The fine detail in images of prominences in the Sun's atmosphere from NASA's Interface Region Imaging Spectrometer (IRIS). Image credit: NASA/LMSAL/IRIS

Sep 11, 2014 Bridging the gap – a new view of the Sun with IRIS

Sen—There is always more we want to know about the Universe and our place in it. For me, understanding this starts with understanding our Sun. So this week I’ve been catching up on the latest developments in solar physics at the European Solar Physics meeting, being held at Trinity College Dublin. The talks have covered the usual subjects such as eruptions and explosions known as coronal mass ejections (CMEs) and solar flares. But one topic has really stood out for me. That’s the new view we now have of the Sun’s middle kingdom—the interface region between the solar surface and the corona. 

One of the basic aspects of the Sun is that it is made of concentric shells of gas. This idea stretches back over a century. The Sun is like an onion but each layer has its own characteristics that distinguish it from the next. The surface layer is known as the photosphere and it has a temperature of around 6000 Kelvin. The outer layer visible during a total solar eclipse is called the corona, which has a temperature in excess of a million Kelvin. Between these two layers is the interface region. 

In fact, the interface region combines what’s traditionally known as the chromosphere and the transition region. One of the great successes of the space age has been that we’ve learned it’s not right to think about it in terms of a layer at all. A better way is to think about the interface region being like a forest where there are trees of relatively dense gas surrounded by less dense material. The trees reach up to different heights so that the top is jagged and irregular. It’s also a tricky region to observe as the gas temperature isn’t uniform and it radiates light at different wavelengths from visible to ultraviolet. 

To get a better view of the interface region NASA launched its IRIS mission last year. The data that have been collected since is so detailed that many speakers at this week’s conference have been showing their spectacular findings. 

We have been treated to movies showing waves throughout the interface region. The forest is dynamic—the trees are swaying in the wind. We’ve seen movies of jets of hot gas that shoot upwards from the trees. OK, my analogy isn’t perfect, but you see what I mean. Both energy and mass flow up through the interface region to heat the corona and feed the constant outflow of the solar wind. It’s been incredible just how dynamic the interface region is. 

The Principal Investigator, or lead, of the IRIS mission is Alan Title and he passed on some wise words at the conference. IRIS took less than four years to build which is a pretty quick turn around in an era where missions can take a decade to be completed after many years of campaigning to get funding. IRIS was also a fraction of the cost of some of the larger missions. So, Alan’s message to young scientists was to learn from IRIS. A good idea can sometimes mean thinking small and important missions to study the Sun needn’t cost the Earth.