That's Not the Aurora Borealis, That's Just STEVE

By: Jesslyn Shields  | 
STEVE (Strong Thermal Emission Velocity Enhancement) shines across the Milky Way at Childs Lake in Manitoba, Canada.  NASA Goddard Spce Flight Center/Flickr

The naming conventions of celestial stuff generally bends toward the whimsically futuristic: magnetar, Thorne-Zytkow object, black dwarf, hypernova. But sometimes astronomers surprise us and christen a space phenomenon with a name like STEVE.

Don't let its prosaic moniker fool you, however: STEVE is a real sight to behold.


STEVE's full name is Strong Thermal Emission Velocity Enhancement, and we can observe it here on Earth with the naked eye. STEVE is an optical phenomenon like the aurora, but this thin, arching smear of lavender light always orients itself on an east-west axis and shows up at latitudes much closer to the equator than the usual northern or southern lights.

This purple braid of light has long been observed and recorded by aurora enthusiasts — possibly for centuries. In fact, it was dubbed "Steve" by a Facebook group of Canadian aurora photographers who kept noticing the phenomenon in southern Canada before it was verified to be something separate from the aurora by the European Space Agency in 2016. "Steve" is the name given to a newly discovered and intriguing hedge by a group of forest animals in the movie "Over the Hedge."


How Is STEVE Different From an Aurora?

STEVE differs from the aurora in ways that are observable from Earth, and also in ways that take specialized equipment to measure. Apart from showing up in a different part of the sky than the aurora, STEVE is unlike the shimmering, slithering green, white and red curtains of the aurora in that it generally appears overhead as a purple band, sometimes barred like a picket fence.

But the science of STEVE sets it even farther apart from the aurora. The aurora has long been understood to be a product of particles of solar radiation co-mingling with the nitrogen and oxygen in Earth's atmosphere at the poles, where the magnetic field of our planet is the thinnest.


The aurora is beautiful, but it's just a visible reminder that without our planet's magnetic field, our atmosphere would be quickly scoured off by fast-moving, unimaginably hot solar plasma. In fact, the color of the lights cast at the poles can tell scientists a lot about the chemistry and location of what's happening in the atmosphere.

What Causes STEVE?

STEVE is a visible reminder of this as well, but its color and location tell us its glow is not cast by electrons and protons of solar radiation interacting with our atmosphere. Instead, STEVE is caused by hot ionized gas, usually put off by particularly volatile solar storms.

Although scientists can't explain why STEVE is able to travel through lower latitudes than the aurora, they have discovered that this gas breaks through our atmosphere and travels in a continuous stream at about 13,300 miles per hour (21,400 kilometers per hour), generating heat with all that speed and friction, lighting up the surrounding gasses until the stream of solar gas putters out.


So, thanks to social media, excellent camera technology and dedicated citizen scientists, now we know about STEVE. What we find about it next is up to the scientists.