By Meghna Murali
Polar lights or ‘auroras’, as they are commonly known, have mesmerized us for many years now. Many consider the auroras to be the souls of their loved ones moving towards an afterlife. This article looks beyond the rhetoric and analyses what actually causes the formation of an aurora. What is it and where does it come from? The popular belief is that chemical reactions in the galaxy are the cause of auroras, but even scientists are not absolutely certain of this conclusion.
Auroras start from the sun
The sun is one of the biggest stars in our milky way. Every second, one million tons of solar matter is blasted by the sun at a very high velocity. This matter is on a collision course with the planets in our solar system. The sun acts as a power source. With the energy building up in the core of the sun, the temperatures soar as high as 14 million degrees. Consequently, the hydrogen atoms in the sun undergo a metamorphosis reaction. They are squeezed together to form another element, which we call Helium. This entire process is commonly known as a nuclear reaction. This reaction releases energy in the form of light, which radiates outwards from the core of the sun.
In the outer layers of the sun, the heat moves in the form of huge eddies called convection cells. As the name suggests, the function of these cells is to transfer heat to the outside of the sun. A plethora of charged gas particles, commonly known as plasma, fight their way up to the surface of the sun to pull the heat in the form of magnetic field lines.
How auroras reach earth
Magnetic fields behave a lot like rubber bands, in so far as that they possess a certain threshold limit and tend to lose electricity and break away if they are stretched beyond a point. These released magnetic fields emit several billion tons of plasma into space. It gives rise to a phenomenon known as a solar storm. The solar storm passes along all the planets in our solar system. After a span of about eighteen hours, the solar storm finally reaches planet Earth.
Scientists have noticed a rather peculiar occurrence when the solar storm reaches earth. The course and nature of the solar storm undergo a complete change upon reaching earth, due to an invisible protective shield around our planet. This shield is known as the magnetosphere and it deflects the storm, causing the surreal experience of an aurora. Daytime auroras occur when magnetic fields couple together and pass on the daylight side of the Arctic Pole. Night-time auroras occur when the rubber-band effect causes the magnetic field to stretch to the South Pole.
The photon-creation process
After travelling 93 million miles across the galaxy, the particles of the sun produce their spectacular light show with the help of some oxygen and nitrogen atoms on earth. The combination reaction between the particles of the sun and oxygen and nitrogen give rise to photons. The oxygen atoms are responsible for the green and red colours. On the other hand, the nitrogen atoms emit blue and deep red hues. The mesmerizing light show that we witness is a combination of the above two reactions.
Auroras are not only limited to earth
The National Aeronautics and Space Administration (NASA) introduced ‘Juno’, a probe spacecraft, in 2016, which was meant to orbit the planet of Jupiter. Jupiter has a very strong magnetic field and dense atmosphere. Unlike earthly auroras, sun-driven auroras are not Jupiter’s brightest auroras. When Juno began orbiting Jupiter, it captured particle data using an instrument, which is known as the Jupiter Energetic Particle Detector Instrument (JEDI). According to Juno’s findings, the electrons are driven by turbulent waves in Jupiter’s magnetic field. This process is comparable to a surfer being propelled ahead of breaking shore waves in the sea.
Creation of auroras on Jupiter
Jupiter has its own source for production of plasma cells. The volcanic ‘Io’ moon expels sulphur dioxide gas particles into space. As ‘Io’ rotates around Jupiter, it acts as an impediment to the plasma and the magnetic field, thus causing a disturbance. This disturbance travels back to Jupiter creating a glowing footprint, giving rise to auroras. A similar activity can be observed on Jupiter’s other moons- Ganymede and Europa.
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