For many years, the auroras seen on our planet were thought to be the souls of the dead moving to the afterlife. An aurora ￼￼￼on Earth is actually caused by the Sun and can be thought of as a form of space weather. Solar winds hit Earth with highly charged particles, but our planet’s magnetic field deflects most of them before they reach the atmosphere. Every so often these winds are boosted by solar flares or coronal mass ejections, which release huge amounts of plasma. When these intense solar winds reach Earth, some of the ionised particles get trapped in the magnetic field. These particles are then accelerated along the field lines toward the poles where they can enter the upper atmosphere, colliding with gas particles that cause them to emit bright light. This process creates the mesmerising aurora borealis and aurora australis, more commonly known as the northern lights and the southern lights respectively.
On Jupiter, Saturn, Uranus and Neptune, auroras form in a similar manner to how they form on Earth. However, on Mars and Venus they form very differently, as neither of these planets possess a significant magnetic field.
On Mars, auroras appear near areas of magnetised rock within the planet’s crust rather than near the poles, when charged solar particles concentrate toward them. This is because it lacks a self-generated magnetic field, possessing only ‘crustal magnetic anomalies’. Scientists found that the location of the light emissions corresponded with the location of the strongest magnetic fields found on Mars. It is thought these anomalies are the last traces of Mars’s planetary magnetic field, which it displayed at some time in its history. This type of aurora formation is totally unique to Mars as far as scientists are aware.
Similar to Mars, Venus does not possess its own planetary magnetic field, but flashes of light from the planet have been identified as auroras. Scientists have found that the same process that causes auroras on Earth can form a gigantic magnetic bubble around Venus, allowing auroras to occur. This is possible due to Venus having a magnetotail, which was formed by ionosphere and solar wind interaction. The fact that magnetic reconnection can occur within Venus’ magnetotail suggests auroras are the cause of the light that scientists have observed emitting from this planet.
Saturn’s auroras differ from Earth’s in their size; they can stretch to amazing heights of 1,000 kilometres (621 miles) above Saturn’s cloud tops. The charged particles come from the Sun’s solar winds blasting past the planet. The particles smash into hydrogen in Saturn’s polar atmosphere, ionising the gaseous atoms, which causes photons to be released and leads to the aurora. This planet’s auroras are actually not visible to the human eye, due to the fact that the emitted light lies in an infrared and ultraviolet spectrum we can’t see. It’s thought that as on Jupiter, Saturn’s moons may also influence the auroras.
Although some of the auroras found on Jupiter form in a similar manner to those on Earth, many are formed due to the trapping of particles within its own magnetic environment. Unlike Saturn’s main aurora that changes size as the solar winds vary, Jupiter’s main auroral ring maintains a constant size. This is due to its formation through interactions within its own magnetic environment. Jupiter’s moons are also believed to be able to influence auroras. Io, Jupiter’s volcanic moon, is thought to produce gases that travel into Jupiter’s atmosphere, where they can contribute to the planet’s aurora formation.
The presence of auroras on Uranus was detected in 2011 by the Hubble Space Telescope. It is thought this was possible due to heightened solar activity during this period, which increased the amount of charged particles carried in solar winds from the Sun. The auroras formed on this giant ice planet appear far away from the north and south poles, unlike on Earth. This is because of the planet’s magnetic field, which is inclined at an angle of 59 degrees to the axis of its spin. These auroras are fainter than their Earth counterparts and last only a couple of minutes, unlike those on our planet, which may last for hours at a time.
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