The Solar Orbiter mission has captured unprecedented high-resolution images of the Sun, revealing the intricate interactions of its magnetic fields and plasma movements. These images, including detailed views of sunspots and the corona, provide valuable insights into solar phenomena.
On March 22, 2023, Solar Orbiter took four stunning new images of the Sun using its PHI (Polarimetric and Helioseismic Imager) and EUI (Extreme Ultraviolet Imager) instruments. The PHI images deliver the sharpest full views of the Sun’s visible surface, mapping its complex magnetic fields and surface dynamics. In contrast, the EUI image showcases the glowing outer atmosphere, known as the corona, in unprecedented detail.
Unveiling the Sun’s Dynamic Nature
The Sun, the most dynamic and complex object in our Solar System, has never been captured in such intricate detail. The ESA-led Solar Orbiter mission uses six advanced imaging instruments to study the Sun, unveiling its multifaceted nature by peeling back its layers.
These latest observations provide Solar Orbiter’s most detailed images of the Sun’s visible surface, or photosphere. The PHI instrument not only captures images in visible light but also measures the direction of the Sun’s magnetic field and tracks the speed and motion of surface material. This offers an extraordinary glimpse into the Sun’s continuously evolving behavior.
An artist’s concept shows Solar Orbiter near the Sun.
PHI’s measurements of the Sun’s photosphere are being directly compared to a new high-resolution image of the Sun’s outer atmosphere, the corona, which was assembled using data from the Extreme Ultraviolet Imager (EUI) on the same day in March 2023. The EUI captures images of the Sun in ultraviolet light.
“The Sun’s magnetic field is crucial to understanding the dynamic behavior of our star, from its smallest features to its largest processes. These new high-resolution maps from Solar Orbiter’s PHI instrument reveal the intricate details of the Sun’s surface magnetic field and plasma flows. They are also essential for interpreting the magnetic field in the Sun’s hot corona, which is being imaged by our EUI instrument,” explains Daniel Müller, Project Scientist for Solar Orbiter.
This latest release builds on a previous set of images from two years ago, when Solar Orbiter shared full images of the Sun taken by the EUI and Spectral Imaging of the Coronal Environment (SPICE) instruments on March 7, 2022.
visible surface of the Sun, also called the photosphere.
High-Resolution Sunspot Analysis
Examining PHI’s detailed visible light image of the Sun reveals the true nature of its "surface": glowing, hot plasma (charged gas) in constant motion. This layer, which has a temperature ranging from 4500 to 6000°C, emits almost all of the Sun's radiation. Beneath this layer, the hot, dense plasma is stirred in the Sun’s "convection zone," much like magma in Earth's mantle. This movement causes the Sun's surface to appear grainy.
The most striking features in the images are the sunspots, which appear as dark spots or holes on the otherwise smooth surface. These sunspots are cooler than their surroundings, meaning they emit less light.
magnetic field on the Sun’s disc.
The Movement and Structure of Solar Plasma
PHI’s magnetic map, also known as a ‘magnetogram’ (image above), reveals that the Sun’s magnetic field is concentrated in the regions of sunspots. The magnetic field lines either point outward (red) or inward (blue) where the sunspots are located. The strength of this magnetic field explains why plasma inside sunspots is cooler. Typically, convection transports heat from the Sun's interior to its surface, but this process is disrupted by charged particles being forced to follow the dense magnetic field lines within and around the sunspots.
In addition, PHI’s velocity map, or ‘tachogram’ (image below), illustrates the speed and direction of material movement at the Sun’s surface. Blue indicates motion towards the spacecraft, while red shows motion away from it. The map highlights that while the plasma on the Sun’s surface generally rotates in sync with the Sun’s overall spin around its axis, the material is pushed outward in regions around the sunspots.
velocity map, also called a ‘tachogram’, shows the line-of-sight speed and direction of movement of material at the Sun’s visible surface.
The Solar Corona: A Hot Plasma Show
EUI’s image of the Sun’s corona (below) reveals the activity occurring above the photosphere. In the areas above the sunspot regions, glowing plasma is seen extending outward. This million-degree plasma follows magnetic field lines that stretch out from the Sun, often linking neighboring sunspots.
This high-resolution image shows the Sun in ultraviolet light, revealing the Sun’s upper atmosphere, the corona.
Technical Achievements in Solar Imaging
The images were captured when Solar Orbiter was less than 74 million kilometers from the Sun. Due to the spacecraft's close proximity, each high-resolution image taken by PHI and EUI only covered a small section of the Sun. After each image was captured, the spacecraft had to tilt and rotate to ensure every part of the Sun's surface was imaged.
To create the full-disc images shown here, all individual images were combined into a mosaic. The PHI and EUI mosaics consist of 25 images each, taken over more than four hours. In the final mosaics, the Sun’s disc spans almost 8000 pixels, showcasing an extraordinary level of detail.
The process of creating the PHI mosaics was a challenging new task. Now that it has been completed, future data processing and mosaic assembly will be faster. The PHI team plans to produce these high-resolution mosaics twice a year.
Collaborative Space Exploration
Solar Orbiter is a space mission resulting from international collaboration between ESA and NASA, operated by ESA.
