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[EN VIDÉO] Kézako: How are the northern lights created? Auroras are caused by the interaction between particles emitted by the sun and…
In recent weeks – even a few months – observations of the northern lights have increased. Even in our latitudes. Because our sun is approaching the maximum activity of its 25th cycle. The phenomenon casts flaming curtains across our sky. But be careful, a physicist from the University of California (USA) warns us today, all of these lights are not, strictly speaking, Aurora Borealis, Aurora Borealis. Intruders can sneak in. And that is the case with the man who has been known as Steve for several years.
This strange phenomenon was again observed at low latitudes
First, let's remember that the Northern Lights arise from collisions between charged particles from our Sun and molecules located at high altitudes – more than 1,000 kilometers – in our atmosphere. They occur primarily in polar regions because our Earth's magnetic field tends to direct charged particles toward the poles. And it is the relaxation of oxygen and nitrogen molecules after the collision that emits the famous red, green or blue halos. Sometimes over thousands of kilometers.
Steve looks just like the Northern Lights
Based on the initial observations, astronomers suspected that the Steve phenomenon – the acronym for Strong Thermal Emission Velocity Enhancement – did not correspond to an aurora borealis. Mainly because in its spectrum there are no individual emission lines characteristic of auroras, but rather a broad spectrum of frequencies around purple. Steve is also observed at lower latitudes. Possibly even to the equator. It is enough to think about a theory according to which this would be due to a warming of our atmosphere, which would produce lights in the form of violet bands. Without really being able to explain it.
By analyzing the spectrum of the green, fence-shaped glow that accompanies the Steve phenomenon, researchers at the University of California came up with the idea. “Their color is extremely green. Only a certain energy range of electrons can produce these types of colors. Electrons that cannot come from space because they would then be far too energetic, explains Claire Gasque, physicist, in a press release. These palisades can only be formed by charged particles that are energized locally. »
A light phenomenon due to an electric field
How ? “Through an electric fieldelectric field parallel to the magnetic fieldmagnetic field of our Earth. » This is confirmed by a physical model. The researchers show in the journal Geophysical Research Letters that a moderate electric field – on the order of 100 millivolts per meter – and at an altitude of around 110 kilometers could accelerate electrons to an energy that would excite oxygen and nitrogen and produce the observed spectrum of lightlight. However, to avoid the risk of disappearing too quickly would require unusual conditions in the area – no doubt caused by the solar storms that trigger the Northern Lights, hence the initial confusion. A lower density of charged plasma and more neutral oxygen and nitrogen atoms, all of which could serve as an insulator that maintains the electric field. Time to make a Steve appear – through related processes – and his fence.
The researchers now want to build a machine that will make it possible to measure the intensity and direction of the electric and magnetic fields in the heart of Steve and his fences. This could happen as early as the first half of 2024. And beyond a proof of advanced theory, it could have implications for how physicists understand the flow of energy between Earth's magnetosphere, which surrounds our Earth and protects it from the solar wind. and the ionosphereIonosphere at the edge of space.
When a mysterious phenomenon was discovered in 2015, Steve reveals himself to astronomers
Article by Nathalie MayerNathalie Mayer published on November 17, 202
Steve is a luminous phenomenon that was first observed by citizen scientists in 2015. Even today, it is amateurs who have drawn the attention of astronomers to a special feature of the phenomenon. Narrow stripes that could help to finally understand its origin.
Steve. In 2017, only he was talked about on social networks. This strange celestial phenomenon resembles – at least visually – an aurora borealis and was first observed by citizen scientists in 2015. A purple band highlighted by a green structure in the shape of a picket fence.
Today, new details were observed about this green structure that could bring astronomers closer to solving the Steve mystery. Tiny little horizontal stripes they imagine could correspond to moving points of light simply stretched across the images through a motion blur effect. A hypothesis that they say is supported by the fact that the tip of a stripe in one image and its end in the next image are aligned.
Did you know ?
Steve – a name that actually corresponds to the acronym for “Strong Thermal Emission Speed Enhancement” – still doesn't seem to want to fit himself into one of the scientists-defined categories of atmospheric luminous phenomena: luminescence, which results from a recombination of atoms that Energy release form of light and can occur anywhere in the world, or the Northern Lights, which arise from electronic bombardment, just around the Earth's magnetic poles.
In principle, these stripes should not be caused by the electron showers responsible for the northern lights. “I’m not entirely sure about this phenomenon yet,” Joshua Semeter, a professor at Boston University, said in a NASA press release. “Because in other sequences there seems to be a tube-like structure that persists from one image to the next. And this does not correspond to a moving point source. »
The contribution of citizen scientists
“These emissions arise through mechanisms that we do not yet fully understand,” the researcher recognizes. But let's still clarify the evidence that scientists now believe exists. So Steve's violet emissions probably result from positive ion movements at supersonic speeds.
The electrons present in this plasma are lighter. Their trajectories appear more chaotic. They can actually form small vortices at the edges of the plasma stream beneath the purple band. Hurricanes that stimulate oxygen pockets and make them glow green. Through radar measurements, scientists know that this type of turbulence phenomenon exists. But they never observed an optical signature. However, in Steve's case, the currents could be so extreme that they become visible.
While astronomers hope that satellite observations can now shed light on the question, there is no doubt that they will not forget the contribution of citizen scientists. “You alerted us to the phenomenon. They see things differently than researchers. Suitors,” notes Elizabeth MacDonald, a researcher at NasaNasa. To capture this new movement, they typically allowed themselves shorter exposure times. “Just for the beauty of the moment,” says amateur astrophotographer Neil Zeller, promising to study his images further to advance science.
Steve: We know more about this strange celestial phenomenon
At first glance, it could be confused with an ordinary aurora borealis. But Steve turns out to be an even stranger celestial phenomenon. Thanks to photos taken by amateurs, astronomers managed to learn a little more.
Article by Nathalie Mayer published on March 12, 2019
“Show us your strange thing.” » This is what VerneVerne the turtle offers to Zamy the squirrel. The scene takes place in “Our Neighbors, Men,” an animated film from 2006. Never in their lives have these little animals that live outside our yards seen anything like this. A huge green barrier – in reality a simple hedge – stands in front of them. So they decide to call him…Steve!
Steve – also acronym for “Strong Thermal Emission Speed Enhancement” – likes this strange celestial phenomenon that caused a stir on social networks in 2017. A glowing structure made up of a purple band, similar to the classic northern lights – although the phenomenon actually occurs too far south. And accompanied by another green structure reminiscent of the shape of a fence. A lot whose origins astronomers still cannot explain.
To learn a little more, the researchers combined observations on the ground and data from the Swarm mission – a European Space Agency (ESAESA) mission designed to study the Earth's magnetic field. Steve would actually be made up of a stream of extremely hot, fast-moving atomic particles.
Steve always keeps part of the secret to himself
Recently, astronomers, particularly from the University of Saskatchewan and Calgary, Canada, turned to a group of amateur aurora hunters, the Alberta AuroraAurora Chasers, to obtain photos of Steve taken simultaneously at two locations hundreds of kilometers apart and were taken from two different angles. Thanks to the stars in the background, they could be aligned precisely.
The researchers determined the altitudes at which these phenomena occur. Between 130 and 270 kilometers for the purple part of Steve and between 95 and 150 kilometers for the green glow – with “stockade posts” at intervals of 15 to 25 kilometers. Both align themselves with similar magnetic field lines.
“A yet-to-be-determined chemiluminescence reaction?”
Values that appear to be consistent with the idea that the green structure accompanying Steve is caused by a precipitation of electrons. As for the violet part of the phenomenon, it could actually be caused by “rivers” of charged particles colliding in Earth's ionosphere. However, researchers believe that a still unknown chemiluminescence reaction may be at the origin of this phenomenon.
Steve: We know the origin of this mysterious purple beam from the auroras
A purple ribbon and at its root a green fence. This is how Steve manifests himself, a natural light phenomenon that rivals the beauty of the northern lights, but which researchers have found difficult to explain. Maybe because it is actually the result of the combination of two different phenomena.
Article by Nathalie Mayer published on April 5th, 2019
In 2017, Steve caused a stir on social media. Steve, for the large improvement in thermal velocity emission. This is what researchers have affectionately called this fascinating light phenomenon. Fascinating because it is observed in regions much further south than those where the Northern Lights traditionally form. And on the one hand it breaks down into a purple band – sometimes pink or red – and on the other hand into a glowing green structure that is reminiscent of the shape of a fence.
Last year, researchers found that the phenomenon – unlike the northern lights – was not due to an interaction between atoms in Earth's upper atmosphere and charged particles from the magnetosphere. However, Steve seems to want to appear especially during magnetic storms.
Now, a new study based on satellite data and photos of Steve shows that the tape and fence that make up Steve are actually manifestations of two different phenomena. The glowing green structure initially appears to be close to an Aurora Borealis. “Even if it occurs outside the aurora zone,” notes Bea Gallardo-Lacourt, a physicist at the University of Calgary (Canada). This is a unique situation. »
Like a light bulb
When high-frequency waves travel from the magnetosphere to the Earth's ionosphere, electrons can be excited and thereby ejected from the magnetosphere. They then create the famous picket fence pattern. And the fact that the phenomenon is observed simultaneously in both hemispheres confirms the hypothesis that its source is thousands of kilometers from Earth.
“No precipitation of particles here”
The mechanism behind the purple band that represents Steve's second trait would be completely different. “In the northern lights there is a precipitation of particles. That is not the case here,” explains Bea Gallardo-Lacourt. By measuring the electric and magnetic fields of the Earth's magnetosphere, it was possible to reveal what lies behind the phenomenon.
At the origin: a “river” of charged particles colliding in the Earth’s ionosphere. Enough to cause heating and the emission of the famous violet glow. A bit like electricity heating the filament of a light bulb until it glows. But some mysteries still remain, such as the fact that Steve never seems to appear between October and February and is always accompanied by the Northern Lights.
What is hiding Steve, the mysterious violet ray of the Northern Lights?
A few months ago, aurora hunters captured a supposedly rare phenomenon in the sky, which at the time was incorrectly called the “proton arc” and affectionately “Steve”. Today researchers offer an explanation.
Article by Nathalie Mayer published on April 24, 2017
When Eric Donovan, a researcher at the University of Calgary, Canada, browsed photos posted on Facebook by aurora hunters, he came across some surprising images: that of a purple-hued trail of light. Fans of the group nicknamed this glowing trail “Steve” and thought it was a proton arc. “Unfairly,” says Eric Donovan.
In fact, the Canadian researcher and his colleagues have since compared these photos and data from the Swarm mission (ESA) – which consists of three satellites designed to investigate the sources of the Earth's magnetic field. “The appearance of Steve coincides with very significant changes in the local electric field,” emphasizes Eric Donovan. At an altitude of about 300 kilometers, a temperature jump of no less than 3,000 °C was recorded, and a 26-kilometer-wide band of gas flowed westward at about 6 km per second, while the surrounding gases moved at about 10 km per second.
Steve, a not so rare phenomenon
The Northern Lights are a magnificent spectacle. Certainly, but why are they interesting for researchers? Now you know that studying the Northern Lights allows scientists to better understand the interactions between the Earth's magnetic field and the charged particles that reach us from the Sun, such as those that make up the solar wind.
Ultimately, the Steve phenomenon proves to be remarkable…often! It had simply never been observed or studied before. Now it's done – even if some details still need to be clarified – thanks on the one hand to an increasingly organized army of aurora hunters and, on the other hand, to increasingly extensive satellite data.