Space Instrument Adds Big Piece to the Solar Corona Puzzle

This is one of the highest-resolution images ever taken of the solar corona, or outer atmosphere. It was captured by NASA's High Resolution Coronal Imager, or Hi-C, in the ultraviolet wavelength of 19.3 nanometers. Hi-C showed that the Sun is dynamic, with magnetic fields constantly warping, twisting, and colliding in bursts of energy. Added together, those energy bursts can boost the temperature of the corona to 7 million degrees Fahrenheit when the Sun is particularly active.  Credit: NASA . High Resolution Image (jpg) - Low Resolution Image (jpg)

Hi-C found interweaved magnetic fields that were braided just like hair. When those braids relax and straighten, they release energy. Hi-C witnessed one such event during its flight, shown in this time series. Credit: NASA . Low Resolution Image (jpg)

 

Hi-C also detected an area where magnetic field lines crossed in an X, then straightened out as the fields reconnected. Minutes later, that spot erupted with a mini solar flare. Images of the same location taken with the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory show the superior resolution of Hi-C. Credit: NASA.   Low Resolution Image (jpg)

Cambridge, MA - The Sun's visible surface, or photosphere, is 10,000 degrees Fahrenheit. As you move outward from it, you pass through a tenuous layer of hot, ionized gas or plasma called the corona. The corona is familiar to anyone who has seen a total solar eclipse, since it glimmers ghostly white around the hidden Sun. 

But how can the solar atmosphere get hotter, rather than colder, the farther you go from the Sun's surface? This mystery has puzzled solar astronomers for decades. A suborbital rocket mission that launched in July 2012 has just provided a major piece of the puzzle.

The High-resolution Coronal Imager, or Hi-C, revealed one of the mechanisms that pumps energy into the corona, heating it to temperatures up to 7 million degrees F. The secret is a complex process known as magnetic reconnection.

"This is the first time we've had images at high enough resolution to directly observe magnetic reconnection," explained Smithsonian astronomer Leon Golub (Harvard-Smithsonian Center for Astrophysics). "We can see details in the corona five times finer than any other instrument."

"Our team developed an exceptional instrument capable of revolutionary image resolution of the solar atmosphere. Due to the level of activity, we were able to clearly focus on an active sunspot, thereby obtaining some remarkable images," said heliophysicist Jonathan Cirtain (Marshall Space Flight Center).

Magnetic braids and loops
 
The Sun's activity, including solar flares and plasma eruptions, is powered by magnetic fields. Most people are familiar with the simple bar magnet, and how you can sprinkle iron filings around one to see its field looping from one end to the other. The Sun is much more complicated.

The Sun's surface is like a collection of thousand-mile-long magnets scattered around after bubbling up from inside the Sun. Magnetic fields poke out of one spot and loop around to another spot. Plasma flows along those fields, outlining them with glowing threads.

The images from Hi-C showed interweaved magnetic fields that were braided just like hair. When those braids relax and straighten, they release energy. Hi-C witnessed one such event during its flight.
It also detected an area where magnetic field lines crossed in an X, then straightened out as the fields reconnected. Minutes later, that spot erupted with a mini solar flare.

Hi-C showed that the Sun is dynamic, with magnetic fields constantly warping, twisting, and colliding in bursts of energy. Added together, those energy bursts can boost the temperature of the corona to 7 million degrees F when the Sun is particularly active.

Selecting the target
 
The telescope aboard Hi-C provided a resolution of 0.2 arcseconds - about the size of a dime seen from 10 miles away. That allowed astronomers to tease out details just 100 miles in size. (For comparison, the Sun is 865,000 miles in diameter.)

Hi-C photographed the Sun in ultraviolet light at a wavelength of 19.3 nanometers - 25 times shorter than wavelengths of visible light. That wavelength is blocked by Earth's atmosphere, so to observe it astronomers had to get above the atmosphere. The rocket's suborbital flight allowed Hi-C to collect data for just over 5 minutes before returning to Earth.

Hi-C could only view a portion of the Sun, so the team had to point it carefully. And since the Sun changes hourly, they had to select their target at the last minute - the day of the launch. They chose a region that promised to be particularly active.

"We looked at one of the largest and most complicated active regions I've ever seen on the Sun," said Golub. "We hoped that we would see something really new, and we weren't disappointed."

Next steps
 
Golub said that data from Hi-C continues to be analyzed for more insights. Researchers are hunting areas where other energy release processes were occurring.

In the future, the scientists hope to launch a satellite that could observe the Sun continuously at the same level of sharp detail.

"We learned so much in just five minutes. Imagine what we could learn by watching the Sun 24/7 with this telescope," said Golub.

This research is being published in the journal Nature in a paper co-authored by Cirtain, Golub, A. Winebarger (Marshall), B. De Pontieu (Lockheed Martin), K. Kobayashi (University of Alabama - Huntsville), R. Moore (Marshall), R. Walsh (University of Central Lancashire), K. Korreck, M. Weber and P. McCauley (CfA), A. Title (Lockheed Martin), S. Kuzin (Lebedev Physical Institute), and C. DeForest (Southwest Research Institute).

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu
 
Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu
 

Solar Corona Revealed in Super-High-Definition

These photos of the solar corona, or million-degree outer atmosphere, show the improvement in resolution offered by NASA's High Resolution Coronal Imager, or Hi-C (bottom), versus the Atmospheric Imaging Assembly on NASA's Solar Dynamics Observatory (top). Both images show a portion of the sun's surface roughly 85,000 by 50,000 miles in size. Hi-C launched on a sounding rocket on July 11, 2012 in a flight that lasted about 10 minutes. The representative-color images were made from observations of ultraviolet light at a wavelength of 19.3 nanometers (25 times shorter than the wavelength of visible light). Credit: NASA. High Resolution Image (jpg)

This time-lapse movie shows activity in the sun's corona on July 11, 2012, with 10 minutes compressed into 10 seconds. It begins with images from the Atmospheric Imaging Assembly (AIA) on board NASA's Solar Dynamics Observatory. About three seconds in, the view switches to super-high-resolution photos of the same region from NASA's High Resolution Coronal Imager (Hi-C). Hi-C flew on a sounding rocket and only took data for about five minutes, so the view switches back to AIA data at the end. The representative-color images were made from observations of ultraviolet light at a wavelength of 19.3 nanometers (25 times shorter than the wavelength of visible light). Credit: NASA. Animation (mov) (8,85 mb)

Same time-lapse movie as above, with ultraviolet light color-coded red

Credit: NASA. Animation (mov) (8,33 mb)

Cambridge, MA - Today, astronomers are releasing the highest-resolution images ever taken of the Sun's corona, or million-degree outer atmosphere, in an extreme-ultraviolet wavelength of light. The 16-megapixel images were captured by NASA's High Resolution Coronal Imager, or Hi-C, which was launched on a sounding rocket on July 11th. The Hi-C telescope provides five times more detail than the next-best observations by NASA's Solar Dynamics Observatory.

"Even though this mission was only a few minutes long, it marks a big breakthrough in coronal studies," said Smithsonian astronomer Leon Golub (Harvard-Smithsonian Center for Astrophysics), one of the lead investigators on the mission.

Understanding the Sun's activity and its effects on Earth's environment was the critical scientific objective of Hi-C, which provided unprecedented views of the dynamic activity and structure in the solar atmosphere.

The corona surrounds the visible surface of the Sun. It's filled with million-degree ionized gas, or plasma, so hot that the light it emits is mainly at X-ray and extreme-ultraviolet wavelengths. For decades, solar scientists have been trying to understand why the corona is so hot, and why it erupts in violent solar flares and related blasts known as "coronal mass ejections," which can produce harmful effects when they hit Earth. The Hi-C telescope was designed and built to see the extremely fine structures thought to be responsible for the Sun's dynamic behavior.

"The phrase 'think globally, act locally' applies to the Sun too. Things happening at a small, local scale can impact the entire Sun and result in an eruption," explained Golub.

Hi-C focused on an active region on the Sun near sunspot NOAA 1520. The target, which was finalized on launch day, was selected specifically for its large size and active nature. The resulting high-resolution snapshots, at a wavelength of 19.3 nanometers (25 times shorter than the wavelength of visible light), reveal tangled magnetic fields channeling the solar plasma into a range of complex structures.

"We have an exceptional instrument and launched at the right time," said Jonathan Cirtain, senior heliophysicist at NASA's Marshall Space Flight Center. "Because of the intense solar activity we're seeing right now, we were able to clearly focus on a sizeable, active sunspot and achieve our imaging goals."

Since Hi-C rode on a suborbital rocket, its flight lasted for just 10 minutes. Of that time, only about 330 seconds were spent taking data. Yet those images contain a wealth of information that astronomers will analyze for months to come.

"The Hi-C flight might be the most productive five minutes I've ever spent," Golub smiled.

The high-resolution images were made possible because of a set of innovations on Hi-C's telescope, which directs light to the camera detector. The telescope includes some of the finest mirrors ever made for a space mission. Initially developed at NASA's Marshall Space Flight Center in Huntsville, Ala., the mirrors were completed with inputs from partners at the Smithsonian Astrophysical Observatory (SAO) in Cambridge, Mass., and a new manufacturing technique developed in coordination with L-3Com/Tinsley Laboratories of Richmond, Calif. The mirrors were made to reflect extreme-ultraviolet light from the Sun by Reflective X-ray Optics LLC of New York, NY, and the telescope was assembled at the SAO labs in Cambridge, Mass.

For more information about Hi-C, visit http://www.nasa.gov/topics/solarsystem/features/hic.html

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Key partners in the development of Hi-C include the University of Alabama in Huntsville; the Smithsonian Astrophysical Observatory; Lockheed Martin's Solar Astrophysical Laboratory in Palo Alto, Calif.; the University of Central Lancashire in Lancashire, England; and the Lebedev Physical Institute of the Russian Academy of Sciences in Moscow.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu