#space physics

He didn’t even use a rocket or anything, just a fancy jet-pack

We’re one step closer to explaining STEVE. This is an odd glow that can light up the night sky. Unlike the shimmery green ribbons that make up the northern lights, STEVE consists of a reddish-purple band of light. Stretching from east to west, it sometimes has a companion row of vertical green stripes. They’re commonly called a “picket fence.”

STEVE is short for Strong Thermal Emission Velocity Enhancement. Citizen scientists have been snapping pictures of STEVE for years, notes Don Hampton. He’s a space physicist at the University of Alaska Fairbanks. But only now, he says, are scientists starting to figure out how STEVE forms. This knowledge may help researchers predict the effects of space weather on satellite signals, he says. Heated particles in the air produce STEVE’s purple ribbon, new satellite data reveal. And electron showers from space create the green picket fence.

Researchers reported the new findings online April 16, 2019 in Geophysical Research Letters.

Yukitoshi Nishimura is a space physicist at Boston University in Massachusetts. He was part of a team that analyzed data collected by satellites that had passed by STEVE events in 2008 and 2016. Those satellites observed particles and waves of energy around the light shows.

Nishimura’s team confirmed that a stream of plasma — electrically charged gas — gives rise to STEVE’s purple smear. That plasma flows west at about 5 kilometers (3 miles) per second. Its flow creates friction. And that heats particles in the air, which causes some to emit a purple light. Different chemicals in the air create different glowing colors, Nishimura notes. His team is not yet sure which cause the purple glow.

“With the picket fence, the story is a little bit different,” says Bea Gallardo-Lacourt. She is a space physicist at the University of Calgary in Canada. When energetic electrons rain down from space, they transfer some of their energy to oxygen molecules in the sky. The excited oxygen glows green.

We are now taking a trip to lovely Saturn! Enceladus is one of her more interesting moons. Unfortunately, it is nowhere near Europa levels of interesting, but it does have a very active interior for being a tiny icy rock. Turns out, the interior is so active that it has a constantly erupting volcano! Now, like Pluto, this volcano is not made of molten rock - it’s far too cold in the outer solar system for that. This one is made of water, originating from the liquid ocean that lies under its icy crust (much like Europa).

This plume of water is actually strong enough that it leaves Enceladus and goes out into space to begin circling Saturn by itself as small icy particles. These particles gradually accumulate over time to create one of Saturn’s famed rings! That’s right; this moon is giving itself up so Saturn can continue to mystify us with her beauty.

Rings actually aren’t that uncommon; Jupiter, Uranus, and Neptune all have them (with Uranus’s being the next largest). However, Saturn’s rings are massive, and probably were formed from one of its moons getting a bit too close and then being sucked in and ripped apart. The rocky part of the moon then went into Saturn while the icy parts flew out to circle Saturn independently. 

These rings are slowly disappearing, though; ice particles run into each other and accumulate over time to create little mini-moons. Other particles are being lost to space, larger moons, and Saturn itself. Therefore, we should thank Enceladus for doing the opposite and giving itself up so Saturn may remain beautiful for a while longer.

If you want to learn more about how they discovered Enceladus’s plume, check out this article: https://science.sciencemag.org/content/311/5766/1422