1st-of-its-kind European spacecraft duo will create mini eclipses in space, transforming how we study the sun

A pair of spacecraft orbiting Earth with the sun in background
The Proba-3 mission includes two spacecraft, Coronagraph (left) and Occulter (right). (Image credit: European Space Agency)

Later this year, the European Space Agency (ESA) will launch the Proba-3 mission into orbit around Earth. This unique project's twin spacecraft will align with each other to create frequent, artificial eclipses in space, which will give researchers near-unlimited access to studying the sun's outer atmosphere, or corona, for the first time.

An upcoming terrestrial solar eclipse on April 8, where the moon temporarily blocks out the sun, will also play a key role in preparing the spacecraft duo for their future work, mission scientists say.

The Proba-3 mission involves a pair of probes known as Coronagraph and Occulter. When in orbit, Occulter will be able to position itself between Coronagraph and the sun so that it perfectly blocks out just enough sunlight to simulate terrestrial eclipses. In doing so, Coronagraph's camera will be able to focus on the corona, which appears as a swirling sea of wispy plasma lines when it is viewed in isolation from the rest of the sun.

It will take the two spacecraft around 19.5 hours to complete a single, highly elliptical (or stretched) orbit around Earth, and they will be in eclipse formation for six continuous hours every rotation. While they are forming an eclipse, the two spacecraft will be around 470 feet (144 meters) apart, which means they must be perfectly aligned for the maneuver to work properly. If the two probes are not in sync, Occulter's shadow could block light from reaching Coronagraph's solar panel array, thereby jeopardizing the spacecraft's power.  

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When in orbit around Earth, Occulter will position itself between Coronagraph and the sun to create mini artificial eclipses. (Image credit: European Space Agency)

During terrestrial eclipses, the sun's corona becomes more visible to us on Earth than at any other time, which allows us to see things that would normally be hidden to us. For example, during the recent "ring of fire" eclipse that occurred above Australia on April 20, 2023, scientists could clearly see a gigantic cloud of magnetized plasma, known as a coronal mass ejection, as it exploded out of the sun

However, terrestrial eclipses last only around five to 10 minutes and happen once or twice a year. The new mission will, therefore, exponentially increase the amount of high-quality data that researchers can analyze. Being able to see the corona in this much detail for prolonged periods every day will allow researchers to study how solar storms explode from the sun and how solar wind is generated, as well as to measure the sun's overall energy output.

During a terrestrial solar eclipse, like this one above Australia in April 2023, the sun's corona becomes clearly visible, allowing researchers to spot events like CMEs (circled). (Image credit: Petr Horálek, Josef Kujal, Milan Hlaváč)

The two spacecraft have been built in part by the private company Redwire Space. Mission scientists were recently given their first look at the almost-finished versions of both probes at a Redwire site in Belgium, and the team was excited but apprehensive to get underway. 

"The satellite hardware was quite something in close up," mission scientist Joe Zender said in a statement. But seeing how small the Coronagraph's camera was, as well as how close it is located to the satellite's solar panel array, also highlights how accurate the probes' alignment must be, he added. "It really brings it home how precisely that small shadow cast by the Occulter will need to be maintained in place," Zender said. 

The spacecraft showcase also gave visiting scientists a glimpse of the new probes. Russell Howard, an astrophysicist and mission scientist for NASA's Parker Solar Probe, praised the ingenuity of this "unique project" and added that having access to the new data "will be spectacular."

Next, researchers will conduct a final test of Coronagraph's cameras by pointing them at the total solar eclipse on April 8, which will be visible across large parts of North America. Depending on how that goes, the most likely launch date for Proba-3 is sometime in September, although a specific date has yet to be announced, Live Science's sister site Space.com reported

If the mission proceeds as scheduled, the launch will coincide with the explosive peak in the sun's 11-year solar cycle, known as solar maximum, which is now expected to be in full swing later this year and should allow the mission to start making discoveries right away.

Harry Baker
Senior Staff Writer

Harry is a U.K.-based senior staff writer at Live Science. He studied marine biology at the University of Exeter before training to become a journalist. He covers a wide range of topics including space exploration, planetary science, space weather, climate change, animal behavior, evolution and paleontology. His feature on the upcoming solar maximum was shortlisted in the "top scoop" category at the National Council for the Training of Journalists (NCTJ) Awards for Excellence in 2023.