NASA’s IRIS take a look at the Sun’s interior
Back in July, NASA launched their new Interface Region Imaging Spectrograph (IRIS) spacecraft. IRIS is designed to study one specific level of the Sun’s atmosphere at unprecedented speed and details, in the hope of resolving one of the greatest mysteries in solar astronomy. The answers it discovers will not only improve our knowledge of how the nearest star works, but will also improve our understanding of the Solar Wind, and help us to better predict space weather events that threaten our modern electronic infrastructure. IRIS is built to study the Sun’s transition region, the thin layer of its atmosphere between the chromosphere and the corona. The uppermost part of the transition region has a temperature about a million Kelvins, while the lowermost parts (only 100 km away) is only about six thousand Kelvins. Ever since this temperature gradient was first measured, physicists have been at a loss to explain how it is possible that the lowest parts of the region, nestled against the Sun’s “surface”, could be a full million degrees colder than the upper surface, exposed to the cold vacuum of space. A few theories have been ventured, involving the strong and twisted magnetic field lines that we know writhe through the area, but we’ve never had the raw data needed to confirm whether these theories are actually true. IRIS will provide those data and (hopefully) solve the mystery. The first results, announced a few months ago, are promising. IRIS is already returning images and spectra of the transition region (which cannot be seen in the visible spectrum) with unprecedented clarity. The Solar Dynamics Observatory has been returning some data on that region, but the simpler, cheaper and more specialized IRIS is significantly outperforming it in both the resolution of its images, and the speed with which it can collect them. It can detect features as small as 250 km across — tiny, compared to the Sun’s 1.4 million kilometer diameter! The enormous ramping of temperature between the bottom and top of the transition region is so important because this energy powers the Corona, a vast shell of superheated gas surrounding the Sun which is only visible to Earth-bound observers during a total eclipse of the Sun. The corona is the source of the solar wind, and other solar weather events. Since Coronal Mass Ejections can damage satellites and ground-based infrastructure (and in fact has done so in the past), it is vital that we understand it better. “With this grand opening of the telescope door and first observations from IRIS we’ve opened a new window into the energetics of the sun’s atmosphere,” said John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington. “The mission is a great example of a successful partnership for science between government, industry, academia, and international institutions. We look forward to the new insights IRIS will provide.”