Launched in December 2024, the paired spacecraft quickly notched two milestones: the first precise formation flight in space and, building on that achievement, the first artificial solar eclipse in orbit. Hundreds of hours of subsequent observations now demonstrate that Proba-3 can reliably deliver continuous imagery of the inner corona, an area where earlier space-based instruments struggled to obtain consistent coverage.

The inner corona is the region where the solar wind accelerates before flowing out through the Solar System to reach satellites and Earth, and it is also the birthplace of most coronal mass ejections. By capturing detailed images in this zone, Proba-3 is enabling researchers to investigate how the solar wind gains speed and how coronal mass ejections are initiated and structured close to the Sun.

A recent time-lapse sequence illustrates this capability by tracking a coronal mass ejection observed over about 90 minutes on 16 July by three European instruments on different missions. In that dataset, the solar disc and low corona, shown in yellow, come from the SWAP extreme-ultraviolet telescope on Proba-2, the outer corona in red is seen by the LASCO C2 coronagraph on SOHO, and the inner corona in green is imaged in detail by Proba-3's ASPIICS coronagraph, which supplies the previously missing segment of the event.

"You can see the CME forming at the edge of the solar disc, captured by Proba-2. It extends into the inner coronal region, which is now visible to us thanks to Proba-3, before reaching the high corona observed by SOHO. The continuity with which we can now observe the CME structure extend outwards from the Sun is incredible," said Andrei Zhukov of the Royal Observatory of Belgium, Principal Investigator for the ASPIICS coronagraph.

This continuous tracking from the solar surface out through the corona allows scientists to follow the evolution of coronal structures across all relevant height ranges. Researchers can now link activity seen in the extreme-ultraviolet low corona directly to structures and dynamics observed higher up, improving models of how eruptions develop.

Proba-3's design effectively creates a total solar eclipse on demand by flying its two spacecraft in a highly controlled formation. One satellite carries the ASPIICS coronagraph, while the other functions as an occulting disc, and by aligning with millimetre precision they block the bright solar disc and expose the faint corona, reproducing the geometry of a natural total eclipse but under controlled orbital conditions.

"Our artificial eclipse images are comparable with those taken during a natural eclipse," said Zhukov. "The difference is that we can create our eclipse once every orbit, which takes 19 hours and 40 minutes, 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 scheduling flexibility lets the mission secure long observing runs that are not possible from the ground. Extended sequences are particularly valuable for tracking the development of coronal mass ejections, waves and other evolving features that cannot be fully characterized during a few minutes of totality.

Proba-3 project scientist Joe Zender noted that the mission has already accumulated about 250 hours of observation time over some 50 orbits. According to Zender, this volume of data is equivalent to what could be gathered by roughly 6000 total eclipse campaigns on Earth, underscoring how the orbital platform transforms the cadence and scale of coronal studies.

The mission timeline over the past year has been driven by increasingly complex formation-flying exercises. After launch on 5 December 2024, the two spacecraft were separated in orbit six weeks later, and in March they executed their first autonomous formation flight, a key step toward routine eclipse operations.

Within a month of that test, Proba-3 met its core technical goal by aligning the two spacecraft in orbit with millimetre-level accuracy and maintaining their relative positions for several hours without ground intervention. This degree of control is essential for keeping the artificial eclipse stable long enough to run extended coronal observing campaigns and to study dynamic events such as coronal mass ejections as they evolve.

Demonstrating this precision, the Coronagraph and Occulter spacecraft now use their formation-flying phases to generate artificial solar eclipses during each orbit. These recurring eclipses provide a platform for sustained, high-resolution monitoring of the inner corona that complements data from Proba-2, SOHO and other heliophysics missions, supporting broader efforts to understand solar activity and its impact on space weather near Earth.

Related Links
European Space Agency
Solar Science News at SpaceDaily