Since becoming operational in July 2025, the pair of Proba-3 satellites has created 57 artificial solar eclipses and collected more than 250 hours of high-resolution video of the Sun's corona - equivalent to the observing time of approximately 5,000 total solar eclipse campaigns carried out on Earth.
Proba-3 creates artificial total solar eclipses by flying its two spacecraft in extremely precise formation. For around five hours at a time, the Occulter spacecraft acts as an artificial Moon, blocking the Sun's direct light so that the Coronagraph spacecraft can observe the solar corona. The mission's ASPIICS coronagraph instrument can see down to 70,000 km from the Sun's surface - one tenth of the Sun's radius - closer than any other space-based coronagraph currently in operation. ASPIICS takes one or two images per minute, which are combined into videos revealing movement in the inner corona that has never previously been observed in optical wavelengths.
"These intricate movements have never been observed in optical wavelengths so low in the Sun's inner corona," noted Joe Zender, ESA's Proba-3 project scientist.
The first results focused on slow solar wind, which is variable and gusty in contrast to the smooth fast solar wind that flows from coronal holes. Scientists think slow solar wind is generated by the Sun's magnetic field lines changing their connections, merging and separating in a process that pushes out blobs of plasma in structures called streamers - large, bright rays in the corona.
Prior research had indicated that close to the Sun's surface, slow solar wind should have speeds around 100 km/s. Instead, the Proba-3 team tracked blobs of plasma moving at 250 to 500 km/s.
"In the inner corona, a region very difficult to observe, we saw slow solar wind gusts moving three to four times faster than expected," said Andrei Zhukov of the Royal Observatory of Belgium, principal investigator of Proba-3's ASPIICS instrument and lead author of the study. "Slow solar wind is naturally not uniform, involving lots of small-scale structures in the Sun's magnetic field that we can see thanks to ASPIICS."
"We can track how solar wind speeds up close to the Sun, we see it all over Proba-3's field of view, and we have already seen speeds and accelerations that surprised us," said Zender. "This first dataset is just the beginning of the much longer journey to fully understand what's happening. Now it's up to theoretical experts to compare this to models of the magnetic field and plasma acceleration in the Sun's corona."
Beyond ASPIICS, Proba-3 carries two additional science instruments. The Digital Absolute Radiometer (DARA) has been continuously measuring the Sun's total energy output with unprecedented accuracy, investigating how solar irradiance changes over time. The 3D Energetic Electron Spectrometer (3DEES) is measuring the number, direction of origin, and energies of electrons in Earth's Van Allen radiation belts, revealing how the belts respond to solar wind and coronal mass ejections.
Most of the data collected by Proba-3 to date remains unanalysed. Scientists are invited to use the publicly available ASPIICS coronagraph data to investigate the workings of the solar corona and space weather. Key open questions to be addressed include what accelerates the solar wind, how the Sun generates coronal mass ejections, and why the solar corona is so much hotter than the Sun's surface.
Proba-3 launched in December 2024 and has since completed more than 60 extremely accurate formation flying orbits, achieving two world firsts - the first precise formation flight of its kind, and the first artificial solar eclipse created in orbit.
Research Report:Ubiquitous Small-scale Dynamics in the Slow Solar Wind Formation Region Observed by Proba-3/ASPIICS
Related Links
Proba-3 at European Space Agency
Solar Science News at SpaceDaily
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