Through the Solar Looking Glass: A Q&A with the Researchers Building the Tools to Uncover the Sun’s Mysteries

The Sun is our closest star and primary source of light and heat, so naturally it makes sense for us to want to learn more about how it works. By taking a closer look at the Sun, we not only deepen our understanding of it, but we also gain valuable insights into the workings of other distant stars. Every star in the universe is driven by the same physics that governs our Sun; which means, in a way, that the Sun is a window to our universe. 

So how do we get to know our neighborhood star?

Lockheed Martin, in partnership with NASA and various research institutions, is actively engaged in the creation of a Medium Class Explorer called the Multi-slit Solar Explorer (MUSE). It contains an innovative multi-slit spectrograph, which splits light into different colors or wavelengths to remotely diagnose the physical properties of gases in the solar atmosphere. This unique instrument will allow scientists to study the Sun in unprecedented detail, up to 35 times faster than current instruments, revealing crucial information about its processes and the origins of solar phenomena. 

To gain a deeper understanding of MUSE, its mission and capabilities, we spoke with the researchers leading its development:

• Bart De Pontieu, a solar astrophysicist, is the Principal Investigator, or PI, of the MUSE mission
• Gary Kushner serves as the project manager.

Both work at Lockheed Martin’s Advanced Technology Center (ATC) in Palo Alto, CA.

Gary Kushner: MUSE is a project years in the making. It actually starts with an existing mission named IRIS, which stands for Interface Region Imaging Spectrograph. We built IRIS for NASA in just under four years and, after its launch into near-Earth orbit in 2013, continue to operate it for NASA and the global science community. With IRIS we intend to better understand how energy and plasma move from a lower layer of the Sun’s surface called the photosphere, through the interface region layer (also called chromosphere) into the very hot outer solar atmosphere, or corona, which has a temperature of millions of degrees, much hotter than the 10,000 degrees Fahrenheit surface of the Sun.  

Bart De Pontieu: IRIS has been a great scientific success. It was designed to study which physical processes are responsible for heating the solar chromosphere to tens of thousands of degrees, hotter than the surface. How is it that the further you move away from the surface, the hotter the solar atmosphere gets, all the way to millions of degrees in the corona? IRIS opened up a window of discovery into the chromosphere region and has revealed evidence for the magnetic waves and electrical currents that are thought to play a role in explaining the heating of the solar atmosphere. With MUSE, we built on the success of IRIS and took into account lessons learned. So, we proposed to build an instrument that is focused on the corona, and that captures its dynamics much faster than ever before.
 

Gary: First, I will note that MUSE is a full team effort. MUSE needs a variety of skills from scientists, engineers, artists, managers, business operations, software developers, teachers, communicators, and more. The success of MUSE is dependent on each team executing at the highest level.

MUSE is a complex project in itself, and a complex team. It is a Principal Investigator-led project, led by Bart, that Lockheed Martin’s ATC builds for the Explorers Program at NASA’s Goddard Space Flight Center. MUSE is a medium class explorer mission within NASA’s Heliophysics Division. The ATC manages the efforts of the Lockheed Martin team that builds the spacecraft and instrument, as well as the several partner institutions that contribute to the instrument, including the Smithsonian Astrophysics Observatory, Montana State University, NASA’s Goddard Space Flight Center, and many science institutes around the world. University of California, Berkeley provides the mission operations center, while the ATC also provides science operations and research after launch. 

Bart: By using spectroscopy, we are trying to figure out the properties of the gas in the Sun’s atmosphere by analyzing the light that it emits. 

A spectrograph is the tool that allows us to capture the light and break it down into its component colors or wavelengths, like red, blue, orange, etc. With the spectrograph we can bend the colors or wavelengths in different directions. We then convert the photons into electrical signals with our detector and measure the strength of the different wavelengths. By carefully studying this spectrum of light, we can remotely diagnose the temperature, density, velocity and turbulent motions of the gases that emit the light. This is key to figure out which physical processes drive the phenomena we observe in the Sun’s atmosphere.

What makes MUSE’s spectrograph so unique and innovative is that it is a multi-slit instrument.

A typical spectrograph is single slit, meaning light enters through one narrow slit. The light captured in this single slit is then spread out into a spectrum, like a rainbow, as the light passes through a prism or diffraction grating. To get a view of a whole scene, we then have to scan that single slit across the scene to make a two-dimensional map of the Sun. This can take a lot of time and can’t capture how fast the Sun’s atmosphere changes while we’re slowly scanning across the solar disk. 

MUSE’s multi-slit spectrograph has 35 of these slits. This means that light can enter through many parallel slits at the same time and allows multiple light sources to be studied simultaneously.  

Because of the multi-slit capability, MUSE can capture data 35 times faster and over a larger field of view than current missions, allowing observations of more flares and eruptions, and resolves smaller details in the Sun’s atmosphere than previous spectrographs. 

Gary: To complement the spectrograph, MUSE has another trick up its sleeve, a second instrument known as a Context Imager. The Context Imager takes high-resolution images of the Sun’s corona to provide context to the spectra and more temperature coverage, which makes MUSE a very powerful instrument.