated to a realistic scale, are continually being added to computer simulations. At the end of the three and a half years, we should not only have a better understanding of asteroids and a possible method of defence.

"We are also planning international space missions in a few years to test the defence methods we have been looking into."

From the large number of asteroids discovered, those that are most suitable for a test mission will be selected for this. Furthermore, there should be a roadmap that could be put into action in the event of a threat to Earth from an asteroid collision. This would be based on realistic events, such as the approach of asteroid Apophis - the orbit of which will bring it dangerously close to Earth in 2029.

The partners
Under the leadership of the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR), the following partners are participating in the EU's NEOShield project: Observatoire de Paris (France), Centre Nationale de la Recherche Scientifique (France), The Open University (Great Britain), Fraunhofer Ernst-Mach-Institut (Germany), The Queen's University of Belfast (Great Britain), Astrium GmbH (Germany), Astrium Limited (Great Britain), Astrium S.A.S. (France), Deimos Space (Spain), SETI Institute Corporation, Carl Sagan Center (USA), TsNIIMash (Russia), University of Surrey (Great Britain).

]]> Thu, 09 FEB 2012 08:59:14 AEST Orlando FL (SPX) Feb 07, 2012 - The Japanese are heading back into space on a second attempt to collect samples from a nearby asteroid. The asteroid selected, 1999 JU3 is a perfect specimen, said Humberto Campins, a University of Central Florida professor and international expert on asteroids and comets.

"Based on our analysis, it should be rich in primitive materials, specifically organic molecules and hydrated minerals from the early days of our solar system," Campins said. "If successful it could give us clues about the birth of water and life in our world."

Campins has been studying the 1999 JU3 for years. He published an article in 1999 in Astronomy and Astrophysics on this asteroid and its potential to hold raw materials and perhaps even evidence of water. It is believed to have come from the asteroid belt located between Mars and Jupiter.

Finding water in asteroids and comets is a major focus of research. NASA and the European Space Agency are both planning trips to recover samples from two asteroids in the next five to seven years through the OSIRIS-REx (NASA) and Marco Polo-R (European Space Agency) missions. Campins is part of both teams.

Since the end of Space Shuttle flights in 2011, robotic missions to collect asteroid samples have become popular. NASA, the European Space Agency and the Japan Aerospace Exploration Agency (JAXA) have all announced missions that could launch as early as 2014.

The samples recovered by these missions could help explain how planets formed, provide information about the origin of organic molecules and life on Earth, and probe the physical structure of an asteroid. Knowing more about the structure of asteroids is important in developing strategies for preventing potentially threatening asteroids from striking earth.

JAXA got into the asteroid lassoing business early. In 2003 it sent off a probe to scoop up a sample from another asteroid near Earth. Although the collection mechanism did not work properly, when the probe returned to earth in 2010 and scientists cracked open the package, they were pleased to find a small amount of asteroidal dust.

]]> Thu, 09 FEB 2012 08:59:14 AEST Pasadena CA (JPL) Jan 31, 2012 - Dawn is scrutinizing Vesta from its low-altitude mapping orbit (LAMO), circling the rocky world five and a half times a day. The spacecraft is healthy and continuing its intensive campaign to reveal the astonishing nature of this body in the mysterious depths of the main asteroid belt.

Since the last log, the robotic explorer has devoted most of its time to its two primary scientific objectives in this phase of the mission. With its gamma ray and neutron detector (GRaND), it has been patiently measuring Vesta's very faint nuclear emanations. These signals reveal the atomic constituents of the material near the surface. Dawn also broadcasts a radio beacon with which navigators on distant Earth can track its orbital motion with exquisite accuracy.

That allows them to measure Vesta's gravity field and thereby infer the interior structure of this complex world. In addition to these top priorities, the spacecraft is using its camera and its visible and infrared mapping spectrometer (VIR) to obtain more detailed views than they could in the higher orbits.

As we have delved into these activities in detail in past logs, let's consider here some more aspects of controlling this extremely remote probe as it peers down at the exotic colossus 210 kilometers (130 miles) beneath it.

Well, the first aspect that is worth noting is that it is incredibly cool! Continuing to bring this fascinating extraterrestrial orb into sharper focus is thrilling, and everyone who is moved by humankind's bold efforts to reach into the cosmos shares in the experience.

The data sent back are providing exciting and important new insights into Vesta, and those findings will continue to be announced in press releases. Therefore, we will turn our attention to a second aspect of operating in LAMO. Last month, we saw that various forces contribute to Dawn moving slightly off its planned orbital path. (That material may be worth reviewing, either to enhance appreciation of what follows or as an efficacious soporific, should the need for one ever arise.)

Now let's investigate some of the consequences. This will involve a few more technical points than most logs, but each will be explained, and together they will help illustrate one of the multitudinous complexities that must be overcome to make such a grand adventure successful.

Far away, traveling through the vast expanse of (mostly) empty space, Dawn only knows where it is because of information the mission control team installs in it. This is typical for interplanetary spacecraft. Earth-orbiting satellites may be able to use the Global Positioning System (GPS) constellation or other means to find their own location, but only a few spacecraft that have gone far from Earth have the means to independently establish their own location.

This should not be confused with a spacecraft's ability to determine its own orientation, which Dawn does with its star trackers, gyros, and sun sensors. In the same way, if you were in a dark and unidentified place on your planet, you could determine the direction you were looking by recognizing patterns of stars, but that would not help you ascertain your position.

Throughout the mission, controllers regularly transmit to the spacecraft a mathematical description of its location in the solar system at any instant over a given period of time. They also provide it with the information needed to calculate where Earth is.

That's how it is able to point its main antenna in the correct direction when it needs to do so. During the Vesta phase of the mission, the probe is given the additional means it needs to determine its location relative to Vesta. All the information sent to the spacecraft is based on navigators' best prediction of where the spacecraft will be in the future.

Dawn remains unaware of any deviations from its expected course, so it always behaves as if it were exactly where it would be if its motion matched the team's projections perfectly, without the discrepancies that are sure to occur.

For the majority of the mission, both in interplanetary cruise and at higher altitude orbits at Vesta, the effects of being slightly off the predicted trajectory are insignificant. In LAMO, they are not.

For Dawn to aim its scientific sensors at Vesta, controllers instruct it to point straight "down." Again, it knows how to compute where "down" is because of the information it was given by navigators. Any disparity between where the craft was predicted to be and where it really is along its orbit causes it to point in a slightly different direction, not quite truly straight down. This does not compromise the observations; it could tolerate larger pointing errors and still capture the desired targets in the field of view of the instruments.

Dawn is a very large spacecraft. Indeed, the wingspan from one solar array tip to the other is 19.7 meters (nearly 65 feet). When it was launched in 2007, this was the greatest span of any probe NASA had ever dispatched on an interplanetary journey. The large area of solar cells is needed to capture faint sunlight in the asteroid belt to meet all of the electrical power needs.

Each solar array wing is the width of a single's tennis court, and the whole spacecraft would reach from a pitcher's mound to home plate on a professional baseball field, although Dawn is engaged in activities considerably more inspiring and rewarding than competitive sports.

Now consider that when Dawn is looking precisely down, directly toward the center of Vesta, its wings are level. If it is pointed off even a little, then one of those long extensions is slightly closer to the massive body it is circling and one is slightly farther away. Because gravity diminishes with increasing distance, the one that is closer is subject to a very slightly stronger pull than the farther other.

If unchecked, that lower side would gently be pulled down even more, thus increasing the difference in gravitational attraction between the two wings still more. Eventually, this would cause Dawn to be oriented so that one wing points straight down toward the ancient surface below and the other points straight up, back into the depths of space. Because this phenomenon depends on the change in gravity from the lower point to the higher one, it is known as "gravity gradient."

Some satellites that orbit Earth are designed to take advantage of the gravity gradient to align their long axis with the planet below, but Dawn (and most other spacecraft) need greater flexibility in where they point.

Rather than accepting the passive method of orienting provided by the gravity gradient, Dawn uses its reaction wheels to train its science instruments on Vesta. By electrically changing the rate at which these devices spin, the ship can control its orientation in the zero-gravity, frictionless conditions of spaceflight.

When a small deviation from the perfect orbit causes it to tip its wings a little when pointing to where it calculates "down" to be, the spacecraft's reaction wheels work to prevent it from succumbing to the gravity gradient, countering the tendency of the wings to deviate still more from being level. As a consequence, the ship remains stable and the wheels gradually spin faster and faster as it conducts its observations.

To reduce the wheels' speeds, mission planners schedule a period almost every day in LAMO during which the spacecraft fires its reaction control system thrusters, a function known as "desaturating the wheels."

Indeed, the principal reason Dawn is outfitted with these small thrusters and a modest supply of conventional rocket propellant known as hydrazine is to manage the speed of the wheels.

The thruster firings not only provide the torque needed to reduce the rotation rate of the wheels, but they also have the incidental effect of propelling the spacecraft slightly. The push is small, changing the orbital speed by no more than about one centimeter per second (around one fiftieth of a mph, or about 120 feet per hour). But that causes Dawn to deviate from its planned orbit, and the accumulated force from all the firings is the largest source of trajectory discrepancies in LAMO.

To summarize so far, once Dawn has any variance at all between the predicted orbital motion that mission controllers have radioed to it and its actual path, its long wings will be tipped a little while it observes Vesta.

In opposing the resultant gravity gradient effect, the reaction wheels will accelerate. When the reaction control system thrusters fire to decelerate the wheels, they will nudge Dawn still more off course, and the cycle will continue.

Of course, engineers have devised strategies to accommodate this contribution (and others) to deviations from the plan. In LAMO, they frequently measure the ship's trajectory and revise their estimates of the future course.

They transmit to the spacecraft a new prediction for the orbit twice a week, so the main computer usually has a very good estimate of where it is relative to Vesta and hence how to orient itself so that its long solar arrays remain level as it acquires its fabulous pictures and other scientific information.

With the updated knowledge of its position, Dawn can aim its sensors accurately and keep the thruster firings from being excessive, even when it is not following its orbit perfectly. This solution works well, but let's continue delving into the consequences of the orbital perturbations.

While the operations team has the capability to provide the ship regularly with a good description of where it will be, it is much more difficult to make such frequent adjustments to its detailed itinerary. The schedule of its myriad activities has to be planned longer in advance. The sequences of commands, which are timed to the second, are very complicated to develop and verify, and the operations team does not have the resources to refine the timing as often as they can send updates on the craft's predicted location.

Engineers took many factors into account in selecting the orbits Dawn uses for its science observations. We saw in November that the orbits are characterized not only by the altitude but also by the orientation of the orbital plane. A subsequent log will explain the choices for the planes more fully, but for now, what matters is that, among other considerations, the orbits were designed to ensure Dawn remains in constant sunlight.

It always has the sun in sight, never entering Vesta's shadow. Keeping Earth in view at all times was not part of the design, and on every one of the more than 600 revolutions around the gigantic rocky body since August 28 (the seventh circuit in survey orbit), the spacecraft has been temporarily behind Vesta from the geocentric point of view. In its present orbit, these occultations last for about half an hour in every 4.3-hour loop.

When Dawn is observing Vesta, that doesn't matter. When it is using its ion propulsion system to transfer from one orbit to another, it also doesn't matter. It does matter, however, when it is in contact with Earth, because Vesta blocks the radio signal. Controllers give the spacecraft a detailed schedule of which data to transmit and when, making the best possible use of the precious communications link that stretches across the solar system.

The timed plan tells it not to send high priority data during the radio blackout, but the timing of the occultations can shift a little as the orbit departs from the plan.

The strategy to deal with the slight deviations in the timing of the interruption in the radio link principally involves including some padding in the plan. The schedule for the transmission of the highest priority data places it well away from the expected gap, so no important losses occur if Dawn is a little ahead in its orbit or a little behind (causing the gap to occur a little earlier or a little later).

But what is there to do during and near the time the craft is predicted to be blocked by Vesta while conducting a communications session? Dawn rotates too slowly to make it worth turning to point its sensors at the surface just for these periods. Of course, it could simply transmit nothing at all. Instead, the team has it transmit data that otherwise would be lost.

There is never enough time to send to Earth all the information the probe generates and collects. So most of the time it is behind Vesta, it broadcasts many of the measurements of its own subsystems that cannot be stored and sent later. And during the periods immediately before and after the expected occultation, when there is a chance that the signal will reach Earth, it sends bonus pictures and VIR spectra.

If the deviations from the planned orbit are small, then the antenna will have an unobstructed view of Earth, and these data will make it home. And if the spacecraft enters the blackout period late (or early), then it will exit late (or early) as well, so the bonus results sent before (or after) the occultation will be received. But in the rest of the cases, well, Dawn will transmit those bits right back where they came from, sending the photos and spectra into the vast rocky surface between the spacecraft and Earth.

Last month we described one of the limitations in how much bonus information could be obtained from LAMO. Now we have another. In summary, because the probe can acquire more images and other data than it is possible to return, it radios some of them during times that it is possible they will make it to Earth.

Because of realistic causes of variation from its predicted orbital path, however, some of these measurements will be transmitted when, from Dawn's perspective, Vesta blocks Earth, thus preventing the broadcast signals from getting through.

The GRaND observations (as well as essential telemetry on the health of the ship) are scheduled to be sent during times that, even with the reasonable range of orbit discrepancies, the communications link will not be obstructed. In this way, mission planners return as much data as possible, taking maximum advantage of the time Dawn points its main antenna to Earth.

Having a sophisticated robot in orbit around the second most massive resident of the asteroid belt presents truly unique opportunities for the exploration of the solar system, and the team has devised every strategy they could to use the time as productively as possible.

The spacecraft aims GRaND at Vesta most of the time in order to develop a good picture of the weak nuclear glow. Controllers schedule three periods per week, each about eight hours, in which it directs its antenna to Earth.

The orbit predictions have been extremely good, matching the actual motion quite well. Moreover, some time is allocated to return the camera and VIR data apart from the times that Vesta might be in the way. As a result, the team has been rewarded with more than 3200 photos from LAMO so far. Every one is bonus, and every one is neat!

]]> Thu, 09 FEB 2012 08:59:14 AEST Washington (AFP) Jan 27, 2012 - An asteroid about the size of a bus shaved by Earth on Friday in what spacewatchers described as a "near-miss," though experts were not concerned about the possibility of an impact.

The asteroid, named 2012 BX34, measured between six and 19 meters in diameter (20 to 62 feet), said Gareth Williams, associate director of the US-based Minor Planet Center which tracks space objects.

The asteroid, which had been unknown before it popped into view from a telescope in Arizona on Wednesday, came within about 60,000 kilometers (37,000 miles) of Earth on Friday at about 1500 GMT, he said.

"It's a near miss. It makes the top 20 list of closest approaches ever observed," Williams told AFP.

NASA had announced on Twitter on Thursday that the asteroid would "safely pass Earth on January 27."

Williams explained that since the asteroid was so small, it could only be detected when it was close to the Earth, but that the fly-by, while a surprise, was not terribly uncommon.

"This came about a sixth of the distance from the Moon," he said. "In the past year we have had some 30 objects that were observed to come within the orbit of the Moon."

Williams said his pager went off in the middle of the night Wednesday after the asteroid was first sighted, but once he checked he went right back to sleep because he knew it would not hit Earth from its projected distance.

But where it goes next is less certain.

"If we have radar on it from last night then we can probably predict it decades into the future," he said.

"If we don't have radar, then we only have a two- to three-day arc of observations and extrapolating that into the future will be very uncertain."

However, since the asteroid is so diminutive, it poses little threat to the vast Earth, he added.

"This object is so small that even if it hits us the next time around it won't survive passage through the atmosphere in one piece," Williams said.

"Objects in that size range -- six to 19 meters -- will typically break up due to the force of entering the atmosphere. All that may remain are a few fist- or football-sized rocks that make it to the ground as meteorites."

In November last year, a much a larger asteroid called 2005 YU55 made its closest fly-by of Earth in 200 years.

The near-spherical asteroid, 1,300 feet (400 meters) in diameter, passed by at a distance of 201,700 miles (324,600 kilometers), as measured from the center of Earth, NASA said.

In 2008, a small asteroid estimated to be a few meters (yards) wide sparked a fireball in the night sky plunged down over Sudan, scattering fragments over the Nubian desert, NASA said.

]]> Thu, 09 FEB 2012 08:59:14 AEST Houston TX (SPX) Jan 26, 2012 - Rice University physicists have gone to extremes to prove that Isaac Newton's classical laws of motion can apply in the atomic world: They've built an accurate model of part of the solar system inside a single atom of potassium.

In a new paper published this week in Physical Review Letters, Rice's team and collaborators at the Oak Ridge National Laboratory and the Vienna University of Technology showed they could cause an electron in an atom to orbit the nucleus in precisely the same way that Jupiter's Trojan asteroids orbit the sun.

The findings uphold a prediction made in 1920 by famed Danish physicist Niels Bohr about the relationship between the then-new science of quantum mechanics and Newton's tried-and-true laws of motion.

"Bohr predicted that quantum mechanical descriptions of the physical world would, for systems of sufficient size, match the classical descriptions provided by Newtonian mechanics," said lead researcher Barry Dunning, Rice's Sam and Helen Worden Professor of Physics and chair of the Department of Physics and Astronomy.

"Bohr also described the conditions under which this correspondence could be observed. In particular, he said it should be seen in atoms with very high principal quantum numbers, which are exactly what we study in our laboratory."

Bohr was a pioneer of quantum physics. His 1913 atomic model, which is still widely invoked today, postulated a small nucleus surrounded by electrons moving in well-defined orbits and shells.

The word "quantum" in quantum mechanics derives from the fact that these orbits can have only certain well-defined energies. Jumps between these orbits lead to absorption or emission of specific amounts of energy termed quanta. As an electron gains energy, its quantum number increases, and it jumps to higher orbits that circle ever farther from the nucleus.

In the new experiments, Rice graduate students Brendan Wyker and Shuzhen Ye began by using an ultraviolet laser to create a Rydberg atom. Rydberg atoms contain a highly excited electron with a very large quantum number. In the Rice experiments, potassium atoms with quantum numbers between 300 and 600 were studied.

"In such excited states, the potassium atoms become hundreds of thousands of times larger than normal and approach the size of a period at the end of a sentence," Dunning said. "Thus, they are good candidates to test Bohr's prediction."

He said comparing the classical and quantum descriptions of the electron orbits is complicated, in part because electrons exist as both particles and waves. To "locate" an electron, physicists calculate the likelihood of finding the electron at different locations at a given time.

These predictions are combined to create a "wave function" that describes all the places where the electron might be found. Normally, an electron's wave function looks like a diffuse cloud that surrounds the atomic nucleus, because the electron might be found on any side of the nucleus at a given time.

Dunning and co-workers previously used a tailored sequence of electric field pulses to collapse the wave function of an electron in a Rydberg atom; this limited where it might be found to a localized, comma-shaped area called a "wave packet." This localized wave packet orbited the nucleus of the atom much like a planet orbits the sun. But the effect lasted only for a brief period.

"We wanted to see if we could develop a way to use radio frequency waves to capture this localized electron and make it orbit the nucleus indefinitely without spreading out," Ye said.

They succeeded by applying a radio frequency field that rotated around the nucleus itself. This field ensnared the localized electron and forced it to rotate in lockstep around the nucleus.

A further electric field pulse was used to measure the final result by taking a snapshot of the wave packet and destroying the delicate Rydberg atom in the process. After the experiment had been run tens of thousands of times, all the snapshots were combined to show that Bohr's prediction was correct: The classical and quantum descriptions of the orbiting electron wave packets matched.

In fact, the classical description of the wave packet trapped by the rotating field parallels the classical physics that explains the behavior of Jupiter's Trojan asteroids.

Jupiter's 4,000-plus Trojan asteroids - so called because each is named for a hero of the Trojan wars - have the same orbit as Jupiter and are contained in comma-shaped clouds that look remarkably similar to the localized wave packets created in the Rice experiments.

And just as the wave packet in the atom is trapped by the combined electric field from the nucleus and the rotating wave, the Trojans are trapped by the combined gravitational field of the sun and orbiting Jupiter.

The researchers are now working on their next experiment: They're attempting to localize two electrons and have them orbit the nucleus like two planets in different orbits.

"The level of control that we're able to achieve in these atoms would have been unthinkable just a few years ago and has potential applications in, for example, quantum computing and in controlling chemical reactions using ultrafast lasers," Dunning said.

The research was funded by the National Science Foundation, the Robert A. Welch Foundation, the Austrian Science Fund and the Department of Energy. Paper co-authors include S. Yoshida of the Vienna University of Technology; C.O. Reinhold of Oak Ridge National Laboratory and the University of Tennessee; and J. Burgdorfer of Vienna University of Technology and the University of Tennessee.

PRL paper is available here

]]> Thu, 09 FEB 2012 08:59:14 AEST Pasadena CA (JPL) Jan 26, 2012 - Though generally thought to be quite dry, roughly half of the giant asteroid Vesta is expected to be so cold and to receive so little sunlight that water ice could have survived there for billions of years, according to the first published models of Vesta's average global temperatures and illumination by the sun.

"Near the north and south poles, the conditions appear to be favorable for water ice to exist beneath the surface," says Timothy Stubbs of NASA's Goddard Space Flight Center in Greenbelt, Md., and the University of Maryland, Baltimore County. Stubbs and Yongli Wang of the Goddard Planetary Heliophysics Institute at the University of Maryland published the models in the January 2012 issue of the journal Icarus. The models are based on information from telescopes including NASA's Hubble Space Telescope.

Vesta, the second-most massive object in the asteroid belt between Mars and Jupiter, probably does not have any significant permanently shadowed craters where water ice could stay frozen on the surface all the time, not even in the roughly 300-mile-diameter (480-kilometer-diameter) crater near the south pole, the authors note.

The asteroid isn't a good candidate for permanent shadowing because it is tilted on its axis at about 27 degrees, which is even greater than Earth's tilt of roughly 23 degrees. In contrast, the moon, which does have permanently shadowed craters, is tilted at only about 1.5 degrees. As a result of its large tilt, Vesta has seasons, and every part of the surface is expected to see the sun at some point during Vesta's year.

The presence or absence of water ice on Vesta tells scientists something about the tiny world's formation and evolution, its history of bombardment by comets and other objects, and its interaction with the space environment.

Because similar processes are common to many other planetary bodies, including the moon, Mercury and other asteroids, learning more about these processes has fundamental implications for our understanding of the solar system as a whole. This kind of water ice is also potentially valuable as a resource for further exploration of the solar system.

Though temperatures on Vesta fluctuate during the year, the model predicts that the average annual temperature near Vesta's north and south poles is less than roughly minus 200 degrees Fahrenheit (145 kelvins). That is the critical average temperature below which water ice is thought to be able to survive in the top 10 feet or so (few meters) of the soil, which is called regolith.

Near Vesta's equator, however, the average yearly temperature is roughly minus 190 degrees Fahrenheit (150 kelvins), according to the new results. Based on previous modeling, that is expected to be high enough to prevent water from remaining within a few meters of the surface. This band of relatively warm temperatures extends from the equator to about 27 degrees north and south in latitude.

"On average, it's colder at Vesta's poles than near its equator, so in that sense, they are good places to sustain water ice," says Stubbs. "But they also see sunlight for long periods of time during the summer seasons, which isn't so good for sustaining ice. So if water ice exists in those regions, it may be buried beneath a relatively deep layer of dry regolith."

The modeling also indicates that relatively small surface features, such as craters measuring around 6 miles (10 kilometers) in diameter, could significantly affect the survival of water ice.

"The bottoms of some craters could be cold enough on average - about 100 kelvins - for water to be able to survive on the surface for much of the Vestan year [about 3.6 years on Earth]," Stubbs explains.

"Although, at some point during the summer, enough sunlight would shine in to make the water leave the surface and either be lost or perhaps redeposit somewhere else."

So far, Earth-based observations suggest that the surface of Vesta is quite dry. However, the Dawn spacecraft is getting a much closer view. Dawn is investigating the role of water in the evolution of planets by studying Vesta and Ceres, two bodies in the asteroid belt that are considered remnant protoplanets - baby planets whose growth was interrupted when Jupiter formed.

Dawn is looking for water using the gamma ray and neutron detector (GRaND) spectrometer, which can identify hydrogen-rich deposits that could be associated with water ice. The spacecraft recently entered a low orbit that is well suited to collecting gamma ray and neutron data.

"Our perceptions of Vesta have been transformed in a few months as the Dawn spacecraft has entered orbit and spiraled closer to its surface," says Lucy McFadden, a planetary scientist at NASA Goddard and a Dawn mission co-investigator. "More importantly, our new views of Vesta tell us about the early processes of solar system formation. If we can detect evidence for water beneath the surface, the next question will be is it very old or very young, and that would be exciting to ponder."

The modeling done by Stubbs and Wang, for example, relies on information about Vesta's shape. Before Dawn, the best source of that information was a set of images taken by NASA's Hubble Space Telescope in 1994 and 1996. But now, Dawn and its camera are getting a much closer view of Vesta.

"The Dawn mission gives researchers a rare opportunity to observe Vesta for an extended period of time, the equivalent of about one season on Vesta," says Stubbs. "Hopefully, we'll know in the next few months whether the GRaND spectrometer sees evidence for water ice in Vesta's regolith. This is an important and exciting time in planetary exploration."

]]> Thu, 09 FEB 2012 08:59:14 AEST Huntsville AL (SPX) Jan 24, 2012 - A paper published in Science raises an intriguing new possibility for astronomers: unearthing comet corpses in the solar wind. The new research is based on dramatic images of a comet disintegrating in the sun's atmosphere last July.

Comet Lovejoy grabbed headlines in Dec. 2011 when it plunged into the sun's atmosphere and emerged again relatively intact. But it was not the first comet to graze the sun. Last summer a smaller comet took the same trip with sharply different results. Comet C/2011 N3 (SOHO) was completely destroyed on July 6, 2011, when it swooped 100,000 km above the stellar surface. NASA's Solar Dynamics Observatory (SDO) recorded the disintegration.

"For the first time, we saw a comet move across the face of the sun and disappear," says Dean Pesnell, a co-author of the Science paper and Project Scientist for SDO at the Goddard Space Flight Center. "It was unprecedented."

In Jan. 20th issue of Science, the research team reported their analysis of the SDO images.

A key finding was the amount of material deposited into the sun's atmosphere. "The comet dissolved into more than a million tons of electrically charged gas," says Pesnell. "We believe these vapors eventually mixed with the solar wind and blew back into the solar system."

Pesnell says it might be possible to detect such "comet corpses" as they waft past Earth. Comets are rich in ice (frozen H2O), so when they dissolve in the hot solar atmosphere, the gaseous remains contain plenty of oxygen and hydrogen. A solar wind stream containing extra oxygen could be a telltale sign of a disintegrated comet. Other elements abundant in comets would provide similar markers.

Comet corpses are probably plentiful. There's a busy family of comets known as "Kreutz sungrazers," thought to be fragments of a giant comet that broke apart hundreds of years ago. Every day or so, SOHO sees one plunge into the sun and vanish. Each disintegration event creates a puff of comet vapor that might be detectable by spacecraft sampling the solar wind.

Why bother? Researchers are beginning to think of sungrazers as 'test particles' for studying the sun's atmosphere--kind of like tossing rocks into a pond. A lot can be learned about the pond by studying the ripples.

Indeed, SDO observed some extraordinary interactions between the sun and the doomed comet. As C/2011 N3 (SOHO) moved through the hot corona, cold gas lifted off the comet's nucleus and rapidly (within minutes) warmed to more than 500,000K, hot enough to shine brightly in SDO's extreme ultraviolet telescopes.

"The evaporating comet gas was glowing as brightly as the sun behind it," marvels Pesnell.

The gas was also rapidly ionized by a process called "charge exchange," which made the gas responsive to the sun's magnetic field. Caught in the grip of magnetic loops which thread the solar corona, the comet's ionized tail wagged back and forth wildly in the moments before final disintegration.

Watching this kind of sun-comet interaction could reveal new things about the thermal and magnetic structure of the solar atmosphere. Likewise, measuring how long it takes for "comet corpses" to reach Earth, and then sampling the gases when they arrive, could be very informative.

"Before SDO, no one dreamed we could observe a comet disintegrate inside the sun's atmosphere," says Pesnell who confesses that even he was a skeptic. But now, "I'm a believer."

The original research described in this story may be found in the Jan. 20th edition of Science: Destruction of Sun-grazing comet C/2011 N3 (SOHO) by C. J. Schrijver, J. C. Brown, K. Battams, P. Saint-Hilaire, W. Liu, H. Hudson, and W. D. Pesnell.

]]> Thu, 09 FEB 2012 08:59:14 AEST Palo Alto, CA (SPX) Jan 23, 2012 - In a paper to be published tomorrow in the journal Science, for the first time ever scientists at the Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) at the Advanced Technology Center (ATC) in Palo Alto, and collaborators at other institutions, have reported observations and analysis of the final death throes of a comet, as it passed across the face of the Sun on July 6, 2011, to vanish in flight.

Using observations from the Atmospheric Imaging Assembly (AIA) instrument on board NASA's Solar Dynamics Observatory (SDO), the comet was first seen about 0.2 solar radii off the limb of the Sun, travelling at nearly 400 miles per second and was tracked for 20 minutes until it disintegrated and evaporated in the low solar corona, about 62,000 miles above the solar surface.

The Extreme-Ultraviolet Imager (EUVI), on one of NASA's twin Solar-Terrestrial Relations Observatories (STEREO), made simultaneous additional observations of the comet's passage from its near-quadrature view relative to the Sun-Earth line.

The comet was discovered on July 4, 2011 by using the Large Angle and Spectrometric Coronagraph (LASCO) on the ESA/NASA Solar and Heliospheric Observatory (SOHO), and was designated comet C/2011 N3 (SOHO). It was the SOHO discovery that alerted Lockheed Martin scientists to watch the AIA data stream for the comet's likely transit across the face of the Sun.

"This unprecedented passage of a comet through the solar atmosphere in view of our AIA cameras presented us with a remarkable opportunity," said LMSAL solar physicist Dr. Karel Schrijver, lead author of the Science paper and AIA principal investigator.

"As we witnessed this comet evaporate as it traversed a known amount of space over a specific period of time, we were able to work backward to estimate its mass just before it reached the Sun.

"We've been able to bracket its size as between 150 and 300 feet long, with a greater likelihood that it lies at the upper end of that range. And it most likely weighed in at as much as 70,000 tons, giving it about the weight of an aircraft carrier, when it first became visible to AIA."

As the comet streaked into the solar atmosphere it had already fractured into many large pieces ranging in size from 30 to 150 feet. The pieces were embedded in the nebulous envelope made up of ice, dust, and gas called the coma, surrounding the comet's nucleus.

The coma was estimated to be about 800 miles across, followed by a glowing tail approximately 10,000 miles long. The tail was seen pulsing from dim to bright to dim again during the journey across the Sun, which suggests that there was further breakup of the individual chunks of comet as it continued to fragment in the intense glow from the Sun's surface. Eventually, the comet evaporated completely.

"I think the light pulses in the tail were one of the most interesting things we witnessed," said Schrijver.

"The comet's tail gets brighter by as much as four times every minute or two. The comet seems first to put a lot of material into that tail, then less, and then the pattern repeats. Only because of these pulses can we measure how fast the tail falls behind the comet as its gases collide with those in the Sun's atmosphere. And that, in turn, helps us measure the comet's weight.

During its 15 years of observations, the LASCO instrument on SOHO has observed more than 2000 comets as they approached the Sun. The population of these Sun-grazing comets is dominated by the Kreutz group, whose members orbit to within one to two solar radii from the solar surface (photosphere) every 500 to 1000 years.

More than 1400 of the comets seen by SOHO are members of the Kreutz group, making it the largest known group of comets, likely originating from the breakup of a progenitor body as recently as 2500 years ago. Only the largest of the Kreutz group comets, with diameters of up to about 330 feet have survived perihelion - their closest approach to the Sun.

Prior to the observations reported in Science, cometary masses were generally derived from lightcurves during their orbits, assumed reflectivity, and estimated mass densities, or by direct imaging for the few comets that have been visited by spacecraft.

LASCO observes a Sun-grazing comet roughly once every three days, and while most fade well before perihelion, several per year should reach the solar corona and be available for further study of cometary properties as well as probes of the solar corona.

The Solar and Astrophysics Laboratory at the ATC conducts basic research into understanding and predicting space weather and the behavior of our Sun, including its impacts on Earth and climate.

It has a 48-year-long heritage of spaceborne solar instruments including the Soft X-ray Telescope on the Japanese Yohkoh satellite, the Michelson Doppler Imager on the ESA/NASA Solar and Heliospheric Observatory, the solar telescope of NASA's Transition Region and Coronal Explorer, the Focal Plane Package on the Japanese Hinode satellite, the Solar X-ray Imagers on GOES-N, -O and -P, the Extreme Ultraviolet Imager instruments on NASA's twin STEREO spacecraft, and the Helioseismic and Magnetic Imager and the Atmospheric Imaging Assembly on NASA's Solar Dynamics Observatory.

The ATC is currently building both the science instrument and spacecraft for NASA's Interface Region Imaging Spectrograph (IRIS), a Small Explorer Mission scheduled for launch in late 2012.

The ATC is the research and development organization of Lockheed Martin Space Systems Company (LMSSC). LMSSC, a major operating unit of Lockheed Martin Corporation, designs and develops, tests, manufactures and operates a full spectrum of advanced-technology systems for national security and military, civil government and commercial customers.

]]> Thu, 09 FEB 2012 08:59:14 AEST Greenbelt MD (SPX) Jan 20, 2012 - On July 6, 2011, a comet was caught doing something never seen before: die a scorching death as it flew too close to the sun. That the comet met its fate this way was no surprise - but the chance to watch it first-hand amazed even the most seasoned comet watchers.

"Comets are usually too dim to be seen in the glare of the sun's light," says Dean Pesnell at NASA's Goddard Space Flight Center in Greenbelt, Md., who is the project scientist for NASA's Solar Dynamic Observatory (SDO), which snapped images of the comet. "We've been telling people we'd never see one in SDO data."

But an ultra bright comet, from a group known as the Kreutz comets, overturned all preconceived notions. The comet can clearly be viewed moving in over the right side of the sun, disappearing 20 minutes later as it evaporates in the searing heat.

The movie is more than just a novelty. As detailed in a paper in Science magazine appearing January 20, 2012, watching the comet's death provides a new way to estimate the comet's size and mass. The comet turns out to be somewhere between 150 to 300 feet long and have about as much mass as an aircraft carrier.

"Of course, it's doing something very different than what aircraft carriers do," says Karel Schrijver, a solar scientist at Lockheed Martin in Palo Alto, Calif., who is the first author on the Science paper and is the principal investigator of the Atmospheric Imaging Assembly instrument on SDO, which recorded the movie.

"It was moving along at almost 400 miles per second through the intense heat of the sun - and was literally being evaporated away."

Typically, comet-watchers see the Kreutz-group comets only through images taken by coronagraphs, a specialized telescope that views the Sun's fainter out atmosphere, or corona, by blocking the direct blinding sunlight with a solid occulting disk.

On average a new member of the Kreutz family is discovered every three days, with some of the larger members being observed for some 48 hours or more before disappearing behind the occulting disk, never to be seen again. Such "sun-grazer" comets obviously destruct when they get close to the sun, but the event had never been witnessed.

The journey to categorizing this comet began on July 6, 2011 after Schrijver spotted a bright comet in a coronagraph produced by the SOlar Heliospheric Observatory (SOHO). He looked for it in the SDO images and much to his surprise he found it. Soon a movie of the comet circulated to comet and solar scientists, eventually making a huge splash on the Internet as well.

Karl Battams, a scientist with the Naval Research Laboratory in Washington, DC, who has extensively observed comets with SOHO and is also an author on the paper, was skeptical when he first received the movie.

"But as soon as I watched it, there was zero doubt," he says. "I am so used to seeing comets simply disappearing in the SOHO images. It was breathtaking to see one truly evaporating in the corona like that."

After the excitement, the scientists got down to work. Humans have been watching and recording comets for thousands of years, but finding their dimensions has typically required a direct visit from a probe flying nearby. This movie offered the first chance to measure such things from afar. The very fact that the comet evaporated in a certain amount of time over a certain amount of space means one can work backward to determine how big it must have been before hitting the sun's atmosphere.

The Science paper describes the comet and its last moments as follows: It was traveling some 400 miles per second and made it to within 62,000 miles of the sun's surface before evaporating.

Before its final death throes, in the last 20 minutes of its existence when it was visible to SDO, the comet was some 100 million pounds, had broken up into a dozen or so large chunks with sizes between 30 to 150 feet, embedded in a "coma" - that is the fuzzy cloud surrounding the comet - of approximately 800 miles across, and followed by a glowing tail of about 10,000 miles in length.

It is actually the coma and tail of the comet being seen in the video, not the comet's core. And close examination shows that the light in the tail pulses, getting dimmer and brighter over time. The team speculates that the pulsing variations are caused by successive breakups of each of the individual chunks that made up the comet material as it fell apart in the Sun's intense heat.

"I think this is one of the most interesting things we can see here," says Lockheed's Schrijver. "The comet's tail gets brighter by as much as four times every minute or two. The comet seems first to put a lot of material into that tail, then less, and then the pattern repeats." Figuring out the exact details of why this happens is but one of the mysteries remaining about this comet movie.

High on the list is to answer the not-so-simple question of why we can see the comet at all. Certainly, there are a few basic characteristics of this situation that help. For one, this comet was big enough to survive long enough to be seen, and its orbit took it right across the face of the Sun.

It was also, says Battams, probably one of the top 15 brightest comets seen by SOHO, which has observed over 2,100 sun-grazing comets to date.

The SDO cameras, in of themselves, also contributed a great deal: despite being far away and relatively small compared to the sun, the comet showed up clearly on SDO's high definition imager.

This imager, called the Atmospheric Imaging Assembly (AIA) takes a picture every 12 seconds so the movement of the comet across the face of the sun could be continuously watched. Most other similar instruments capture images every few minutes, which makes it hard to track the movement of an object that's only visible for 20 minutes.

But ultimately, the fact that one can see this comet against the background of the sun means there is some physical process not yet understood.

"Normally," says Goddard's Pesnell, "a comet passing in front of the sun absorbs the light from the sun. We would have expected a black spot against the sun, not a bright one. And there's not enough stuff in the corona to make it glow, the way a meteor does when it goes into Earth's atmosphere. So one of the really big questions is why do we see it at all?"

Figuring out this question should offer information not only about material in the comet, but also about the sun's atmosphere - and so this opens up the door to a new niche of study. Assuming, of course, that one can spot some more comets.

So far SDO has only seen the one passing in front of the sun, though SDO did spot Comet Lovejoy traveling through the corona, as it went behind the sun and reappeared.

Stay tuned, as new sun-grazing comets appear every few days . . .

]]> Thu, 09 FEB 2012 08:59:14 AEST Subscribe to our daily selection of space, military, environment and energy newsletters responseText http://visitor.constantcontact.com/manage/optin/ea?v=0016gbbKsaiGSpQFojVO8ZoHw%3D%3D