Solar Orbiter Unveils Stunning Images of the Sun’s Surface and Magnetic Activity

The Sun is undoubtedly the most dynamic and complex object in the Solar System, and the task of studying its structure and behavior falls to the multi-instrument Solar Orbiter spacecraft.

Today, the mission is releasing the most detailed views of the Sun’s visible surface, taken on March 22, 2023. These data not only reveal the dynamic activity of the Sun’s surface, but could also provide new perspectives on the relationship between its turbulent surface and its outer atmosphere, helping to better understand the processes that regulate its activity.

*Solar Orbiter’s new Sun images, assembled from high-resolution observations made on 22 March 2023. Credits: ESA & NASA/Solar Orbiter/PHI Team-EUI Team*

How Solar Orbiter captures the details of the Sun

To study an extreme environment like the Sun, the Solar Orbiter spacecraft is equipped with six imaging instruments. Among them, the Polarimetric and Helioseismic Imager (PHI) and the Extreme Ultraviolet Imager (EUI) are the key contributors to these observations.

*Illustration of the ten instruments on the Solar Orbiter. The remote sensing instruments are six imaging instruments used to analyze the Sun. Credits: ESA-S.Poletti*

PHI, which captures images in visible light, can not only observe the surface of the Sun (the photosphere) but also measure the direction of the magnetic field and map the movement of plasma on the surface.

This information is crucial for understanding how solar matter moves and interacts, allowing detailed observations of sunspots and plasma motion.
On the other hand, the EUI observes the Sun in ultraviolet light, providing images of the corona and the outer solar atmosphere.

*This map shows the different zones of the Sun. In visible light it is possible to capture the* ***photosphere*** *with its* ***granulation*** *and* ***sunspots****. When we observe in ultraviolet light the* ***corona*** *with its* ***mass ejections*** *appear. Credits: ESA–S.Poletti*

To obtain the highest-resolution images yet, the Solar Orbiter was less than 74 million kilometers from our star. Being so close to the Sun means that each image taken by the spacecraft can only capture a small portion of an object with a volume of 1.3 million Earths.

Thanks to the spacecraft’s ability to tilt and rotate, data from different angles are then combined into a mosaic to create images of the entire solar disk.

The following new mosaics are composed of 25 images each, taken over a period of more than four hours. The solar disk has a diameter of nearly 8000 pixels in the full mosaics, revealing an incredible amount of detail.

The photosphere and the magnetic field

Looking at the Sun in visible light, it is possible to capture the photosphere: the surface composed of plasma that is constantly moving and has a temperature between 4500 and 6000 °C.

*PHI’s view of the Sun in visible light collected at a wavelength of 617 nanometers. Credits: ESA & NASA/Solar Orbiter/PHI Team*

Almost all of the Sun’s radiation comes from this layer, so at the wavelengths of visible light at which humans have evolved to see.

This zone acts as an interface between the Sun’s inner layers and its outer atmosphere, so heat transfer by convection of the subsurface material occurs at this interface, giving the photosphere its characteristic grainy appearance.

The most remarkable features of the image, however, are the sunspots. These look dark because they are colder than their surroundings and so emit less light.

To explore this phenomenon, another of the four new images from the Sun Probe is needed: a magnetic map of the Sun.

*PHI’s map of the Sun’s* ***magnetic field****, the most detailed ‘magnetogram’ of the Sun to date. Credits: ESA & NASA/Solar Orbiter/PHI Team*

This map illustrates how the magnetic field is concentrated in sunspot regions, showing a complex network of lines of force pointing inward (blue) or outward (red) just at these regions.

This strong localized magnetic field explains why the plasma inside sunspots is cooler. Normally, convection moves heat from the Sun’s interior to its surface, but this phenomenon is disrupted by charged particles that are forced to follow the lines of the dense magnetic field in and around sunspots.

Analysis of these very high-resolution images could lead to further discoveries about the magnetic field.

The velocity map and the UV light view

Plasma motion, captured by velocity maps, also called ‘tachograms’, adds a new level of understanding to solar dynamics.

*PHI’s* ***velocity map*** *of the Sun’s surface. Blue regions are moving towards the spacecraft and red regions are moving away. Credits: ESA & NASA/Solar Orbiter/PHI Team*

It is easy to see that the plasma motion appears to be uniform, generally rotating with the overall spin of the Sun around its axis. But again, around the sunspots, the plasma is pushed outward by the effect of the magnetic field.

This plasma ejection caused by the magnetic field around the sunspots is best observed in the wavelengths of ultraviolet light, resulting in the most spectacular image of the four.

*EUI’s detailed view of the Sun in* ***UV light****. Credits: ESA & NASA/Solar Orbiter/EUI Team*

Looking beyond the photosphere, the EUI images reveal extraordinary details of the corona, the Sun’s hot outer atmosphere.

In this region, plasma superheated to millions of degrees forms spectacular arcs of light that extend into space, following the magnetic lines that connect the active regions of the photosphere.

These match the sunspot regions seen in the visible light image, magnetic map and velocity map taken by the Solar Orbiter’s Polarimetric and Helioseismic Imager (PHI) instrument on the same day.

The new ultra-high-resolution images from Solar Orbiter represent a remarkable step forward in our ability to study the Sun.

With these detailed observations, we can learn more about the dynamics between the photosphere and the corona, providing a clearer view of the complex processes that govern its activity.