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This is the corona, our sun's outer atmosphere. This fiery hell can reach temperatures of 10 million°, but just 1,500 km beneath this inferno. The surface is significantly cooler. This arguably makes no sense. How can the temperature increase as it moves away from the source? Surely that's the wrong way round. Known as the coronal heating problem, this is one of the greatest unanswered questions in astrophysics, and it's been baffling scientists for decades. Over the years, there's been theories and clues about its cause, but it's hard to get answers about something you can't easily see other than the occasional fleeting
glimpse during solar eclipses. So, the inner corona has remained largely unobserved. But in December 2024, all that changed. The European Space Agency launched two tiny satellites that together are revolutionizing our understanding of the sun, working in perfect synchrony to make the once invisible visible. I'm Alex Mccoan and you're watching Astramm. Today we're heading into orbit with the Prober 3 mission as its first findings are released. We'll explore how these two minissats have opened up a window into the sun's most inaccessible
region and get to grips with the extraordinary engineering that makes flying in millimeter precision formation possible. On the 5th of December 2024, ISA's Proverb 3 lifted off on a PSLV XL rocket from the Satish Dawan Space Center, Shrih Harikotta, India. This mission didn't necessarily garner headlines, but it was quietly set to change the face of solar exploration and break a few engineering records in the process. Because Proverb 3 isn't just one satellite, but two. This pair of fully autonomous mini sets have to fly in millimeter perfect formation through a highly elliptic orbit of Earth all whilst positioned 1 and a half football pitches apart. And that's easier said than done. Why would we want to do this,
you might ask? Well, they were being sent to study the sun and one area in particular, the corona. Why is the sun's atmosphere hotter than its surface? What drives the charged particles in the solar wind? And how do billions of tons of magnetized plasma erupt from our star in one go? These questions have haunted solar physicists for decades. And the answers to all of them are believed to be hiding in the same uncharted region of the sun. Yes, the corona. But observing this outermost part of the sun's atmosphere has always been a challenge. It's a million times dimmer than our stars visible surface, the photosphere, meaning this region gets somewhat lost in the sun's light.
Observations aren't impossible, per se. We do get a fleeting glimpse during eclipses. These spectacular events offer an excellent snapshot of the corona, and over the centuries have not only led to the discovery of the corona itself, but also that of ionized iron within. The first evidence of the coroner's extreme temperatures. The problem with total eclipses, though, is that they only last for a few brief minutes, and they're rare, only occurring every 18 months or so. Add to that the fact that the paths of total eclipses are often in remote areas or over the ocean, which is pretty impractical when it comes to using high power telescopes, as they aren't exactly what you'd call portable. Thankfully,
though, we do have another alternative. In the 1930s, a French astronomer called Bernard Leot started using an occultting disc to act like an artificial moon, blocking out the sun's surface to create a mini eclipse. Instantly, observing time went from minutes to hours. And using these new instruments called coronagraphs, we've been able to keep almost constant tabs on the corona. We can track its temperature and composition and look for changes in the flow of the solar wind. But yes, there's a butt. There are once again limitations. Groundbased chronographs have to compete with daytime brightness and atmospheric light scattering, making the dimmest parts of the corona, or the bit closest to the sun, almost impossible to see. It therefore remains
mostly unseen and unstudied. To solve the mystery of the sun's corona, we needed a better view. And for that we needed to get rid of at least some of the background light. We can't make the sun dimmer. So the easiest thing to do is get rid of the atmospheric scattering. In other words, we needed to get coronagraphs into space. Space-based coronagraphs have revolutionized our coronal understanding. On the 14th of December 1971, an early space-based mission of this kind called the Orbiting Solar Observatory 7 saw a coronal mass ejection for the first time. Since then, we've seen tens of thousands of them. I'm sure you've seen some of the spectacular images sent back by the Solar and Heliospheric Observatory or SOHO that launched in 1995 and the Solar
Terrestrial Relations Observatory or STEREO that launched in 2006. I personally love how you can see the solar weather events erupting from the surface when the star itself is blocked out and how each craft specializes in different regions above the sun, giving us one large image when put together. each of them their own part of the puzzle. But once again, even coronagraphs in space have issues. Just like on Earth, the glare of the sun can be too strong. Soho, in particular, cannot see closer than 1.7 solar radi. And most of the interesting phenomena start much closer than that. Parker Solar Probe and Solar Orbiter, both much closer to the sun, also have chronograph instruments, but they suffer with the
same issue, as well as internal light scattering and defraction that degrade images when the occultter, the bit blocking the sun, is too close to the camera lens. And that's something that you can't really get around on a 3 m tall probe. Scientists needed yet another way to look at the sun if they ever hope to unlock the secrets of the corona. You may have heard that a total solar eclipse is coming to parts of Europe on the 12th of August, while parts of the northern United States will see a partial eclipse. Now, you probably can't fit a space telescope in your pocket. But if you're looking for a much more portable way to go eclipse watching, today's sponsor, Dwarf Lab, might have the answer. The Dwarf Mini is
a compact app control telescope that's as small as a light novel, making it extremely portable. With the official solar filters correctly installed, its solar mode and automated tracking can locate and keep the sun centered, while photo, burst, and video time-lapse modes let you record the event in different ways. And it's good for more than just the eclipse. Its lifesting feature takes multiple images and then combines them into one crisp image, making it a great beginnerfriendly way to image the moon, galaxies, and other deep space objects. Just be sure to practice with it before the day of the eclipse. And use Dwarf Lab's solar filters and eye certified protection. You don't want to get eye
damage by looking at the sun directly. Dwarf Lab has a great eclipse guide to get you started. So check it out. Scan my QR code or click my link in the description below. The solar eclipse travel kit is 10% off through the 31st of July. And if you're watching after the promotion has ended, you can use our code astron 5 when purchasing from the dwarf lab store. Now that you're sorted, how are scientists tackling the challenges of seeing the corona when 3 m space telescopes aren't getting the job done? The solution to put the occulta further away, specifically on another spacecraft. And to do that, engineers had to create the world's first pair of fully autonomous satellites that can
simulate artificial solar eclipses on demand. And most crucially, without having to worry about other solar radiation, so-called parasitic light, leaking into the image. Proverb 3 is the fourth in issa's project for onboard autonomy, a line of experimental missions designed to work without constant human monitoring on the ground. And this is the most ambitious mission yet. Two small satellites, one containing the coronagraph and the other the occulta fly 144 m apart, holding their relative positions with millimetric precision to simulate a single giant spacecraft. This gets around the issue other space chronographs have with the two parts being too close together. And perhaps most impressively of all, the idea is that they're able to do this autonomously.
That might not necessarily sound overly impressive, but trust me, it is. In fact, it's never been done before. Just to prove my point, let's get into the nitty-gritty of how the mission works. First up, the satellites take a highly elliptical path around Earth. If they had been launched into a standard low Earth orbit, the constant need for corrective thruster use would have burned up the propellant in as little as half an hour, making for a very short mission. Instead, an elongated elliptical orbit was chosen, starting at an altitude of 600 km above Earth at its nearest and reaching the farthest point of 60,500 km once every 19 hours and 36 minute long orbit.
Imagine it like a roller coaster loop. At the bottom of the loop near the Earth, the satellites are moving the fastest. As they begin to go around the loop, they slow down from 10 km/s to 1 km/s. Because of the slower speed, they spend more time at the top of the loop, or in this case, they spend more time at the furthest point of their orbit away from Earth, called the apogee. This gives them maximum solar observation time. And when they're closer to Earth, the pair are set for a safe flyby. Then as they approach Apogee, they are given a signal to move into active formation, taking about two hours to prepare to observe the corona. Then like self-driving cars, only way more precise, the satellites
align themselves using a suite of absolute and relative positioning technologies from GPS receivers and radio links to optical cameras and LEDs, a laser link, and even shadow position sensors. Each of these hands off to the next with increasing precision. It starts with cameras that recognize the constellations around them called star trackers. These allow each spacecraft to know exactly which direction is pointing at any given moment during their low orbit or below 20,200 km. The spacecraft uses GPS signals and continuously exchanges ranging information and data through interatellite radio links. Then comes the vision based system to help two spacecraft determine their position relative to each other. A wide angle
camera on each spacecraft tracks a pattern of flashing LEDs on the other, giving a rough first read on distance and orientation. A narrower camera then locks onto a smaller LED target, refining that to around 1 cm of accuracy. But even a centimeter isn't precise enough. The occulta spacecraft fires a laser at the reflector on the chronograph which bounces it straight back. That system called the fine lateral and longitudinal sensor narrows positioning down to a single millimeter. And finally, to make sure the shadow is falling exactly where it needs to, photo detectors monitor its edges in real time. If it drifts even slightly, a correction fires instantly. To keep the whole system as stable as possible,
neither spacecraft has any moving parts. Apart from a single rotating filter wheel on the chronograph, everything else is locked in place. With the two spacecraft aligned perfectly, a precisely controlled shadow is cast from one satellite to the other, blocking our stars fiery disc and thus creating artificial eclipses that allow us to collect sustained observations of the sun's corona. Usually from Earth, the corona can only be glimpsed naturally for a matter of minutes during a total solar eclipse. But the idea with prob 3 was for it to reproduce the same effect as a solar eclipse for hours at a time, as much as
5 and 1/2 hours of its nearly 20our orbit. For the first time ever, these tiny satellites have opened up the chance for us to observe the corona on a consistent basis. But it was all uncharted territory. Even the slightest slip in the satellite's formation and the eclipse is gone. taking with it the opportunity to study the corona. As the team turned the spacecraft on for calibration, no one really knew if it would all work. Just as stray light can ruin images on Earth, it could hear, too. The team really weren't sure whether or not light would defract and leak around the edges of the occulta. Thankfully, though, they had nothing to worry about. As the first
data came through on the 25th of March 2025, it was clear that the prob 3 team had achieved the millimeter precision needed. Andre Zurkov, the chronograph's principal investigator, said it was so unbelievable that it just worked from the first time. Before Proverb 3, we could see as close as 0.7 solar radi from the sun's surface. Now, we could see down to 70,000 km above the sun's surface, which is just 0.1 solar radi. Put simply, no other space-based chronograph can observe the light scattering of particles in the sun's corona this close to the sun. Proof of concept complete. It was time to move on to the science. The mission carries two scientific instruments. The first of
which is the chronograph. is called the ASPIX or the association of spacecraft for polytric and imaging investigation of the corona of the sun and it images both the quiescent and eruptive corona in other words both when it's calm and during more specific solar weather events. The second instrument is DRA the digital absolute radiometer designed to measure the total solar irradiance or TSI. Whilst calibration was ongoing, the team kept the results under wraps. But on the 16th of June 2025, images from the first artificial solar eclipse were released. And not only were they spectacular to look at, they gave a glimpse into the valuable data yet to come. And by December of 2025, a year into the mission, the satellites have
created more than 50 artificial eclipses and provided hundreds of hours of invaluable observational data about our sun's corona. So, what has it found? The corona is where the solar wind picks up speed before streaming outward across the entire solar system, eventually washing over the Proverb 3 spacecraft and reaching Earth itself. It's a continuous stream of charged particles that are constantly flowing outward from the sun in all directions, filling the entire solar system. The corona is where most coronal mass ejections are born. massive eruptions of magnetized plasma that when aimed at Earth can knock out
satellites, disrupt GPS, and overwhelm power grids. Take a look at this composite image made up of three sets of images taken over an hour and a half by instruments on different missions. All observing the same coronal mass ejection or CME event on the 16th of July, 2025. The yellow at the center shows the sun's disc and lower atmosphere captured in ultraviolet by an extreme ultraviolet telescope carried by probe 2, a previous issa mission that also studies the sun. In red, it shows the outer corona as seen by the last code 2 chronograph on Soho. And in green is the middle layer, the inner corona imaged for the first time with this kind of clarity and continuity by probe the aspix chronograph filling in the gap that has
existed between those two instruments for decades. You can watch the CME forming at the sun's edge, expanding through the inner corona and pushing outward into the outer atmosphere in one continuous unbroken view. And in April 2026, the first science from Prober 3 followed being published in the Astrophysical Journal Letters. It revealed that solar wind structures in the inner corona can travel up to four times faster than previously thought. This set of images shows the sun in ultraviolet light as seen artificially colored in yellow captured by prob 2. Surrounding it is a grayscale area captured in visible light by prob 3. You can see how the solar wind is moving
away from the sun in all directions, but in some regions, such as around the bottom of the video, material also falls back towards the sun. In the second half of the video, a coronal mass ejection is then visible, expanding out towards the right. What we've learned is that the inner corona is far busier and more turbulent than previously expected. It's filled with tiny, constantly moving blobs and streams of plasma. Some flowing outward and some actually flowing back toward the sun. These structures are moving at speeds ranging from 14 to 520 km/s. So exceptionally quick and 3 to four times faster than previous instruments had measured in this region. This means our existing models of how solar wind accelerates have been significantly off.
Understanding these small-cale dynamics is key to answering how the slow solar wind forms, how the corona gets so hot, and how solar eruptions are triggered. All of which directly affect our ability to forecast space weather. But there's still a long way to go. Proba 3 is only at the start of its life and scientists behind the scenes are scouring the data. I've been assured that new publications and findings are already on the way. That's as long as the precision formation flying can continue though. I know it sounds as if the mission has all gone smoothly, but as ever, it's not been without hiccups.
Earlier this year, the Proviser team actually lost the Chronograph spacecraft. It vanished uncontactable for a whole month. So what happened? Well, in Andre's own words, there was a software glitch and it lost the orientation towards the sun. And well, when the solar panel is not looking towards the sun, then the battery is not charging. And if the battery is not charging, then the power is down and the spacecraft is in trouble. Facing away from the sun, Proverb 3's chronograph was unable to enter safe mode to preserve its battery. And as this happened at a weekend, the operators weren't working, so it wasn't corrected
in time. This might sound surprising, but remember, Proverb 3 is meant to be autonomous, so it should be able to survive a weekend unsupervised. Apparently not. Tracking the missing half of Proverb 3 using the camera on the occulting satellite, the team were eventually able to find the chronograph and managed to command it to turn towards the sun. At worst, the two spacecraft drifted 80 km apart, an enormous separation for a pair designed to fly less than 150 m from one another. Thankfully, both satellites are now online and back together. They recently turned both spacecraft back on and it appears there's been no lasting damage.
As of early June, they are back on their observing schedule. Perhaps we're a little way off fully autonomous after all. Even having a month-long sabbatical, Robber 3 has collected more than 250 hours of highresolution video of the corona over 57 artificial eclipses. To put this into perspective, the average total eclipse on Earth lasts for about 7.5 minutes. Proverb 3 has already captured 2,000 times that. In that time, it hasn't quite solved the three great coronal questions. But for the first time in the history of solar science, there is an instrument dedicated to doing so. Watching the solar corona with the consistency, resolution, and sensitivity needed to see what is actually happening. And we really are
only at the start. Andre Sukov and his team are already preparing the next batch of images and discoveries to be released. And in December 2026, Proverb 3 will surpass its nominal mission period of 2 years. After that point, researchers from around the world can begin requesting specific observations they want Proverb 3 to make, opening up the mission to the greater global physics community. Looking beyond solar science, Proverb 3 is also quite simply an engineering marvel. No one expected its precision formation flying to work as well as it does, and the mission has gone a long way to proving the experimental concept of autonomous satellites flying in precise unity. I
personally am looking forward to seeing what future missions may use this technology and whether it can unlock any of the other big questions that still linger out in the cosmos. I really hope you enjoyed learning about how important eclipses are. We're actually live streaming the upcoming solar eclipse on the 12th of August. We'll see you there at 6:30 p.m. BST and we'll be online to answer all your questions, too. See you there. Thanks for watching. If you've been enjoying Astramm's videos and want to help keep this channel thriving, I want
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