Ready for Launch: NASA's IRIS Spacecraft

The photosphere is the visible surface of the sun, sort of like the Earth's surface. It's what we see when we observe the sun in visible light. It's where you find sunspots. The temperature at the photosphere is 6,000 Kelvin (5,700°C, 10,300°F) The layers of the sun above the photosphere are called the solar atmosphere.

On top of the photosphere is the chromosphere. The chromosphere has a very small density—it's actually less dense than the Earth's atmosphere. A funny thing starts to happen as you travel out of the sun through the chromosphere. The temperature drops at first, by a couple thousand K, and then increases. The outer edge of the chromosphere is 35,000K.

The next layer of the sun is called the transition region. The solar transition region is the layer of solar atmosphere in between the chromosphere and the corona. It's called the transition region, because the solar matter acts differently above and below. One example of this, is the temperature. The temperature of the sun skyrockets through the transition region. Remember, the temperature of the photosphere is 6,000K? The temperature of the corona is closer to that of the interior of the sun. The internal temperature of the sun is somewhere around 15,700,000K. The temperature of the sun's corona is 5,000,000K, and can even exceed 15,000,000K.

NASA's IRIS spacecraft will study the sun's chromosphere and corona. This will help us better understand the solar transition region, and how the sun's photosphere and chromosphere interact with the corona.

Here's the mission statement from NASA:

Understanding the interface between the photosphere and corona remains a fundamental challenge in solar and heliospheric science. The Interface Region Imaging Spectrograph (IRIS) mission opens a window of discovery into this crucial region by tracing the flow of energy and plasma through the chromosphere and transition region into the corona using spectrometry and imaging. IRIS is designed to provide significant new information to increase our understanding of energy transport into the corona and solar wind and provide an archetype for all stellar atmospheres. The unique instrument capabilities, coupled with state of the art 3-D modeling, will fill a large gap in our knowledge of this dynamic region of the solar atmosphere. The mission will extend the scientific output of existing heliophysics spacecraft that follow the effects of energy release processes from the sun to Earth.

IRIS will launch on June 26th, at 7:27PM PDT/10:27PM EDT. Find out more about IRIS at www.nasa.gov/iris.