Steve’ Lights Up Night Sky and Puzzles Astronomers

When you look into the night’s sky, you’d expect to see stars, the moon, an occasional meteor and, if you’re lucky, rippling curtains of light created by the impact of the sun’s energetic particles raining through our atmosphere. If you’re really lucky, you also might see Steve.

Steve is a newly identified and mysterious space weather phenomenon that — with the help of social media, a dedicated team of citizen scientists and a European fleet of satellites — may finally get the recognition it deserves.

The streak in the sky came to the attention of researcher Eric Donovan, who works at the University of Calgary, Canada, after chatting with members of the Alberta Aurora Chasers, a group of enthusiasts who observe and photograph the aurora borealis (also known as the northern lights). By turning to social media, dozens of other observer reports were collected, meaning that Steve actually was well-known.

The phenomenon got its name from the 2006 animated movie «Over the Hedge» in which the characters name a talking hedge «Steve» to make it less scary.

But what’s so peculiar is that there’s no clear explanation as to what Steve really is. Yet.

Appearing as a long and beautiful purple ribbon of light in the sky during periods of auroral activity, it was originally thought to be an aurora itself. Auroras are generated when particles from the sun, mainly electrons, interact with the gases in our atmosphere.
To the naked eye, most auroras will appear green — that’s the color oxygen glows when hit by these particles. But Steve looks and behaves very differently.

In the past, sightings of «Steve» have been attributed to «proton arcs.» These auroras occur when solar wind protons (not electrons) precipitate through the atmosphere. But there’s a problem with this explanation: Proton auroras generate mainly UV light, radiation that isn’t visible to the naked eye. Also, if they were to generate any visible light, the light would be very diffuse. Steve is obviously a very different beast as it generates a very visible purplish hue.

To research this mystery further, Donovan turned to space for help.

The European Space Agency currently has a trio of satellites called Swarm flying in formation over Earth’s poles. They’re charged with monitoring Earth’s magnetic field. A bit like a Fitbit can monitor your physical activity levels, Swarm can precisely monitor fluctuations in the magnetism surrounding our planet.

In this age of ultra-responsive social media, Donovan used the Aurorasaurus website to track eyewitness accounts of auroras around the globe and collate these accounts with all-sky cameras in the Northern Hemisphere. All-sky cameras are excellent tools to monitor the whole night’s sky with their 360-degree field of view.

With all this data in hand, Donovan found a sighting of Steve at just the right time — the Swarm satellites had made an orbital pass directly overhead, and they were recording the conditions of the magnetic field and atmosphere below.

«The temperature 300 kilometers above Earth’s surface jumped by 3000-degrees Celsius and the data revealed a 25-kilometer-wide ribbon of gas flowing westwards at about 6 kilometers per second (over 13,000 miles per hour) compared to a speed of about 10 meters per second (200 miles per hour) either side of the ribbon,» said Donovan in an ESA news release.
In other words, Steve is made from very hot and speedy gas.

«It turns out that Steve is actually remarkably common, but we hadn’t noticed it before. It’s thanks to ground-based observations, satellites, today’s explosion of access to data and an army of citizen scientists joining forces to document it,» he added. «Swarm allows us to measure it and I’m sure will continue to help resolve some unanswered questions.»

That’s handy because the sun and Earth have a magnetic relationship. Eruptions in the solar atmosphere can have dramatic effects on the environment surrounding our planet, creating geomagnetic storms, triggering auroras and driving global electric currents. So far, it’s not clear how Steve fits into this relationship, but through efforts by enthusiasts, scientists and satellites, we may soon find out what triggers this mysterious yet surprisingly common sight in our atmosphere.

«It is amazing how a beautiful natural phenomenon, seen by observant citizens, can trigger scientists’ curiosity,» added ESA Swarm mission scientist Roger Haagmans.

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