The ICON (Ionospheric Connection Explorer) mission is now in orbit and sending back valuable data about Earth’s ionosphere, after 28 months of repeated launch delays. Over two years of waiting didn’t seem very long to Principal Investigator Thomas Immel, however, because he had already waited a lifetime for the data ICON is collecting. The inspiration for the mission came from an image captured during an Apollo mission around the time Immel was born.
Immel grew up in Illinois, but he wound up at the University of Alaska Fairbanks for graduate school because “Alaska” begins with an A. (Immel says, “Back in the old days, you went to the library and got the book on grad schools in the US, and Alaska was on the first page, so I applied to Alaska, and I got in.”) In Alaska, the extreme weather made it easy to focus on studying, and also brought the graduate students together. “Everybody would be in an emergency situation at one time or another,” Immel remembers. “My cabin froze solid when it was about 50 below, and friends came and helped me out.”
On the desk in Immel’s freezing cabin was a book that contained a mystery. Figure 1 was an ultraviolet view of planet Earth, taken from the surface of the moon in 1972 by Commander John Young of Apollo 16.
In this ultraviolet view, daylight excites the ions and free electrons of Earth’s ionosphere, making them glow. Fainter bands of glowing plasma are visible on the night side of the planet: the Southern Lights at the south pole as well as two distinct bands of plasma near the equator. Those two bands are clearly coming together and collapsing into one point–at least, that seemed clear to Immel. The consensus of the day was that the bands of plasma couldn’t actually be coming together, because Earth’s magnetic field lines should trap them and keep them parallel. Scientists at the time assumed that the image must be flawed: the plasma bands only appeared to converge because of a trick of perspective or some sort of warping in the imager. However, Immel was convinced that the plasma bands were crossing the magnetic field lines and converging. He could see that the ionosphere was collapsing–and he was determined to figure out why.
After graduate school, Immel went to Southwest Research Institute in Texas for two years, where he worked on the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) mission. Imagers on the IMAGE spacecraft recreated John Young’s UV view of Earth over and over, showing the converging plasma bands. IMAGE confirmed that the collapse of the ionosphere was no illusion, no anomaly, but an unexplained phenomenon happening regularly all around the planet.
The Space Sciences Lab (SSL) developed the FUV (Far UltraViolet) imagers for IMAGE, and Immel “started scheming about how to get out to California” so he could work on ultraviolet imagers, too. He joined SSL in June of 2000 and began laying the groundwork for a new mission that would help him understand why Earth’s ionosphere behaves in such unexpected ways. As he worked to convince NASA of the importance of such a mission, some of the best advice Immel received was: “Tell your story!” Communicating his fascination with that original Apollo 16 image turned out to be instrumental in getting the ICON heliophysics explorer mission approved in 2013.
ICON launched on October 10, 2019, after repeated delays caused by technical problems with the launch vehicle. While frustrating, in some ways those delays were a positive development for the ICON science team. “We got to spend a lot more time on the simulations of the instruments, so much that we’re getting exactly what we expect out of the payload, which is really remarkable,” says Immel.
ICON has only just begun sending back data, but the mission is already beginning to transform our understanding of the ionosphere. It is becoming clear that plasma in the ionosphere is influenced not only by space weather from above, but also by terrestrial weather from below. There are tides in the atmosphere, similar to ocean tides but more complicated and driven by buoyancy rather than gravity. These atmospheric tides push bands of plasma around in predictable patterns, forcing them across Earth’s magnetic field lines and causing the collapse that caught Immel’s imagination way back in grad school. He is eager to find out what else the new data will reveal.
Ep 1: Space Sciences Lab team member profiles, an ongoing series.