IRIS Mission Logo
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IRIS Mission Logo

December 11, 2012
The Interface Region Imaging Spectrograph (IRIS) is a NASA Small Explorer Mission to observe how solar material moves, gathers energy, and heats up as it travels through a little-understood region in the sun's lower atmosphere. Tracking how material and energy move through this region is a crucial part of understanding the dynamics of the sun. Such information can help explain what causes the ejection of solar material -- from the steady stream of the solar wind to larger, explosive eruptions such as coronal mass ejections (CMEs) -- that travels toward Earth and causes space weather that can disrupt human technology. Visible in ultraviolet light, the two regions closest to the sun are called the chromosphere and the transition region. They form a violently dynamic interface region in which hot and cold plasma are mixed over a range of heights, stretching from the sun's surface to several thousand miles up. This location is where one of the most mysterious occurrences on the sun takes place. Usually the closer you get to a heat source, such as a fire, the hotter it gets -- but the solar atmosphere doesn't do that. The solar atmosphere gets hotter as it gets further away from the sun, and scientists don't yet have enough information to distinguish between various theories on why this happens. The atmosphere changes from 6,000 K at the surface to about a million K at the top of the transition region. The temperatures continue to increase up to millions of degrees in the sun's upper atmosphere, the corona, but since the lowermost layers contain more material, the strongest heating is believed to occur there. Tracking the complex processes within these layers of the solar atmosphere requires instrument and modeling capabilities that are within technological reach for the first time. IRIS is the first mission designed to simultaneously observe the range of temperatures specific to the chromosphere and transition region at very high spatial and temporal resolution -- going beyond earlier missions that were lower resolution or did not cover a wide range of temperatures. IRIS also draws on state of the art computer modeling sophisticated enough to deal with the complexity of this area. In combination, IRIS's resolution, wide temperature coverage and computer modeling will enable scientists to map plumes of solar material as they move throughout the region and to pinpoint where in their travels they gain energy and heat. The mission's general science objectives are to answer the following questions: Which types of non-thermal energy dominate in the chromosphere and beyond? How does the chromosphere regulate mass and energy supply to the corona and heliosphere? How do magnetic flux and matter rise through the lower atmosphere and what role does flux emergence play in flares and mass ejections?

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