Solar Orbiter probe captures the Sun's poles

The Solar Orbiter probe was the first instrument in history to observe the poles of our daytime star. This will help us better understand the Sun's magnetic field, its activity cycles and space weather. Experts from the Space Research Centre of the Polish Academy of Sciences participated in the creation of the probe.

All the planets of the Solar System, as well as the probes that traverse this system, move on orbits placed on one plane – the so-called ecliptic plane. The exception is the European-American Solar Orbiter probe, whose orbit is intentionally inclined to this plane, so as to enable observation of the solar poles.

At the time the spacecraft's video was taken, Solar Orbiter was observing the Sun at an angle of 17 degrees, allowing it to capture the star's south pole.

"For the first time in history, we see the solar south pole at an angle of 17 degrees, much greater than we can see from Earth. This means less foreshortening, a better view of the pole and more information that we have been waiting for a whole generation," commented Dr. Tomasz Mrozek, a heliophysicist from the Solar Physics Team of the CBK PAN in Wrocław, who works on the mission, for PAP.

As he assessed, this is still just the beginning. "In the coming years, subsequent Venus gravity assists will take Solar Orbiter even higher above the ecliptic and we will see the poles at an angle greater than 30 degrees. Observations of the poles will primarily allow us to remove (literally) black spots from models of the Sun. Until now, we had to assume the conditions in these places, without knowing exactly what the areas around the poles actually look like. Thanks to the new data, the quality of the models of the 11-year activity of the Sun will improve significantly, and our understanding of solar magnetism will become more complete," added Dr. Mrozek.

The European Space Agency (ESA) Director of Science, Prof. Carole Mundell, quoted in the press release, pointed out that the Sun is our closest star, the source of life, but also a potential threat to modern energy systems in space and on Earth. "That is why it is so important that we understand how it works and learn to predict its behavior. These new, unique images from our Solar Orbiter mission are starting a new era of solar research," she emphasized.

The collection of images sent back by the spacecraft shows the sun’s south pole, captured on March 16-17. At the time, the spacecraft was observing the star from an angle of 15 degrees below the solar equator, the first observation from such a large angle — made just days before it reached its current maximum of 17 degrees.

The images were taken by the spacecraft's three science instruments: the Polarimetric and Helioseismic Imager (PHI), the Extreme Ultraviolet Imager (EUI), and the Spectral Imaging of the Coronal Environment (SPICE).

PHI images the sun in visible light and maps its surface magnetic field. EUI shows the sun in ultraviolet light, revealing the million-degree charged gas in the sun's corona. SPICE records light emitted by charged gas at different temperatures above the sun's surface, revealing the different layers of its atmosphere.

By analyzing the complementary observations from the three instruments, scientists can learn how material moves around the sun's outer layers. This could reveal unexpected structures such as polar vortices—swirling masses of gas similar to those seen around the poles of Venus and Saturn.

These groundbreaking observations also have implications for understanding the Sun's magnetic field and why it reverses every 11 years or so, coinciding with the star's peak activity. Current models and solar cycle forecasts still cannot accurately predict when and with what intensity the Sun will reach its peak activity.

One of the first scientific discoveries made from the new observations is that the Sun's magnetic field in the region of its south pole is currently chaotic.

While an ordinary magnet has a clearly defined north and south pole, magnetic field measurements from the PHI instrument show that the Sun's south pole has both north and south magnetic fields at the same time.

This phenomenon occurs only for a short time in each solar cycle—during the solar maximum, when the Sun's magnetic field reverses. After this reversal, one polarity should become dominant, eventually taking over the Sun's poles.

Meanwhile, in about 5–6 years, the Sun will reach its next solar minimum — a period when its magnetic field is most ordered and its activity level is lowest.

“How this polarization buildup occurs is not yet fully understood, so Solar Orbiter arrived at high latitudes at the perfect time to observe the whole process from a unique perspective,” said mission scientist Prof. Sami Solanki.

The strongest magnetic fields occur in two bands on either side of the sun's equator, the scientists explained. The dark red and dark blue areas indicate active regions, where the magnetic field is concentrated in sunspots in the photosphere.

Meanwhile, both the Sun's south and north poles are dotted with red and blue spots, showing that on a small scale, the Sun's magnetic field has a complex and constantly changing structure.

At the same time, the SPICE instrument precisely measured the speeds at which the solar material clumps moved. The resulting velocity map shows how the solar material moves in a specific layer of the Sun.

It is also crucial that the Doppler measurements used reveal how particles are ejected from the Sun in the form of the solar wind. Understanding the mechanism of the formation of the solar wind is one of the main scientific goals of the Solar Orbiter mission.

These are just the first observations made by Solar Orbiter from its new, inclined orbit. The full data set from the first full pole-to-pole flyby is expected to be obtained by October of this year. In subsequent years, all ten of the spacecraft's science instruments will collect data.

Experts from the Space Research Centre of the Polish Academy of Sciences who participated in the creation of the probe participated in the research and engineering work on the STIX X-ray spectrometer (X-ray Spectrometer/Telescope). This instrument is responsible for observing accelerated electrons - it determines the time and source of their emission, its intensity and spectral characteristics. Data obtained using STIX help explain the mechanism of electron acceleration on the Sun and how they are transported into interplanetary space.

Experts from CBK PAN took part in the development of the data processing unit of this instrument (including electronics and some software), created a housing for the data processing unit and for the power supply unit supplied by the Czech group, and performed thermal modeling of the STIX instrument and its subsystems.

Marek Matacz (PAP)

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