New views of Sun's atmosphere reveal structures unknown to science

Launched late last month, NASA's Interface Region Imaging Spectrograph (IRIS) is designed to observe little-explored lower layers of the Sun's multi-level atmosphere in unprecedented detail – and its first images are already turning up surprises.


On the left is a section of the Sun as seen by NASA's Solar Dynamics Observatory. On the right, the same section as seen by IRIS. Notice the increased levels of detail.

IRIS is equipped with a suite of ultraviolet-sensing and spectrographic instruments that enables it to peer past the Sun's outer atmosphere into the chromosphere, the so-called "interface region" that serves as an energy conduit between the Sun's low-level photosphere and its outer corona. When it comes to solar dynamics, astrophysicists hypothesize the chromosphere is where the magic happens. Somewhere in this region, surface temperatures (which hover in the range of 5,000–6,000 Kelvin) skyrocket to the 1,000,000–3,000,000 Kelvin temperatures observed in the Sun's roiling outer sheath. It drives solar wind, and gives rise to the ultraviolet emissions that affect Earth.


As IRIS's telescope door opened for the first time ever on July 17, the imaging spectrograph began to observe the sun. IRIS's first images show a multitude of thin, fiber-like structures that have never been seen before. The observations reveal enormous contrasts in density and temperature throughout this region, even between neighboring loops only a few hundred miles apart. The images also show spots that rapidly brighten and dim, which provide clues to how energy is transported and absorbed throughout the region.

"The quality of the images and spectra we are receiving from IRIS is amazing — this is just what we were hoping for," said Alan Title, IRIS principal investigator at Lockheed Martin in Palo Alto, Calif. "There is much work ahead to understand what we're seeing, but the quality of the data will enable us to do that."

Read more about the IRIS mission and its first glimpse of this mysterious solar region here and here. For more on the the chromosphere and the rest of the Sun's atmosphere, check out this handy animated guide from the University of South Wales.

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