Launched in February 2020, the European Space Agency’s (ESA) Solar Orbiter probe has been looping around the Sun with a special purpose in mind: Studying the poles of our star.
The planets orbit the Sun in a single plane, called the ecliptic. This means we’re roughly even with the Sun’s equator and don’t see its poles from Earth The Solar Orbiter mission, however, was designed with a tilted orbit in mind, allowing the spacecraft to see what we here on Earth cannot, allowing us to study the entire Sun.
But Solar Orbiter’s path didn’t start out tilted. It’s thanks to Venus, which provides periodic gravity assists as the spacecraft orbits in resonance with the planet, that Solar Orbiter has been able to pump up its inclination, reaching a tilt of 17° relative to the Sun’s equator following its last Venus flyby in February this year.
And today, ESA has released the first images and videos to ever show the Sun’s poles, imaged from a latitude of 17° south on the Sun. They bring our star’s entire south pole into view for the first time.
The corona
The snapshot above is from observations taken March 23 by the mission’s Extreme Ultraviolet Imager (EUI). It shows the superheated gas of the Sun’s corona, or outermost atmosphere, which reaches millions of degrees. Exactly how the corona reaches such high temperatures remains a mystery that researchers are hoping missions like Solar Orbiter will unlock.
As its name suggests, EUI views the Sun in ultraviolet light, which is more energetic than the light our eyes see. Visible are plumes and arches of hot plasma within the corona, whose shape and behavior is governed by the solar magnetic field.
Flowing material
This velocity map, produced by the Spectral Imaging of the Coronal Environment (SPICE) imaging spectrograph, shows how super-hot excited carbon atoms (called ions) are moving at the Sun’s south pole. Here, blue colors show material moving toward the spacecraft (outward from the Sun), while red is material falling back toward the Sun. Darker shades represent faster speeds, with faster movement associated with plumes or jets of material.
The map shows carbon within the Sun’s so-called transition region, where temperatures in our star’s atmosphere shoot up from tens of thousands to hundreds of thousands of degrees. This region separates the inner and outer atmosphere of the Sun — at the top is where the superheated corona begins.
A magnetic mess
If you’re thinking the pole of the Sun so far looks pretty much like the rest of our star — here’s where things change. Our Sun is a magnetic machine, with its strong magnetic field driving its behavior. That magnetic field drives the ever-flowing solar wind of charged particles that stream throughout the solar system. It also dictates how and when sunspots, prominences, and the huge ejections of material that create bigger space weather events occur.
And Solar Orbiter, with its highly inclined orbit, is seeing more details of the Sun’s magnetic field than ever before.
Right now, the Sun is at a special time in its 11-year cycle, having reached solar maximum late last year. This is a period of increased activity (as we’ve seen from abundant and far-reaching aurorae over the past year) as our star’s poles prepare to flip polarity, meaning its north and south magnetic poles will swap places.
Getting a view of the poles now is will show us what’s going on there as this change gets underway. The behavior of material ebbing and flowing there is a proxy for the behavior of the magnetic field there, while viewing more of the Sun overall lets us better see the boundary between its magnetic northern and southern regions, which will change as the switch gets underway.
According to the ESA release, Solar Orbiter’s first look has revealed that the magnetic field at the Sun’s south pole “is currently a mess.” This image, taken by the Polarimetric and Helioseismic Imager (PHI), shows the polarity (or direction) of the solar magnetic field at the Sun’s south pole. Blue indicates a positive magnetic field pointing outward, while red indicates a negative magnetic field pointing inward.
Rather than possessing a single overwhelming polarity, as under normal conditions, PHI has revealed that instead the Sun’s south pole is awash in both positive and negative magnetic fields — a short-lived phenomenon that only occurs around solar maximum. Within the next few years, once the poles fully flip, the north and south pole should each settle into a single magnetic polarity once more.
Terra incognita no more
“We didn’t know what exactly to expect from these first observations — the Sun’s poles are literally terra incognita,” said PHI team lead Sami Solanki of the Max Planck Institute for Solar System Research (MPS) in Germany, in the press release.
And these first images are only the tip of the iceberg. The complete dataset containing our first views of both solar poles, which will include observations from all 10 of the spacecraft’s instruments, won’t arrive in scientists’ hands until October.
Even that is just the beginning as well: Solar Orbiter will continue to bump the tilt of its orbit ever higher in the coming years, ultimately imaging the Sun from a latitude of 33° by the end of the decade. Its next “bump” will take it from an inclination of 17° to 24°, when it flies by Venus on Christmas Eve next year and again uses the gravity of the planet to adjust its orbit.
“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 behavior,” said Carole Mundell, Director of Science at ESA. “These new unique views from our Solar Orbiter mission are the beginning of a new era of solar science.”
