Solar Orbiter's First Images of the Sun's South Pole — What They Reveal About Our Star

Solar Orbiter’s first images of the Sun’s south pole are the most scientifically consequential solar observations in a generation. For as long as humanity has studied the Sun, the poles have remained almost entirely unseen: tilted at only 7.25 degrees relative to Earth’s orbital plane, they are perpetually foreshortened into near-invisible crescents at the limb of the solar disk from any ecliptic-plane vantage point.

On its latest high-latitude pass, Solar Orbiter inclined its orbit sufficiently above the solar equatorial plane to capture high-resolution extreme ultraviolet images of the south pole directly — the first true images of a region that has defined the limits of solar observation for four hundred years.

Why the Poles Matter

The Sun’s activity cycle — the approximately 11-year oscillation between solar minimum and solar maximum that governs sunspot number, flare frequency, and the intensity of the solar wind — is driven by the magnetic dynamo operating in the Sun’s interior. The current scientific understanding is that this dynamo involves the interaction of differential rotation (the equatorial regions rotate faster than the poles) with convection and magnetoconvection.

The polar regions are where the solar magnetic cycle’s remnant field from the previous cycle accumulates as the poles reverse polarity — an event that occurs approximately at solar maximum, roughly six months after the cycle’s activity peak. The polar magnetic field strength, measured during solar minimum, is one of the best predictors available for the intensity of the following solar cycle.

But these measurements have historically been made from the ecliptic plane — the same plane as Earth’s orbit — where the polar regions are seen at a steep viewing angle. Magnetograms and emission maps of the polar regions from ground-based and Earth-orbit telescopes are strongly affected by geometric projection, making it difficult to extract the true polar field distribution.

Solar Orbiter’s inclined orbit allows it to view the poles at progressively higher angles, reducing the projection foreshortening and eventually providing nearly overhead views of each pole in turn. What it sees there will fundamentally constrain the solar dynamo models that underpin solar cycle prediction — with direct operational consequences for space weather forecasting.

What the Images Show

The Solar Orbiter images of the south pole reveal a complex, dynamic magnetic environment that differs substantially from models based on ecliptic-plane observations.

The polar region is populated by small-scale bright features — dubbed “campfires” in earlier Solar Orbiter observations — that appear to be sites of localised magnetic reconnection releasing energy into the lower corona. At the poles, the density of these features and their spatial organisation differ from the equatorial distribution in ways that are informing revised models of how the polar field is structured and transported.

The images also reveal dark, elongated coronal holes extending from the south pole across a significant latitude range. Coronal holes are regions where the magnetic field is open — field lines extending out into the heliosphere rather than looping back into the Sun’s surface. They are the sources of the fast solar wind, and polar coronal holes are responsible for the high-latitude fast wind streams that dominate the heliospheric structure during solar minimum.

Seeing the spatial extent and boundary structure of the south polar coronal hole at high resolution and from above provides new constraints on where and why the boundary between open and closed field transitions — a boundary whose dynamics are poorly reproduced by current global corona models.

The Instrument Making It Possible

The primary imaging instrument responsible for these observations is the Extreme Ultraviolet Imager (EUI), built by a European consortium led by the Royal Observatory of Belgium. EUI observes the solar corona and chromosphere in extreme ultraviolet wavelengths at which hot, magnetised plasma emits most of its radiation.

EUI’s High Resolution Imager (HRI) achieves an angular resolution of 1 arcsecond at the spacecraft’s closest approach to the Sun (0.28 AU), corresponding to a physical resolution of approximately 200 km on the solar surface. For comparison, the Sun’s diameter is 1.4 million km — the resolution is comparable to resolving a single feature 200 metres across on a sphere 1.4 million km in diameter.

The Full Sun Imager (FSI) channel provides wider field coverage that captures the full solar disk at each polar viewing opportunity, enabling context for the fine-scale HRI observations.

Solar Cycle Forecasting and Space Weather

The motivation for understanding polar field dynamics extends well beyond academic solar physics. Space weather — the collective term for the effects of the solar wind, energetic particle events, and geomagnetic storms on Earth’s near-space environment — is a genuine operational concern for satellite operators, power grid managers, aviation authorities, and military space users.

Solar cycle 25, which began in late 2019, has exceeded most forecasts in its intensity. The Solar Cycle 25 Prediction Panel, convened by NASA and NOAA, issued a consensus forecast of a moderate cycle with a maximum sunspot number around 115. By late 2024, the cycle was already approaching 200 — close to the intensity of the most active modern cycles.

The implications of underestimating a solar cycle’s intensity are significant: satellites designed for an anticipated radiation environment may degrade faster than planned, ground systems may not be prepared for the frequency of geomagnetic disturbances, and operators of power infrastructure may have less time to implement protective switching procedures during major storm events.

Solar Orbiter’s polar observations, feeding into improved dynamo models, are one of the routes to better predictions for Solar Cycle 26. The scientific foundation is the images. The operational application is the forecast. Both depend on seeing the part of the Sun that we had never truly seen before. For the in-situ counterpart to Solar Orbiter’s remote sensing — a spacecraft that flies directly through the solar corona rather than observing it from outside — see Parker Solar Probe’s closest-ever images of the Sun.