Cassini Catches Titan Naked in the Solar Wind

This diagram depicts conditions observed by NASA's Cassini spacecraft during a flyby in Dec. 2013, when Saturn's magnetosphere was highly compressed, exposing Titan to the full force of the solar wind. Image credit: NASA/JPL-Caltech

Researchers studying data from NASA's Cassini mission have observed that Saturn's largest moon, Titan, behaves much like Venus, Mars or a comet when exposed to the raw power of the solar wind. The observations suggest that unmagnetized bodies like Titan might interact with the solar wind in the same basic ways, regardless of their nature or distance from the sun.

Titan is large enough that it could be considered a planet if it orbited the sun on its own, and a flyby of the giant moon in Dec. 2013 simulated that scenario, from Cassini's vantage point. The encounter was unique within Cassini's mission, as it was the only time the spacecraft has observed Titan in a pristine state, outside the region of space dominated by Saturn's magnetic field, called its magnetosphere.

"We observed that Titan interacts with the solar wind very much like Mars, if you moved it to the distance of Saturn," said Cesar Bertucci of the Institute of Astronomy and Space Physics in Buenos Aires, who led the research with colleagues from the Cassini mission. "We thought Titan in this state would look different. We certainly were surprised," he said.

The solar wind is a fast-flowing gale of charged particles that continually streams outward from the sun, flowing around the planets like islands in a river. Studying the effects of the solar wind at other planets helps scientists understand how the sun's activity affects their atmospheres. These effects can include modification of an atmosphere's chemistry as well as its gradual loss to space.

Titan spends about 95 percent of the time within Saturn's magnetosphere. But during a Cassini flyby on Dec. 1, 2013, the giant moon happened to be on the sunward side of Saturn when a powerful outburst of solar activity reached the planet. The strong surge in the solar wind so compressed the sun-facing side of Saturn's magnetosphere that the bubble's outer edge was pushed inside the orbit of Titan. This left the moon exposed to, and unprotected from, the raging stream of energetic solar particles.

Using its magnetometer instrument, which is akin to an equisitely sensitive compass, Cassini has observed Titan many times during the mission's decade in the Saturn system, but always within Saturn's magnetosphere. The spacecraft has not been able to detect a magnetic field coming from Titan itself. In its usual state, Titan is cloaked in Saturn's magnetic field.

This time the influence of Saturn was not present, allowing Cassini's magnetometer to observe Titan as it interacted directly with the solar wind. The special circumstance allowed Bertucci and colleagues to study the shockwave that formed around Titan where the full-force solar wind rammed into the moon's atmosphere.

At Earth, our planet's powerful magnetic field acts as a shield against the solar wind, helping to protect our atmosphere from being stripped away. In the case of Venus, Mars and comets -- none of which is protected by a global magnetic field -- the solar wind drapes around the objects themselves, interacting directly with their atmospheres (or in the comet's case, its coma). Cassini saw the same thing at Titan.

Researchers thought they would have to treat Titan's response to the solar wind with a unique approach because the chemistry of the hazy moon's dense atmosphere is highly complex. But Cassini's observations of a naked Titan hinted at a more elegant solution. "This could mean we can use the same tools to study how vastly different worlds, in different parts of the solar system, interact with the wind from the sun," Bertucci said.

Bertucci noted that the list of similarly unmagnetized bodies might include the dwarf planet Pluto, to be visited this year for the first time by NASA's New Horizons spacecraft.

"After nearly a decade in orbit, the Cassini mission has revealed once again that the Saturn system is full of surprises," said Michele Dougherty, principal investigator of the Cassini magnetometer at Imperial College, London. "After more than a hundred flybys, we have finally encountered Titan out in the solar wind, which will allow us to better understand how such moons maintain or lose their atmospheres."

The new research is published today in the journal Geophysical Review Letters.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's 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. JPL designed, developed and assembled the Cassini orbiter. The magnetometer team is based at Imperial College, London, U.K.

Source: Nasa

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SOHO and Hinode Offer New Insight Into Solar Eruptions

Scientists are trying to understand the precise details of what creates giant explosions in the sun's atmosphere, such as this solar eruption from Oct. 14, 2012, as seen by NASA's Solar Dynamic Observatory. Image Credit: NASA/SDO/Amari

The sun is home to the largest explosions in the solar system. For example, it regularly produces huge eruptions known as coronal mass ejections – when billions of tons of solar material erupt off the sun, spewing into space and racing toward the very edges of the solar system. Scientists know that these ejections, called CMEs, are caused by magnetic energy building up on the sun, which suddenly releases. But the details of what causes the build up and triggers the release are not precisely understood.

A journal paper in Nature magazine on Oct. 23, 2014, used data from NASA missions to present an example of how something called a magnetic flux rope builds up over time until it is so unstable that even the slightest perturbation will send it flying. Understanding what triggers CMEs is crucial not only for better understanding of our sun, but also to lay the groundwork for predicting when such giant explosions might happen.

"We looked at a well-studied CME from 2006," said Tahar Amari first author on the Nature paper at Ecole Polytechnique in France. "We knew that there had been a great deal of data available for this CME and much analysis already done, but no one had created a comprehensive picture of what happened."

Amari and his colleagues used a traditional meteorology technique to examine the event: Gather observations from the days before the CME to track how the event grew over time. They used observations from the European Space Agency and NASA's Solar and Heliospheric Observatory, or SOHO, and the Japanese Aerospace Exploration Agency and NASA's Hinode, as well as from the Paris-Meudon Observatory.

Scientists created this model to examine the magnetic field before a giant solar eruption – a coronal mass ejection – which occurred on Dec. 13, 2006. The orange lines show magnetic field lines. The grey line represents what's called a flux rope, which built up the day before the event. Image Credit: Amari/Ecole Poytechnique

The team wanted to see if they could distinguish between two broad theories about how the magnetic energy develops. The first model describes a situation in which a series of loops of magnetic fields on the sun – known as an arcade – is the start of every active region CME. 

This arcade has a weak point at the top, a place where the energy from below can burst through once it's great enough. During the eruption a flux rope forms, which can be seen inside the CME as it surges away from the sun.

The second model assumes that the flux rope is there before the CME erupts. In this theory, no weak point is required. Instead, the flux rope gains more and more energy, and becomes increasingly unstable until a disturbance on the sun causes it to release the energy out into space.

Amari and his team used magnetic data from the surface obtained by Hinode, but they also needed magnetic data for the sun's atmosphere, the corona, which is strongly affected by its magnetic field.

"The corona is so hot that most of the techniques to measure the magnetic field don't work," said Amari. "So we developed an efficient and accurate model to compute the magnetic field there, based on the data we had from the surface, and the equations governing the physics of the low corona above active regions."

With these two data sets in hand, the team examined what happened in the four days before the 2006 CME erupted. They could see the magnetic energy building; it was clear something was emerging. Only, however, on the last day did a flux rope develop and only then did it have enough energy built up to power a CME eruption. At this point, some small disruption was enough of a nudge to make the flux rope erupt.

A model of the eruption of a giant magnetic rope that led to a coronal mass ejection on the sun in December 2006.

A model of the eruption of a giant magnetic rope that led to a coronal mass ejection on the sun in December 2006. The model showed that magnetic fields built up for several days before the eruption.

"In this case no weak point up in the atmosphere was needed to allow the energy to be released," said Amari. "There is, instead, a kind of critical value of energy, a value we can compute based on seeing an active magnetic region on the sun. Beneath that value the magnetic field will stay quiet. Above that, it is likely to erupt. There is also a critical height for rising flux rope, beyond which the magnetic loops above can no longer keep it confined."

The team explored the initial conditions from this event and put the information into another dynamical model the team had developed. The simulation mirrored what was actually seen, with an eruption occurring only when the critical energy and height were reached on the last day.

Amari points out that just because this CME contained a flux rope prior to eruption, it doesn't mean that other CMEs can’t erupt based on other physical catalysts. But it clearly describes one mechanism that is at work on the sun.

By measuring and calculating the magnetic fields on the sun, coupled with determining how to measure the critical tipping point where a CME can erupt, the paper offers new ways to determine the possibility of eruption from any given active area on the sun.

Source: Nasa

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Black holes follow the rules

Artist's impression of a black hole at the centre of a galaxy. Credit: Gabriel Pérez Díaz.

Rather than having random sizes, massive black holes seem to follow a predictable rule in relation to the physical properties of the galaxy in which they are located.

Research at Swinburne University of Technology has shown that it is possible to predict the masses of black holes in galaxies for which it was previously thought not possible.

In large galaxies, the central black hole is related to the mass of the spheroid-shaped distribution of stars at the centre of the galaxy, known as the galaxy’s 'bulge'.

Some astronomers have claimed that the size of black holes at the centres of galaxies with small bulges was unrelated to the bulge.

Even the four million solar mass black hole in the bulge of our Milky Way galaxy was thought to be arbitrarily low relative to trends defined by their more massive, and therefore easier to detect, counterparts.

However, in previous work Swinburne Professor Alister Graham, lead-author of the current research, identified a new relationship involving black holes in galaxies with small bulges.  He demonstrated that the black hole in the bulge of the Milky Way was not set by chance but instead followed an astronomical rule.

“The formula is quadratic, in that the black hole mass quadruples every time the bulge mass doubles,” Professor Graham said. “Therefore, if the bulge mass increases 10 times, the black hole mass increases 100 times.”

Now, after studying more than 100 galaxies with black holes 4 to 40 times less massive than our Milky Way's black hole, they too have been found to follow this same rule.

"It turns out that there is yet more order in our Universe than previously appreciated,” Professor Graham said.

"This is exciting not just because it provides further insight into the mechanics of black hole formation, but because of the predictions it allows us to make."

The gravitational collapse of massive stars can produce black holes up to a few tens of times the mass of our Sun. And black holes that are one-tenth of a million to ten billion times the mass of our Sun have been identified at the centres of giant galaxies. However, there is a missing population of intermediate-mass black holes.

Astronomers don't know if this is because of observational difficulties in finding them, or if the massive black holes at the centres of galaxies start life as 100,000 solar mass seed black holes that formed in the early Universe.

This latest result, which extends the new rule to 40-times lower masses, gives astronomers some confidence that it may extend even further, so the smallest bulges might host these missing intermediate-mass black holes. 

"If confirmed, it would imply tremendous black hole appetites", co-author of the study, Dr Nicholas Scott, said. "There would need to be a dramatic growth of these small black holes relative to their host bulge, with the bulges growing via the creation of stars out of gas clouds while the black holes devour both gas and stars."

The researchers have identified a few dozen candidate galaxies in which they think intermediate-mass black holes may be hiding.  Future observations, with facilities such as the Square Kilometre Array and space-based X-ray telescopes, are expected to help resolve this black hole mystery.

Source: Swinburne

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Helping outdoor workers reduce skin cancer risk

QUT health promotion specialist Dr Marguerite Sendall is reducing skin cancer risk for outdoor workers. Credit: Image courtesy of Queensland University of Technology

Skin cancer is one of the biggest fears for one in two outdoor workers and when the boss and staff work together the sun safe message gets through, a QUT study has found.

The study, which found more than 50 per cent of outdoor workers rated UV radiation exposure at work as one of their biggest concerns, also identified how a workplace intervention could improve workers' behaviours and attitudes towards sun protection to reduce their risk of skin cancer.

QUT in collaboration with Cancer Council Queensland and Curtin University worked with 14 Queensland outdoor workplaces from farming, construction, public service and local government industries to develop personalized sun protection action plans.

After adopting these individualized plans, the number of workers who reported using sun protection increased significantly.

Professor Michael Kimlin and Associate Professor Monika Janda, from QUT's AusSun Research Lab, led the intervention program and the results have been published in the Journal of Occupational and Environmental Medicine titled "Changes in Outdoor Workers' Sun-Related Attitudes, Beliefs and Behaviours: A Pre-Post Workplace Intervention."

"The message is simple, outdoor workers who see their workplace, supervisors and bosses supporting sun protection measures will follow their lead," Professor Janda said.

"Providing better programs, which take into account the specific workplace tasks and culture can make a difference."

QUT health promotion specialist Dr Marguerite Sendall, who was involved at the grassroots level in implementing the workplace interventions, said the study worked closely with workplaces to develop and implement a tailored sun safety plan, encouraging sun awareness and supporting sun protection practices at work.

"The program was about working together in partnership with workplaces, taking into account their individual circumstances and environment, and developing realistic and sustainable strategies," Dr Sendall said.

"It was this partnership and customized strategies that made this study a success and led to significant improvements in the way workplaces and employees approached sun safety."

Dr Sendall said after the 12 months intervention, the results revealed when a workplace was sun safe there was a significant improvement in the attitudes and behaviours of outdoor workers when it came to sun protection.

"For example, the proportion of workers who checked their skin for early signs of skin cancer increased after the intervention program, with 80 per cent reporting they had conducted a skin check in the previous 12 months," Dr Sendall said.

"Ten per cent more workers also had their skin checked by a doctor.

"The study found after the intervention, 20 per cent more workers said they usually or 

always seek natural shade, 25 per cent more workers wore broad-brimmed hats, 19 per cent more wore long-sleeved collared shirts and 16 per cent wore long trousers," she said.

Dr Sendall said there was also a shift in outdoor worker attitudes.

"The proportion of workers who agreed their workplace enforced sun protection and agreed their supervisors protected themselves increased by 10 per cent to 76 per cent of all workers," she said.

One of the workplaces to take part in the study was Goondiwindi Regional Council and workplace champion Andrew Singh said the tailored intervention had produced tangible results.

"At our council, after introducing the intervention, the road construction crew adopted a number of sun safe initiatives," Mr Singh said.

"For example, the council provided portable shade structures to be used during breaks, vehicle windows were tinted and our staff swapped baseball-style caps for broad-brimmed hats.

"Overall, what we found was workers were keen to follow these sun safe measures as they saw their initiatives were welcomed and keenly supported by the mayor, councillors and management."

Dr Sendall said the study highlighted the importance of a consistent sun safe workplace culture.

"Despite ongoing public health campaigns, outdoor workers remain a difficult to reach group but if we can take care in making the sun protection program really relevant to their personal circumstances and work environment, the potential health benefits are significant."

Source: Queensland University of Technology

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Large coronal hole near the sun's north pole

The European Space Agency/NASA Solar and Heliospheric Observatory, or SOHO, captured this image of a gigantic coronal hole hovering over the sun’s north pole on July 18, 2013, at 9:06 a.m. EDT.
Credit: ESA & NASA/SOHO

The European Space Agency/NASA Solar and Heliospheric Observatory, or SOHO, captured this image of a gigantic coronal hole hovering over the sun's north pole on July 18, 2013, at 9:06 a.m. EDT. Coronal holes are dark, low density regions of the sun's outermost atmosphere, the corona. They contain little solar material, have lower temperatures, and therefore, appear much darker than their surroundings.

Coronal holes are a typical feature on the sun, though they appear at different places and with more frequency at different times of the sun's activity cycle. The activity cycle is currently ramping up toward what is known as solar maximum, currently predicted for late 2013. During this portion of the cycle, the number of coronal holes decreases. During solar max, the magnetic fields on the sun reverse and new coronal holes appear near the poles with the opposite magnetic alignment. The coronal holes then increase in size and number, extending further from the poles as the sun moves toward solar minimum again. At such times, coronal holes have appeared that are even larger than this one.

The holes are important to our understanding of space weather, as they are the source of a high-speed wind of solar particles that streams off the sun some three times faster than the slower wind elsewhere. While it's unclear what causes coronal holes, they correlate to areas on the sun where magnetic fields soar up and away, failing to loop back down to the surface, as they do elsewhere.

Source: NASA/Goddard Space Flight Center

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NASA's SDO sees massive filament erupt on sun

Eruptive events on the sun can be wildly different. Some come just with a solar flare, some with an additional ejection of solar material called a coronal mass ejection (CME), and some with complex moving structures in association with changes in magnetic field lines that loop up into the sun's atmosphere, the corona. Credit: Image courtesy of NASA/Goddard Space Flight Center

Eruptive events on the sun can be wildly different. Some come just with a solar flare, some with an additional ejection of solar material called a coronal mass ejection (CME), and some with complex moving structures in association with changes in magnetic field lines that loop up into the sun's atmosphere, the corona.

On July 19, 2012, an eruption occurred on the sun that produced all three. A moderately powerful solar flare exploded on the sun's lower right limb, sending out light and radiation. Next came a CME, which shot off to the right out into space. And then, the sun treated viewers to one of its dazzling magnetic displays -- a phenomenon known as coronal rain.

Over the course of the next day, hot plasma in the corona cooled and condensed along strong magnetic fields in the region. Magnetic fields, themselves, are invisible, but the charged plasma is forced to move along the lines, showing up brightly in the extreme ultraviolet wavelength of 304 Angstroms, which highlights material at a temperature of about 50,000 Kelvin. This plasma acts as a tracer, helping scientists watch the dance of magnetic fields on the sun, outlining the fields as it slowly falls back to the solar surface.

Source: NASA/Goddard Space Flight Center

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Lightning expected to increase by 50 percent with global warming

Today's climate models predict a 50 percent increase in lightning strikes across the United States during this century as a result of warming temperatures associated with climate change. Credit: © Sondem / Fotolia

Today's climate models predict a 50 percent increase in lightning strikes across the United States during this century as a result of warming temperatures associated with climate change.

Reporting in the Nov. 14 issue of the journal Science, University of California, Berkeley, climate scientist David Romps and his colleagues look at predictions of precipitation and cloud buoyancy in 11 different climate models and conclude that their combined effect will generate more frequent electrical discharges to the ground.

"With warming, thunderstorms become more explosive," said Romps, an assistant professor of earth and planetary science and a faculty scientist at Lawrence Berkeley National Laboratory. "This has to do with water vapor, which is the fuel for explosive deep convection in the atmosphere. Warming causes there to be more water vapor in the atmosphere, and if you have more fuel lying around, when you get ignition, it can go big time."

More lightning strikes mean more human injuries; estimates of people struck each year range from the hundreds to nearly a thousand, with scores of deaths. But another significant impact of increased lightning strikes would be more wildfires, since half of all fires -- and often the hardest to fight -- are ignited by lightning, Romps said. More lightning also would likely generate more nitrogen oxides in the atmosphere, which exert a strong control on atmospheric chemistry.

While some studies have shown changes in lightning associated with seasonal or year-to-year variations in temperature, there have been no reliable analyses to indicate what the future may hold. Romps and graduate student Jacob Seeley hypothesized that two atmospheric properties -- precipitation and cloud buoyancy -- together might be a predictor of lightning, and looked at observations during 2011 to see if there was a correlation.

"Lightning is caused by charge separation within clouds, and to maximize charge separation, you have to loft more water vapor and heavy ice particles into the atmosphere," he said. "We already know that the faster the updrafts, the more lightning, and the more precipitation, the more lightning."

Precipitation -- the total amount of water hitting the ground in the form of rain, snow, hail or other forms -- is basically a measure of how convective the atmosphere is, he said, and convection generates lightning. The ascent speeds of those convective clouds are determined by a factor called CAPE -- convective available potential energy -- which is measured by balloon-borne instruments, called radiosondes, released around the U.S. twice a day.

"CAPE is a measure of how potentially explosive the atmosphere is, that is, how buoyant a parcel of air would be if you got it convecting, if you got it to punch through overlying air into the free troposphere," Romps said. "We hypothesized that the product of precipitation and CAPE would predict lightning."

Using U.S. Weather Service data on precipitation, radiosonde measurements of CAPE and lightning- strike counts from the National Lightning Detection Network at the University of Albany, State University of New York (UAlbany), they concluded that 77 percent of the variations in lightning strikes could be predicted from knowing just these two parameters.

'Blown away'

"We were blown away by how incredibly well that worked to predict lightning strikes," he said.

They then looked at 11 different climate models that predict precipitation and CAPE through this century and are archived in the most recent Coupled Model Intercomparison Project (CMIP5). CMIP was established as a resource for climate modelers, providing a standard protocol for studying the output of coupled atmosphere-ocean general circulation models so that these models can be compared and validated.

"With CMIP5, we now have for the first time the CAPE and precipitation data to calculate these time series," Romps said.

On average, the models predicted an 11 percent increase in CAPE in the U.S. per degree Celsius rise in global average temperature by the end of the 21st century. Because the models predict little average precipitation increase nationwide over this period, the product of CAPE and precipitation gives about a 12 percent rise in cloud-to-ground lightning strikes per degree in the contiguous U.S., or a roughly 50 percent increase by 2100 if Earth sees the expected 4-degree Celsius increase (7 degrees Fahrenheit) in temperature. This assumes carbon dioxide emissions keep rising consistent with business as usual.

Exactly why CAPE increases as the climate warms is still an area of active research, Romps said, though it is clear that it has to do with the fundamental physics of water. Warm air typically contains more water vapor than cold air; in fact, the amount of water vapor that air can "hold" increases exponentially with temperature. Since water vapor is the fuel for thunderstorms, lightning rates can depend very sensitively on temperature.

In the future, Romps plans to look at the distribution of lightning-strike increases around the U.S. and also explore what lightning data can tell climatologists about atmospheric convection.

Romps' co-authors are Jacob Seeley, also of the Department of Earth and Planetary Science at UC Berkeley, and David Vollaro and John Molinari of the Department of Atmospheric and Environmental Sciences at UAlbany.

The work was supported by the U.S. Department of Energy's Office of Advanced Scientific Computing Research and Office of Biological and Environmental Research, and the National Science Foundation.

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Source: University of California - Berkeley

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Asteroids made easy: 'Patch of asteroid' being built inside a satellite

ASU researchers build their own "patch of asteroid" inside of a small spinning satellite seen here in this artist rendering. Credit: Sean Amidan

A dozen astronauts have walked on the moon, and several rovers have been piloted on Mars, giving us a good understanding of these off-world environments. But when it comes to asteroids, scientists enter uncharted territory.

Landing on an asteroid is notoriously difficult.

Asteroids have very little gravity because they have very little mass. Most of them appear to be rubble piles held together loosely, with surfaces covered in boulders and gravels and fine materials, much like the moon, but with a lot more cohesion. On an asteroid, a rock the size of a bank building weighs as much as a cricket on Earth, making an astronaut like a superman. But what would you anchor to, what you would land on and how would you move around?

Because scientists and engineers don't know the most basic mechanical properties of an asteroid, sending a billion dollar landing mission to an asteroid is risky, and even likely to fail, until some preliminary investigations are conducted, requiring years of lead time.

A team at Arizona State University is looking to mitigate that risk and improve that schedule by building its own "patch of asteroid" inside of a small, spinning satellite costing less than $100,000. The project is called the Asteroid Origins Satellite, or AOSAT I.

"Landing on asteroids is one of the biggest challenges of our time," roboticist Jekan Thanga said.

Thanga, an assistant professor in the School of Earth and Space Exploration at ASU, is the engineering principal investigator for AOSAT I. "And space agencies worldwide, including NASA, are very focused on meeting that challenge."

Erik Asphaug, a planetary scientist and professor at ASU, is the science principal investigator for AOSAT I. He and Thanga plan on launching a miniature satellite later this year that will serve as the world's first CubeSat microgravity laboratory. A CubeSat is a modular small satellite with a 10-by-10 centimeter base and various unit lengths. AOSAT I will be a 3U configuration, about the size of a loaf of bread, with two spun-up laboratories in the outer units, each housing a patch of real asteroid surface material.

In the first flight, one chamber will be filled to a depth of a few centimeters with very fine material representative of interstellar dust, or the fine "ponds" seen on several asteroids. 

The second chamber, otherwise identical, will be filled with bits of shock-fragmented chondrite meteorite material. Once launched into space and freely orbiting, these rocks will just tumble around -- itself an interesting experiment. But to build a realistic regolith surface for scientists to explore, the satellite is spun, to create microgravity-like conditions.

"We're taking asteroid material that landed on Earth and sending it back into space," Asphaug said. "It's a low-cost laboratory that really physically builds a patch of asteroid. It'll be asteroid gravity. It'll be made of asteroid stuff. We can do all sorts of experiments."

To simulate the gravity field of a 300-meter-diameter asteroid, AOSAT I spins once every 4.5 minutes. It can spin faster to reproduce the regolith (surface material) conditions for much larger asteroids. This spin configuration is easily attained and stabilized by off-the-shelf approaches, making it a great approach for students to learn on.

While much of the CubeSat is off-the-shelf, the approach is novel. CubeSats have typically been used to test engineering designs in space, since it is a really constrained and relatively new form factor. Great science has been performed on CubeSats, although this has only been observational so far. CubeSats have not yet been used to do "test tube and beaker-type" experiments of the sort that are planned for AOSAT I, Thanga said.

Experiments will be conducted robotically in the end chambers. When AOSAT I is not spinning, it is a zero-gravity capsule. Here, experiments will be done to understand how dust clumps together to form asteroids -- a process that plays out in zero gravity over long timescales. A simple robotic plunger is being designed to interact with the patch of regolith, and can be used to accrete a globule of particles, a miniature rubble pile asteroid that can be spun and shaken, observed by stereo cameras.

When AOSAT I starts to spin, these piles of grains will get accelerated to the outer walls. Observing that process will tell us much about nebular grain behavior and microgravity particle flows on asteroids, for example, following the formation of a crater.

Once the spinning AOSAT I has stabilized (once per few minutes), experiments will be conducted to give a better understanding of what asteroid surfaces are like. "The questions are very basic, and that's what makes this so much fun," says Asphaug. When you push slowly on a rock, does it lock into place or does it push aside the other rocks and slide into the surface? Do patterns form when you send a vibration through the regolith? Does cohesion dominate overwhelmingly over gravity, so that rocks stick together into aggregates? What happens when you charge the particles?

Asphaug and Thanga hope to answer these questions to help determine what kinds of devices would be best for landing on real asteroids. "An asteroid could just be lots of rock, just grouped together into this larger entity, but there's nothing holding it together," Thanga said. "So if something is going to grapple and try to land on this, there's nothing to grapple to."

Despite the small scale of the experiments (the asteroid patch will be slightly smaller than a CD case), Asphaug and Thanga are confident in the real-world applications of AOSAT.

"These rocks might not be able to tell the difference, whether they are in the AOSAT centrifuge or back on their home asteroid," says Asphaug. Once the AOSAT is spun up to mimic the gravity field of a ~300 m asteroid (gravity field 10-5 that of Earth), then it can be used to test mechanisms for asteroid landing. The first AOSAT will use a simple arm that does some basic interactions, while next generation AOSATs will be configured with more advanced robotic equipment.

Thanga uses the analogy of a wind tunnel to describe the scientific approach to their experiments. In a wind tunnel, researchers subject small-scale models of aircraft to conditions they expect in flight. The calculations and designs are then scaled up and applied to the real thing. "We can test asteroids in this wind tunnel-like analogous system, prove and disprove theories, and get a better understanding of our models," says Thanga.

Landing on an asteroid may be extremely difficult, but it's also an extremely desirable goal, from many points of view. Mining asteroids, colonizing asteroids or using asteroids as stepping stones to Mars and the other planets used to be the stuff of science fiction. Now it is on the desk of NASA administrators, who are being asked to find ways to divert hazardous asteroids, and to discover new ways to utilize asteroids, and to involve asteroids as part of the astronaut pathway to Mars.

Viranga Perera, a graduate student at ASU who is managing the project systems engineering, thinks it is "fascinating that this very low-cost AOSAT platform can be used to study such a fundamental concept as planetary accretion, and that it can serve as a test bed for future asteroid sample return missions."

The School of Earth and Space Exploration is an academic unit in ASU's College of Liberal Arts and Sciences.

Source:  Arizona State University College of Liberal Arts and Sciences

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Magnetic fields frozen into meteorite grains tell a shocking tale of solar system birth

Magnetic field lines (green) weave through the cloud of dusty gas surrounding the newborn Sun. In the foreground are asteroids and chondrules, the building blocks of chondritic meteorites. While solar magnetic fields dominate the region near the Sun, out where the asteroids orbit, chondrules preserve a record of varying local magnetic fields. Credit: Science

The most accurate laboratory measurements yet made of magnetic fields trapped in grains within a primitive meteorite are providing important clues to how the early solar system evolved. The measurements point to shock waves traveling through the cloud of dusty gas around the newborn Sun as a major factor in solar system formation.

The results appear in a paper published Nov. 13 in the journal Science. The lead author is graduate student Roger Fu of MIT, working under Benjamin Weiss; Steve Desch of Arizona State University's School of Earth and Space Exploration is a co-author of the paper.

"The measurements made by Fu and Weiss are astounding and unprecedented," says Desch. 
"Not only have they measured tiny magnetic fields thousands of times weaker than a compass feels, they have mapped the magnetic fields' variation recorded by the meteorite, millimeter by millimeter."

Construction debris
It may seem all but impossible to determine how the solar system formed, given it happened about 4.5 billion years ago. But making the solar system was a messy process, leaving lots of construction debris behind for scientists to study.

Among the most useful pieces of debris are the oldest, most primitive and least altered type of meteorites, called the chondrites (KON-drites). Chondrite meteorites are pieces of asteroids, broken off by collisions, that have remained relatively unmodified since they formed at the birth of the solar system. They are built mostly of small stony grains, called chondrules, barely a millimeter in diameter.

Chondrules themselves formed through quick melting events in the dusty gas cloud -- the solar nebula -- that surrounded the young sun. Patches of the solar nebula must have been heated above the melting point of rock for hours to days. Dustballs caught in these events made droplets of molten rock, which then cooled and crystallized into chondrules.

Tiny magnets
As chondrules cooled, iron-bearing minerals within them became magnetized like bits on a hard drive by the local magnetic field in the gas. These magnetic fields are preserved in the chondrules even down to the present day.

The chondrule grains whose magnetic fields were mapped in the new study came from a meteorite named Semarkona, after the place in India where it fell in 1940. It weighed 691 grams, or about a pound and a half.

The scientists focused specifically on the embedded magnetic fields captured by "dusty" olivine grains that contain abundant iron-bearing minerals. These had a magnetic field of about 54 microtesla, similar to the magnetic field at Earth's surface, which ranges from 25 to 65 microtesla.

Coincidentally, many previous measurements of meteorites also implied similar field strengths. But it is now understood that those measurements detected magnetic minerals contaminated by Earth's magnetic field, or even from hand magnets used by meteorite collectors.

"The new experiments," Desch says, "probe magnetic minerals in chondrules never measured before. They also show that each chondrule is magnetized like a little bar magnet, but with 'north' pointing in random directions."

This shows, he says, they became magnetized before they were built into the meteorite, and not while sitting on Earth's surface.

Shocks and more shocks
"My modeling for the heating events shows that shock waves passing through the solar nebula is what melted most chondrules," Desch explains. Depending on the strength and size of the shock wave, the background magnetic field could be amplified by up to 30 times.
He says, "Given the measured magnetic field strength of about 54 microtesla, this shows the background field in the nebula was probably in the range of 5 to 50 microtesla."

There are other ideas for how chondrules might have formed, some involving magnetic flares above the solar nebula, or passage through the sun's magnetic field. But those mechanisms require stronger magnetic fields than what is measured in the Semarkona samples.

This reinforces the idea that shocks melted the chondrules in the solar nebula at about the location of today's asteroid belt, which lies some two to four times farther from the sun than Earth now orbits.

Desch says, "This is the first really accurate and reliable measurement of the magnetic field in the gas from which our planets formed."

Source: Arizona State University

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Sun's rotating 'magnet' pulls lightning towards UK

Big Ben and Houses of Parliament, London, UK. The Sun may be playing a part in the generation of lightning strikes on Earth by temporarily 'bending' the Earth's magnetic field and allowing a shower of energetic particles to enter the upper atmosphere. Credit: © TTstudio / Fotolia

The Sun may be playing a part in the generation of lightning strikes on Earth by temporarily 'bending' the Earth's magnetic field and allowing a shower of energetic particles to enter the upper atmosphere.

This is according to researchers at the University of Reading who have found that over a five year period the UK experienced around 50% more lightning strikes when the Earth's magnetic field was skewed by the Sun's own magnetic field.

The Earth's magnetic field usually functions as an in-built force-field to shield against a bombardment of particles from space, known as galactic cosmic rays, which have previously been found to prompt a chain-reaction of events in thunderclouds that trigger lightning bolts.

It is hoped these new insights, which have been published today, 19 November, in IOP Publishing's journal Environmental Research Letters, could lead to a reliable lightning forecast system that could provide warnings of hazardous events many weeks in advance.

To do so, weather forecasters would need to combine conventional forecasts with accurate predictions of the Sun's spiral-shaped magnetic field known as the heliospheric magnetic field (HMF), which is spewed out as the Sun rotates and is dragged through the solar system by the solar wind.

Lead author of the research Dr Matt Owens said: "We've discovered that the Sun's powerful magnetic field is having a big influence on UK lightning rates.

"The Sun's magnetic field is like a bar magnet, so as the Sun rotates its magnetic field alternately points toward and away from the Earth, pulling the Earth's own magnetic field one way and then another."

In their study, the researchers used satellite and Met Office data to show that between 2001 and 2006, the UK experienced a 50% increase in thunderstorms when the HMF pointed towards the Sun and away from Earth.

This change of direction can skew or 'bend' the Earth's own magnetic field and the researchers believe that this could expose some regions of the upper atmosphere to more galactic cosmic rays--tiny particles from across the Universe accelerated to close to the speed of light by exploding stars.

"From our results, we propose that galactic cosmic rays are channelled to different locations around the globe, which can trigger lightning in already charged-up thunderclouds. The changes to our magnetic field could also make thunderstorms more likely by acting like an extra battery in the atmospheric electric circuit, helping to further 'charge up' clouds," Dr Owens continued.

The results build on a previous study by University of Reading researchers, also published in Environmental Research Letters, which found an unexpected link between energetic particles from the Sun and lightning rates on Earth.

Professor Giles Harrison, head of Reading's Department of Meteorology and co-author of both studies, said: "This latest finding is an important step forward in our knowledge of how the weather on Earth is influenced by what goes on in space. The University of Reading's continuing success in this area shows that new insights follow from atmospheric and space scientists working together."

Dr Owens continued: "Scientists have been reliably predicting the solar magnetic field polarity since the 1970s by watching the surface of the Sun. We just never knew it had any implications on the weather on Earth. We now plan to combine regular weather forecasts, which predict when and where thunderclouds will form, with solar magnetic field predictions. This means a reliable lightning forecast could now be a genuine possibility."

Source:  Institute of Physics

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Invisible shield found thousands of miles above Earth blocks 'killer electrons'

Scientists have discovered an invisible shield roughly 7,200 miles above Earth.
Credit: Andy Kale, University of Alberta

A team led by the University of Colorado Boulder has discovered an invisible shield some 7,200 miles above Earth that blocks so-called "killer electrons," which whip around the planet at near-light speed and have been known to threaten astronauts, fry satellites and degrade space systems during intense solar storms.

The barrier to the particle motion was discovered in the Van Allen radiation belts, two doughnut-shaped rings above Earth that are filled with high-energy electrons and protons, said Distinguished Professor Daniel Baker, director of CU-Boulder's Laboratory for Atmospheric and Space Physics (LASP). Held in place by Earth's magnetic field, the Van Allen radiation belts periodically swell and shrink in response to incoming energy disturbances from the sun.

As the first significant discovery of the space age, the Van Allen radiation belts were detected in 1958 by Professor James Van Allen and his team at the University of Iowa and were found to be composed of an inner and outer belt extending up to 25,000 miles above Earth's surface. In 2013, Baker -- who received his doctorate under Van Allen -- led a team that used the twin Van Allen Probes launched by NASA in 2012 to discover a third, transient "storage ring" between the inner and outer Van Allen radiation belts that seems to come and go with the intensity of space weather.

The latest mystery revolves around an "extremely sharp" boundary at the inner edge of the outer belt at roughly 7,200 miles in altitude that appears to block the ultrafast electrons from breeching the shield and moving deeper towards Earth's atmosphere.

"It's almost like theses electrons are running into a glass wall in space," said Baker, the study's lead author. "Somewhat like the shields created by force fields on Star Trek that were used to repel alien weapons, we are seeing an invisible shield blocking these electrons. It's an extremely puzzling phenomenon."

A paper on the subject was published in the Nov. 27 issue of Nature.

The team originally thought the highly charged electrons, which are looping around Earth at more than 100,000 miles per second, would slowly drift downward into the upper atmosphere and gradually be wiped out by interactions with air molecules. But the impenetrable barrier seen by the twin Van Allen belt spacecraft stops the electrons before they get that far, said Baker.

The group looked at a number of scenarios that could create and maintain such a barrier. The team wondered if it might have to do with Earth's magnetic field lines, which trap and control protons and electrons, bouncing them between Earth's poles like beads on a string. 

The also looked at whether radio signals from human transmitters on Earth could be scattering the charged electrons at the barrier, preventing their downward motion. Neither explanation held scientific water, Baker said.

"Nature abhors strong gradients and generally finds ways to smooth them out, so we would expect some of the relativistic electrons to move inward and some outward," said Baker. "It's not obvious how the slow, gradual processes that should be involved in motion of these particles can conspire to create such a sharp, persistent boundary at this location in space."

Another scenario is that the giant cloud of cold, electrically charged gas called the plasmasphere, which begins about 600 miles above Earth and stretches thousands of miles into the outer Van Allen belt, is scattering the electrons at the boundary with low frequency, electromagnetic waves that create a plasmapheric "hiss," said Baker. The hiss sounds like white noise when played over a speaker, he said.

While Baker said plasmaspheric hiss may play a role in the puzzling space barrier, he believes there is more to the story. "I think the key here is to keep observing the region in exquisite detail, which we can do because of the powerful instruments on the Van Allen probes. If the sun really blasts Earth's magnetosphere with a coronal mass ejection (CME), I suspect it will breach the shield for a period of time," said Baker, also a faculty member in the astrophysical and planetary sciences department.

"It's like looking at the phenomenon with new eyes, with a new set of instrumentation, which give us the detail to say, 'Yes, there is this hard, fast boundary,'" said John Foster, associate director of MIT's Haystack Observatory and a study co-author.

Source: University of Colorado at Boulder

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Origin of long-standing space mystery revealed: Origin of the 'theta aurora'

The night side of the terrestrial magnetosphere forms a structured magnetotail, consisting of a plasma sheet at low latitudes that is sandwiched between two regions called the magnetotail lobes. The lobes consist of the regions in which Earth's magnetic field lines are directly connected to the magnetic field carried by the solar wind. Different plasma populations are observed in these regions -- plasma in the lobes is very cool, whereas the plasma sheet is more energetic. The diagram labels by two red dots the location of an ESA Cluster satellite and NASA's IMAGE satellite on 15 September 2005, when particular conditions of the magnetic field configuration gave rise to a phenomenon known as 'theta aurora.'  Credit: ESA/NASA/SOHO/LASCO/EIT

University of Southampton researcher has helped solve a long-standing space mystery -- the origin of the 'theta aurora'.

Auroras are the most visible manifestation of the Sun's effect on Earth. They are seen as colourful displays in the night sky, known as the Northern or Southern Lights. They are caused by the solar wind, a stream of plasma -- electrically charged atomic particles -- carrying its own magnetic field, interacting with Earth's magnetic field.

Normally, the main region for this impressive display is the 'auroral oval', which lies at around 65-70 degrees north or south of the equator, encircling the polar caps.
However, auroras can occur at even higher latitudes. One type is known as a 'theta aurora' because seen from above it looks like the Greek letter theta -- an oval with a line crossing through the centre.

While the cause of the auroral oval emissions is reasonably well understood, the origin of the theta aurora was unclear until now.

Researchers observed particles in the two 'lobe' regions of the magnetosphere. The plasma in the lobes is normally cold, but previous observations suggested that theta auroras are linked with unusually hot lobe plasma.

Dr Robert Fear from the University of Southampton (formerly at the University of Leicester, where much of the research took place), and lead author of the paper published in Science this week, says: "Previously it was unclear whether this hot plasma was a result of direct solar wind entry through the lobes of the magnetosphere, or if the plasma is somehow related to the plasma sheet on the night side of Earth.

"One idea is that the process of magnetic reconnection on the night side of Earth causes a build-up of 'trapped' hot plasma in the higher latitude lobes."

The mystery was finally solved by studying data collected simultaneously by the European Space Agency's (ESA) Cluster and NASA's IMAGE satellites on 15 September 2005. While the four Cluster satellites were located in the southern hemisphere magnetic lobe, IMAGE had a wide-field view of the southern hemisphere aurora. As one Cluster satellite observed uncharacteristically energetic plasma in the lobe, IMAGE saw the 'arc' of the theta aurora cross the magnetic footprint of Cluster.

"We found that the energetic plasma signatures occur on high-latitude magnetic field lines that have been 'closed' by the process of magnetic reconnection, which then causes the plasma to become relatively hot," says Dr Fear.

"Because the field lines are closed, the observations are incompatible with direct entry from the solar wind. By testing this and other predictions about the behaviour of the theta aurora, our observations provide strong evidence that the plasma trapping mechanism is responsible for the theta aurora," he adds.

"The study highlights the intriguing process that can occur in the magnetosphere when the interplanetary magnetic field of the solar wind points northwards," adds Philippe Escoubet, ESA's Cluster project scientist.

"This is the first time that the origin of the theta aurora phenomenon has been revealed, and it is thanks to localised measurements from Cluster combined with the wide-field view of IMAGE that we can better understand another aspect of the Sun-Earth connection," he adds.

Source: University of Southampton

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Solar activity impacts polar ozone

Scientists have been able to confirm, for the first time, the long-term implications of solar-driven electron impact on the upper middle atmosphere ozone. Credit: NASA

The increase in greenhouse gases explains, to a large extent, the rise in the average temperature of Earth. According to the research study published in Nature Communications today, the Sun affects middle atmosphere ozone with potential implications on smaller scale to regional, but not global, climate.

Humankind is responsible for the global warming of our climate by increasing the amount of greenhouse gases in the atmosphere. However, according results published today, fluctuations in the activity of the Sun impact middle atmosphere ozone, providing a potential link to regional scale climate variability. This climate variability is not a trend, like climate change, but rather year-to-year fluctuations following solar activity. "The detected ozone variation may in part help understand the alternation of local mild and cold winter seasons, as hints have been obtained in previous research that the ozone changes in the middle atmosphere may link as far as the surface of Earth and affect, among other things, polar wind streams," Finnish Meteorological Institute researcher Dr Pekka Verronen reflects.

The research team was able to confirm, for the first time, the long-term implications of solar-driven electron impact on the upper middle atmosphere ozone. The results showed strong effects in the polar latitudes. The amount of ozone at 70-80 km altitude was found to vary more than 30 percent during a solar cycle, a period of approximately 11 years. The ozone variation between the extremes of the Sun's activity is so great that it is likely to impact the temperature balance of the atmosphere. These temperature changes can in turn have an effect on atmospheric winds.

Electrons from space: Auroras and ozone loss

According to the research study conducted by the Finnish Meteorological Institute, University of Otago and the British Antarctic Survey, the electrons, similar to those behind the aurora, cause significant solar cycle variation in the polar mesosphere ozone. The amount of ozone is smaller when more electrons enter the atmosphere. "These results are only the first step but an important one, allowing us to better understand the long-term impacts of this type of solar activity, and its role in regional climate variability," says Dr Monika Andersson who lead the study at Finnish Meteorological Institute.

Earth's radiation belts are regions in near-Earth space that contain vast quantities of solar energetic electrons, trapped there by Earth's magnetic field. During magnetic storms, which are solar wind-driven, the electrons accelerate to high speeds and enter the atmosphere in the polar regions. In the atmosphere, the electrons ionize gas molecules, leading to the production of ozone-depleting catalyst gases. Based on currently available satellite observations, electron precipitation may, during solar storms lasting a few days, reduce ozone in the upper atmosphere (60-80 km) as much as 90 per cent on a momentary basis.

Source: Finnish Meteorological Institute

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