NASA Mission Provides Its First Look at Martian Upper Atmosphere

Three views of an escaping atmosphere, obtained by MAVEN’s Imaging Ultraviolet Spectrograph. By observing all of the products of water and carbon dioxide breakdown, MAVEN's remote sensing team can characterize the processes that drive atmospheric loss on Mars.Image Credit: University of Colorado/NASA. Hi Res Image

NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has provided scientists their first look at a storm of energetic solar particles at Mars, produced unprecedented ultraviolet images of the tenuous oxygen, hydrogen, and carbon coronas surrounding the Red Planet, and yielded a comprehensive map of highly-variable ozone in the atmosphere underlying the coronas.

The spacecraft, which entered Mars' orbit Sept. 21, now is lowering its orbit and testing its instruments. MAVEN was launched to Mars in November 2013, to help solve the mystery of how the Red Planet lost most of its atmosphere.

"All the instruments are showing data quality that is better than anticipated at this early stage of the mission," said Bruce Jakosky, MAVEN Principal Investigator at the University of Colorado, Boulder. "All instruments have now been turned on -- although not yet fully checked out -- and are functioning nominally. It's turning out to be an easy and straightforward spacecraft to fly, at least so far. It really looks as if we're headed for an exciting science mission."

Solar energetic particles (SEPs) are streams of high-speed particles blasted from the sun during explosive solar activity like flares or coronal mass ejections (CMEs). Around Earth, SEP storms can damage the sensitive electronics on satellites. At Mars, they are thought to be one possible mechanism for driving atmospheric loss.

A solar flare on Sept. 26 produced a CME that was observed by NASA satellites on both sides of the sun. Computer models of the CME propagation predicted the disturbance and the accompanying SEPs would reach Mars on Sept. 29. MAVEN's Solar Energetic Particle instrument was able to observe the onset of the event that day.

"After traveling through interplanetary space, these energetic particles of mostly protons deposit their energy in the upper atmosphere of Mars," said SEP instrument lead Davin Larson of the Space Sciences Laboratory at the University of California, Berkeley. "A SEP event like this typically occurs every couple weeks. Once all the instruments are turned on, we expect to also be able to track the response of the upper atmosphere to them."

The hydrogen and oxygen coronas of Mars are the tenuous outer fringe of the planet's upper atmosphere, where the edge of the atmosphere meets space. In this region, atoms that were once a part of carbon dioxide or water molecules near the surface can escape to space. These molecules control the climate, so following them allows us to understand the history of Mars over the last four billion years and to track the change from a warm and wet climate to the cold, dry climate we see today. MAVEN observed the edges of the Martian atmosphere using the Imaging Ultraviolet Spectrograph (IUVS), which is sensitive to the sunlight reflected by these atoms.

"With these observations, MAVEN's IUVS has obtained the most complete picture of the extended Martian upper atmosphere ever made," said MAVEN Remote Sensing Team member Mike Chaffin of the University of Colorado, Boulder. "By measuring the extended upper atmosphere of the planet, MAVEN directly probes how these atoms escape to space. The observations support our current understanding that the upper atmosphere of Mars, when compared to Venus and Earth, is only tenuously bound by the Red Planet's weak gravity."

IUVS also created a map of the atmospheric ozone on Mars by detecting the absorption of ultraviolet sunlight by the molecule.

"With these maps we have the kind of complete and simultaneous coverage of Mars that is usually only possible for Earth," said MAVEN Remote Sensing Team member Justin Deighan of the University of Colorado, Boulder. "On Earth, ozone destruction by refrigerator CFCs is the cause of the polar ozone hole. On Mars, ozone is just as easily destroyed by the byproducts of water vapor breakdown by ultraviolet sunlight. Tracking the ozone lets us track the photochemical processes taking place in the Martian atmosphere. We'll be exploring this in more complete detail during MAVEN's primary science mission."

There will be about two weeks of additional instrument calibration and testing before MAVEN starts its primary science mission. This includes an end-to-end test to transmit data between NASA's Curiosity rover on the surface of Mars and Earth using the MAVEN mission's Electra telecommunications relay. The mission aims to start full science gathering in early to mid-November.

MAVEN's principal investigator is based at the University of Colorado's Laboratory for Atmospheric and Space Physics. The university provided two science instruments and leads science operations, as well as education and public outreach, for the mission. The University of California at Berkeley's Space Sciences Laboratory also provided four science instruments for the mission. NASA's Goddard Space Flight Center in Greenbelt, Maryland manages the MAVEN project and provided two science instruments for the mission.  Lockheed Martin built the spacecraft and is responsible for mission operations. NASA's Jet Propulsion Laboratory in Pasadena, California provides navigation and Deep Space Network support, as well as the Electra telecommunications relay hardware and operations.

For more about MAVEN, visit:  http://www.nasa.gov/maven

Dwayne Brown
Headquarters, Washington
202-358-1726
dwayne.c.brown@nasa.gov

Nancy Jones / Bill Steigerwald
Goddard Space Flight Center, Greenbelt, Md.
301-286-0039 / 301-286-5017
nancy.n.jones@nasa.gov / william.a.steigerwald@nasa.gov

Source:  NASA's Goddard Space Flight Center

How NASA Watches CMEs

Two main types of explosions occur on the sun: solar flares and coronal mass ejections. Unlike the energy and x-rays produced in a solar flare – which can reach Earth at the speed of light in eight minutes – coronal mass ejections are giant clouds of solar material that take one to three days to reach Earth. Once at Earth, these ejections, also called CMEs, can impact satellites in space or interfere with radio communications. During CME Week from Sept. 22 to 26, 2014, we explore different aspects of these giant eruptions that surge out from the star we live with.

Space weather models combined with real time observations help scientists track CMEs. These images were produced from a model known as ENLIL named after the Sumerian storm god. It shows the journey of a CME on March 5, 2013, as it moved toward Mars.  Image Credit: NASA/Goddard/SWRC/CCMC. Download video

A March 5, 2013, CME as seen by the Solar and Heliospheric Observatory. Combining the information gleaned from such imagery with state-of-the-art models helps scientists better understand how CMEs move toward, and affect, Earth. Image Credit: ESA/NASA/SOHO/Jhelioviewer 

Those who study Earth's weather have a luxury of data points to study. From thousands of weather stations measuring temperature and rainfall to satellites tracking storm fronts up in space, meteorologists can watch detailed maps of the weather as it sweeps across land or sea.

Compared to this, the study of space weather – including CMEs – is a much younger science, with far fewer observatories available. However, our resources have grown dramatically in the last decade: NASA currently flies 18 missions to study the sun's effects at Earth and on the entire solar system, a field known as heliophysics, and additionally launches numerous short-flight rockets for observations of solar impacts in and above Earth's atmosphere. Coupled with improved computer modeling, keeping an eye on – and getting a better understanding of – CMEs has taken a giant leap forward in the 21^st century.

"Over the past ten years, we have had a major breakthrough in understanding space weather," said Antti Pulkkinen a space weather scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "We can now track the basic properties of CMEs. When our solar observatories see a CME, we can tell what direction it's going in and how fast it's traveling."

Improved observations combined with improved models has led to hybrid descriptions of a CME, relying partially on computer simulations and partially on actual observations. NASA houses a collection of space weather models available for public access at the Community Coordinated Modeling Center at Goddard. Together with observations they can provide a holistic picture of any given CME.

For example, NASA's Solar and Terrestrial Relations Observatory, or STEREO, might see a CME erupt on the sun. When that imagery is combined with observations from the European Space Agency and NASA's Solar and Heliospheric Observatory, or SOHO, scientists can create a 3-dimensional picture of the giant cloud. Scientists then input this data into a model and then track how the CME unfolded and spread through space until it passed by NASA observatories closer to Earth. These observatories can directly measure the magnetic fields and speed of the CME as it passes by, as well as see how it affected Earth's own magnetic fields – the magnetosphere.

By gathering data from numerous observatories, scientists can create models and explore what-if scenarios about what would happen near Earth due to a given CME. Watch the video to learn more about what scientists can see in these models. Image Credit: NASA/Bridgman/Duberstein. Download video

Such information on the CME's entire path opens the door to understanding why any given characteristic of the CME near the sun might lead to a given effect near Earth. Each additional piece of the puzzle helps us better understand just what causes these giant eruptions -- and whether or not any particular CME could pose a hazard to astronauts as well as technology in space and on the ground.

Related Links
 

• More on CME Week    

• More on STEREO  

• More on SOHO 

• Other NASA Sun-Earth missions

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md.

Mapping the Journey of a Giant Coronal Mass Ejection

Two main types of explosions occur on the sun: solar flares and coronal mass ejections. Unlike the energy and X-rays produced in a solar flare – which can reach Earth at the speed of light in eight minutes – coronal mass ejections are giant clouds of solar material that take one to three days to reach Earth. Once at Earth, these ejections, also called CMEs, can impact satellites in space or interfere with radio communications. During CME Week from Sept. 22 to 26, 2014, we explore different aspects of these giant eruptions that surge out from our closest star.

Three NASA observatories work together to help scientists track the journey of a massive coronal mass ejection, or CME, in July 2012. Image Credit: NASA/SDO/STEREO/ESA/SOHO/Wiessinger. Download video

On July 23, 2012, a massive cloud of solar material erupted off the sun's right side, zooming out into space. It soon passed one of NASA's Solar Terrestrial Relations Observatory, or STEREO, spacecraft, which clocked the CME as traveling between 1,800 and 2,200 miles per second as it left the sun. This was the fastest CME ever observed by STEREO.

Two other observatories – NASA's Solar Dynamics Observatory and the joint European Space Agency/NASA Solar and Heliospheric Observatory -- witnessed the eruption as well. The July 2012 CME didn't move toward Earth, but watching an unusually strong CME like this gives scientists an opportunity to observe how these events originate and travel through space.

STEREO's unique viewpoint from the sides of the sun combined with the other two observatories watching from closer to Earth.Together they helped scientists create models of the entire July 2012 event. They learned that an earlier, smaller CME helped clear the path for the larger event, thus contributing to its unusual speed.

Such data helps advance our understanding of what causes CMEs and improves modeling of similar CMEs that could be Earth-directed.

Watch the movie to see how NASA's solar-observing missions worked together to track this CME.

Related Links 

• More on CME Week   

• More on the July 23, 2012 CME

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md.

Mid-Level Solar Flare Seen by NASA's SDO

NASA's Solar Dynamics Observatory captures images of the sun in many wavelengths of light at the same time, each of which is typically colorized in a different color. Each wavelength shows different aspects of the same event, as seen in these three images of a solar flare on March 12, 2014.Image Credit: NASA/SDO/Goddard Space Flight Center

A solar flare erupts on the far right side of the sun, in this image captured by NASA's Solar Dynamics Observatory. The flare peaked at 6:34 p.m. EDT on March 12, 2014. Image Credit: NASA/SDO/Goddard Space Flight Center

The sun emitted a mid-level solar flare, peaking at 6:34 p.m. EDT on March 12, 2014, and NASA's Solar Dynamics Observatory, or SDO, captured an image of it. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however -- when intense enough -- they can disturb the atmosphere in the layer where GPS and communications signals travel.

To see how this event may impact Earth, please visit NOAA's Space Weather Prediction Center at http://spaceweather.gov, the U.S. government's official source for space weather forecasts, alerts, watches and warnings.

This flare is classified as an M9.3 flare, just slightly weaker than the most intense flares, which are labeled X-class. The letters denote broad categories of strength, while the numbers provide more information. An M2 is twice as intense as an M1, an M3 is three times as intense, etc.

This M9.3 flare was emitted by an active region — a magnetically strong and complex region on the sun's surface — labeled AR 11996.  

Updates will be provided as they are available on the flare and whether there was an associated coronal mass ejection, or CME, another solar phenomenon that can send solar particles into space and affect electronic systems in satellites and on Earth. 

Related Links

• Frequently Asked Questions Regarding Space Weather 

• View Other Past Solar Activity

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md.

Sun Emits Powerful Solar Flares

This movie shows 23 of the 26 M- and X-class flares on the sun between 1800 UT Oct. 23 and 1500 UT Oct. 28, 2013, as captured by NASA’s Solar Dynamics Observatory. It also shows the coronal mass ejections — great clouds of solar material bursting off the sun into space — during that time as captured by the ESA/NASA Solar and Heliospheric Observatory. Music: “Stella Nova” by Lars Leonhard, courtesy of the artist and Ultimae records. 

 

The sun emitted a significant solar flare – its fourth X-class flare since Oct. 23, 2013 — peaking at 5:54 p.m. on Oct. 29, 2013. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth’s atmosphere to physically affect humans on the ground, however — when intense enough — they can disturb the atmosphere in the layer where GPS and communications signals travel. This disrupts the radio signals for as long as the flare is ongoing, anywhere from minutes to hours.

To see how this event may impact Earth, please visit NOAA’s Space Weather Prediction Center, the U.S. government’s official source for space weather forecasts, alerts, watches and warnings.

This flare is classified as an X2.3 class flare. “X-class” denotes the most intense flares, while the number provides more information about its strength. An X2 is twice as intense as an X1, an X3 is three times as intense, etc.

Increased numbers of flares are quite common at the moment, since the sun’s normal 11-year activity cycle is ramping up toward solar maximum conditions. Humans have tracked this solar cycle continuously since it was discovered in 1843, and it is normal for there to be many flares a day during the sun’s peak activity.

Posted by: Soderman/SSERVI Staff
Source: NASA/SSERVI

NASA Spacecraft Capture an Earth Directed Coronal Mass Ejection

The SOHO LASCO C2 instrument captured this image of the Earth-directed CME. SOHO's coronographs are able to take images of the solar corona by blocking the light coming directly from the Sun with an occulter disk. The location of the actual sun is shown with an image taken by SDO. Image Credit: ESA & NASA/SOHO, SDO

The SOHO LASCO C3 instrument captured this coronographic image of the Earth-directed CME. The bright white object to the right is the planet Mercury. Image Credit: ESA & NASA/SOHO

On August 20, 2013 at 4:24 am EDT, the sun erupted with an Earth-directed coronal mass ejection or CME, a solar phenomenon which can send billions of tons of particles into space that can reach Earth one to three days later. These particles cannot travel through the atmosphere to harm humans on Earth, but they can affect electronic systems in satellites and on the ground.

Experimental NASA research models, based on observations from NASA’s Solar Terrestrial Relations Observatory show that the CME left the sun at speeds of around 570 miles per second, which is a fairly typical speed for CMEs.

Earth-directed CMEs can cause a space weather phenomenon called a geomagnetic storm, which occurs when they funnel energy into Earth's magnetic envelope, the magnetosphere, for an extended period of time. The CME’s magnetic fields peel back the outermost layers of Earth's fields changing their very shape. In the past, geomagnetic storms caused by CMEs of this strength have usually been mild.

Magnetic storms can degrade communication signals and cause unexpected electrical surges in power grids. They also can cause aurora.

NOAA's Space Weather Prediction Center (http://swpc.noaa.gov) is the U.S. government's official source for space weather forecasts, alerts, watches and warnings.

Updates will be provided if needed.

Susan Hendrix
NASA's Goddard Space Flight Center, Greenbelt, Md. 

Sun Releases Slow CME

These three images show a coronal mass ejection, or CME, erupting into space on May 26, 2013. The pictures were captured by the ESA/NASA Solar Heliospheric Observatory with its coronagraph, which blocks out the bright light of the sun to better see its dimmer atmosphere, the corona. Credit: ESA&NASA/SOHO.  › View larger - › View unlabeled version

On May 26, 2013 at 3:24 p.m. EDT, the sun erupted with a coronal mass ejection or CME, a solar phenomenon that can send billions of tons of solar particles into space that can affect electronic systems in satellites. Experimental NASA research models show that the CME was not Earth-directed and it left the sun at 550 miles per second. It may, however, pass by STEREO A and its mission operators have been notified. The spacecraft can be put into safe mode if warranted.

NOAA's Space Weather Prediction Center (http://swpc.noaa.gov) is the U.S. government's official source for space weather forecasts, alerts, watches and warnings.

Updates will be provided as needed.


Related Links

› Frequently Asked Questions Regarding Space Weather
› View Other Past Solar Activity

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, MD.

Spring Fling: Sun Emits a Mid-Level Flare

The M6.5 flare on the morning of April 11, 2013, was also associated with an Earth-directed coronal mass ejection (CME), another solar phenomenon that can send billions of tons of solar particles into space and can reach Earth one to three days later. CMEs can affect electronic systems in satellites and on the ground. Experimental NASA research models show that the CME began at 3:36 a.m. EDT on April 11, leaving the sun at over 600 miles per second.

The joint ESA/NASA Solar Heliospheric Observatory (SOHO) captured this series of images of a coronal mass ejection (CME) on the morning of April 11, 2013 over the course of 3:48 EDT to 4:36 DT. Mars can be seen on the left. Credit: ESA&NASA/SOHO/GSFC.  › View larger, unlabeled version

SOHO also captured this coronagraphic (a telescopic attachment designed to block out the direct light from a star so that nearby objects can be seen) image of the CME as it moves further out into the heliosphere. Credit: ESA&NASA/SOHO/GSFC .  › View larger, unlabeled version

Earth-directed CMEs can cause a space weather phenomenon called a geomagnetic storm, which occurs when they connect with the outside of the Earth's magnetic envelope, the magnetosphere, for an extended period of time.

The recent space weather also resulted in a weak solar energetic particle (SEP) event near Earth. These events occur when very fast protons and charged particles from the sun travel toward Earth, sometimes in the wake of a solar flare. These events are also referred to as solar radiation storms. Any harmful radiation from the event is blocked by the magnetosphere and atmosphere, so cannot reach humans on Earth. Solar radiation storms can, however, disturb the regions through which high frequency radio communications travel.

NOAA's Space Weather Prediction Center (http://swpc.noaa.gov) is the United States Government official source for space weather forecasts, alerts, watches and warnings. NASA and NOAA – as well as the US Air Force Weather Agency (AFWA) and others -- keep a constant watch on the sun to monitor for space weather effects such as geomagnetic storms. With advance notification many satellites, spacecraft and technologies can be protected from the worst effects.

Updates will be provided as they are available.

 

NASA's Solar Dynamics Observatory captured this image of an M6.5 class flare at 3:16 EDT on April 11, 2013. This image shows a combination of light in wavelengths of 131 and 171 Angstroms. Credit: NASA/SDO.  › View full disk image

The sun emitted a mid-level flare, peaking at 3:16 a.m. EDT on April 11, 2013.

Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however -- when intense enough -- they can disturb the atmosphere in the layer where GPS and communications signals travel. This disrupts the radio signals for as long as the flare is ongoing, anywhere from minutes to hours.

This flare is classified as an M6.5 flare, some ten times less powerful than the strongest flares, which are labeled X-class flares. M-class flares are the weakest flares that can still cause some space weather effects near Earth. This flare produced a radio blackout that has since subsided. The blackout was categorized as an R2 on a scale between R1 and R5 on NOAA’s space weather scales.

This is the strongest flare seen so far in 2013. Increased numbers of flares are quite common at the moment, since the sun's normal 11-year activity cycle is ramping up toward solar maximum, which is expected in late 2013. Humans have tracked this solar cycle continuously since it was discovered, and it is normal for there to be many flares a day during the sun's peak activity.

Updates will be provided as need on the flare and its associated coronal mass ejection (CME), another solar phenomenon that can send solar particles into space and affect electronic systems in satellites and on Earth.


What is a solar flare? What is a CME?

For answers to these and other space weather questions, please visit the Spaceweather Frequently Asked Questions page.

Related Link

› View Past Solar Activity
› High resolution imagery

Karen C. Fox
NASA Goddard Space Flight Center, Greenbelt, MD

NASA's SDO Provides First Sightings of How a CME Forms

Solar scientists have long known that at the heart of the great explosions of solar material that shoot off the sun -- known as coronal mass ejections or CMEs – lies a twisted kink of magnetic fields known as a flux rope. But no one has known when or where they form. Now, for the first time, NASA's Solar Dynamics Observatory as captured a flux rope in the very act of formation. Credit: NASA/Goddard Space Flight Center . › Download hi-res video

On July 18, 2012, a fairly small explosion of light burst off the lower right limb of the sun. Such flares often come with an associated eruption of solar material, known as a coronal mass ejection or CME – but this one did not. Something interesting did happen, however. Magnetic field lines in this area of the sun's atmosphere, the corona, began to twist and kink, generating the hottest solar material – a charged gas called plasma – to trace out the newly-formed slinky shape. The plasma glowed brightly in extreme ultraviolet images from the Atmospheric Imaging Assembly (AIA) aboard NASA’s Solar Dynamics Observatory (SDO) and scientists were able to watch for the first time the very formation of something they had long theorized was at the heart of many eruptive events on the sun: a flux rope.

Eight hours later, on July 19, the same region flared again. This time the flux rope's connection to the sun was severed, and the magnetic fields escaped into space, dragging billions of tons of solar material along for the ride -- a classic CME.

The image on the left shows a series of magnetic loops on the sun, as captured by NASA's Solar Dynamics Observatory on July 18, 2012. The image on the right has been processed to highlight the edges of each loop and make the structure more clear. A series of loops such as this is known as a flux rope, and these lie at the heart of eruptions on the sun known as coronal mass ejections (CMEs.) This is the first time scientists were able to discern the timing of a flux rope's formation. Credit: NASA/SDO/Goddard Space Flight Center.  › View larger

"Seeing this structure was amazing," says Angelos Vourlidas, a solar scientist at the Naval Research Laboratory in Washington, D.C. "It looks exactly like the cartoon sketches theorists have been drawing of flux ropes since the 1970s. It was a series of figure eights lined up to look like a giant slinky on the sun."

More than just gorgeous to see, such direct observation offers one case study on how this crucial kernel at the heart of a CME forms. Such flux ropes have been seen in images of CMEs as they fly away from the sun, but it's never been known – indeed, has been strongly debated – whether the flux rope formed before or in conjunction with a CME's launch. This case shows a clear-cut example of the flux rope forming ahead of time. Vourlidas is a co-author, along with Spiro Patsourakos and Guillermo Stenborg, of a paper on these results published in the Astrophysical Journal on Jan. 31, 2013.

Spotting such a foreshadowing of a CME could help scientists develop ways to predict them, says Dean Pesnell, the project scientist for SDO at NASA's Goddard Space Flight Center in Greenbelt, Md. "By telling us when and where flux ropes will erupt," Pesnell says. "SDO helps us predict a major source of space weather."

Scientific research is always a dance between hypothesis and experimental confirmation, and the history of the flux rope is no exception. Plasma physicists suggested that such coils of magnetic field lines were at the heart of flares in the 1970s and spacecraft near Earth provided in-situ measurements that occasionally traced out helical structures inside CMEs. Later, the flux ropes were spotted in images of CMEs captured by the joint ESA/NASA Solar Heliospheric Observatory (SOHO) – which launched in 1995 – using the mission's Large Angle and Spectrometric Coronagraph (LASCO), a telescope that blocks out the bright light of the solar disk in order to better see the tenuous corona around it. They are now a regular appearance on coronagraph and heliospheric imaging observations.

When it came to watching them form in a CME, however, the task was much harder. Since CMEs can form quite suddenly – known as impulsive CMEs – the associated flux ropes are smaller and closer to the surface, making it difficult to spot them amongst the many structures in the corona.

In the absence of direct observational evidence, theorists have produced two theories based on general physics of plasmas and magnetic fields of how and when the flux rope might form. In one, the magnetic structure of the rope exists before the CME, and as it evolves over time it twists and kinks becoming increasingly unstable. Eventually it erupts from the sun, releasing enormous amounts of energy and solar plasma. In the second version, the CME erupts when looping magnetic field lines are severed from the sun's surface. While the great blob of solar material streams off the sun, the fields reconnect with each other to form a classic flux rope shape.

On July 19, 2012, SDO captured images of a solar flare in numerous wavelengths. The 131 Angstrom wavelength, shown here in the middle and colorized in teal, portrays particularly hot material on the sun, at 10 million Kelvin, which is why the incredibly hot flare shows up best in that wavelength. The 131 wavelength was also able to show kinked magnetic fields known as a flux rope that lay at the heart of a coronal mass ejection (CME), which also erupted at the same time as the flare. Credit: NASA/Goddard Space Flight Center. › View larger

"In this case, we saw this big eruption on July 19," says Vourlidas. "We wanted to analyze the eruption and we started going back in time – a few minutes, then an hour, then eight hours. And then we saw it. A flux rope that looked just like the cartoons scientists have been drawing for decades."

Vourlidas credits this first sighting to three things. First, the team looked far enough back in time, when previous searches have often only looked a few minutes back. Second, the sun obliged its viewers with the perfect angle at which to see the tell-tale loops of the flux rope. SDO's cameras could look right down the center of the rope, like looking down the tunneled center of a slinky. Third, AIA’s cameras capture imagery that no other cameras do: light at the 131 Angstrom wavelength, which shows solar material heated to temperatures of 10,000,000 K (18,000,000 F / 10,000,000 C). In images of the same region at the same time showing cooler material, the flux rope doesn't show up at all. AIA scientists chose to include a filter to view this unprecedentedly high temperature because they posited that flares could heat the corona to those temperatures. Apparently the same incredibly hot plasma helped highlight the flux rope that would later give rise to a CME.

Over the course of the next eight hours after the July 18 flux rope formed, the rope did show up faintly in images of cooler material, suggesting that the hot material from the flare cooled down over time as the flux rope also rose in space. Then eight hours later, on July 19, the material got hot again, the region flared, and the flux rope escaped into space.

"We could verify that the flux rope was there in the coronagraph from SOHO. We could see the typical slinky structure with multiple round loops inside it," says Vourlidas. "We looked at it with other NASA telescopes, too. We looked at it with everything we've got. It's a wonderful time to be a solar physicist, because thanks to the large number of telescopes we have in space at the moment, we can see things like this from every angle." 

By looking at the very hottest material in the sun's atmosphere (on the left) scientists could observe the tell tale signs of the twisted magnetic fields of a flux rope – which lay at the heart of coronal mass ejections (CMEs). The flux rope doesn't show up in a nearly simultaneous image of cooler material (on the right). These images were captured by NASA's Solar Dynamics Observatory on July 19, 2012. Credit: NASA/SDO.  › View larger

 

Vourlidas says that images from NASA's Solar Terrestrial Relations Observatory (STEREO) also helped with analysis. Since the two STEREO spacecraft observe the sun from a different perspective than does SDO, the team got a top-down view of the flux rope with STEREO-A’s EUV Imager, which helped unravel the 3-D structure of the flux rope. The foot points of the rope touched in widely separated areas of the solar surface – an interesting structural development in of itself that is worth further study.

The team will certainly look for other examples in the images of the hottest plasma, searching for evidence of pre-formed flux ropes further back in time. But even one such example of direct evidence adds an important step to the constant scientific cycle of theory and observation, helping refine and improve the theories of what causes these giant explosions on the sun.

For more information about NASA's SDO mission, visit: www.nasa.gov/sdo

For high resolution versions of this media, visit: http://svs.gsfc.nasa.gov/vis/a010000/a011100/a011180/

 

NASA's Solar Fleet Peers Into Coronal Cavities

Scientists want to understand what causes giant explosions in the sun's atmosphere, the corona, such as this one. The eruptions are called coronal mass ejections or CMEs and they can travel toward Earth to disrupt human technologies in space. To better understand the forces at work, a team of researchers used NASA data to study a precursor of CMEs called coronal cavities. Credit: NASA/Solar Dynamics Observatory (SDO) . View Larger

The sun's atmosphere dances. Giant columns of solar material – made of gas so hot that many of the electrons have been scorched off the atoms, turning it into a form of magnetized matter we call plasma – leap off the sun's surface, jumping and twisting. Sometimes these prominences of solar material, shoot off, escaping completely into space, other times they fall back down under their own weight. 

The prominences are sometimes also the inner structure of a larger formation, appearing from the side almost as the filament inside a large light bulb. The bright structure around and above that light bulb is called a streamer, and the inside "empty" area is called a coronal prominence cavity. 

 Such structures are but one of many that the roiling magnetic fields and million-degree plasma create in the sun's atmosphere, the corona, but they are an important one as they can be the starting point of what's called a coronal mass ejection, or CME. CMEs are billion-ton clouds of material from the sun’s atmosphere that erupt out into the solar system and can interfere with satellites and radio communications near Earth when they head our way.

 "We don't really know what gets these CMEs going," says Terry Kucera, a solar scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "So we want to understand their structure before they even erupt, because then we might have a better clue about why it's erupting and perhaps even get some advance warning on when they will erupt."

 Kucera and her colleagues have published a paper in the Sept. 20, 2012, issue of The Astrophysical Journal on the temperatures of the coronal cavities. This is the third in a series of papers -- the first discussed cavity geometry and the second its density -- collating and analyzing as much data as possible from a cavity that appeared over the upper left horizon of the sun on Aug. 9, 2007 (below). By understanding these three aspects of the cavities, that is the shape, density and temperature, scientists can better understand the space weather that can disrupt technologies near Earth. 

 The faint oval hovering above the upper left limb of the sun in this picture is known as a coronal cavity. NASA’s Solar and Terrestrial Relations Observatory (STEREO) captured this image on Aug. 9, 2007. A team of scientists extensively studied this particular cavity in order to understand more about the structure and magnetic fields in the sun's atmosphere. Credit: NASA/STEREO. View Larger

 The Aug. 9 cavity lay at a fortuitous angle that maximized observations of the cavity itself, as opposed to the prominence at its base or the surrounding plasma. Together the papers describe a cavity in the shape of a croissant, with a giant inner tube of looping magnetic fields -- think something like a slinky -- helping to define its shape. The cavity appears to be 30% less dense than the streamer surrounding it, and the temperatures vary greatly throughout the cavity, but on average range from 1.4 million to 1.7 million Celsius (2.5 to 3 million Fahrenheit), increasing with height.

 Trying to describe a cavity, a space that appears empty from our viewpoint, from 93 million miles away is naturally a tricky business. "Our first objective was to completely pin down the morphology," says Sarah Gibson, a solar scientist at the High Altitude Observatory at the National Center for Atmospheric Research (NCAR) in Boulder, Colo. who was an author on all three cavity papers. "When you see such a crisp clean shape like this, it’s not an accident. That shape is telling you something about the physics of the magnetic fields creating it, and understanding those magnetic fields can also help us understand what’s at the heart of CMEs."

 To do this, the team collected as much data from as many instruments from as many perspectives as they could, including observations from NASA’s Solar Terrestrial Relations Observatory (STEREO), ESA and NASA’s Solar and Heliospheric Observatory (SOHO), the JAXA/NASA mission Hinode, and NCAR's Mauna Loa Solar Observatory.

 They collected this information for the cavity’s entire trip across the face of the sun along with the sun’s rotation. Figuring out, for example, why the cavity was visible on the left side of the sun but couldn’t be seen as well on the right held important clues about the structure’s orientation, suggesting a tunnel shape that could be viewed head on from one perspective, but was misaligned for proper viewing from the other. The cavity itself looked like a tunnel in a crescent shape, not unlike a hollow croissant. Magnetic fields loop through the croissant in giant circles to support the shape, the way a slinky might look if it were narrower on the ends and tall in the middle – the entire thing draped in a sheath of thick plasma. The paper describing this three-dimensional morphology appeared in The Astrophysical Journal on Dec. 1, 2010.

 Next up, for the second paper, was the cavity’s density. Figuring out density and temperature was a trickier prospect since one’s point of view of the sun is inherently limited. Because the sun’s corona is partially transparent, it is difficult to tease out differences of density and temperature along one’s line of sight; all the radiation from a given line hits an instrument at the same time in a jumble, information from one area superimposed upon every other.

 Using a variety of techniques to tease density out from temperature, the team was able to determine that the cavity was 30% less than that of the surrounding streamer. This means that there is, in fact, quite a bit of material in the cavity. It simply appears dim to our eyes when compared with the denser, brighter areas nearby. The paper on the cavity’s density appeared in The Astrophysical Journal on May 20, 2011.

 "With the morphology and the density determined, we had found two of the main characteristics of the cavity, so next we focused on temperature," says Kucera. "And it turned out to be a much more complicated problem. We wanted to know if it was hotter or cooler than the surrounding material – the answer is that it is both."

 Ultimately, what Kucera and her colleagues found was that the temperature of the cavity was not – on average – hotter or cooler than the surrounding plasma.

 However, it was much more varied, with hotter and cooler areas that Kucera thinks link the much colder 10,000 degrees Celsius (17,000 F) prominence at the bottom to the million to two million degrees Celsius (1.8 million to 3.6 million degrees Fahrenheit) corona at the top. Other observations of cavities show that cavity features are constantly in motion creating a complicated flow pattern that the team would like to study further.

 While these three science papers focused on just the one cavity from 2007, the scientists have already begun comparing this test case to other cavities and find that the characteristics are fairly consistent. More recent cavities can also be studied using the high-resolution images from NASA’s Solar Dynamics Observatory (SDO), which launched in 2010.

 "Our point with all of these research projects into what might seem like side streets, is ultimately to figure out the physics of magnetic fields in the corona," says Gibson. "Sometimes these cavities can be stable for days and weeks, but then suddenly erupt into a CME. We want to understand how that happens. We’re accessing so much data, so it’s an exciting time – with all these observations, our understanding is coming together to form a consistent story."

Related Links - NASA's Solar Fleet

• STEREO web

• SDO website

• SOHO website

• Hinode website

Karen C. Fox

NASA Goddard Space Flight Center, Greenbelt, MD