Investigating the Aurora
Aurora Borealis - Credit: Soerfm

Investigating the Aurora

18/12/2019Written by Hannah Baker

Two Missions Over a Century Apart

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The aurora flickers at the edge of our world, illuminating the invisible boundary between Earth and space. In the far north and far south of the planet, light dances around the poles where the solar wind collides with the atmosphere. It has long been a source of awe and wonder, but only with the development of space technology have its mysteries started to come to light.

Kristian Birkeland

At the end of the 19th century scientist Kristian Birkeland (1867-1917) led a series of expeditions to the far north of Norway. Fascinated by magnets since childhood, Birkeland longed to understand the nature of the aurora and its relation to the Earth’s magnetic field. His first expedition ended abruptly when his team were caught in a blizzard before reaching their mountain top destination. Only just escaping with their lives, one of the team was so badly frost bitten his career as a surgeon was cut short.

Two years later, Birkeland spent a whole winter in the Haldde mountains at almost a thousand metres above sea level. The conditions were perilous. At this latitude darkness prevails all winter. His small team were besieged by hurricane gales which destroyed several of their instruments. Poor ventilation meant smoke from their coal fire filled their small dwelling, creating a health hazard. Just as spring approached, one of his assistants was killed by an avalanche.

 

Kritian Birkeland and his Terrella experiment

However, all this was not in vain. Birkeland’s magnetic field experiments allowed him to formulate a theory. He was the first to put forward the idea that energetic particles are ejected from sunspots, collide with the Earth, and are guided to the polar regions by the Earth’s magnetic field. This is essentially our current understanding of how the aurora forms.

Back in the comfort of his laboratory in Oslo, Birkeland built experiments to prove his theory. He placed a magnetized metal sphere, which he called a planeterrella, inside a vacuum chamber. The sphere was coated in a substance that would glow when hit by electrons, simulating the Earth’s aurora.

See a planeterrella in action at Space Lates – The Next Frontiers in Astronomy 18 January 2020

Skylark - On loan from the Science Museum Group

Yet despite his observations and experiments, he was limited by the technology of the day and he could not definitively prove his theory from the ground. He was ridiculed by mainstream scientists and died under mysterious circumstances after taking 20 times the recommended dose of a sleeping aid. It was another sixty years before satellites confirmed he was right all along

Scientists still brave the far north to conduct experiments, but they now have the ability to fly rockets directly into the aurora.

Sounding rockets, like the National Space Centre’s Skylark, shoot up to altitudes of between 30 and 150 kilometres and fall back to Earth. Their short flights provide a five to ten-minute window to collect data from a region which is too high for balloons but too low for satellites.

On 5 April 2019, strange lights appeared over the far north of Norway. In contrast to the usual greens and pinks of the aurora, bright blue and turquoise patterns lingered in the sky, gradually dispersing into the aurora. These ethereal clouds were the result of tracers released into the upper atmosphere by two sounding rockets of NASA’s Auroral Zone Upwelling Rocket Experiment (AZURE). The colours helped to track the flow of particles in the upper atmosphere to improve our understanding of how the solar wind powers the aurora.

Sounding rocket firing into the aurora - Credit: NASA/Christopher Perry

AZURE is part of a larger international programme called The Grand Challenge Initiative – CUSP. From launch sites at Andøya Space Center and Svalbard Rocket Range scientists can fire rockets to directly measure the solar wind. This is because the magnetic bubble surrounding the Earth dips inward above the Norwegian and Greenland Seas, allowing particles from the Sun to funnel in toward the planet. This region, known as the polar cusp, is one of the few places on Earth where particles from space can enter Earth’s atmosphere. CUSP is a series of missions designed to study this area where Earth and space interact.

Over a century after Birkeland’s death, there is still more to discover about the aurora.

Find out more about the aurora here.

About the Author: Hannah Baker is the Assistant Curator at the National Space Centre