The lowest reaches of space glow with bright bands of color called airglow.
In 2019, NASA’s ICON mission sent a 600-pound toddler-sized spacecraft 360 miles off the ground and into the ionosphere, the poorly understood uppermost stratum of the atmosphere. ICON beamed back a steady stream of scientific breakthroughs, critical data, and stunning imagery of the glowing interface between Earth and space. Discoveries include the first-ever measurement of violent interaction between terrestrial and space weather during the Hunga Tonga-Hunga Ha’apai volcanic eruption and the first direct observation of the long-theorized electric ionospheric dynamo as it responded to lower atmosphere wind patterns. NASA called an official end to the extended mission after scientists lost communication with the high-tech extreme weather reporter in November of 2022. NASA attempted to troubleshoot and regain transmission for eight months and declared the mission complete in July 2024.
ICON’s mission was critical to modern-day society that depends on the ionosphere to host a large population of manmade satellites that orbit the Earth, retaining them just within Earth’s gravitational pull and protecting them from space weather. Radio wave communications rely on the ionosphere to ricochet and volley transmissions around the Earth in a relay of signals. Space weather, as well as Earth’s weather, can cause a disruption in communications, GPS, and satellite function when the paths of the radio waves are altered by the unpredictable electric currents surging through the ionosphere. ICON provided unprecedented documentation of these changes in the density and composition being initiated by both Earth weather and the space weather sent across the solar system by the sun. The results of the mission have laid the groundwork for a bright future of scientific discovery and revelation as researchers sift through the data collected during ICON’s prolific mission.
The ICON satellite carried four state-of-the-art imaging and sampling instruments and orbited the equator while actively sampling and making measurements of the gases, charged particles, and wind speeds that comprised the atmosphere in which it flew. It snapped images of the ethereal auroras, rivers of charged particles, ionosphere dynamos, and snaking channels of airglow.
The Hunga-Tonga-Hunga Ha’apai volcanic eruption sent pressure waves into the upper atmosphere, … [+] causing extreme winds and anomalous electrical currents that were observed by NASA’s ICON and the ESA satellite swarm.
ICON provided aerial images of the behemoth submarine Tonga volcanic eruption that occurred on January 15, 2022. The eruption not only sent seismic energy booming through the earth and tsunamic waves propagating around the world but also caused ‘hurricane-force winds’ in the upper atmosphere measured at 450 mph by the MIGHTI wind imaging tool onboard ICON. Tonga’s pressure wave dispatched anomalous electric currents through the ionosphere. ICON’s FVM tool could measure the speed and motion of the charged particles that swirled in the wake of the atmospheric tide cause by the eruption. The Tonga eruption completely reversed the eastern flow-direction of the equatorial electrojet, a streaming electrical current circling the Earth, and caused a surge in the current approximately 5 times its normal intensity. These observations up-ended the previously reigning top-down theory that only the sun, moon (lunar tides), and space weather could impact the ionosphere’s weather patterns and electrical currents. Instead, Earth’s weather pattern and events caused daily changes in the density, composition and movement of the charged sea of swirling particles that makeup the ionosphere.
What is the Ionosphere, according to ICON?
Earth’s Ionosphere is the Earth-space boundary layer of the atmosphere that is bombarded by high-energy radiation from the sun, flowing rivers of charged ions from space, and other space weather. Space weather occurs mostly in the form of blasts of ionized particles from the sun that travel outward into space, where they are intercepted by the planetary bodies in their path. The charged space particles collide with our atmosphere, dislodging electrons and subatomic particles from normally neutral gases and creating free-flying negatively charged electrons and positively charged gases. These ionized gases glow when they eventually relax into a more stable state, regaining an electron and emitting visual light in the process. The auroral events visible at high latitudes, like the Aurora Borealis, are the experiential results of this process. Airglow is like an aurora that can be seen at all latitudes but is too faint to observe with the naked eye.
Earth’s airglow captured by Scott Kelly in the International Space Station.
ICON’s FUV and EUV imaging instruments, designed and built at UC Berkley and UIUC’s Grainger Engineering laboratory captured the glimmering airglow as it slithered across the globe. ICON observed nightly shifts in how the ions amassed and flowed, changes that are now attributed to both solar radiation (or lack thereof at night) and Earth’s weather patterns. The ionosphere itself thickens during the day and thins at night, a phenomenon that is also caused by a solar eclipse. The shadow of the moon caused a thinning in the ionosphere as it protected part of the Earth from solar bombardment, leaving fewer ionized particles in the ionosphere as the charged particles relax and recombine into neutral gases. These results show that the chemical composition, density and structure of this boundary layer are sensitive and responsive on a much shorter time frame than previously imagined.
Scientists continue to unwrap the breakthrough discoveries NASA’s ICON provided during its primary and extended missions, including revelatory observations on the wind-fueled ionospheric dynamo, Earth’s natural magnetosphere-ionosphere electrical generator, airglow patterns, and the strong wind patterns that are affected by both space and earth weather. Practically, these revelations will enhance scientists’ ability to predict disruptions in communications, GPS, and satellite function.
