The enchanting auroras, with their vibrant displays of green, red, and purple curtains, have long captivated observers of the night sky. However, the recent emergence of peculiar aurora-like phenomena — the mauve and white streaks known as “Steve” and their often accompanying glowing green “picket fence” — has intrigued scientists and sky-watchers alike.
First identified in 2018 as distinct from the more familiar auroras, Steve, named after a character in a 2006 children’s movie, and the picket fence phenomenon were initially believed to be products of the same physical processes as the auroras. However, this assumption left many questions unanswered about the origins of their unique glowing emissions.
Enter Claire Gasque, a promising graduate student in physics at the University of California, Berkeley. Gasque has proposed an intriguing explanation for these phenomena, suggesting a physical mechanism vastly different from those responsible for the traditional auroras.
“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.”
Collaborating with the Space Sciences Laboratory (SSL) at Berkeley, Gasque advocates for a NASA mission to launch a rocket into an aurora to validate her hypothesis. This research coincides with the sun entering a more active phase of its 11-year cycle, making this an opportune moment for studying rare events like Steve and the picket fence.
Gasque’s research focuses on the peculiar behavior of electric fields in the upper atmosphere. She suggests that these fields, parallel to Earth’s magnetic field, might produce the color spectrum observed in the picket fence phenomenon.
This hypothesis challenges existing models of auroral light and energy generation and has significant implications for our understanding of the interaction between Earth’s magnetosphere and the ionosphere.
Common auroras result from solar wind energizing particles in Earth’s magnetosphere, causing oxygen and nitrogen molecules in the upper atmosphere to emit specific frequencies of light.
Steve, however, exhibits a broad range of frequencies centered around purple or mauve, without the blue light typical of the most energetic particle interactions in auroras. Interestingly, Steve and the picket fence occur at lower latitudes than typical auroras, potentially even near the equator.
Gasque’s research posits that the emissions from the “picket fence” are generated by low-altitude electric fields parallel to Earth’s magnetic field. Employing a widely accepted physical model of the ionosphere, she demonstrated that a parallel electric field of approximately 100 millivolts per meter at an altitude of about 110 km could accelerate electrons.
This acceleration is sufficient to energize oxygen and nitrogen atoms, resulting in the emission of the spectrum of light observed in the “picket fence” and “Steve” aurora. She also identified unique conditions in this region, such as a reduced plasma density and an increased presence of neutral oxygen and nitrogen atoms. These could serve as an insulator, preventing the electric field from short-circuiting.
“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.”
Brian Harding, an assistant research physicist at SSL and co-author of Gasque’s paper, highlights the significance of this discovery.
“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. We just didn’t know what it was,” said Brian. “Claire’s paper showed that parallel electric fields are capable of explaining this strange spectrum.”
The team proposes launching rockets from Alaska to measure electric and magnetic fields within these phenomena, aiming to validate their hypotheses. This endeavor aligns with NASA’s Low Cost Access to Space (LCAS) program and is expected to deepen our comprehension of the upper atmosphere’s chemistry and physics. Initially, the target would be what’s known as an enhanced aurora, which is a normal aurora with “Steve” and “picket fence”-like emissions embedded in it.
“The enhanced aurora 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. The hypothesis is that these are also created by parallel electric fields, but they are a lot more common than the picket fence,” Gasque said.
The plan is not only “to fly a rocket through that enhanced layer to actually measure those parallel electric fields for the first time,” she said, but also send a second rocket up to measure the particles at higher altitudes, “to distinguish the conditions from those that cause the auroras.” Eventually, she hopes for a rocket that will fly directly through “Steve and the “picket fence.”
Gasque credits her success to collaborations with experts studying various atmospheric layers, including the mesosphere and stratosphere. This interdisciplinary approach enabled significant progress in understanding the difference between an aurora and Steve.
Harding, Gasque, and their colleagues submitted a proposal to NASA for a sounding rocket campaign this fall, anticipating a response about its selection in the first half of 2024. Gasque and Harding view the experiment as a crucial step towards comprehending the chemistry and physics of the upper atmosphere, ionosphere, and Earth’s magnetosphere.
“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 said. “We really don’t know. Claire’s paper is the first step in the chain of that understanding.”
The team eagerly awaits NASA’s decision on their proposed rocket campaign, anticipated in the first half of 2024.
In summary, the research led by Claire Gasque marks a pivotal advancement in space physics. Gasque has shed light on the elusive nature of “Steve” and the “picket fence” as being something other than an aurora. As the solar cycle progresses, these findings promise not only to unravel the mysteries of these phenomena but also to enhance our broader understanding of the dynamic interplay between Earth and space.
Auroras, commonly known as the Northern and Southern Lights, stand as a mesmerizing natural light show in the Earth’s polar skies. They occur due to the fascinating interplay between the Earth’s atmosphere and solar winds.
As discussed in detail above, scientists believed that the “Steve” and the “picket fence” phenomenon resulted from the same physical processes as an aurora. However, this belief left many questions unanswered about the origins of their unique glowing emissions.
The Sun, a powerhouse of energy and particles, constantly emits solar winds, streams of charged particles. These particles, on their journey towards Earth, encounter the Earth’s magnetic field, which plays a crucial role in the formation of auroras.
Upon reaching Earth, the solar winds get influenced by its magnetic field. The Earth’s magnetic field, extending into space, acts as a shield and directs these particles towards the poles. Here, the magnetic field lines funnel these charged particles into the Earth’s upper atmosphere.
The core phenomenon of auroras occurs when these charged particles, primarily electrons, collide with gases like oxygen and nitrogen in the Earth’s atmosphere. This collision transfers energy to the gas molecules, exciting them and causing them to emit light – the essence of auroral displays.
The specific colors of the aurora and of Steve, ranging from greens and reds to blues and purples, depend on the type of gas involved and the altitude of these interactions.
Solar activity significantly impacts the intensity and frequency of auroras. During the solar maximum, increased solar flares and coronal mass ejections result in more intense and frequent auroras. Conversely, the solar minimum leads to reduced auroral activity.
Beyond their visual splendor, auroras offer valuable insights into the Earth’s magnetosphere dynamics and its interaction with solar radiation. The study of auroras contributes to our understanding of how the Earth’s magnetic field protects us from harmful solar emissions.
Auroras have held a special place in various cultures, inspiring myths and folklore. From being seen as the Valkyries’ shields in Norse mythology to representing ancestral spirits in indigenous beliefs, auroras have been a source of wonder and inspiration throughout history.
In summary, auroras, with their breathtaking beauty, are more than just a visual spectacle. They are a dynamic interaction between solar winds and our planet’s magnetic field, offering insights into Earth’s protective shield and continuing to captivate people across cultures and generations.
The full study is published in the journal Geophysical Research Letters.
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