The Sun’s outer atmosphere—the corona—only reveals itself during total solar eclipses, which happen about every 18 months on Earth, and are only visible along a narrow path. These events offer scientists a rare opportunity to observe the Sun’s violent surface—but now, they won’t have to wait on the cosmos to do so.
On Monday, June 16, the European Space Agency (ESA) announced that its Proba-3 mission created the world’s first artificial total solar eclipse. The mission’s two satellites, the Occulter and the Coronagraph, autonomously aligned in space to blot out the Sun’s surface and capture images of the corona. Proba-3’s success won’t just expand access to solar data—it also demonstrates an entirely new level of satellite formation flying.
“I was absolutely thrilled to see the images, especially since we got them on the first try,” said Andrei Zhukov, principal investigator for the Association of Spacecraft for Polarimetry and Imaging Investigation of the Corona of the Sun (ASPIICS) at the Royal Observatory of Belgium, according to the ESA announcement.
The agency launched the Proba-3 mission on December 5, 2024, sending the Occulter and Coronagraph to solar orbit. In May, the two satellites achieved something no spacecraft had done before: Occulter and Coronagraph autonomously aligned in space with millimeter (0.04-inch) precision and maintained their relative position for hours without any intervention from ground control.
To create the artificial eclipse, the two satellites had to align with roughly 500 feet (150 meters) between them, allowing Occulter’s 4.6-foot (1.4-meter) disc to cast a 3-inch (8-centimeter) shadow on Coronagraph’s optical instrument. This blotted out the surface of the Sun from Coronagraph’s perspective, allowing it to photograph the wispy corona.
“Our ‘artificial eclipse’ images are comparable with those taken during a natural eclipse,” Zhukov said. “The difference is that we can create our eclipse once every 19.6-hour orbit, while total solar eclipses only occur naturally around once, very rarely twice a year. On top of that, natural total eclipses only last a few minutes, while Proba-3 can hold its artificial eclipse for up to 6 hours.”
This first round of coronal images offers a glimpse into the valuable data this eclipse-making mission will produce, according to ESA. Studying the corona is scientifically valuable for a number of reasons. For one, the corona drives solar wind—the continuous flow of charged particles from the Sun into outer space—and explosive jets of highly magnetized plasma called coronal mass ejections. Observing these forces is crucial to understanding solar weather, which can affect Earth’s satellites, communication systems, and power grids.
Insights from Proba-3 and subsequent corona-imaging missions could help scientists better prepare for the threat of a severe solar storm. In May, participants from several U.S. agencies ran the first-ever solar storm emergency drill, revealing major shortcomings in scientists’ ability to forecast space weather and protect critical infrastructure.
The corona may also hold the answer to a scientific mystery. This outer layer of the Sun’s atmosphere extends millions of miles out into space, but somehow reaches temperatures about 200 times hotter than the surface of the Sun. Experts have described this puzzling phenomenon, dubbed the coronal heating problem, as “one of the most vexing questions in modern solar physics.”
The Proba-3 mission aims to solve this mystery by using Coronagraph’s optical instrument to study the corona very close to the Sun’s surface, according to ESA. This state-of-the-art instrument reduces the amount of stray light that reaches the detector, allowing it to capture more detail and detect fainter features than traditional coronagraphs have in the past.
“Current coronagraphs are no match for Proba-3, which will observe the Sun’s corona down almost to the edge of the solar surface,” said Jorge Amaya, space weather modeling coordinator at ESA, in the agency’s announcement. “So far, this was only possible during natural solar eclipses.”
In addition to conducting valuable solar science, Proba-3 paves the way for autonomous precision formation flying that will be crucial for future multi-spacecraft missions such as ESA’s Laser Interferometer Space Antenna (LISA).
Proba-3 will observe the Sun’s corona for about two years, capturing images once only possible during rare celestial alignments. The flood of new observations should drastically improve scientists’ understanding of our home star—the force that makes life here on Earth possible.
