Thin ribbons of purple and white light, called STEVE, but I’m not sure why, that sometimes appear in the night sky were dubbed a new type of aurora when brought to scientists’ attention in 2016. But new research suggests these mysterious streams of light are not an aurora at all but an entirely new celestial phenomenon.
The atmospheric phenomenon ‘STEVE’ appears as a
purple and green light ribbon in the sky. Credit: © Ryan / Fotolia
Amateur photographers had captured the new phenomenon, called STEVE, on film for decades. But the scientific community only acknowledged STEVE in 2016. When scientists first looked at images.
STEVE, they realized the lights were slightly different than light from typical auroras but were not sure what underlying mechanism was causing them.
In a new study, researchers analyzed a STEVE event in March 2008 to see whether it was produced in a similar manner as the aurora, which happens when showers of charged rain down into Earth’s upper atmosphere. The study’s results suggest STEVE is produced by a different atmospheric process than the aurora, making it an entirely new type of optical phenomenon.
“Our main conclusion is that STEVE is not an aurora,” said Bea Gallardo-Lacourt, a space physicist at the University of Calgary in Canada and lead author of the new study in Geophysical Research Letters, a journal of the American Geophysical Union. “So right now, we know very little about it. And that’s the cool thing, because this has been known by photographers for decades. But for the scientists, it’s completely unknown.”
Auroras are produced when electrons and protons from Earth’s magnetosphere, the region around Earth dominated by its magnetic field, rain down into the ionosphere, a region of charged particles in the upper atmosphere. When these electrons and protons become excited, they emit light of varying colors, most often green, red and blue.
STEVE is an entirely new phenomenon distinct from typical auroras. The POES-17 satellite detected no charged particles raining down to the ionosphere during the STEVE event, which means it is likely produced by an entirely different mechanism.
The researchers said STEVE is a new kind of optical phenomenon they call “skyglow.” Their next step is to see whether the streams of fast ions and hot electrons in the ionosphere are creating STEVE’s light, or if the light is produced higher up in the atmosphere.
B. Gallardo-Lacourt, J. Liang, Y. Nishimura and E. Donovan. On the Origin of STEVE: Particle Precipitation or Ionospheric Skyglow? Geophysical Research Letters, 2018 DOI: 10.1029/2018GL078509