The region between the Sun's surface and its hot, million-degree corona is a complex interface zone. Only a few thousand kilometers deep, within it the density of the gas drops by a factor of about one million, while the temperature increases from about five thousand to one million kelvin. Almost all of the mechanical energy that drives solar activity and solar atmospheric heating is converted into heat and radiation within this interface, with only a small amount leaking through to power coronal heating and drive the solar wind. Multiple physical processes act within this region to shape the intricate system of magnetic fields, energetic particles, and radiation that in turn power the corona and the solar wind.
Despite the importance of the interface region it remains poorly understood, in part just because it is so complex and in part because modeling the process requires measurements over a wide spectral range (from the visible to the extreme ultraviolet) with high enough spatial resolution to identify small features. As a result, it presents a challenging target for observers and modelers alike. The Interface Region Imaging Spectrograph (IRIS) mission was launched on 27 June 2013 to address these issues. IRIS is a NASA solar mission to which the CfA and its staff contributed its twenty centimeter telescope as well as a science team. IRIS advances previous rocket studies by using novel, high-throughput, and high-resolution instrumentation, efficient numerical simulation codes, and powerful, massively parallel supercomputers to aid interpretation of the data.
The CfA team consists of P.N. Cheimets, E.E. DeLuca, L. Golub, R. Gates, E. Hertz, S. McKillop, S. Park, T. Perry, W.A. Podgorski, K. Reeves, S. Saar, P. Testa, H. Tian, and M. Weber. They and their colleagues have just published the first paper from IRIS, detailing the instrumental performance and the initial sixty-day observing program. The paper reports that IRIS is working well, and achieving excellent spatial and spectral resolution, temporally resolved observations as short 1.5 seconds, and velocity information as small as one kilometer a second.
YouTube video link:
"The Interface Region Imaging Spectrograph (IRIS)," B. De Pontieu et al., Solar Physics, 289, 2733, 2014.