Breathtaking images of the aurora borealis and aurora australis, visible at significantly lower latitudes than usual, inundated social media on Friday and Saturday. For scientists studying space weather, the auroras, generated by an intense solar storm, provided compelling evidence that the Sun is approaching the apex of its 11-year cycle of activity.
Operators of satellites, managers of electrical grids, and other custodians of critical technological infrastructure are presently evaluating the repercussions of this unprecedented occurrence — the most severe geomagnetic storm since 2003. However, it appears that most major systems have withstood the impact.
This is heartening news because further storms are anticipated: the most potent geomagnetic storms of a solar cycle often transpire after the 'solar maximum', which is projected to occur later this year. Nature elucidates the recent events and what solar physicists are expecting in the days ahead.
Why is this happening now?
The immediate trigger is a conglomerate of sunspots, identified as active region 3664, which emerged below the Sun’s equator on the hemisphere currently facing Earth. This cluster spans roughly 17 times the diameter of Earth and is likely the most extensive and intricate sunspot region observed during the ongoing solar cycle, which commenced in 2019, according to Shawn Dahl, a space weather forecaster at the US National Oceanic and Atmospheric Administration’s Space Weather Prediction Center in Boulder, Colorado.
Commencing around 8 May, active region 3664 discharged at least seven eruptions of magnetized plasma, known as coronal mass ejections, hurtling towards Earth at velocities of up to 1,800 kilometers per second. Accompanied by surges of charged particles and other solar remnants, these coronal mass ejections overwhelmed space weather monitoring instruments. Solar physicist Ryan French of the National Solar Observatory in Boulder describes the encounter as "mesmerizing" — initially, in the influx of data, and subsequently, in the "unfiltered wonder" of witnessing the aurora.
How big was this storm?
Then there were the auroras. Earth's magnetic field shields life forms, including humans, from the impacts of solar storms by diverting harmful particles away from the planet. However, when material from coronal mass ejections collides with the magnetic field, it releases energy into Earth's upper atmosphere. Chemical elements like oxygen and nitrogen in the atmosphere become ionized and emit light in various hues, forming auroras. Typically, these phenomena are observed near Earth's poles, but on 10 May, due to the intensity of the solar storm, auroras were visible at remarkably low latitudes, even in Mexico.
"Unforgettable," remarks Steph Yardley, a space physicist at Northumbria University in Newcastle-upon-Tyne, UK. The auroras were so active that she had to gaze southward, rather than northward, from her vantage point in Scotland to witness them.
What impacts did it have?
The solar storm disrupted radio and GPS communications worldwide. Starlink, a branch of the aerospace company SpaceX offering broadband internet via over 5,000 satellites, experienced temporary signal degradation. Space-weather physicist Tamitha Skov speculated on the social media platform X (formerly Twitter) that this might be due to communication disruptions or changes in Earth's atmosphere density causing satellite drag.
In anticipation of the heightened solar activity, electrical grid operators implemented protective measures as geomagnetic storms can induce additional electrical currents, leading to power outages. New Zealand's electrical transmission service temporarily deactivated some circuits across the country to prevent equipment damage.
NASA assured on 10 May that there was no threat to the four US and three Russian astronauts aboard the International Space Station. Although three individuals are aboard China's Tiangong space station, no precautionary measures were reported there.
Certain satellites ceased scientific observations. For example, NASA's Chandra X-ray Observatory paused astronomical data collection as a precautionary measure before the storm and safeguarded its instruments against radiation blasts. Additionally, NASA's ice-measuring ICESat-2 satellite halted scientific operations automatically during the storm due to unexpected rotation, likely caused by increased atmospheric drag, according to an agency spokesperson.
What else can scientists learn from the storm?
There could be fresh revelations forthcoming. The European Space Agency's Solar Orbiter probe is currently positioned nearly behind the Sun relative to Earth, granting it a distinct vantage point of the storm. Active region 3664 is now transitioning away from the side of the Sun visible from Earth and into the field of view of Solar Orbiter. "We should gain further insights in the coming days regarding whether this sunspot continues its vigorous activity on the far side of the Sun," remarks David Williams, the spacecraft's instrument operations scientist. NASA's Parker Solar Probe, currently conducting a series of dives through the Sun's outer atmosphere, finds itself at the outermost extent of its elliptical orbit around the Sun, potentially offering an additional perspective, although the data transmission to Earth may take time.
Scientists anticipate a coronal mass ejection to impact Mars in the forthcoming days, according to Shannon Curry, a planetary scientist at the University of Colorado in Boulder. This collision could be observed by NASA's MAVEN spacecraft, which orbits the red planet.
When could the next big storm affect Earth?
At any given moment. Researchers anticipate the ongoing solar cycle to reach its climax at some point this year, attributed to the abundance of sunspots under observation. Historically, the most significant storms tend to occur several months to even years following this designated peak. Additionally, as the solar cycle advances, sunspots tend to emerge nearer to the equatorial region of the Sun, heightening the likelihood of coronal mass ejections directed towards Earth rather than dispersing into space, as noted by Dahl.
