Studying The Sun’s Dramatic Temperature Variations


This story by Michael Mecham and Frank Morring, Jr. ran in the July 8 edition of Aviation Week & Space Technology.

Spaceborne study of the Sun has produced spectacular images like these over the years, but still leaves much about our nearest star cloaked in mystery. Now an ultraviolet (UV) telescope with unusually high spectral bandwidth will try to solve one of the most puzzling—why temperatures vary so dramatically between the Sun's surface and the upper limits of its turbulent atmosphere. will focus on the interface region in the Sun's atmosphere , shown in this image collected by Japan's Hinode spacecraft, in the hope it will reveal why the corona above it gets so much hotter. Credit: JAXA/Hinode 

NASA 's Interface Region Imaging Spectrograph (IRIS) mission received “a great insertion orbit” from its three-stage Orbital Sciences Pegasus XL air-launched booster June 27, hitting a 400-mi.-high Sun-synchronous orbit that should carry it well beyond its nominal two-year operational life. 's IRIS spacecraft will image about 1% of the Sun with each shot of its ultraviolet telescope , resolving images as small as 150-mi. across. Credit: Lockheed Martin

The $170 million mission fields a 20-cm (8-in.) UV telescope and spectrograph designed to record the ultraviolet light emitted in the transitional region that stretches from the Sun's surface —where temperatures are a mere 10,000F—to its corona, or upper atmosphere, where they reach several million degrees. The mission will study solar and plasma physics, space weather and astrophysics to gain a better understanding of how the Sun's internal convective flows power its atmospheric activity. Spikes in that activity can interrupt electrical grids and disrupt communications satellites. combined images taken with Europe's Proba-2 spacecraft and from the ground at Atoll Hao in French Polynesia during a total solar eclipse in July 2010 to produce this illustration of the extended corona . Credit: ESA/Proba-2 consortium/SWAP team/Institut d'Astrophysique de Paris (CNRS & UPMC), S. Koutchmy/J. Mouette 

With a liftoff weight of 140 kg (300 lb.), IRIS has a power rating of 200 watts. Its most prominent feature is its 3-meter (9.8-ft.)-long UV telescope built by the Smithsonian Astrophysical Observatory. massive coronal hole in blue shows a 400,000-mi.-wide opening in the Sun's magnetic field that lets the solar wind spew out at 400-500 mi./sec., twice its normal speed. Credit: NASA /SDO 

The spacecraft's multi-channel imaging spectrograph , built by Lockheed Martin Sensing and Exploration Systems from a design collaboration with Montana State University, will observe in the extreme ultraviolet wavelengths between 1,200-3,000 angstroms, far higher than previous missions. particles from an Earth-directed coronal mass ejection (CME) March 15 show up clearly in these occluded images from the Solar Heliospheric Observatory. Credit: ESA/NSA/SOHO 

The instrument's mirrors, polished by L-3 Communications SSG-Tinsley Inc. in Richmond, Calif., have a quality better than the Hubble Space Telescope's, says Principal Investigator Alan Title, a senior fellow at the Lockheed Martin Advanced Technology Center in Palo Alto, Calif. CME above produced this aurora over Prudhoe Bay, Alaska, two days later, reflecting a geomagnetic storm rated G2 fading to G1 on a five-point scale. Storms that are more severe can damage satellites and disrupt power grids.

“IRIS will show the solar chromosphere in more detail than has ever been observed before,” says Adrian Daw, deputy project scientist. “My opinion is that we are bound to see something we didn't expect to see.”

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