Seeing Both Sides of the Sun at the Same Time

As everybody who saw May’s spectacular auroral displays knows, the Sun is in its most active period in 11 years. The active region sunspot group that unleased the giant X-class flare rotated around the Sun, away from our direct view. But, that isn’t keeping the Solar Orbiter from spotting what’s happening with it and other active regions as they travel around on the Sun.

This European Space Agency solar satellite continuously observed the region as it transited the solar far side. The onboard x-ray instrument (STIX) watched in real time as that sunspot group (dubbed AR3664) belched out another massive flare on May 20th. That outburst is currently the record-holder for strongest flare of the current solar cycle. If it was aimed toward Earth, we’d have seen fantastic auroral displays again. However, the flare could have posed a huge threat to our satellites, communications services, and even astronauts in orbit.

Observing the Whole Sun

Scientists were, until relatively recently, limited to a view of one side of the Sun at the same time, from both Earth-based and space-based observatories and missions. That point of view limits how much information we can get about solar activities. Thanks to the Solar Observer, however, that view is changing and scientists take advantage of its position in space to see the far side of the Sun. It watches from an eccentric orbit that takes it as close as 60 solar radii to the Sun. That’s even closer than the orbit of Mercury. It makes this close approach every half-year.

Solar Orbiter’s view of the sunspot group AR3664 vs. Earth-centric view of the Sun. Courtesy: ESA & NASA/Solar Orbiter/EUI

The Solar Orbiter has returned the closest-ever images of our star, measures the solar wind, and studies the solar polar regions. “Solar Orbiter’s position, in combination with other missions watching the Sun from Earth’s side, gives us a 360-degree view of the Sun for an extended period of time. This will only happen three more times in the future of Solar Orbiter, so we are in a unique situation to observe active regions on the far side that will then rotate into Earth’s view,” said ESA Solar Orbiter Project Scientist Daniel Müller.

Solar Orbiter’s Mission to Observe the Sun

Data from Solar Orbiter allow scientists to understand solar activity and provide improved space weather forecasts. Solar physicists use the term “space weather” as a catch-all for the kinds of geomagnetic storms caused by solar outbursts. Usually, these occur in the form of X-class flares and coronal mass ejections. They happen more frequently during solar maximum—the most active time of the Sun’s 11-year cycle of sunspots. That heightened activity poses a real threat to Earth and human technologies on and off planet.

In the case of sunspot group AR3664, measurements from Solar Orbiter, in conjunction with Mars Express and the BepiColumbo spacecraft showed that it was still very active as it transited around the Sun. The May 20th outburst, for example, turned out to be an estimated class of X12. “This makes it the strongest flare yet of the current solar cycle, and in the top ten flares since 1996,” said ESA research fellow Laura Hayes.

A simulation of charged particles moving out from the Sun through the inner solar system after the outburst of May 27th, 2024. Courtesy: EUHFORIA/J. Pomoell

The Sun continued to be active even as it rotated around toward Earth and erupted again on May 27th. According to Müller, Earth dodged a bullet because the storm bypassed us. “If this flare and coronal mass ejection had been directed towards Earth, it would have caused another major geomagnetic storm for sure. But even like this, it resulted in a strong radio blackout over North America.”

Tracking An Active Sunspot Region

The same pesky sunspot region continues to be active as the Sun rotates and brings it around again and again and spacecraft capture evidence of its eruptions. The May 20th outburst also sent a shower of fast-moving ions and electrons across space. Solar Orbiter’s energetic particle detector measured them, and BepiColumbo and Mars Express were affected. The energetic particles hit memory storage on both spacecraft. That caused numerous errors during spacecraft operations. Interestingly, the memory problems also provided an alternate way to detect space weather events.

The offending sunspot group was also associated with a huge coronal mass ejection, which the Orbiter’s magnetometer measured almost immediately. This outburst was so massive that the Solar and Heliospheric Observatory (SOHO) captured a view from its Lagrange point orbit. It did it again on June 11th, emitting yet another X-class flare. It’s probably only a matter of time before it aims one at Earth again.

The May 27th coronal mass ejection from the Sun as seen by the SOHO and Solar Dynamics Observatories. Courtesy: SOHO (ESA & NASA), NASA/SDO/AIA, JHelioviewer/D. Müller

Solar Missions and Space Weather

Thanks to observations from Solar Orbiter and other spacecraft such as the Parker Solar Probe, scientists should be on the watch for outbursts and issue warnings in time for satellite operators, space agencies, and others to prepare. Solar Orbiter’s views of the entire Sun are just the start of complete real-time solar observations. There’s another mission, called Vigil, being designed to monitor the Sun and improve space weather predictions. It won’t launch until at least 2031 and will do its work from an L5 position in space.

“Adding Vigil’s data to our space weather services can give us forecasts up to 4–5 days earlier for certain space weather effects and provides more detail than ever before. Such early warnings give astronauts time to take shelter, and operators of satellites, power grids and telecommunication systems time to take protective measures,” said Giuseppe Mandorlo, Vigil Project Manager at ESA.

For More Information

Can’t Stop, Won’t Stop: Solar Orbiter Shows the Sun Raging On
Solar Orbiter Mission

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