The hyperactive sunspot region responsible for the stunning auroras in early May was still highly active as it rotated away from Earth’s view. ESA’s Solar Orbiter mission detected this same region producing the largest solar flare of the current solar cycle. Observing the Sun from all sides, ESA missions provide critical insights into how active sunspot regions evolve and persist, improving space weather forecasting.
Earlier this year, the biggest solar storm to hit Earth in over 20 years caused an intense geomagnetic storm, creating beautiful auroras at much lower latitudes than usual. The instigator, an active sunspot region named AR3664, rotated away from Earth’s view around 14 May, sending out the strongest flare yet (class X8.79), which caused significant radio blackouts on Earth. Despite moving out of view, the region continued to be active.
Observing the Sun’s far side on 20 May, Solar Orbiter’s X-ray instrument recorded a massive flare with an estimated class of X12. “This makes it the strongest flare yet of the current solar cycle,” said ESA research fellow Laura Hayes. Notably, X-class flares are the highest category, and the higher the number following the X, the stronger the flare.
Most missions that study the Sun observe the side facing Earth, but Solar Orbiter takes a unique route through the Solar System. The spacecraft’s position allows it to observe the Sun’s far side for extended periods. “Solar Orbiter’s position, in combination with other missions watching from Earth’s side, gives us a 360-degree view of the Sun for an extended period,” explains Daniel Müller, Solar Orbiter Project Scientist at ESA.
Following the flare on 20 May, Solar Orbiter’s Energetic Particle Detector (EPD) detected a surge in high-speed ions and electrons. During this period, other ESA missions observed an increase in memory errors on their computers, likely caused by solar energetic particles.
Sunspot drives massive solar flare
Soon after, the Metis coronagraph onboard Solar Orbiter observed a significant ‘coronal mass ejection’, while the MAG magnetometer detected its impact at the spacecraft about a day later. This eruption released a huge bubble of plasma, causing significant fluctuations in the magnetic field measured at the spacecraft. The data from these observations help track particle and electromagnetic field movements, enhancing the accuracy of solar activity simulations.
The observations made by Solar Orbiter, Mars Express, and BepiColombo confirmed that AR3664 remained active while out of Earth’s view, serving as a warning when the region reappeared. When it rotated back into view on 27 May, the region emitted powerful radiation and bursts of particles. “If this flare and coronal mass ejection had been directed towards Earth, it would have caused another major geomagnetic storm,” notes Daniel Müller.
Despite not being Earth-directed, it resulted in a strong radio blackout over North America. As recently as 11 June, Solar Orbiter recorded another back-of-the-Sun X-class solar flare from AR3664. Understanding the behavior of regions like AR3664 throughout their lifetimes is essential for predicting how solar outbursts will affect Earth.
ESA missions provide valuable monitoring throughout the Solar System, using space science for Earth’s benefit. Solar Orbiter’s observations offer a preview of what ESA’s space weather forecasting mission will achieve. By monitoring the Sun’s left side (as seen from Earth), the spacecraft will provide a continuous feed of near real-time data on potentially hazardous solar activity before it becomes visible from Earth.
Adding Vigil’s data to our space weather services can give us forecasts up to 4–5 days earlier for certain space weather effects, providing more detail than ever before,” says Giuseppe Mandorlo, Vigil Project Manager at ESA. This early warning capability is critical, allowing astronauts and satellite operators time to take protective measures. Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA.
