Two spacecraft mimicked a solar eclipse to capture rare images of the Sun’s corona. The mission also helps predict hazardous space weather.
During a natural solar eclipse, heliophysicists have a rare opportunity to investigate the Sun’s corona, the outermost layer of its atmosphere, in ways that are not normally possible.
The Sun’s inner regions shine so intensely that they overwhelm the faint light of the corona, making it invisible to most astronomical instruments. Only when the Moon passes in front of the Sun and casts a shadow on Earth can the corona be seen. However, eclipses are uncommon, brief, and visible only along narrow tracks across the planet. As a result, researchers must go to great lengths to position their instruments in the right place at the right time to study these fleeting events.
To overcome these limitations and deepen understanding of the Sun, scientists at the European Space Agency have developed and launched a new probe capable of producing artificial eclipses.
Meet Proba-3
The spacecraft, named Proba-3, is designed to mimic the effect of a natural solar eclipse. One of the probes, which appears nearly circular from the front, orbits closer to the Sun and blocks its intense central light, functioning much like the Moon during an eclipse. This creates a shadow that falls onto a second probe equipped with a camera to capture images of the artificial eclipse.
Coordinating two spacecraft so that one consistently casts a shadow on the other is a highly complex challenge. Proba-3 serves as a test mission to demonstrate this precise formation-flying technology, which will be essential for many future space projects.
The methods being developed could support upcoming missions, such as spacecraft designed to dock with and remove inactive satellites or advanced telescopes that place sensitive instruments far from their primary mirrors.
At the same time, the mission offers researchers an added advantage: the ability to capture valuable images of the Sun’s corona, giving scientists new opportunities to study its structure and behavior.
An immense challenge
The two satellites launched in 2024 and entered orbits that approach Earth as close as 372 miles (600 kilometers) – that’s about 50% farther from Earth than the International Space Station – and reach more than 37,282 miles (60,000 km) at their most distant point, about one-sixth of the way to the Moon.
During this orbit, the satellites move at speeds between 5,400 miles per hour (8,690 kilometers per hour) and 79,200 mph (127,460 kph). At their slowest, they’re still moving fast enough to go from New York City to Philadelphia in one minute.
While flying at that speed, they can control themselves automatically, without a human guiding them, and fly 492 feet (150 meters) apart – a separation that is longer than the length of a typical football stadium – while still keeping their locations aligned to about one millimeter.
They needed to maintain that precise flying pattern for hours in order to take a picture of the Sun’s corona, and they did it in June 2025.
The Proba-3 mission is also studying space weather by observing high-energy particles that the Sun ejects out into space, sometimes in the direction of the Earth. Space weather causes the aurora, also known as the northern lights, on Earth.
While the aurora is beautiful, solar storms can also harm Earth-orbiting satellites. The hope is that Proba-3 will help scientists continue learning about the Sun and better predict dangerous space weather events in time to protect sensitive satellites.
Adapted from an article originally published in The Conversation.
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