Solar Photosphere: Hot explosions on the cool sun

Sizzling star: Hot explosions in an active region of the Sun. 

In this image of the photosphere that was obtained at the end of September 2013 with the help of IRIS, the explosions are the bright spots. 

The image shows a sector with a size of 50,000 kilometers by 25 000 kilometers. 

Credit: NASA

The Sun is more spirited than previously thought. Apart from the solar eruptions, huge bursts of particles and radiation from the outer atmosphere of our star, also the cooler layer right below can be the site of explosions: in some areas magnetic energy builds up and discharges within only a few minutes in temperature eruptions of up to 100000 degrees.

Researchers under the lead of the Max Planck Institute for Solar System Research have now for the first time found evidence of such short-lived heat pockets in data from NASA's space telescope IRIS (Interface Region Imaging Spectrograph).

The Sun is an incredibly hot place, but even though in all its layers the temperatures are daunting, some are hotter than others.

With a temperature of approximately 5000 degrees, the Sun's visible surface, the photosphere, for example, is comparatively cool.

Going outward from there, the temperatures within the Sun's atmosphere rise, first moderately and then sharply, until they reach one million degrees.

"Our analysis shows, that this temperature distribution is not the same everywhere, and is constantly in motion", says Prof. Dr. Hardi Peter from the MPS, the paper's first author.

Together with an international team of scientists, Peter analyzed data from the space telescope IRIS taken from active regions on the Sun.

These regions within the photosphere are characterized by high magnetic field strengths and are the "birth places" of the dark sunspots, which cover the Sun's surface, at some times more, at others less abundantly.

"In these regions we found heat pockets as big as half of Germany. They are up to 20 times as hot as their surroundings", the astrophysicist describes. The heat pockets flash up for only minutes and then return to their normal state.

The amount of energy released during these explosions would be sufficient to provide all of Germany with electrical power for 8000 years.

The massive photospheric explosions cannot be spotted in visible light, but leave traces in the ultraviolet radiation the Sun emits into space.

IRIS can split this ultraviolet radiation into its constituting wavelengths more precisely than any other solar observatory before. In addition, it offers an unprecedented spatial resolution.

When IRIS opened its eyes to the Sun for the first time in July of last year, it could discern structures with a size of only 250 kilometers and examine radiation from such small regions separately.

"To our great surprise, we found well-defined areas within the active regions emitting radiation quite unlike the radiation from their vicinity", says Peter.

The researchers discovered characteristic wavelengths that special highly ionized atoms within the solar plasma such as triply ionized silicon ions emit into space.

"The presence of these wavelengths within the spectra points to very high temperatures", says Peter.

Only under such conditions can silicon loose three of its electrons, but in which of the Sun's layers did this temperature arise? Truly within the cool photosphere? Or maybe, and this would be much less spectacular, farther outside in the much hotter atmosphere?

The spectral data from IRIS proved to be so detailed that the researchers could extract further decisive clues.

For example, they were able to infer the density of the solar plasma where the radiation originated. In addition, they showed that the radiation had encountered singly-ionized iron ions on its way outward. These ions occur only in cooler regions.

"All in all, we found a coherent picture: the unusual radiation must originate in the cool outer photosphere" says Peter.

The researchers believe that the strong magnetic fields in the photosphere provide the necessary energy for the explosions.

In the area of the sun spots, the magnetic field lines protrude in a loop-like fashion from the Sun's surface; hot plasma flows there. When these flows are short-circuited, the explosions occur.

"The new results have fundamentally changed our understanding of the Sun's outer buildup", says Peter. "Instead of a stable temperature distribution, there are apparently dynamical processes within the cool photosphere that can turn everything topsy turvy."

Already in 1917, the American physicist Ferdinand Ellermann discovered areas with higher temperatures within the photosphere.

However, they differed from their surroundings only by a few thousand degrees and can therefore be considered rather minor temperature deviations. Whether the newly discovered explosions are linked to this phenomenon, is still unclear.

One of the other publications in Science magazine, to which scientists from the MPS have contributed, also paints a new picture of the processes on the Sun.

Researchers under the lead of the Harvard-Smithsonian Center for Astrophysics found that the solar wind, the continuous stream of particles from the Sun, does not leave the Sun's surface uniformly, but locally in highly energetic jets. These observations, too, are based on data from IRIS.

More information: 
H. Peter et al. "Hot Explosions in the Cool Atmosphere of the Sun." Science, 17 October 2014 - DOI: 10.1126/science.1255726

H. Tian et al. "Prevalence of Small-scale Jets from the Networks of the Solar Transition Region and Chromosphere." Science, 17 October 2014 - DOI: 10.1126/science.1255732

NASA SDO: IRIS captures New information about sun's atmosphere

NASA’s Solar Dynamics Observatory provided the outer image of a coronal mass ejection on May 9, 2014. 

The IRIS mission views the interface region that lies between the sun’s photosphere and corona in unprecedented detail for researchers to study.

Credit: NASA, Lockheed Martin Solar & Astrophysics Laboratory

NASA's Interface Region Imaging Spectrograph (IRIS) has provided scientists with five new findings into how the sun's atmosphere, or corona, is heated far hotter than its surface, what causes the sun's constant outflow of particles called the solar wind, and what mechanisms accelerate particles that power solar flares.

The new information will help researchers better understand how our nearest star transfers energy through its atmosphere and track the dynamic solar activity that can impact technological infrastructure in space and on Earth.

Details of the findings appear in the current edition of Science "On the prevalence of small-scale twist in the solar chromosphere and transition region"DOI: 10.1126/science.1255732

"These findings reveal a region of the sun more complicated than previously thought," said Jeff Newmark, interim director for the Heliophysics Division at NASA Headquarters in Washington.

"Combining IRIS data with observations from other Heliophysics missions is enabling breakthroughs in our understanding of the sun and its interactions with the solar system."

The first result identified heat pockets of 200,000 degrees Fahrenheit, lower in the solar atmosphere than ever observed by previous spacecraft.

Scientists refer to the pockets as solar heat bombs because of the amount of energy they release in such a short time.

Identifying such sources of unexpected heat can offer deeper understanding of the heating mechanisms throughout the solar atmosphere.

For its second finding, IRIS observed numerous, small, low lying loops of solar material in the interface region for the first time.

The unprecedented resolution provided by IRIS will enable scientists to better understand how the solar atmosphere is energized.

A surprise to researchers was the third finding of IRIS observations showing structures resembling mini-tornadoes occurring in solar active regions for the first time.

These tornadoes move at speeds as fast as 12 miles per second and are scattered throughout the chromosphere, or the layer of the sun in the interface region just above the surface.

These tornados provide a mechanism for transferring energy to power the million-degree temperatures in the corona.

Another finding uncovers evidence of high-speed jets at the root of the solar wind. The jets are fountains of plasma that shoot out of coronal holes, areas of less dense material in the solar atmosphere and are typically thought to be a source of the solar wind.

The final result highlights the effects of nanoflares throughout the corona. Large solar flares are initiated by a mechanism called magnetic reconnection, whereby magnetic field lines cross and explosively realign.

These often send particles out into space at nearly the speed of light. Nanoflares are smaller versions that have long been thought to drive coronal heating.

IRIS observations show high energy particles generated by individual nanoflare events impacting the chromosphere for the first time.

"This research really delivers on the promise of IRIS, which has been looking at a region of the sun with a level of detail that has never been done before," said De Pontieu, IRIS science lead at Lockheed Martin in Palo Alto, California.

"The results focus on a lot of things that have been puzzling for a long time and they also offer some complete surprises."

More Information
Science "On the prevalence of small-scale twist in the solar chromosphere and transition region"DOI: 10.1126/science.1255732

Most Water in Lunar Soil generated by Solar Wind

This is a composite image of the lunar nearside taken by the Lunar Reconnaissance Orbiter in June 2009, note the presence of dark areas of maria on this side of the moon. Credit: NASA

A pair of researchers with the Sorbonne Universités, Muséum National d'Histoire Naturelle, has determined that most of the water in the soil on the surface of the moon was formed due to protons in the solar wind colliding with oxygen in lunar dust, rather than from comet or meteorite impacts.

In their paper published in Proceedings of the National Academy of Sciences, Alice Stephant and François Robert describe their study and the results they found.

When NASA astronauts brought back soil and rock samples from the moon, it was assumed by most in the scientific community that everything they found was dry, that there was no water in any of it.

Subsequent analysis using newer techniques has revealed that not only is there water beneath the surface in some places, but the dust on the surface also has small amounts as well.

Once this became known, most scientists assumed the water got there due to comet or meteorite impacts, in this new effort, the research pair suggests that conventional thinking is wrong once again and that the water, at least in the surface dust, comes about due to the impact of solar wind on tiny dust particles.

In studying tiny grains of lunar soil samples, the researchers found that the reduction of oxygen from silicates in the soil by protons from the solar wind was almost certainly the means by which the water was generated.

They came to that conclusion through determining the lithium isotope ratio in the samples (plagioclase rock found on the surface of the moon) which gave the isotope ratio for the hydrogen, from that they were able to calculate the deuterium-hydrogen ratio which they compared to the amount of water actually in the granule sample.

They found that on average, the granules contained just 15 percent water from somewhere else (presumably comets or meteorites) leaving the rest to have been formed due to the solar wind interaction. They note also that for some samples, all of the water was due to solar wind interaction.

The duo is quick to point out that their conclusions only relate to water found on the surface of the moon, where the water below the surface came from is still up for conjecture.

More information: "The negligible chondritic contribution in the lunar soils water" - Alice Stephant, PNAS, DOI: 10.1073/pnas.1408118111

The latest observations of interstellar particles

Credit: NASA /Goddard /Adler /U. Chicago /Wesleyan

With all the news about Voyager 1 leaving the heliosphere and entering interstellar space you might think that the probe is the first spacecraft to detect interstellar particles.

That isn't entirely true, and the latest observations of interstellar particles has found some very interesting results.

The heliosphere is generated by the Sun's solar wind, a stream of charged (ionized) particles that flows outward from the Sun.

The solar wind interacts with the magnetic field of the sun, and together they create a kind of diffuse bubble of charged particles around the sun known as the heliosphere.

While this heliosphere prevents any interstellar charged particles from reaching us, it is less effective at preventing uncharged interstellar particles from reaching us.

Most of the interstellar wind is ionized like the solar wind, but there are some neutral particles (mostly hydrogen) that moves with the interstellar wind.

Since neutral particles don't interact strongly with the Sun's magnetic field, some of them can slip into the heliosphere, where we can detect them.

This neutral hydrogen comes from the local cloud, seen below, a very tenuous cloud of hydrogen that surrounds our stellar region.

The motion of this hydrogen relative to the Sun depends on the Sun's motion through the cloud and the motion of the cloud itself.

The Sun's motion through the galaxy is quite steady, and it was thought that the cloud's motion was also steady, but long term observations of the hydrogen flow through our solar system has found this is not the case.

In a recent paper in Science researchers compared hydrogen flow measurements from the IBEX satellite (taken during 2009-2010) with observations from Ulysses (1992-2002) and other observations (1972-1978).

What they found was that over the course of 30 years the direction has changed by about 6 degrees.

This may seem like a slow and gradual change, but on a cosmic scale it is huge. The local cloud is about 30 light years across, and the Sun moves through it at a speed of (only) about 50,000 mph (22 km/sec).

While variations in the hydrogen flow are expected as it interacts with variations in the solar wind, those variations average out.

Observing such a rapid change in flow (on a cosmic scale) means either there is turbulent flow within the cloud itself, or the interstellar wind is more dynamic than originally thought.

We've long known that the solar wind is quite dynamic due to the Sun's activity. Now we're finding the interstellar wind may be active as

More information: "Decades-long changes of the interstellar wind through our solar system." Frisch PC, et al. Science. 2013 Sep 6;341(6150):1080-2. DOI: 10.1126/science.1239925

Voyager 1 spacecraft might not have reached interstellar space

The heliosphere, in which the Sun and planets reside, is a large bubble inflated from the inside by the high-speed solar wind blowing out from the Sun. 

Pressure from the solar wind, along with pressure from the surrounding interstellar medium, determines the size and shape of the heliosphere. 

The supersonic flow of solar wind abruptly slows at the termination shock, the innermost boundary of the solar system. 

The edge of the solar system is the heliopause. 

The bow shock pushes ahead through the interstellar medium as the heliosphere plows through the galaxy. 

Credit: Southwest Research Institute

In 2012, the Voyager mission team announced that the Voyager 1 spacecraft had passed into interstellar space, traveling further from Earth than any other manmade object.

But, in the nearly two years since that historic announcement, and despite subsequent observations backing it up, uncertainty about whether Voyager 1 really crossed the threshold continues.

There are some scientists who say that the spacecraft is still within the heliosphere, the region of space dominated by the Sun and its wind of energetic particles, and has not yet reached the space between the stars.

Now, two Voyager team scientists have developed a test that they say could prove once and for all if Voyager 1 has crossed the boundary.

The new test is outlined in a study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union (AGU).

The scientists predict that, in the next two years, Voyager 1 will cross the current sheet, the sprawling surface within the heliosphere where the polarity of the sun's magnetic field changes from plus to minus.

The spacecraft will detect a reversal in the magnetic field, proving that it is still within the heliosphere but, if the magnetic field reversal doesn't happen in the next year or two as expected, that is confirmation that Voyager 1 has already passed into interstellar space.

"The proof is in the pudding," said George Gloeckler, a professor in atmospheric, oceanic and space sciences at the University of Michigan in Ann Arbor and lead author of the new study.

Gloeckler has worked on the Voyager mission since 1972 and has been a vocal opponent of the view that Voyager 1 has entered interstellar space.

He said that, although the spacecraft has observed many of the signs indicating it may have reached interstellar space, like cosmic rays, Voyager 1 did not see a change in magnetic field that many were expecting.

"This controversy will continue until it is resolved by measurements," Gloeckler said.

This artist’s concept shows the Voyager 1 spacecraft entering the space between stars. 

The Voyager mission team announced in 2012 that the Voyager 1 spacecraft had passed into interstellar space, but some scientists say it is still within the heliosphere, the region of space domininated by the Sun and its wind of energetic particles. 

In a new study, two Voyager team scientists are proposing a test that they say could prove once and for all of Voyager 1 has crossed the boundary. 

Credit: NASA/JPL-Caltech

If the new prediction is right, "this will be the highlight of my life," he said. "There is nothing more gratifying than when you have a vision or an idea and you make a prediction and it comes true."

The Voyager 1 and 2 spacecraft were launched in 1977 to study Jupiter and Saturn. The mission has since been extended to explore the outermost limits of the Sun's influence and beyond.

Voyager 2, which also flew by Uranus and Neptune, is on its way to interstellar space.

More information: Geophysical Research Letters DOI: 10.1002/2014GL060781

MAVEN: Mars atmosphere could give clues to its past water loss - Video

NASA's Mars MAVEN mission (arriving 21 September 2014) will detect and measure how the solar wind interacts with the Red Planet’s atmosphere, giving clues to where its water went and why.

Credit: NASA / GSFC

Supercomputers capture turbulence in the solar wind

Solar storms unleash bursts of radiation that can reach crew and passengers on commercial flights at certain altitudes and latitudes. 

Eventually the system could be used to log radiation exposure over longer periods of time for pilots and flight crews. 

Credit: NASA

As inhabitants of Earth, our lives are dominated by weather.

Not just in the form of rain and snow from atmospheric clouds, but also a sea of charged particles and magnetic fields generated by a star sitting 93 million miles away—our Sun.

This phenomenon is called solar wind.

When strong magnetic storms occur on the Sun, tons of highly energetic particles are released into the solar wind.

If these particles were free to hit the Earth, the radiation would cause life-threatening damage to our DNA, debilitate power grids, disrupt communications networks and damage electronic devices.

Fortunately for us, the Earth's magnetic dipole field and magnetosphere act as an invisible shield barring these particles from plummeting through the atmosphere.

However, this magnetic shield is not perfect and during particularly intense solar storms the magnetosphere can "crack," allowing charged particles to seep in and wreak havoc on the Earth's technological infrastructure—an event calledspace weather.

Homa Karimabadi

Scientists currently do not have the ability to accurately predict the severity of a space weather event or where it will have the most impact but a team of researchers led by University of California, San Diego's (UCSD's) Homa Karimabadi is hoping to change that.

"One of the challenges in developing accurate predictive forecasts is that the solar wind is turbulent, and the details of turbulence are not well understood," says Karimabadi, who heads the space plasma simulation group at UCSD.

Because turbulence in the solar wind occurs on widely different scales of physics—from planet-size to the sub-atomic—it is especially difficult to study but using supercomputers at the National Institute of Computational Sciences (NICS), Karimabadi and his colleagues managed to simulate all the scales of solar wind turbulence at once—for the first time ever.

Burlen Loring

To make sense of this massive dataset, they tapped Lawrence Berkeley National Laboratory (Berkeley Lab) Visualization Specialist Burlen Loring, who developed custom analysis tools using supercomputers at the National Energy Research Scientific Computing Center (NERSC).

Loring's work allows researchers to study turbulence in unprecedented detail, and the results may hold clues about some of the processes that lead to destructive space weather events. This work was published in Physics of Plasmas.

More information: Read the paper: hpcvis.com/PhysPlasmas_20_012303.pdf

NASA WIND Spacecraft captures image of Magnetosphere

A complex system of charged particles from the Sun and magnetic structures piles up in front of the Earth. 

Scientists now hope to better understand this area in front of the Bow shock, known as the foreshock, as it can help explain how energy from the rest of space makes its way into the magnetosphere.

Earth is seen as a tiny speck surrounded by an enormous magnetic 'bubble' surging through space in this image released by Nasa.

Far from the usual view of a blue and green globe spinning peacefully in the solar system, the dramatic picture illustrates the speed and energy of the magnetosphere that surrounds Earth as it moves around the sun.

Scientists studying data collected by Nasa's WIND spacecraft have used it to create a more detailed snapshot of the way solar particles streaming in from the sun bounce off the bubble.

Nasa researchers have been examining data from WIND - which travelled through the region at the boundary of the magnetosphere 17 times between 1998 and 2002 - to find out more about the 'dramatic' changing conditions within the complex, turbulent system called the foreshock.

As the magnetosphere ploughs through space, it sets up a standing bow wave or bow shock - much like that in front of a moving ship. The foreshock lies just in front of this bow wave.

Conditions in the foreshock change in response to solar particles streaming in from the sun, moving magnetic fields and a host of waves sweeping through the region, according to Nasa.

Lynn Wilson, deputy project scientist for Wind at Nasa's Goddard Space Flight Center in Greenbelt, Maryland, explained how 'cool squiggles' she stumbled upon in the data 'turned out to be a special kind of magnetic pulsations called short large amplitude magnetic structures, which we call SLAMS for short'.

Studying the region around these 'rogue waves' and how they propagate may help to establish what accelerates narrow jets of charged particles back out into space and away from Earth.

David Sibeck

David Sibeck, a space scientist at Goddard who is co-author of the paper, explained how space weather events that seem small can have 'profound effects downstream', from affecting GPS satellites to prompting solar storms.

'The front of the magnetosphere is right in the line between sun and Earth, so it's a crucial place to understand which small things can lead to big results,' he said.

'What happens to Earth's magnetic field depends on what's happening here at the front of the bow shock and what's happening there is dramatic.

'It's going to affect how much energy moves into the magnetosphere. Once inside the magnetosphere, it can create powerful solar storms and impact communications and GPS satellites that we depend on daily.'

According to Nasa: 'The more we know about what happens in the frothy, turbulent area in front of Earth, the more we know about how the solar wind and other material bursting off the sun may be able to penetrate into near Earth-space.'

ESA Venus Express: Venus's Tail in the Solar Wind

A comparison of the ionosphere of Venus under different solar wind conditions. 

Credit: ESA/Wei et al. (2012).

Measurements obtained with ESA's Venus Express spacecraft have shed new light on the interaction between the solar wind and the second planet from the Sun.

During a rare period of very low density solar outflow, the ionosphere of Venus was observed to become elongated downstream, rather like a long-tailed comet.

Scientists have long known about the existence of the solar wind, a continuous outflow of electrons and protons which flows at high speed across interplanetary space. However, this stream of charged particles is highly variable, both in speed and density.

Under normal conditions, the solar wind has a density of 5 - 10 particles per cubic cm at Earth's orbit, but occasionally the solar wind almost disappears, as happened in May 1999.

Although such unusual episodes have been studied near Earth, which is surrounded by a strong magnetic field, there have been very few opportunities to study what happens near planets with negligible magnetic fields, such as Venus.

A rare opportunity to examine what happens when a tenuous solar wind arrives at Venus came 3 - 4 August 2010, following a series of large coronal mass ejections on the Sun.

NASA's STEREO-B spacecraft, orbiting downstream from Venus, observed that the solar wind density at Earth's orbit dropped to the remarkably low figure of 0.1 particles per cubic cm and persisted at this value for an entire day.

Meanwhile, Venus Express, which is in an extremely elliptical, near-polar orbit, was able to study the interaction between this sparse solar wind and the planet's ionosphere - the electrically charged region of its upper atmosphere.

The ionosphere is created by incoming extreme ultraviolet light and X-rays from the Sun which splits the atoms in the upper atmosphere of Venus and creates a layer of electrons and ions.

Moon Water: Scientists Consider Solar Wind as Origin

Glass beads within moon rocks suggest that water seen on the lunar surface originates from the solar wind, researchers say.

These findings suggest that other airless bodies in the solar system may also possess water on their surfaces, investigators added.

Arguments raged for years as to whether the moon harboured frozen water or not.

Recent findings confirmed that water does wet the moon, although its surface remains drier than any desert on Earth.

"With the cost of $25,000 for taking one pint of water to the moon, it is essential that we develop processes of producing water from the materials on the moon," said the study's lead author, Yang Liu, at the University of Tennessee at Knoxville. "This is paramount to human settlement of the moon in the near future."

"This water would be of most value as rocket fuel — liquid hydrogen and liquid oxygen," Liu added.

"Until the recent discovery of water in and on the moon, this was going to be a very energy-intensive endeavor to separate these elements from the lunar rocks and soil."

"Now we have ready sources of water that can be consumed by plants and humans, but also broken up into its constituent elements — oxygen and hydrogen. Thus, we could use the moon as a jump-board for missions to Mars and beyond."

Signs Changing Fast: Voyager at Solar System Edge

Voyager 1, which launched on Sept. 5, 1977, is 11 billion miles (18 billion kilometers) from the sun. Voyager 2, which launched on Aug. 20, 1977, is close behind, at 9.3 billion miles (15 billion kilometers) from the sun.

Two of three key signs of changes expected to occur at the boundary of interstellar space have changed faster than at any other time in the last seven years, according to new data from NASA's Voyager 1 spacecraft.

For the last seven years, Voyager 1 has been exploring the outer layer of the bubble of charged particles the sun blows around itself. In one day, on July 28, data from Voyager 1's cosmic ray instrument showed the level of high-energy cosmic rays originating from outside our solar system jumped by five percent.

During the last half of that same day, the level of lower-energy particles originating from inside our solar system dropped by half. However, in three days, the levels had recovered to near their previous levels.

A third key sign is the direction of the magnetic field, and scientists are eagerly analyzing the data to see whether that has, indeed, changed direction. Scientists expect that all three of these signs will have changed when Voyager 1 has crossed into interstellar space. A preliminary analysis of the latest magnetic field data is expected to be available in the next month.

"These are thrilling times for the Voyager team as we try to understand the quickening pace of changes as Voyager 1 approaches the edge of interstellar space," said Edward Stone, the Voyager project scientist based at the California Institute of Technology, Pasadena, Calif.

"We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space."

The levels of high-energy cosmic ray particles have been increasing for years, but more slowly than they are now. The last jump - of five percent - took one week in May. The levels of lower-energy particles from inside our solar system have been slowly decreasing for the last two years.

Scientists expect that the lower-energy particles will drop close to zero when Voyager 1 finally crosses into interstellar space.

"The increase and the decrease are sharper than we've seen before, but that's also what we said about the May data," Stone said. "The data are changing in ways that we didn't expect, but Voyager has always surprised us with new discoveries."

Voyager 1, which launched on Sept. 5, 1977, is 11 billion miles (18 billion kilometers) from the sun. Voyager 2, which launched on Aug. 20, 1977, is close behind, at 9.3 billion miles (15 billion kilometers) from the sun.

"Our two veteran Voyager spacecraft are hale and healthy as they near the 35th anniversary of their launch," said Suzanne Dodd, Voyager project manager based at NASA's Jet Propulsion Laboratory, Pasadena. "We know they will cross into interstellar space. It's just a question of when."

Electric Moon Jolts the Solar Wind

With the moon as the most prominent object in the night sky and a major source of an invisible pull that creates ocean tides, many ancient cultures thought it could also affect our health or state of mind – the word “lunacy” has its origin in this belief.

Now, a powerful combination of spacecraft and computer simulations is revealing that the moon does indeed have a far-reaching, invisible influence – not on us, but on the Sun, or more specifically, the solar wind.

The solar wind is a thin stream of electrically conducting gas called plasma that’s constantly blown off the surface of the Sun in all directions at around a million miles per hour.

When a particularly fast, dense or turbulent solar wind strikes Earth’s magnetic field, it can generate magnetic and radiation storms that are capable of disrupting satellites, power grids, and communication systems.

The magnetic “bubble” surrounding Earth also pushes back on the solar wind, creating a bow shock tens of thousands of miles across over the day side of Earth where the solar wind slams into the magnetic field and abruptly slows from supersonic to subsonic speed.

Unlike Earth, the moon is not surrounded by a global magnetic field. “It was thought that the solar wind crashes into the lunar surface without any warning or ‘push back’ on the solar wind,” says Dr. Andrew Poppe of the University of California, Berkeley.

Recently, however, an international fleet of lunar-orbiting spacecraft has detected signs of the moon’s presence “upstream” in the solar wind. “We’ve seen electron beams and ion fountains over the moon’s day side,” says Dr. Jasper Halekas, also of the University of California, Berkeley.

These phenomena have been seen as far as 10,000 kilometers (6,214 miles) above the moon and generate a kind of turbulence in the solar wind ahead of the moon, causing subtle changes in the solar wind’s direction and density.

The electron beams were first seen by NASA’s Lunar Prospector mission, while the Japanese Kaguya mission, the Chinese Chang’e mission, and the Indian Chandrayaan mission all saw ion plumes at low altitudes.

NASA’s ARTEMIS mission has now also seen both the electron beams and the ion plumes, plus newly identified electromagnetic and electrostatic waves in the plasma ahead of the moon, at much greater distances from the moon.

“With ARTEMIS, we can see the plasma ring and wiggle a bit, surprisingly far away from the moon,” says Halekas. ARTEMIS stands for “Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun”.

“An upstream turbulent region called the ‘foreshock’ has long been known to exist ahead of the Earth’s bow shock, but the discovery of a similar turbulent layer at the moon is a surprise,” said Dr. William Farrell of NASA’s Goddard Space Flight Center in Greenbelt, Md. Farrell is lead of the NASA Lunar Science Institute’s Dynamic Response of the Environment At the Moon (DREAM) lunar science center, which contributed to the research.

Computer simulations help explain these observations by showing that a complex electric field near the lunar surface is generated by sunlight and the flow of the solar wind.

The simulation reveals this electric field can generate electron beams by accelerating electrons blasted from surface material by solar ultraviolet light.

Also, related simulations show that when ions in the solar wind collide with ancient, “fossil” magnetic fields in certain areas on the lunar surface, they are reflected back into space in a diffuse, fountain-shaped pattern.

These ions are mostly the positively charged ions (protons) of hydrogen atoms, the most common element in the solar wind.

NASA MARS HiRise Image: The Serpent Dust Devil

A towering dust devil casts a serpentine shadow over the Martian surface in this image acquired by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.

The scene is a late-spring afternoon in the Amazonis Planitia region of northern Mars.

The view covers an area about four-tenths of a mile (644 meters) across. North is toward the top.

The length of the dusty whirlwind's shadow indicates that the dust plume reaches more than half a mile (800 meters) in height. The plume is about 30 yards or meters in diameter.

A westerly breeze partway up the height of the dust devil produced a delicate arc in the plume. The image was taken during the time of Martian year when the planet is farthest from the sun.

Just as on Earth, winds on Mars are powered by solar heating. Exposure to the sun's rays declines during this season, yet even now, dust devils act relentlessly to clean the surface of freshly deposited dust, a little at a time.

This view is one product from an observation made by HiRISE on Feb. 16, 2012, at 35.8 degrees north latitude, 207 degrees east longitude.

Other image products from the same observation are at http://www.uahirise.org/ESP_026051_2160 .

NASA Messenger: Mercury's magnetic field counteracted by Solar wind

The Messenger space probe - which took this image - has confirmed that the innermost planet has a magnetic field 150 times weaker than that of Earth. Researchers have now found an explanation for this. 

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mercury, the smallest of the eight planets with a diameter of 4900 kilometres and the closest to the Sun, looks more like the Moon than the Earth from the outside.

It is the only rocky planet that has a global magnetic field like Earth. But why is its magnetic field so much weaker than Earth’s?

Scientists at the Technische Universität Braunschweig and the Max Planck Institute for Solar System Research have now presented a new explanation: the solar wind counteracts Mercury’s internal dynamo and thus weakens its magnetic field.

Planetary magnetic fields are generated by flows in the hot, liquid iron cores of the planets.

Measurements made by Mariner 10 in 1974/75 showed that Mercury also has a magnetic field. According to the standard models, the dynamo effect in its metal core should generate similar field strengths to those on Earth.

Mercury’s magnetic field is 150 times weaker than that of our planet, however. This has recently been confirmed by the Nasa space probe Messenger.

How can the large discrepancy in the field strength be explained? This question has now been answered by a group headed by Karl-Heinz Glassmeier at the Technische Universität Braunschweig.

The solar wind – a constant stream of charged particles – plays a significant role. At an average distance from the Sun of only 58 million kilometres – around one third of the distance of the Earth – Mercury is much more exposed to these particles.

“We must keep in mind that Mercury stongly interacts with the surrounding solar wind,” says Daniel Heyner, lead author of the article published in Science and doctoral student at the International Max Planck Research School (IMPRS) in Katlenburg-Lindau.

This interaction drives strong electrical currents in the magnetosphere of the planet, whose magnetic fields counteract the internal dynamo effect.

The team’s new computer models show that a dynamo with this type of feedback is actually possible.

“These types of simulation of the dynamo process are the only possibility to sort of look into the iron core and to predict the strength and structure of the magnetic field,” says Johannes Wicht from the Max Planck Institute for Solar System Research, whose model made a significant contribution to the study.

The results show unambiguously that the feedback ultimately causes the weak magnetic field. “The dynamo process in Mercury’s interior is almost nipped in the bud by the interaction,” explains Glassmeier.

The researchers at the TU Braunschweig and the Max Planck Institute for Solar System Research are eagerly awaiting the next magnetic field measurements from the Messenger space probe and the observations of the two satellites of the European-Japanese mission BepiColombo.

The mission will carry an instrument developed by the TU Braunschweig. Starting in 2020 the researchers want to measure Mercury’s magnetic field with great precision.

The new data should allow the confirmation of this fascinating new idea of a dynamo weakened by the solar wind.


More information: Daniel Heyner, Johannes Wicht, Natalia Gómez-Pérez, Dieter Schmitt, Hans-Ulrich Auster, Karl-Heinz Glassmeier, Evidence from Numerical Experiments for a Feedback Dynamo Generating Mercury’s Magnetic Field, Science, 23 December 2011. DOI: 10.1126/science.120729

Lunar Ionosphere: Our Mysterious Moon

How can a world without air have an ionosphere? Somehow the Moon has done it.

Lunar researchers have been struggling with the mystery for years, and they may have finally found a solution. But first, what is an ionosphere?

Every terrestrial planet with an atmosphere has one. High above the planet's rocky surface where the atmosphere meets the vacuum of space, ultraviolet rays from the sun break apart atoms of air. This creates a layer of ionized gas--an "ionosphere."

Here on Earth, the ionosphere has a big impact on communications and navigation. For instance, it reflects radio waves, allowing shortwave radio operators to bounce transmissions over the horizon for long-range communications. The ionosphere also bends and scatters signals from GPS satellites, sometimes causing your GPS tracker to mis-read your position.

The first convincing evidence for an ionosphere around the Moon came in the 1970s from the Soviet probes Luna 19 and 22. Circling the Moon at close range, the orbiters sensed a layer of charged material extending a few tens of km above the lunar surface containing as many as 1000 electrons per cubic centimeter-a thousand times more than any theory could explain.

Radio astronomers also found hints of the lunar ionosphere when distant radio sources passed behind the Moon's limb.

The idea of an "airless Moon" having an ionosphere didn't make much sense, but the evidence seemed compelling.

As a matter of fact, the Moon isn't quite as airless as most people think. Small amounts of gas created by radioactive decay seep out of the lunar interior; meteoroids and the solar wind also blast atoms off the Moon's surface.

The resulting shroud of gas is so thin, however, that many researchers refuse to call it an atmosphere, preferring instead the term "exosphere."

The density of the lunar exosphere is about a hundred million billion times less than that of air on Earth-not enough to support an ionosphere as dense as the ones the Luna probes sensed.

For 40 years, the Moon's ionosphere remained a mystery until Tim Stubbs of the Goddard Space Flight Center published a possible solution earlier this year. The answer, he proposes, is moondust.

Stubbs--a 30-something scientist who wasn't even born when the Moon's ionosphere was discovered-read the accounts of Apollo 15 astronauts who reported seeing a strange glow over the Moon's horizon. Many researchers believe the astronauts were seeing moondust.

Solar wind is rhombic-shaped

The plasma beta represents the ratio of kinetic to magnetic pressure in the cosmic plasma. 

The anisotropy is the ratio of the perpendicular and parallel temperatures to the magnetic field lines. 

The number of measured values is shown in colour (red corresponds to many values, blue to few values). 

Why the measurements take on the characteristic rhombic shape is explained by a new model by Bochum's physicists. Source: Physical Review Letters.

Why the temperatures in the solar wind are almost the same in certain directions, and why different energy densities are practically identical, was until now not clear.

With a new approach to calculating instability criteria for plasmas, Bochum researchers lead by Prof. Dr. Reinhard Schlickeiser (Chair for Theoretical Physics IV) have solved both problems at once. They were the first to incorporate the effects of collisions of the solar wind particles in their model.

This explains experimental data significantly better than previous calculations and can also be transferred to cosmic plasmas outside our solar system. The scientists report on their findings in Physical Review Letters.

Temperatures and pressures in the cosmic plasma
The solar wind consists of charged particles and is permeated by a magnetic field. In the analysis of this plasma, researchers investigate two types of pressure: the magnetic pressure describes the tendency of the magnetic field lines to repel each other, the kinetic pressure results from the momentum of the particles.

The ratio of kinetic to magnetic pressure is called plasma beta and is a measure of whether more energy per volume is stored in magnetic fields or in particle motion.

In many cosmic sources, the plasma beta is around the value one, which is the same as energy equipartition. Moreover, in cosmic plasmas near temperature isotropy prevails, i.e. the temperature parallel and perpendicular to the magnetic field lines of the plasma is the same.

Explaining satellite data
For over a decade, the instruments of the near-earth WIND satellite have gathered various solar wind data. When the plasma beta measured is plotted against the temperature anisotropy (the ratio of the perpendicular to the parallel temperature), the data points form a rhombic area around the value one.

"If the values move out of the rhombic configuration, the plasma is unstable and the temperature anisotropy and the plasma beta quickly return to the stable region within the rhombus" says Prof. Schlickeiser.

However, a specific, detailed explanation of this rhombic shape has, until now, been lacking, especially for low plasma beta.

ESA Venus Express: Earth’s twin planet?

Mars, Earth and Venus are immersed in a flow of plasma, an ionised and highly variable gas originating from the Sun, called the solar wind.

While Earth has a planetary magnetic field, which can deviate the flow of solar wind, Venus (and Mars) don’t.

Gases in the upper atmospheres of these planets are ionised and can thus interact with the solar wind.

Venus is as large as Earth and it is difficult for its atmosphere to escape due to the planet’s gravity.

The solar wind is the best source of energy to accelerate the upper atmosphere’s charged particles, giving them enough energy to escape. This is why Venus loses its atmosphere due to interaction with the solar wind.

To understand this phenomenon, the key questions that the instruments studying plasma on Venus Express must answer are: what and how much of the atmosphere is lost, and where is it lost?

Right now, solar activity is at its minimum in the 11-year cycle, making the solar wind weaker than average. The critical question now is how solar wind interacts with Venus when solar activity is low.

 The magnetometer (MAG) on board ESA’s Venus Express detected wave signals that show evidence of lightning in the atmosphere.

Credits: ESA (Animation by C. Carreau)

Extreme Space Weather at Mercury Blasts the Planet's Poles

The solar wind sandblasts the surface of planet Mercury at its poles, according to new data from a University of Michigan instrument on board NASA's MESSENGER spacecraft.

The sodium and oxygen particles the blistering solar wind kicks up are the primary components of Mercury's wispy atmosphere, or "exosphere," the new findings assert.

Through interacting with the solar wind, they become charged in a mechanism that's similar to the one that generates the Aurora Borealis on Earth.

The findings are published in the Sept. 30 edition of Science.

The Fast Imaging Plasma Spectrometer (FIPS,) made by U-M scientists, has taken the first global measurements of Mercury's exosphere and magnetosphere in an effort to better understand how the closest planet to the sun interacts with its fiery neighbor.

The measurements confirmed scientists' theories about the composition and source of the particles in Mercury's space environment.

"We had previously observed neutral sodium from ground observations, but up close we've discovered that charged sodium particles are concentrated near Mercury's polar regions where they are likely liberated by solar wind ion sputtering, effectively knocking sodium atoms off Mercury's surface," said FIPS project leader Thomas Zurbuchen, a professor in the Department of Atmospheric, Oceanic and Space Sciences and Aerospace Engineering at the U-M College of Engineering.

Earth and Mercury are the only two magnetized planets in the solar system, and as such, they can somewhat deflect the solar wind around them.

The solar wind is a squall of hot plasma, or charged particles, continuously emanating from the sun. Earth, which has a relatively strong magnetosphere, can shield itself from most of the solar wind. Mercury, which has a comparatively weak magnetosphere and is 2/3 closer to the sun, is a different story.

"Our results tell us is that Mercury's weak magnetosphere provides very little protection of the planet from the solar wind," Zurbuchen said.

Studying Mercury's magnetosphere and space environment helps scientists understand fundamental science about the sun.

Structures of the solar wind as it travels toward and impacts Earth

Newly reprocessed archival data from STEREO-A/SECCHI show details of the first Earth-directed coronal mass ejection (CME) of the STEREO mission, from inception on December 12, 2008, to Earth impact on December 15, 2008. 

New processing enables following the details of the CME with the wide-field heliospheric imager cameras, out to impact with the Earth 93 million miles from the Sun. 

Credit: SwRI/NASA.

Using data collected by NASA's STEREO spacecraft, researchers at Southwest Research Institute and the National Solar Observatory have developed the first detailed images of solar wind structures as plasma and other particles from a coronal mass ejection (CME) traveled 93 million miles and impacted Earth.

The images from a December 2008 CME event reveal an array of dynamic interactions as the solar wind, traveling at speeds up to a million miles per hour, shifts and changes on its three-day journey to Earth, guided by the magnetic field lines that spiral out from the Sun's surface.

Observed structures include the solar wind piling up at the leading edge of a CME, voids in the interior, long thread-like structures, and rear cusps.

Quiet periods show a magnetic disconnection phenomenon called a plasmoid, "puffs" that correlate with in-situ density fluctuations, and V-shaped structures centered on the current sheet - a heliospheric structure in which the polarity of the Sun's magnetic field changes from north to south.

"For the first time, we can see directly the larger scale structures that cause blips in the solar wind impacting our spacecraft and Earth," said SwRI's Dr. Craig DeForest, lead author of an Astrophysical Journal article released online yesterday.

"There is still a great deal to be learned from these data, but they are already changing the way we think about the solar wind."

"For 30 years," said co-author Dr. Tim Howard, also of SwRI, "we have been trying to understand basic anatomy of CMEs and magnetic clouds, and how they correspond to their source structures in the solar corona. By tracking these features through the image data we can establish what parts of a space weather storm came from which parts of the solar corona, and why."

The team used a combination of image processing techniques to generate the images over a distance of more than 1 AU (astronomical unit), overcoming the greatest challenge in heliospheric imaging, that of extracting faint signals amid far brighter foreground and background signals.

Small "blobs" of solar wind tracked by the team were more than 10 billion times fainter than the surface of the full Moon and 10 thousand times fainter than the starfield behind them.

"These data are like the first demonstration weather satellite images that revolutionized meteorology on Earth," said DeForest. "At a glance it is possible to see things from a satellite that cannot be extracted from the very best weather stations on the ground. But both types of data are required to understand how storms develop."

In particular, the new images reveal the shape and density of Jupiter-sized clouds of material in the so-called empty space between planets; in contrast, in-situ probes such as the WIND and ACE spacecraft reveal immense detail about the solar wind, at a single point in space.

Space Weather is predicting Auroras

Sky watchers should be alert for auroras when the solar wind arrives on August 22-24.

NOAA forecasters estimate a 35% to 50% chance of geomagnetic activity.

Aurora alerts: text, voice