Following a flyby of Venus in February that successfully increased its orbital inclination around the Sun, the European Space Agency’s Solar Orbiter recently imaged the Sun’s poles for the first time. The images are the first to show how the Sun’s immense magnetic field interacts at its poles, and will improve scientists’ understanding of the solar cycle and solar weather.
While the images are the first of the solar poles ever taken, they are not the last. Over the next five years, Solar Orbiter’s orbit will continue to increase in inclination, giving scientists unparalleled views of the Sun’s northern and southern poles.
Given the location of Earth and the other planets within the Sun’s ecliptic plane, every photograph ever taken of the Sun is taken facing directly at the solar equator. Solar Orbiter is the first spacecraft to ever significantly shift the inclination of its heliocentric orbit beyond the ecliptic plane. This shift in inclination — 17 degrees to be exact — allowed its cameras to view the Sun’s south pole for the first time.
“The Sun is our nearest star, giver of life and potential disruptor of modern space and ground power systems, so it is imperative that we understand how it works and learn to predict its behaviour. These new, unique views from our Solar Orbiter mission are the beginning of a new era of solar science,” said Prof. Carole Mundell, who serves as the Director of Science for the European Space Agency (ESA).
Solar Orbiter first got a glimpse of the south pole on March 16 when it was 15 degrees below the solar equator. Throughout the following day, the spacecraft imaged the south pole through a variety of filters as part of the mission’s first high-angle observation campaign, which continued until Solar Orbiter reached its maximum orbital inclination of 17 degrees.
The spacecraft used three of its instruments to capture the images and measurements. The Polarimetric and Helioseismic Imager (PHI) provides high-resolution and full-disk measurements of the Sun’s photosphere’s vector magnetic field. The Extreme Violet Imager (EUI) provides imagery of the atmospheric layers of the photosphere, or the layer of a star’s outer atmosphere from which light is radiated. Lastly, the Spectral Imaging of the Coronal Environment (SPICE) instrument collects extreme ultraviolet imagery and spectroscopic measurements of the plasma properties of the Sun’s corona.
“We didn’t know what exactly to expect from these first observations — the Sun’s poles are literally terra incognita,” says PHI instrument team lead Prof. Sami Solanki of the Max Planck Institute for Solar System Research in Germany.
Diagram showing Solar Orbiter’s suite of instruments. (Credit: ESA)
For the first high-angle observation program, PHI imaged the Sun in visible light and mapped its surface magnetic field, EUI imaged the Sun in ultraviolet light and its corona, and SPICE imaged light radiating from charged gas of varying temperatures above the Sun’s surface.
The observations made by the three instruments highlighted how material moves within the Sun’s outer layers and could reveal polar vortices similar to those seen at Saturn’s poles. Furthermore, observing the Sun’s polar regions will reveal more about the Sun’s intense magnetic field and why it flips every 11 years. Solar activity usually peaks when this magnetic field flips, but current models struggle to predict exactly when the Sun will reach its most active state and how powerful its peak will be.
One such discovery made regarding the Sun’s magnetic field is that, at the solar south pole, the Sun’s magnetic field is quite a mess. Measurements from PHI showed that both north and south polarity magnetic fields are present at the south pole. Normally, planetary poles will feature one of the two polarities, not both.
PHI data showing the “messy” magnetic field at the solar south pole. Each red and blue patch indicated a different magnetic polarity. (Credit: ESA/NASA/Solar Orbiter/PHI Team/J. Hirzberger (MPS))
Interestingly, however, this “mess” only briefly occurs during a solar maximum, when the Sun’s magnetic field flips and is at its most active state. Given that the Sun reached its most recent solar maximum in October 2024 and will continue to stay highly active until September or October, the observations were not unexpected. After the magnetic field flips and the Sun’s activity begins to die down, a single polarity will build up and take over at each of the Sun’s poles. The magnetic field will reach its most orderly state in five to six years, when the Sun reaches its solar minimum.
“How exactly this build-up occurs is still not fully understood, so Solar Orbiter has reached high latitudes at just the right time to follow the whole process from its unique and advantageous perspective,” Solanki said.
PHI’s observations and mapping of the Sun’s magnetic field further highlighted the complexity of the magnetic field at solar maximum. The strongest magnetic fields were identified in two large bands on either side of the Sun’s equator. Furthermore, multiple “sunspots” were noted in the PHI data, or regions where the magnetic field is heavily concentrated on the Sun’s surface.
PHI’s complete map of the Sun’s magnetic field. The darker the shade of red or blue, the stronger the magnetic field. (Credit: ESA/NASA/Solar Orbiter/PHI Team/J. Hirzberger (MPS))
While PHI mapped the Sun’s magnetic field, SPICE was busy measuring the spectral lines emitted by chemical elements — such as hydrogen, carbon, and oxygen — within the solar surface, revealing what happens in different atmospheric layers above the Sun’s surface. What’s more, the SPICE team successfully performed a “Doppler measurement” with the instrument for the first time, during which SPICE precisely tracked spectral lines to measure the velocities of clumps of solar material.
The team performed multiple Doppler measurements during the first high-angle observations, creating a velocity map that revealed how solar material moves at different layers of the Sun’s atmosphere.
These measurements can reveal how solar material is ejected from the Sun during coronal mass ejections and other solar events. The ejected solar material, then known as “solar wind,” is responsible for the incredible aurora light shows we see on Earth, Jupiter, Mars, and many other planets. Investigating the origins of solar wind is one of Solar Orbiter’s key scientific objectives, and the latest polar observations are just the first of many that will reveal more about solar wind and how it is created.
SPICE’s velocity map of the Sun’s south pole. The red and blue colors represent the different motions of material, with red highlighting material moving away from Solar Orbiter. (Credit: ESA/NASA/Solar Orbiter/SPICE Team/M. Janvier (ESA)/J. Plowman (SwRI))
“Doppler measurements of solar wind setting off from the Sun by current and past space missions have been hampered by the grazing view of the solar poles. Measurements from high latitudes, now possible with Solar Orbiter, will be a revolution in solar physics,” says SPICE team leader Frédéric Auchère of the University of Paris-Saclay in France.
All of these findings stem from Solar Orbiter’s first pass in its newly inclined orbit. As its orbital inclination continues to increase, so will the spacecraft’s visibility of the poles and its ability to research them. In fact, much of the data collected from the first passes has yet to be analyzed. Though Solar Orbiter has already completed its first full “pole-to-pole” flight, the complete data set of that is expected to arrive in October.
“This is just the first step of Solar Orbiter’s ‘stairway to heaven’: in the coming years, the spacecraft will climb further out of the ecliptic plane for ever better views of the Sun’s polar regions. These data will transform our understanding of the Sun’s magnetic field, the solar wind, and solar activity,” said Solar Orbiter project scientist Daniel Müller.
(Lead image: Solar Orbiter image of the Sun’s south pole. Credit: ESA/NASA/Solar Orbiter/EUI Team/D. Berghmans (ROB))
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