The Sun, the heart of our Solar System, has long been a subject of fascination for scientists and astronomy enthusiasts alike. Thanks to the European Space Agency's (ESA) groundbreaking Solar Orbiter mission, we are now granted unprecedented insights into the Sun's dynamic and complex nature. Equipped with an impressive array of six imaging instruments, the Solar Orbiter is peeling back the layers of this fiery star and revealing its many faces.

Today, we are thrilled to announce the release of the highest-resolution images of the Sun’s visible surface, also known as the photosphere, captured to date. These stunning visuals were produced using the Polarimetric and Helioseismic Imager (PHI), which not only photographs the Sun in visible light but also measures the direction of its magnetic field and how various parts of the surface move.

By comparing PHI’s detailed images of the photosphere with new photos of the Sun’s outer atmosphere, or corona—captured by the Extreme Ultraviolet Imager (EUI) on the same day in March 2023—we gain deeper insights into the interplay between the Sun’s surface and its turbulent corona. Daniel Müller, Project Scientist for the Solar Orbiter mission, remarks, "The Sun's magnetic field is critical for understanding its dynamic character. These high-resolution maps illustrate the intricate beauty of the Sun's surface magnetic fields and flows in exquisite detail."

This remarkable release follows a similar one from two years prior, where the Solar Orbiter showcased full images of the Sun taken by its EUI and Spectral Imaging of the Coronal Environment (SPICE) instruments.

Unveiling the Mysteries of Sunspots and Magnetic Fields

A close examination of PHI’s images reveals the Sun's "surface" as a constantly moving expanse of hot plasma, with temperatures ranging between 4500 to 6000 °C. This dynamic layer is akin to Earth's magma, with hot, dense plasma swirling beneath, creating a grainy texture.

The most captivating features found in these images are the sunspots—dark patches on the Sun's surface that appear cooler and consequently emit less light compared to their surroundings. The PHI’s magnetogram unveils that the Sun's magnetic field is notably strong in these sunspot regions, where it can either point outward (indicated in red) or inward (in blue). This concentrated magnetic field inhibits the normal convection process, causing the plasma in sunspots to remain cooler.

Additionally, PHI's velocity map, or "tachogram," illustrates the movement of material on the Sun's surface. The colors here—blue depicting material moving towards the spacecraft and red indicating movement away—show that while the plasma typically rotates with the Sun’s overall spin, it is pushed outward near the sunspots.

EUI’s imaging of the corona provides an awe-inspiring view of what dances above the photosphere. Here, bright plasma can be seen bending and protruding outward along magnetic field lines, often linking neighboring sunspots. This captivating display hints at the magnetic interactions that occur above sunspots, contributing to solar activity.

A Technical Feat: Stitched Together for Stunning Clarity

These pioneering images were captured when Solar Orbiter orbited less than 74 million kilometers from the Sun. However, each high-resolution shot only covers a fraction of the vast solar surface. The spacecraft had to rotate strategically to capture every part of the Sun’s face.

To create the full-disc images we're showcasing today, researchers meticulously stitched together a mosaic of 25 images from both PHI and EUI, taken over a stretch of more than four hours. The final compositions deliver nearly 8000 pixels in diameter, revealing astonishing details that promise to enhance our understanding of solar behavior.

The image processing for the PHI mosaics was a complex challenge, but as techniques improve, the team anticipates quicker assembly of such high-resolution mosaics in the future, aiming to provide these detailed glimpses into the Sun’s life at least twice a year.

Isn’t our Sun captivating? These new insights not only deepen our understanding of solar mechanics but may also enhance our knowledge about space weather phenomena that affect our planet. Stay tuned for more astonishing discoveries as solar research continues to evolve!