First artificial eclipse in orbit delivers unprecedented glimpse of Sun’s corona

The breakthrough comes after the twin satellites, carrying Coronagraph and Occulter, achieved the remarkable feat of flying 150 meters apart in near-perfect sync, creating an orbiting total eclipse for scientific study.

Unlike traditional coronagraphs, which must contend with stray light and Earth’s atmosphere, Proba-3 performed this delicate maneuver entirely in space.

Precision in outer space

The Occulter blocked out the Sun’s bright disk with a 1.4-meter shield, casting an 8-centimeter-wide shadow onto the Coronagraph’s optical instrument, ASPIICS, which then captured the faint, ghostly halo of the corona.

With its 5-centimeter aperture, ASPIICS is able to see much closer to the Sun’s surface and with greater clarity than ever before.

“Each full image – covering the area from the occulted Sun all the way to the edge of the field of view – is actually constructed from three images. The difference between those is only the exposure time, which determines how long the coronagraph’s aperture is exposed to light. Combining the three images gives us the full view of the corona,” said Andrei Zhukov, Principal Investigator for ASPIICS at the Royal Observatory of Belgium.

This artificial eclipse can be generated every 19.6 hours and held for up to six hours, a vast improvement over the fleeting minutes of natural eclipses, which occur barely once or twice a year.

The solar corona, mysteriously hotter than the surface beneath it, is central to understanding the solar wind and coronal mass ejections. These violent bursts of particles can spark auroras or disrupt communications and power grids on Earth.

Proba-3’s early observations are already helping refine solar models, especially with the support of ESA’s Virtual Space Weather Modelling Centre and KU Leuven’s COCONUT software.

“Seeing the first data from ASPIICS is incredibly exciting. Together with the measurements made by another instrument on board, DARA, ASPIICS will contribute to unraveling long-lasting questions about our home star,” says Joe Zender, ESA’s Proba-3 project scientist.

Aiming for autonomy

Proba-3’s formation flying relies on a suite of advanced positioning systems developed under ESA’s General Support Technology Programme.

Mission manager Damien Galano said that the satellites achieved their first precise alignment autonomously, with ground control ready to step in, though future operations aim for full autonomy.

“Having two spacecraft form one giant coronagraph in space allowed us to capture the inner corona with very low levels of stray light in our observations, exactly as we expected.,” Galano said.

“Although we are still in the commissioning phase, we have already achieved precise formation flying with unprecedented accuracy. This is what allowed us to capture the mission’s first images, which will no doubt be of high value to the scientific community.

The mission also carried two other scientific instruments including the Digital Absolute Radiometer (DARA), which measures the Sun’s total energy output, and the 3D Energetic Electron Spectrometer (3DEES), which studies electron activity in Earth’s radiation belts.

Built by a 14-country consortium led by Spain’s Sener, with key input from Belgium and India, Proba-3 launched aboard a PSLV-XL rocket from Sriharikota in December 2024.

Scientists are now working to extend the eclipse observation window and feed the data into models that could forecast solar activity with greater accuracy.

“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,” says Jorge Amaya, Space Weather Modelling Coordinator at ESA.

 “This huge flow of observations will help refine computer models further as we compare and adjust variables to match the real images. Together with the team at KU Leuven, which is behind one such model, we have been able to create a simulation of Proba-3’s first observations.”