For centuries, observing a total solar eclipse has been the only way to truly see the sun’s wispy outer atmosphere, called the corona. These rare celestial events, where the moon perfectly blocks the sun’s bright disk, allow scientists a fleeting glimpse of this mysterious region. Now, the European Space Agency (ESA) has achieved something remarkable: creating an artificial solar eclipse in space, providing unprecedented, long-duration views of the sun’s corona.
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This breakthrough comes from ESA’s Proba-3 mission, a pioneering project featuring two satellites flying together with incredible precision. Launched in late 2024, this mission isn’t just about taking pretty pictures; it’s about unlocking the secrets of the solar corona, a region that influences space weather and can impact technology here on Earth.
Why Study the Sun’s Corona?
The sun’s corona is a puzzle. It’s the outermost layer of the sun’s atmosphere, extending millions of miles into space. Counterintuitively, it’s much hotter than the sun’s visible surface – reaching temperatures over two million degrees Fahrenheit! Understanding why the corona is so hot and how it generates phenomena like the solar wind is crucial for solar physicists. The solar wind constantly streams charged particles towards Earth, and powerful bursts from the corona, like coronal mass ejections, can disrupt satellites, communication systems, and even power grids.
Greenish inner solar corona image
From Earth, the corona is hidden by the sun’s overwhelming brightness. Only during a total solar eclipse, when the moon perfectly covers the sun’s disk, does the faint corona become visible. But these natural eclipses are short, lasting only a few minutes at any given location, and they only happen rarely.
How Proba-3 Creates an Eclipse in Space
This is where Proba-3 comes in. Instead of waiting for the moon, Proba-3 uses two satellites flying in precise formation. One satellite, called the Occulter, acts as an artificial moon, carrying a 1.4-meter disk designed to block the sun’s light. It flies exactly 150 meters (about the length of a football field and a half) in front of the second satellite, the Coronagraph.
The Coronagraph satellite holds the scientific instrument, called ASPIICS, which needs to see the corona without being blinded by the sun’s direct light. The Occulter casts a tiny 8 cm shadow precisely onto the Coronagraph’s imager, perfectly mimicking the alignment of a natural total solar eclipse.
This “artificial eclipse” isn’t just a fleeting moment. Because the satellites can maintain their formation, they can hold this eclipse-like condition for up to six hours during each orbit. Compare that to just a few minutes during a natural event! This gives scientists dramatically more time to observe the corona in detail.
A view of the inner solar corona in polarized white light, processed to appear violet, helping scientists study dust scattering.
The Engineering Marvel: Precision Formation Flying
Achieving and maintaining this precise 150-meter separation in space is an incredible engineering challenge. The Proba-3 satellites follow a highly elliptical orbit, ranging from 373 miles (600 km) at their closest point to Earth to a staggering 37,000 miles (60,000 km) at their furthest.
It’s at this furthest point (called apogee) that they perform their magic. Away from the stronger pull of Earth’s gravity and atmospheric drag, the satellites can fly in formation autonomously, using sophisticated navigation systems to stay perfectly aligned for hours. This is the world’s first precision formation flying mission on this scale.
First Glimpses: Images from the Artificial Eclipse
ESA has released the first images captured by the ASPIICS instrument during these artificial eclipses. Scientists say these views of the inner corona are comparable in quality to those taken during natural total solar eclipses.
The images reveal the intricate structures and dynamics of the corona. The ASPIICS instrument can capture light in different ways – visible light (like our eyes see, but through filters), polarized white light (which helps distinguish between light from the corona and light scattered by dust), and specific spectral lines.
Observing the corona in the ‘coronal green line,’ emitted by superheated iron atoms (up to 2 million degrees), reveals hot structures like this loop extending from the sun’s surface.
Observing in spectral lines allows scientists to see where different elements are present and their temperatures. For example, the ‘coronal green line’ seen in one image corresponds to iron atoms that have lost half their electrons due to the extreme heat. This lets researchers map the hottest parts of the corona.
Each final image is actually a composite, created by combining multiple exposures captured with different timing. This technique ensures that both the bright inner corona and the fainter outer regions are clearly visible in a single picture.
Illustration showing the two Proba-3 satellites, the Occulter and the Coronagraph, flying precisely 150 meters apart to block the sun and study the corona.
What’s Next for Proba-3?
The Proba-3 mission is planned to last for two years. During this time, the satellites will perform their artificial eclipse routine repeatedly, collecting approximately 1,000 hours of precious data and images of the sun’s corona.
ESA maintains an open data policy, making the raw data and images available online for scientists and the public. This wealth of data will help researchers around the world piece together the mysteries of the corona, improve our understanding of solar physics, and enhance our ability to predict space weather.
Orbital diagram of Proba-3, showing its highly elliptical path and the phase near apogee (furthest point from Earth) where the artificial eclipse observations take place.
By creating its own eclipses on demand, Proba-3 is opening a new window into the sun’s corona, offering unprecedented opportunities to study this vital, yet elusive, part of our star. This mission highlights the power of innovative engineering to overcome observation challenges and expand our knowledge of the universe.
