Sky lights called "Steve" are challenging what we know about auroras

In the last few years, observers have noticed unusual streaks of mauve and white lights called Steve, along with a glowing green feature known as the picket fence, appearing near the usual displays of auroras.

The more familiar auroras, with their greens, reds, and purples, have long been attributed to energized particles from the solar wind interacting with Earth’s upper atmosphere. But these new features raise fresh questions.

The mystery of the beautiful lights called “Steve” and the picket fence first came to light in 2018, when scientists realized that their properties differ sharply from normal auroras.

After a time, many wondered if these lights might share the same origins as the classic auroras, or if they might arise from a different set of conditions.

Claire Gasque, a graduate student in physics at the University of California, Berkeley, has stepped up to propose a new explanation.

A closer look at the Steve lights

The night sky often offers surprises, and sometimes these surprises challenge long-standing thinking and call for detailed study.

Gasque, working at the Space Sciences Laboratory (SSL) at Berkeley, suggests that a separate physical process could be responsible for these unusual lights.

She argues that the time has come to question old assumptions and look for new answers.

“This would upend our modeling of what creates light and the energy in the aurora in some cases,” Gasque said. “It’s really cool, one of the biggest mysteries in space physics right now.”

Gasque believes that a NASA mission to send a rocket into an aurora would help confirm her ideas.

With the sun’s activity ramping up in its 11-year cycle, this might be a good moment to catch rare phenomena and learn something new in the process.

New mechanism is making the sky glow

The idea of launching rockets to measure electric and magnetic fields inside these glowing events has gained momentum.

Gasque thinks that electric fields parallel to Earth’s magnetic field might be creating the picket fence colors.

Traditional auroras come from charged particles streaming down from space and energizing oxygen and nitrogen molecules, producing familiar colors.

But Steve’s purple or mauve tones do not match the pattern, and the picket fence appears in latitudes where auroras typically do not form. Gasque sees this as a sign that something else is going on.

Electrons in the atmosphere

Gasque’s research shows that a parallel electric field of about 100 millivolts per meter at an altitude of about 110 km could energize electrons enough to produce the observed colors.

She also points out that this region has special conditions, like reduced plasma density and more neutral atoms. This environment might allow the field to do its work without shorting out.

“If you look at the spectrum of the picket fence, it’s much more green than you would expect. And there’s none of the blue that’s coming from the ionization of nitrogen,” Gasque said.

“What that’s telling us is that there’s only a specific energy range of electrons that can create those colors, and they can’t be coming from way out in space down into the atmosphere, because those particles have too much energy.”

Instead, she said, “the light from the picket fence is being created by particles that have to be energized right there in space by a parallel electric field, which is a completely different mechanism than any of the aurora that we’ve studied or known before.”

Steve lights get a new layer of complexity

Brian Harding, an assistant research physicist at SSL and a co-author on Gasque’s work, appreciates the significance of these findings.

“The really interesting thing about Claire’s paper is that we’ve known for a couple of years now that the Steve spectrum is telling us there’s some very strange physics going on,” Harding enthused.

“We just didn’t know what it was. Claire’s paper showed that parallel electric fields are capable of explaining this strange spectrum.”

The team plans to set their sights first on something called the enhanced aurora, which is basically this bright layer that’s embedded in the normal aurora.

“The colors are similar to the picket fence in that there’s not as much blue in them, and there’s more green from oxygen and red from nitrogen,” Gasque explained.

“The hypothesis is that these are also created by parallel electric fields, but they are a lot more common than the picket fence.”

NASA, we need your help

They have submitted a proposal to NASA for a sounding rocket campaign that, if selected, would launch from Alaska.

The team aims to fly a rocket through that enhanced layer to actually measure those parallel electric fields for the first time, and also send one higher to distinguish the conditions from those that cause the auroras.

What’s next for the Steve lights?

Gasque credits cooperation with experts focused on different parts of the atmosphere for making progress.

She hopes that a successful campaign will pave the way for a direct measurement of Steve and the picket fence themselves.

The plan is to learn how these electric fields form and what they mean for the transfer of energy between Earth and space. Harding expects future work to break new ground in understanding these electric fields.

“It’s fair to say that there’s going to be a lot of study in the future about how those electric fields got there, what waves they are or aren’t associated with, and what that means for the larger energy transfer between Earth’s atmosphere and space,” Harding concluded.

“We really don’t know. Claire’s paper is the first step in the chain of that understanding.”

If NASA gives the green light, the team could start making these measurements very soon. As the solar cycle moves forward, new opportunities will arise to see these phenomena again.

Gasque’s work suggests that Steve and the picket fence are something else entirely, reshaping how scientists look at lights in the night sky and the processes that power them.

The full study is published in the journal Geophysical Research Letters.

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