How scientists created an ‘artificial' total solar eclipse to unlock the Sun's secrets

Indian Express

19-06-2025

The sun's corona (or outer atmosphere) has proved a difficult subject for solar scientists on Earth to study, appearing only in a total solar eclipse. This phenomenon, occurring once in around 18 months, was their only opportunity to observe parts of the corona. However, with Proba-3's recent mission, research can advance at a much quicker pace.
The European Space Agency (ESA) on June 16, announced that the Proba-3 mission had created an 'artificial total solar eclipse' in orbit. This was achieved as the mission's two spacecraft – the Coronagraph and the Occulter – flew in formation 150 metres apart, and aligned so that the Occulter's disc covered the sun's disc, casting a shadow onto the Coronagraph's optical instrument.
'I was absolutely thrilled to see the images, especially since we got them on the first try,' Andrei Zhukov, principal investigator for ASPIICS at the Royal Observatory of Belgium, said in a statement.
The mission was launched in December 2024. It involved sending both satellites into the solar orbit. In March this year, both spacecraft flew 150 metres apart, in formation up to to a millimetre's precision, without control from the Earth for several hours.
When creating the artificial solar eclipse, the satellites aligned in formation based on the position of the Sun. Then, Occulter's 1.4-metre large disc would be used to block the sun's disc. This would cast a shadow of approximately 8 centimetre, across the Coronagraph's optical instruments, positioned behind the Occulter. Thanks to the precision, these instruments were able to provide the images of the corona.
'Our 'artificial eclipse' images are comparable with those taken during a natural eclipse. 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,' Zhukov explained.
This mission could prove crucial for solar scientists, with previously unseen angles of the elusive corona becoming available for study. One benefit could be the study of solar wind, described by the ESA as 'the continuous flow of matter from the Sun into outer space.' Driven by the corona, these winds usually consist of charged particles, and constantly rain down upon the Earth as well.
However, this can be interrupted by coronal mass ejections (CMEs), or solar storms. This subsequently affects space weather, which in turn can affect Earth's power grids, communication systems, and satellite operations.
With the data from the Proba-3 mission and any subsequent missions focused on corona imaging, solar scientists can be better prepared for the potential threat of a severe solar storm – which NASA describes as 'a sudden explosion of particles, energy, magnetic fields, and material blasted into the solar system by the Sun'.
Another question that Proba-3 would be able to solve is how the corona, which extends millions of miles across space, but still reaches temperatures above a million degrees Celsius, burns much hotter than the surface. To understand the reasoning, Proba-3 is attempting to study the corona at a minimal distance from the sun's surface.
Due to the quality of the equipment, fewer stray rays would hit the detector, more details would be captured, and fainter features would be detected as compared to a traditional coronagraph.
'Current coronagraphs are no match for Proba-3, which will observe the Sun's corona down almost to the edge of the solar surface. So far, this was only possible during natural solar eclipses,' Jorge Amaya, Space Weather Modelling Coordinator at ESA, said in the ESA release.
Alongside the key data provided by Proba-3, its precision flying in formation also paved the way for future missions, such as the ESA's Laser Interferometer Space Antenna (LISA), scheduled to launch in 2035. This mission will contain three identical spacecraft, arranged in an equilateral triangle formation, trailing behind the Earth in its orbit around the Sun.
The mission is scheduled to last two years, aiming to capture images of the corona for further study, and then re-enter the Earth's atmosphere five years post-launch, as per the ESA.
(This article has been curated by Purv Ashar, who is an intern with The Indian Express)