Strange giant aurora seen from Earth for the first time

On Christmas Eve 2022, a massive aurora lit up the sky for thousands of kilometers around the North Pole¹. The light show gave scientists a unique view of the ‘polar rain aurora’, a rare twinkling phenomenon that forms when energetic electrons from the Sun cascade into Earth’s polar regions.

Auroras are formed when charged particles flowing from the Sun strike and interact with Earth’s magnetic field. Their energy is usually transformed into light displays of dancing green curtains, towering red pillars or other spectacles like those that dazzled sky watchers around the world in May.

Polar auroras are a special type that form when electrons traveling directly from the Sun’s corona, or outermost atmosphere, crash into Earth’s atmosphere. Polar auroras are a special type that form when electrons traveling directly from the Sun’s corona, or outermost atmosphere, crash into Earth’s atmosphere. These auroras are rare because there are rarely enough of these electrons hitting the atmosphere to generate a glow. And other types of charged particles often interfere with these electrons, preventing the formation of polar rain auroras.

When the wind died down

But for 28 hours in December 2022, the flood of other solar particles – known as the solar wind – dropped to a trickle. The rain’s polar electrons flowed unhindered to Earth, creating a green glow that stretched more than 3,000 kilometers across the North Pole.

Anyone looking up that night in the high Arctic might have been able to spot it, says Keisuke Hosokawa, a space physicist at Tokyo Electro-Communications University who led the team reporting the discovery today in Advances in science. Unlike the distinct curtains and pillars of light of standard auroras, this auroral glow was spread across the sky.

Viewing the Sun – close-up images from space rewrite solar science

Scientists have occasionally seen polar auroras in observations from satellites looking down on the poles.². Since 2011, Hosokawa has been running a robotic camera from the sky over the Norwegian islands of Svalbard in the Arctic Ocean, hoping to capture the first land-based view of the polar rain aurora. He didn’t make it until January 2023, when he browsed the data from about three weeks earlier. The aurora from that period was dismissed as “very different” from other types of aurora, he says.

Hosokawa then checked images of the polar regions taken by US military weather satellites at the same time as the Svalbard observations. In these, he saw the auroral glow that filled almost the entire northern polar cap.

Satellites have spotted small-scale polar rain auroras in recent decades, but the most recent observation of a large one was in May 1999 – when the solar wind also temporarily faded. Studying polar auroras can help scientists understand how the solar wind interacts with Earth’s magnetic field, says study co-author Yongliang Zhang, a space physicist at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland.