Video: NASA’s PUNCH mission sees the Sun’s corona in action

Here on Earth, we think about the Sun in an overwhelmingly positive way. It’s the giver of nearly all light and energy received on Earth’s surface, and the primary driver of life on our planet. The process of photosynthesis requires the Sun, and the day/night cycle signals to organisms when to wake and when to sleep. Seasonal variations, due to Earth’s axial tilt and our latitude on the planet, determine the amount of energy we receive, with temporal variations in the Sun’s energy output being small compared to its overall flux.

And yet, the Sun is not a constant emitter of energy at all, but rather varies and fluctuates due to an incredibly complex suite of astrophysical phenomena. The Sun isn’t just a ball of plasma that radiates light out into space, but contains a complex internal magnetic field, an ultra-hot diffuse halo known as the corona, and launches particles — via solar flares and coronal mass ejections — that stream all throughout the Solar System, impacting planets and their moons and causing all sorts of complex physical phenomena.

Tracking this space weather, and understanding and quantifying the risks to Earth, is the prime goal of heliophysics: the study of the Sun. Just months old, NASA’s PUNCH satellite promises to revolutionize our understanding of these space weather phenomena. Yet just as it’s beginning, impending cuts to solar physics in the United States threaten to turn out the lights just as huge advances are about to happen. Here’s what everyone should know.

An early photographic plate of stars (circled) identified during a solar eclipse all the way back in 1900. The disk of the Sun, blocked here by the Moon during a total eclipse, is the brightest part of the Sun. When it is obscured, the much fainter solar corona can be seen even with the naked human eye. The corona, much hotter but fainter and less dense than the Sun, is the launching point for much of the space weather in our Solar System.

The fact that our Sun is more than what it seems, and that it possesses a corona at all, has been known since ancient times. Every time there’s a total solar eclipse, when the Moon passes in front of the Sun as viewed from Earth and blocks out the solar disk entirely, the much fainter, more extended light from the corona can be revealed. Even with the unaided human eye, even before the invention of telescopes, magnifying devices, coronagraphs, or spaceflight, the Sun’s corona can be directly observed under the right conditions. In modern times, we’ve learned that the corona is larger and more important than any ancient scientist had imagined.

Shaped by magnetism, the Sun’s corona is incredibly hot: hundreds of times hotter than the Sun’s photosphere, or the outer layer of the Sun from which most of the observed sunlight originates. This extreme coronal heating is due to a combination of energy transport, magnetic fields, and the corona’s low-density nature. In fact, the Sun’s corona is not even gravitationally bound to the Sun, but rather streams outward all throughout the Solar System, primarily along the equator of the Sun’s rotational plane. As viewed with long-exposure photography during modern solar eclipses, we can see that the Sun’s corona actually extends as far as we’re able to keep making observations.

The solar corona, as shown here, is imaged out to 25 solar radii during the 2006 total solar eclipse. The longer the duration of a total solar eclipse, the darker the sky becomes and the better the corona and background astronomical objects can be seen. Experienced, serious eclipse photographers can construct images such as these from their eclipse data, showcasing the extent of the solar corona.

This is very important, not just for scientific reasons in our quest to better understand the Sun and all stars, but because space weather — including coronal mass ejections — can severely impact the Earth. For all of our planet’s history, Earth has had a magnetic field: a core-driven magnetic dynamo that makes our planet behave as though there were a very strong bar magnet within the interior: giving our planet north and south magnetic poles that are alternately nearly aligned or anti-aligned with our world’s rotational axis. It isn’t just that the Earth’s outer layers spin, but its interior, too, including its metallic inner and outer cores, whose motions and interactions drive our magnetic field’s existence.

The Sun also has a magnetic field: complex and full of switchbacks, which ebbs and flows in an 11-year cycle. During the peak of this solar cycle, many phenomena occur at once.

• Sunspots are more numerous, larger, and exhibit greater temperature differences than at other times.
• Space weather events, like solar flares and coronal mass ejections, are more numerous than at all other times.
• And the strongest space weather events, X-class solar flares and the most energetic coronal mass ejections, all occur at or near the peak of this cycle.

These space weather events can occur in any direction, but what matters for us is how they do or don’t impact the Earth.

Solar coronal loops, such as those observed by NASA’s Solar Dynamics Observatory (SDO) satellite here in 2014 (near the solar cycle peak), follow the path of the magnetic field on the Sun. When these loops ‘break’ in just the right way, they can emit coronal mass ejections, which have the potential to impact Earth. The connection between the solar corona just above the photosphere and the outer phenomena that pervade the rest of the Solar System requires measuring all the in-between locations with the proper instruments.

Even though most space weather events occur in the plane of the Sun’s equator, meaning that they’re going to be almost perfectly aligned with Earth’s orbit around the Sun, the Earth isn’t everywhere in its orbit at once. From our perspective, there are two types of directions we can see whenever a space weather event like a coronal mass ejection, for example, occurs.

1. A coronal mass ejection can come out laterally, as though it were being emitted in one particular direction from the Sun. From the perspective of planet Earth, that can look like it’s going off almost anywhere: left, right, up, down, or out at an angle. When we see these lateral coronal mass ejections occur, we can breathe a sigh of relief, as that space weather event went off in a different direction than the imaginary line connecting the Sun to the Earth.
2. Alternatively, however, a coronal mass ejection can appear to make a halo, and those “halo coronal mass ejections” are the most terrifying space weather events of all. The reason for this is simple: if you see a coronal mass ejection make a halo-shape from your perspective, that’s your warning that it’s headed directly at you; the main “flare” is headed in your direction, but because it’s shaped like a cone and you’re inside of that cone, you’ll see a full 360° burst surrounding the Sun. These are the events that are inevitably going to impact the Earth, and monitoring the Sun is key to understanding what dangers these events do and don’t pose to us.

When a coronal mass ejection appears to extend in all directions relatively equally from our perspective, a phenomenon known as an annular or “halo” CME, that’s an indication that the energetic particles emitted by the Sun are likely headed right for our planet. If the ejection were directed away from us, we would see it emerge from one limb of the Sun instead.

The first thing that we have to understand is that the Sun has a magnetic field (and so does its corona), and the Earth, independently, also has a magnetic field, and that these magnetic fields are three-dimensional objects in space. When a space weather event is launched, the Sun’s field — which determines the alignment of the particles emanating from the Sun — will have radial components to it, which are the components that are oriented perpendicular to the imaginary line connecting the Sun to the Earth, and will also have line-of-sight components to it, which is the component of the magnetic field along the Sun-Earth line. (Solar astronomers call this the z-direction, and this component of the Sun’s magnetic field is known as B_z.)

The Earth’s magnetic field also has a three-dimensional shape to it, but this shape is well understood at present, giving us a magnetosphere surrounding our planet. When the Sun’s magnetic field along the Sun-Earth line points north, then the Sun’s field and the Earth’s field add up, and this diverts charged particles away from planet Earth. Even a strong space weather event will have minimal effects on the Earth if it originates when the Sun’s line-of-sight magnetic field points north. But if the Sun’s magnetic field points south, the opposite conditions occur: the Sun’s and Earth’s magnetic field partially cancel and link up, which allows energy from the solar wind to penetrate into Earth’s atmosphere, with often spectacular consequences.

Looking north from approximately 46 degrees north latitude, the aurora on May 10, 2024 appears green and pink to the camera’s eyes. The Big Dipper shines brightly in this frame, which captures arguably the most spectacular auroral display on Earth since 2003.

The most visually spectacular consequence — experienced across Earth at various times in 2024 and 2025 — are the aurorae: both the aurora borealis in the northern hemisphere and the aurora australis in the southern. When there exists a strong magnetic connection between the Earth and the Sun, charged particles can get funneled down around the magnetic poles to the atmosphere, where they’ll collide with various atoms and molecules, ionize them, and produce aurorae of various characteristic colors: greens most prominently, often accompanied by reds and sometimes even with blues and purples in there as well.

But there’s also the potential for more devastating consequences, particularly in our modern, electrified era. The fact that space weather events are largely driven by interplanetary magnetic fields and involve fast-moving charged particles means that the magnetic fields experienced on Earth and in the space environment around Earth will change with time. Changing magnetic fields, as has been known since the 19th century, can induce electrical currents, and this can cause electronic devices and computers to malfunction, lose control, catch fire, or short out. Strong space weather events can lead to multi-trillion dollar disasters, and can destroy enormous amounts of infrastructure both on Earth and in low-Earth orbit.

The Daniel K. Inoue Solar Telescope (DKIST) is the world’s largest and most powerful solar telescope. It is the first solar observatory to resolve individual solar granules and to reveal sub-granule features, enabling us to track features on the Sun’s photosphere to higher precision than ever before.

That’s why continuously monitoring the Sun, including at the solar surface in high-resolution, as well as monitoring the solar corona and the line-of-sight connecting the Earth to the Sun is so vitally important. We don’t just want to understand the Sun and these space weather events; we want to be protected against them. On the ground, the NSF’s Daniel K. Inoue Solar Telescope (DKIST), commissioned in 2020 and operated by the National Solar Observatory, is the most powerful solar telescope in the world. It observes the Sun at the highest resolution ever, resolving the smallest solar granules ever seen, and also measures the Sun’s magnetic field to precisions never obtained before.

Meanwhile, we can also go to space and equip our spacecrafts with coronagraphs, enabling us to view the Sun’s corona at high contrast: seeing the faint light from it even against the backdrop of stars, planets, and the Moon. Previous orbiting solar telescopes, such as NASA’s SOHO and SDO, have helped us view the solar corona and track space weather, allowing us to observe solar flares and coronal mass ejections in all directions: including those dreaded “halo” space weather events. However, one limitation is that these telescopes all only have narrow fields-of-view, and while they allow us to track the launch of these space weather events, we haven’t been able to track them all the way from the Sun to the Earth.

This view of one of the four NASA PUNCH satellites at Astrotech Space Operations shows a solar array deployment test conducted just two months prior to launch: in January of 2025.

In addition to that limitation, there’s also the fact that polarimetry — or the ability to measure how much magnetization causes the optical rotation of polarized light — only extends to the short distances over which observations can be acquired. We know, in our very real Solar System, that the Sun’s magnetic field and corona literally spreads out across all of interplanetary space:

• from the Sun to the Earth,
• out past where all the planets orbit and into the Kuiper belt,
• and even beyond that out to interstellar space, where the Voyager spacecraft now are.

And yet, with observatories like SDO and SOHO, we can only perform polarimetry on these space weather events up to a few solar radii away from the Sun.

That’s why it’s so exciting that NASA’s PUNCH mission, co-launched on March 11 of 2025 along with the SPHEREx mission, has finally begun to open its eyes onto the Sun. Unlike the prior generations of spacecraft that have been launched to observe the Sun, PUNCH is actually a constellation of satellites in polar orbit around the Earth: ensuring that all four of them can always monitor the Sun at once. One of them is a narrow-field imager, similar to SOHO and SDO, allowing it to probe the inner few solar radii around the Sun to track coronal mass ejections and solar flares right as they get launched. This narrow-field imager spacecraft allows us to track the emergence of space weather and the transport of energy right as it leaves the corona itself with better-than-ever polarimetry: an important part of the story.

This narrow-field imager image of the Sun, taken with one of the four PUNCH spacecraft, shows a coronal mass ejection (north) being emitted from the Sun’s corona in detail on June 3, 2025. This narrow-field view, which is a part of the total PUNCH field of view, represents the inner white, dotted circle on the broader-field PUNCH images and videos.

But the colossal leap forward with PUNCH comes from its other three spacecraft: an array of wide-field imagers. Unlike all previous solar observatories from space, PUNCH can view areas around the Sun that are comparable to the Earth-Sun distance itself: up to over 100 million kilometers away from the Sun. We can watch coronal mass ejections and solar flares fly off to greater distances than ever before, allowing us to infer the magnetic field in interplanetary space in the inner Solar System from direct polarimetry measurements: something we’ve never done before.

Most spectacularly, however, what we can do with PUNCH is track those dreaded “halo” coronal mass ejections — for the first time — from their origin in the corona all the way here, to Earth, continuously. The ability to track Sun-to-Earth space weather, fully, in all three dimensions, has been something that’s eluded solar astronomers for the entire history of the field, and with PUNCH, it’s a goal that’s at last within reach. By combining the largest fields-of-view ever with the capacity to measure polarimetry, as PUNCH stands for “Polarimeter to Unify the Corona and Heliosphere,” we are poised to finally measure space weather, including halo coronal mass ejections, from its origin within the Sun and the solar corona all the way to our world.

Under any other circumstances, this news — announced by Craig DeForest on June 10, 2025 at the American Astronomical Society’s 246th meeting — would signal a remarkable advance in the field of solar astronomy, and would prepare us, for the first time, to have the potential to connect space weather that originates on the Sun’s surface, which we observe with DKIST, with the solar corona and all the way to Earth, which we can observe with PUNCH. The ability to track magnetization and the transport of energy across a full 150,000,000 kilometers, for the first time ever, not only would deepen our understanding of space weather, but would help protect Earth from and warn Earth of these events as never before.

And yet, we may never get the chance to use these observatories in concert the way they were designed. Just a hours after the first PUNCH results were revealed, the National Solar Observatory held a town hall and announced that the proposed 2026 budget would be insufficient for them to keep operating DKIST: the flagship solar observatory here on Earth. At a time when science should be advancing on all fronts, as we have the people, the facilities, and the observatories all ready to go, the proposed budget — called an “extinction-level event” by many at the American Astronomical Society’s latest meeting — threatens to set US science back decades. Instead of building a brighter future, the roadmap abdicates our scientific leadership, de-funds thousands of supremely skilled workers, and is forcing world-class facilities to face the possibility of closure.

NASA’s PUNCH mission, still being commissioned and calibrated, is showing us what’s possible if we continue to invest in science. Unless we abruptly change course and commit to exactly that, as a nation, the next generation of scientific progress will have to be spearheaded by the rest of the world alone.