For the first time, a hurricane has been detected in Earth's upper atmosphere. In 2014, satellites recorded a huge flowing swirl of plasma extending high into the magnetosphere that lasted for hours before dispersing.
Although we've never seen anything like this before, its detection suggests that space hurricanes, as they are known, could be a common planetary phenomenon.
"Until now, it was uncertain that space plasma hurricanes even existed, so to prove this with such a striking observation is incredible," said space environment physicist Mike Lockwood of the University of Reading in the UK.
Hurricanes in Earth's lower atmosphere are common: powerful, rotating weather systems around a relatively calm centre, accompanied by strong winds and lashing rain that can cause vast amounts of damage in a very short time.
Space hurricanes, the new work reveals, are not dissimilar to their lower atmosphere cousins.
The detections were made on 20 August 2014, and revealed during a retrospective analysis led by Shandong University in China. According to the data, the hurricane appeared over the North Pole, extending to a diameter of 1,000 kilometres (621 miles).
It reached from 110 kilometres to 860 kilometres in altitude, and consisted of plasma with multiple spiral arms, swirling in an anticlockwise direction at speeds up to 2,100 metres per second (6,900 feet per second). The centre, however, was almost still, just like in hurricanes at lower altitudes.
Unlike other hurricanes, however, the space hurricane rained electrons into the ionosphere. This had a stunning effect: a huge, cyclone-shaped aurora below the hurricane. The whole thing lasted nearly eight hours, depositing vast amounts of energy and momentum into the ionosphere.
Conditions were otherwise quiet, which posed a mystery. A rain of charged particles into the ionosphere from the solar wind is what usually produces glowing green aurorae at Earth's higher latitudes, but solar conditions at the time were relatively quiet. So the team turned to modelling to determine what caused the plasma ruckus.
"Tropical storms are associated with huge amounts of energy, and these space hurricanes must be created by unusually large and rapid transfer of solar wind energy and charged particles into the Earth's upper atmosphere," Lockwood explained.
We know that reconnecting magnetic field lines can transfer solar wind energy into the magnetosphere and ionosphere, so the team modelled this process and found that a reconnecting interplanetary magnetic field can produce the features they observed in the space hurricane, even when the solar wind is low. In fact, the low solar wind might be key - it allows for more efficient magnetic reconnection.
It also means that such storms might be quite common.
"Plasma and magnetic fields in the atmosphere of planets exist throughout the universe, so the findings suggest space hurricanes should be a widespread phenomena," Lockwood said.
There are implications for Earth, too. Knowing that aurorae can be the product of space hurricanes, and what these aurorae look like, could help us identify other such storms in the future.
It also shows that, even when geomagnetic conditions are relatively quiet, space can whip up extreme weather that can impact life on Earth, and the skies above it.
"This study suggests that there are still existing local intense geomagnetic disturbance and energy depositions which is comparable to that during super storms. This will update our understanding of the solar wind-magnetosphere-ionosphere coupling process under extremely quiet geomagnetic conditions," said space physicist and first author, Qing-He Zhang of Shandong University.
"In additional, the space hurricane will lead to important space weather effects like increased satellite drag, disturbances in High Frequency radio communications, and increased errors in over-the-horizon radar location, satellite navigation and communication systems."
The research has been published in Nature Communications.