A pair of satellites just launched into space that may help scientists solve long–standing mysteries about the Sun’s corona and how it ties in to space weather.
Solar eclipses are a wonder to behold, not just for the public, but also for scientists attempting to study the Sun’s atmosphere (the corona). Much of the solar activity that we see takes place in the corona, or at least has a strong impact on it. Also, some aspects of space weather — the solar wind and coronal mass ejections — are heavily influenced by what goes on in the corona. This makes the study of the solar atmosphere extremely important, as it could be the key to keeping us safe from black-out causing solar storms.
Researchers have plenty of data about the inner and outer corona — the regions closest to the Sun’s surface and farthest out from the Sun. The inner corona is revealed in nearly every image taken by solar-observing satellites, such as NASA’s Solar Dynamics Observatory (SDO), the NASA/ESA Solar and Heliospheric Observatory (SOHO), the Deep Space Climate Observatory (DSCOVR), and the GOES geostationary weather satellites. Coronagraphs on board SOHO and GOES-19 image the outer corona as part of their daily observations, tracking streams of the solar wind and the eruption of coronal mass ejections.
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The view on the left, from NASA SDO, shows an immense CME erupting from the Sun, with the inner corona visible as well. On the right, the coronagraph on SOHO captures this same CME after it has erupted into space. (NASA, NASA/ESA)
However, views of the ‘mid-corona’ remain elusive. Telescopes that observe the Sun’s surface and inner corona aren’t sensitive enough to see activitiy in the mid-corona. Meanwhile, coronagraphs are so sensitive that — by necessity — the disk they use to block the direct light from the Sun also blocks the mid-corona from being captured in their imagery.
The only time the mid-corona is reliably viewable is during the brief time when the Moon completely blocks the Sun, at totality of a total solar eclipse.
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The April 8, 2024 total solar eclipse gave skywatchers and scientists, alike, a magnificent view of the Sun’s whispy corona. (NASA/Keegan Barber)
The rarity of total solar eclipses, along with the challenge of reaching the parts of the world each is visible from, and the potential for cloudy skies to ruin the view, makes studying the mid-corona difficult. Plus, even when everything goes perfectly, scientists still only get around 3-7 minutes to record coronal activity before totality ends. Then, it’s another 18-month wait (at least) before they get their next chance.
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Eclipses on demand
A new mission just launched into orbit on December 4 that aims to fill that gap in our knowledge.
Proba-3 is a European Space Agency mission composed of two small satellites that will fly in tight formation, in a wide elliptical orbit around Earth. Each time the pair reaches apogee (their farthest distance from Earth), they will align perfectly, just 150 metres apart from one another, so that one blocks out the Sun for the other and produces a total solar eclipse, just as we would see one from the ground.
Proba-3 orbit – ESA
The orbit of the Proba-3 satellites, to produce artificial solar eclipses to study the Sun. (ESA)
Orbiting Earth once every 20 hours or so, the satellite pair will simulate a total solar eclipse for a total of 6 hours out of each of those orbits. During that time, it will take images with a coronagraph once every minute, with the potential to boost that to once every 30 seconds to capture any exceptional activity.
While the next total solar eclipse here on Earth isn’t until August 2026, just a single artificial eclipse recorded by Proba-3 will provide scientists with around 100 times more data than they could collect during that celestial event. With a planned operational mission of around 2 years, Proba-3 will provide scientists with unprecedented data on the entire corona.
Proba-3 Occulter eclipsing Sun for Coronagraph spacecraft ESA
This artist’s conception drawing of the Proba-3 mission shows the satellite pair in the process of producing an artificial solar eclipse, revealing the details of the entire solar corona for imaging and study. (ESA)
“Despite its faintness, the solar corona is an important element of our Solar System, larger in expanse than the Sun itself, and the source of space weather and the solar wind,” Andrei Zhukov, the lead scientist for Proba-3’s ASPIICS coronagraph, said in an ESA press release.
“At the moment we can image the Sun in extreme ultraviolet to image the solar disc and the low corona, while using Earth- and space-based coronagraphs to monitor the high corona. That leaves a significant observing gap, from about three solar radii down to 1.1 solar radii, that Proba-3 will be able to fill,” Zhukov explained. “This will make it possible, for example, to follow the evolution of the colossal solar explosions called Coronal Mass Ejections as they rise from the solar surface and the outward acceleration of the solar wind.”
Proba-3 double spacecraft
This infographic shows the two Proba-3 spacecraft close-up, in the process of producing a solar eclipse, providing ingight into how the satellites accomplish this amidst their precision flying maneuvers. (ESA)
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With Proba-3 now in space, having launched on December 5 from Satish Dhawan Space Centre in Sriharikota, India, it will be a few months until the pair is set up to begin observations.
The timing of the mission is nearly perfect, though, as NASA and NOAA just recently announced that the Sun is currently in its period of maximum activity, which should last for at least the next year.
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