Twist, Nanoflares, Loops, ‘Bombs’ and Jets: New Solar Findings Revealed by IRIS Observatory

These images show an active solar region on June 4, 2014. The image on the left shows the chromosphere (approximately 17,500 degrees F), whereas the image at right shows the transition region, both the site of the twisting motions observed with IRIS. Image Credits: (left) IRIS/LMSAL-NASA, courtesy of Tiago Pereira, University of Oslo. (right) IRIS/LMSAL-NASA, courtesy of Bart De Pontieu. 

Just above the sun’s surface lie twisting tornadoes that accelerate plasma to speeds of over 100,000 km/hr (62,000 mph). New findings by Lockheed Martin scientists show these motions are not only more common than previously thought but also appear to heat plasma from 10,000 degrees F to at least 100,000 degrees.

An international team led by Lockheed Martin scientists discovered this and other findings that show how the sun’s atmosphere is energized. The team is using the Interface Region Imaging Spectrograph (IRIS), which has been providing new insight into the inner workings of the sun’s atmosphere since it launched in June 2013.

The discoveries were published this week in a special section of the journal Science.

“Our results provide new insight into what drives the counterintuitive rise of temperature from the 10,000 degree surface to millions of degrees in the sun’s outer atmosphere, or corona,” said Dr. Bart De Pontieu, IRIS lead scientist. 

To address this long-standing problem, NASA launched IRIS, an Earth-orbiting small explorer satellite with a 20 cm telescope onboard, which was built by Lockheed Martin.

“IRIS splits the sun’s near and far ultraviolet light into its constituents, in order to remotely probe the physical conditions in the interface region,” De Pontieu said.

The interface region consists of the relatively cool chromosphere (~10,000 to 20,000 degrees F) and transition region (a few hundred thousand degrees). Recent research suggested that it is here, at the interface between surface and corona, that answers to some of the more vexing unresolved questions in solar physics might be found.

“Our findings can apply beyond our solar system,” said Dr. Alan Title, IRIS principal investigator. “The physical processes that occur in our sun can occur in other, much more distant stars, so this is a local laboratory for wide-ranging discovery.”

This video shows IRIS spectra of the chromosphere at the solar north pole. We see gases that are moving at high velocity towards us and away from us. It is also a scan through various heights in the solar atmosphere. This type of data can be used to make maps of the velocities of the solar chromosphere that reveal the twisting motions on small scales. Credit: IRIS/LMSAL-NASA, movie courtesy of Tiago Pereira,

IRIS discoveries

Details of these discoveries are in a new issue of Science. Five articles leverage high-resolution IRIS images and spectra to present major advances in understanding how the solar atmosphere is energized.

  • Nanoflares: Scientists find compelling evidence for the presence of high-energy particles generated during coronal nanoflares. These are small-scale events long thought to drive coronal heating through the release of energy when magnetic field lines reconnect. This result provides new insight into how these electrons are accelerated to such high energies.
  • Transition Region Loops: Small-scale magnetic loops were found in high-resolution images of IRIS and advanced 3-D models, resolving a long-standing debate about the nature of the emission in the transition region. These results vindicate a view that this emission does not originate in the usual transition region between the surface and hot loops, but occurs in previously undiscovered loop-like structures.
  • Solar “bombs”: Researchers saw in high-resolution spectra a solar atmosphere turned upside down: hot plasma at 100,000 Kelvin (nearly 180,000 degrees Fahrenheit) is found closer to the solar surface than previously imagined. The plasma is sandwiched by cool plasma both below and above, and heated by “bombs,” where magnetic fields reconnect and lead to rapid heating. These unexpected results will likely lead to a reassessment of other phenomena in the low solar atmosphere, such as the mysterious Ellerman bombs, discovered almost a century ago.
  • Jets in the Wind: Scientists uncover evidence of high-speed jets at the root of the solar wind, a high-speed, continuous stream of particles that permeates space around the Earth. The jets are fountains of plasma that appear to undergo rapid heating from 20,000 to 180,000 degrees F and may provide hot plasma to the solar wind.
  • Twist: As described at the opening of this article, one paper shows the chromosphere is full of twisting motions on spatial scales of a few hundred miles. These motions are a sign of magnetic waves and support recent theories about heating of the solar chromosphere and corona.

Together, these results provide critical pieces in the still-unsolved puzzle of how the sun shapes and affects the heliosphere, the sun’s outer atmosphere in which we live. With solar activity at high levels, scientists are expecting more advances from the imaging spectrograph onboard IRIS, especially regarding solar flares and coronal mass ejections, which are violent explosions that cause bouts of bad space weather that threaten power grids, satellites and astronauts.

The IRIS observatory was designed—and the mission is managed by—Lockheed Martin. The Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, built the telescope. Montana State University in Bozeman, Montana designed the spectrograph. NASA's Ames Research Center in Mountain View, California provides mission operations and ground data systems. NASA's Goddard Space Flight Center in Greenbelt, Maryland manages the Small Explorer Program for NASA's Science Mission Directorate in Washington, D.C. The Norwegian Space Centre is providing regular downlinks of science data. Other contributors include the University of Oslo, Norway and Stanford University in Stanford, California.

Now let’s look at the same region (as above) in a different way. This video shows plasma moving toward Earth at various speeds (in blue) and plasma moving away from us (in red). The appearance of linear structures that form pairs of blue and red are the locations of “twist” where the plasma is moving with velocities at approximately 10 to 30 km/s (6 to 18 miles/s). Credit: IRIS/LMSAL-NASA, movie courtesy of Tiago Pereira, University of Oslo.

October 16, 2014

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