A ground-based observing facility tasked with recording the flare of the northern lights has captured images of an inexplicable pale grey glow amid the streaks of green and red, providing researchers with new details into the mystery. While the bright intrusion itself has been seen before by sky watchers in the far north, nobody has had a good explanation for its appearance.
Making use of the new spectral data, a team of researchers led by scientists at the University of Calgary in Canada might at last have a solution in sky chemistry, likening the bleached islands of white and grey to the recently described meteorological oddity with the relatively whimsical name 'STEVE'.
For the most part, the Sun keeps its swirling soup of charged particles contained by gravity and a tangled net of magnetic fields. Every now and then forces align that see tiny amounts of plasma squirt free in our direction. Earth's magnetic cage steers most of this energetic shower into space, but in extreme cases a fraction of the solar particles collide with the atmosphere , causing its molecules to glow in a rich palette of color defined by their elemental make-up and concentration.
While green and pink hues are expected in these luminescent displays as the glow produced by oxygen and nitrogen at different altitudes, occasional splashes of white and grey have had no simple explanation. Auroras aren't the only show in town, however. Our planet's atmosphere can shed light through other energetic processes, some a little more complex than others.
Plain old sunlight can cause molecules to fall apart and recombine, for example, spilling a faint light that can be seen in Earth's shadow known as nightglow. Several years ago, a greyish-mauve sweep of light, affectionately named Steve by aurora enthusiasts retrospectively transformed into an acronym for Strong Thermal Emission Velocity Enhancement , presented physicists with a mystery to solve.
