Using Remote Sensing to Understand Steve in the Sky

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In the popular animated movie Over the Hedge, the woodland creatures are confronted with something they can’t explain. Slightly frightened by this thing they do not know, they elect to name the unknown thing ‘Steve’. By naming the unknown thing, the characters find themselves speaking of Steve as if it is something they know and therefore don’t have to be scared of.

Scientists took a scene from the movie and applied it to real life. When they observed something in the sky they didn’t understand and couldn’t readily identify, they called it Steve.

The Aurora Borealis and Steve

Steve appears like an aurora borealis, but doesn’t behave like the traditional aurora that we are accustomed to seeing. These lights appeared like white or pale purple ribbons behind streaks of green light, much like the fence posts in the movie Over the Hedge.

The lights first became something to be speculated about in 2017, when multiple reports and photographic evidence became available through the Aurora Chasers Facebook group. 

STEVE (Strong Thermal Emission Velocity Enhancement) and the Milky Way at Childs Lake, Manitoba, Canada. Image: Krista Trinder/NASA, public domain.
STEVE (Strong Thermal Emission Velocity Enhancement) and the Milky Way at Childs Lake, Manitoba, Canada. Image:  Krista Trinder/NASA, public domain.

The photographs taken in 2017 and in the years since have been used to understand the position of these new lights in the sky as they relate to the aurora borealis. Once the European Space Agency confirmed the existence of Steve, they began to study this phenomena with more detailed instruments.

Using Remote Sensing To Map Steve in the Sky

The ESA used data from their Swarm mission to show that the lights known as Steve were caused by hot atomic particles moving in an incredibly fast stream. Using photos taken from different angles, researchers were able to locate where in the night sky the lights occurred using the constellations and positions of the nearby stars.

It was determined that the Steve lights occurred at a higher altitude in the sky than did the standard aurora borealis, although they were aligned on similar lines of Earth’s magnetic field. 

(a) Altitude profile retrieved for Steve and picket fence under the assumption that both phenomena extend along the Earth's magnetic field. The altitude markers are superimposed on a section of Robert Downie's (O1) photograph already shown in Figure 1. (b) Mean red, green, and blue normalized channel brightness for each row of pixels of the image shown in (a). Source: Archer et al., 2019
(a) Altitude profile retrieved for Steve and picket fence under the assumption that both phenomena extend along the Earth’s magnetic field. The altitude markers are superimposed on a section of Robert Downie’s (O1) photograph already shown in Figure 1. (b) Mean red, green, and blue normalized channel brightness for each row of pixels of the image shown in (a). Source: Archer et al., 2019

What Causes Steve?

The aurora borealis is caused by electrons raining down and striking Earth’s atmosphere. The atoms emit lights that we can see from the ground, often in striking greens, purples, and reds.

Although Steve appears like the aurora borealis, it’s light is usually a pale purple or white, which causes scientists to believe that it is caused by a different source than electrons. Hot atmospheric gasses have been pinpointed as one potential explanation for Steve. 

Steve is made up of a fast moving stream of extremely hot particles called a sub auroral ion drift, or SAID. Image: NASA, public domain.
Steve is made up of a fast moving stream of extremely hot particles called a sub auroral ion drift, or SAID. Image: NASA, public domain.

Researchers as well as citizen scientists are continuing to work towards understanding Steve as this phenomena continues to light up the dark night sky. 

Read More About Steve

European Space Agency. Steve over the picket fence. 27 November 2019. Retrieved from http://www.esa.int/Applications/Observing_the_Earth/Swarm/Steve_over_the_picket_fence

Mystery of Purple Lights in Sky Solved With Citizen Scientists’ Help. (2018, March 14). Retrieved from https://www.nasa.gov/feature/goddard/2018/mystery-of-purple-lights-in-sky-solved-with-help-from-citizen-scientists

Archer, W. E., St.‐Maurice, J. P., Gallardo‐Lacourt, B., Perry, G. W., Cully, C. M., Donovan, E., … & Eurich, D. (2019). The vertical distribution of the optical emissions of a Steve and Picket Fence event. Geophysical Research Letters, 46(19), 10719-10725. https://doi.org/10.1029/2019GL084473

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