The Proba-3 satellites, a remarkable feat of engineering by the European Space Agency, have been making waves in the field of solar science since their launch in July 2025. These satellites have already achieved an impressive feat, creating 57 artificial solar eclipses and collecting over 250 hours of high-resolution videos of the Sun's atmosphere, the corona. This is equivalent to the observing time of about 5000 total solar eclipse campaigns carried out on Earth, a testament to the satellites' capabilities and the value of their data.
But the real excitement lies in the science behind Proba-3's mission. For the first time, we can carefully track how material from the Sun moves through the inner corona, where space weather is born. The first results, recently published in The Astrophysical Journal Letters, reveal that solar wind structures in the inner corona travel three to four times faster than scientists thought. This discovery is a game-changer, as it challenges our understanding of the Sun's behavior and the dynamics of space weather.
Before Proba-3, a total solar eclipse seen from Earth was the best way to observe the Sun's inner corona. However, these events are rare, occurring only once every 18 months and lasting at most a few minutes. Proba-3, on the other hand, creates artificial total solar eclipses by flying its two spacecraft in an extremely precise formation. For around five hours at a time, the Occulters spacecraft acts like an artificial Moon, blocking the Sun's direct light so the other spacecraft, the Coronagraph, can see the Sun's corona.
The ASPIICS coronagraph instrument on Proba-3 can observe down to 70,000 km from the Sun's surface, one-tenth of the Sun's radius. This level of detail is unprecedented, as no other space-based coronagraph can observe the light scattering off particles in the Sun's corona this close to the Sun. ASPIICS takes one or two images per minute, which are combined into videos that reveal intricate movements in the hard-to-observe inner corona. These movements have never been observed in optical wavelengths so low in the Sun's inner corona.
One of the most fascinating findings from Proba-3's data is the discovery of 'slow' solar wind speeds close to the Sun. Solar wind, like wind on Earth, can be fast or slow, smooth, or gusty. Fast solar wind usually flows in a smooth current from magnetic structures called coronal holes. In contrast, slow solar wind is variable and gusty, making it more challenging to understand. Scientists believe that slow solar wind is generated by the Sun's magnetic field lines changing how they are connected, merging, and separating again, pushing out blobs of plasma in so-called 'streamers'.
However, Proba-3's observations have revealed that slow solar wind gusts in the inner corona are moving three to four times faster than expected. This is a significant finding, as it challenges our understanding of the Sun's magnetic field and plasma acceleration in the corona. Andrei Zhukov, the principal investigator of Proba-3's ASPIICS instrument and the lead author of the study, notes that slow solar wind is naturally not uniform and involves lots of small-scale structures in the Sun's magnetic field that can be seen thanks to ASPIICS.
The implications of this discovery are far-reaching. It raises a deeper question about the nature of slow solar wind and its relationship to the Sun's magnetic field. It also highlights the importance of Proba-3's data in advancing our understanding of the Sun's behavior and the dynamics of space weather. As Joe Zender, ESA's Proba-3 project scientist, points out, this first dataset is just the beginning of a much longer journey to fully understand what's happening.
The exciting part is that most of the data collected by Proba-3 so far is yet to be analyzed. Scientists are invited to use ASPIICS coronagraph data to investigate the workings of the Sun's corona and space weather. Key open questions that remain to be answered include what accelerates the solar wind, how the Sun flings out material in coronal mass ejections, and why the solar corona is so much hotter than the Sun itself.
In conclusion, Proba-3's mission is a remarkable achievement, pushing the boundaries of our understanding of the Sun and space weather. The satellites' ability to create artificial solar eclipses and observe the Sun's inner corona in unprecedented detail is a testament to the power of space exploration. As we continue to analyze Proba-3's data, we can expect to uncover more fascinating insights into the Sun's behavior and the complex dynamics of space weather.
