The Sun’s polar regions remain among the most enigmatic and least explored domains in solar physics. Despite decades of observation from Earth-orbiting satellites and ground telescopes, our vantage points have largely been confined to the ecliptic plane—the narrow band of space where Earth and most planets circle the Sun. This limitation has left the sun’s high-latitude poles shrouded in mystery, obscuring critical insights into the sun’s magnetic environment and dynamic processes that shape solar activity and influence space weather across the solar system.
The polar regions play an outsized role in the solar magnetic cycle, yet their magnetic fields and plasma flows are difficult to characterize from traditional viewpoints. Deep within these poles lie the seeds of the 11-year solar magnetic cycle; the polar magnetic fields act as the global dipole component, reversing direction with each cycle. Furthermore, measurements from missions like Ulysses have shown that the fast solar wind—a high-speed stream of charged particles that fills much of interplanetary space—originates predominantly from large, low-density coronal holes near the poles. Understanding these outflows and the magnetic field configuration at the poles is therefore fundamental to decoding solar-terrestrial interactions.
The solar dynamo mechanism—a complex interplay of plasma motions, magnetic field generation, and the sun’s differential rotation—has been a topic of intense study, yet the exact pathways remain elusive. The convection zone’s internal plasma flows that contribute to the dynamo process are especially murky at high latitudes. Conflicting helioseismic data has even suggested unconventional flow patterns such as poleward circulation at the convection zone base, challenging classical dynamo models. Observations directly focused on magnetic fields and plasma flows at the poles would be invaluable in resolving these contradictions and refining theoretical frameworks.
Additionally, the origins of the fast solar wind emerging from the polar coronal holes continue to be debated. While some suppose that it emanates mainly from dense plume structures within these holes, others point to the less dense inter-plume regions as key sources. Furthermore, the mechanisms accelerating the solar wind remain uncertain—whether wave-particle interactions, magnetic reconnection, or hybrid processes dominate is an open question. Direct imaging from a polar vantage, complemented by in-situ plasma and magnetic field measurements, is critical to settle these debates.
Space weather phenomena—such as solar flares and coronal mass ejections (CMEs)—can disrupt modern technological systems on Earth and in orbit. Historically, tracking their propagation has been limited to views constrained near the ecliptic, impeding comprehensive models of their evolution and impact. Observing the Sun’s poles provides a unique perpendicular perspective, offering a holistic view of how these large-scale magnetic structures emerge, evolve, and travel through interplanetary space. This could enable more accurate predictions and mitigation strategies for space weather hazards.
Historically, our first glimpse beyond the ecliptic arrived with the Ulysses mission, launched in 1990. Ulysses performed several high-inclination orbits around the Sun and provided groundbreaking in-situ measurements of the fast solar wind and magnetic fields at the poles, though it lacked remote sensing instruments to image the solar surface and atmosphere directly. The Solar Orbiter spacecraft, launched more recently, marks substantial progress by venturing to latitudes near 34°, but even this does not provide a full polar perspective.
Over the years, multiple mission concepts aimed at unlocking the polar mysteries have been proposed, including the Solar Polar Imager (SPI), POLARIS, SPORT, Solaris, and HISM. These missions envisioned employing various orbital strategies, from solar sails to gravity assists, to achieve the high inclinations necessary for polar observation. Each was designed to host instruments capable of capturing both remote sensing data and direct measurements of fields and particles originating from the poles—yet none have materialized into operational missions to date.
Enter the Solar Polar-orbit Observatory (SPO), a groundbreaking mission planned for launch in January 2029. SPO will harness a Jupiter gravity assist maneuver to dramatically alter its orbital inclination, steering it out of the ecliptic and into a unique trajectory that achieves inclinations as high as 75°. This will enable extended observations of the solar poles—windows exceeding 1000 days per pass—unprecedented in solar exploration history. The mission’s nominal duration of 15 years, including an eight-year extended phase, aligns well with capturing the solar cycle from minimum to maximum and observing critical magnetic reversals anticipated around 2035.
SPO’s instrumentation suite has been meticulously designed to address the key scientific challenges of polar exploration. Remote sensing tools include a Magnetic and Helioseismic Imager (MHI) to map magnetic fields and plasma flow patterns on the solar surface, as well as the Extreme Ultraviolet Telescope (EUT) and X-ray Imaging Telescope (XIT), which will monitor dynamic processes in the solar atmosphere at the poles. Complementing these are coronagraphs—VISible-light CORonagraph (VISCOR) and Very Large Angle CORonagraph (VLACOR)—capable of imaging the expansive solar corona and solar wind streams out to 45 solar radii. In-situ instruments, including magnetometers and particle detectors, will sample charged particles and magnetic fields directly, linking the remote observations to physical conditions in the heliosphere.
Importantly, SPO is expected to operate synergistically with an expanding fleet of solar observatories, including NASA’s STEREO, Hinode, Solar Dynamics Observatory (SDO), Interface Region Imaging Spectrograph (IRIS), the Advanced Space-based Solar Observatory (ASO-S), Solar Orbiter, India’s Aditya-L1, and upcoming L5 missions like ESA’s Vigil and China’s LAVSO. Collectively, these spacecraft will deliver an unprecedented all-sky 4π coverage of the Sun, with SPO’s polar vantage filling a critical observational gap to provide a near-global understanding of solar dynamics.
The scientific implications of SPO extend well beyond academic discoveries. Unraveling the solar dynamo’s high-latitude processes will pave the way for improved solar cycle forecasts, which bear significant implications for predicting space weather hazards. Insight into the origin and acceleration of the fast solar wind can enhance heliospheric models, essential for the safety and design of spacecraft and the protection of astronauts. Furthermore, SPO’s ability to monitor and track eruptive events from the poles could revolutionize space weather forecasting, mitigating risks to satellites, telecommunications, navigation systems, aviation, and terrestrial power grids.
Ultimately, the Solar Polar-orbit Observatory offers a rare and transformative opportunity to finally decode the sun’s polar puzzle—a key to understanding the star that not only shapes our cosmic neighborhood but also sustains life on Earth. By capturing high-resolution images and direct measurements of the solar poles over more than a decade, SPO will fundamentally reshape our understanding of the solar magnetic cycle, the fast solar wind, and the dynamics of space weather propagation throughout the solar system.
With its ambitious technological and scientific goals, the SPO mission stands poised to propel solar physics into a new era—moving humanity from an equatorial perspective to a full-sphere understanding of our star. This leap may hold the key to predicting the Sun’s future behavior with unprecedented accuracy and safeguarding the increasingly space-dependent civilization of tomorrow.
Subject of Research: Solar polar regions, solar magnetic cycle, fast solar wind, space weather propagation
Article Title: Probing Solar Polar Regions
News Publication Date: 2-Jul-2025
Web References: http://dx.doi.org/10.11728/cjss2025.04.2025-0054
Image Credits: Beijing Zhongke Journal Publishing Co. Ltd., courtesy of Zhenyong Hou and Jiasheng Wang at Peking University
Keywords
Solar polar regions, solar dynamo, magnetic cycle, fast solar wind, coronal holes, space weather, Solar Polar-orbit Observatory, SPO mission, solar corona, helioseismology, Jupiter gravity assist, solar magnetic reconnection, coronal mass ejections
