Many people on Earth know about auroras. They are considered some of the most mysterious and enchanting sights on our planet. Known as the aurora borealis and the aurora australis (or the Northern lights and Southern lights, respectively), they are typically seen at high and low latitudes, near the North and South Poles. However, it wasn’t until 2016 that we first saw the auroras of another planet in our solar system – Jupiter.
The cause of these auroras has now been discovered, but before we dig into Jupiter’s volcanic moon, and learn how that distant planet’s auroras are formed, let’s first take a peek at the auroras here on Earth.
The Auroras of Earth
As mentioned, the North and South Poles of our planet are often illuminated by colorful bands of light, commonly called the auroras. The Northern Lights, due to there being more land mass in the northern hemisphere, tend to get more of the attention, and with good reason. They are typically greenish in color, although they can also appear as red, blue, yellow or red bands in the sky. They appear in a number of different forms, but tend to stretch from east to west, across both horizons.
These stunning scenes are caused by the Sun, in basic terms. Our star gives off a solar wind, basically powerful bursts of protons and neutrons that barrel towards Earth at incredible speeds. That wind is much worse when there is a solar storm, and a billion-ton cloud of gas and charged particles is thrown directly at our planet. This fast-moving stream of highly charged particles can vary in strength and speed, but when it comes in contact with Earth’s magnetosphere, something magnificent happens.
The magnetosphere is intended to keep our planet safe from this deadly radiation, and it does a very good job, but some of the energy from the solar wind will sneak into this protective bubble around our planet. That energy can be stored as electromagnetic energy, but this can cause an imbalance in the magnetosphere, which is not good news! The excess energy is given off in the form of accelerating electrons. When these electrons strike the air molecules in our atmosphere, namely oxygen and nitrogen, they excite the particles to higher energy states. When the electrons pass by and the air molecules settle back to lower energy states, they emit colored light. Nitrogen molecules typically give off a green color, while oxygen molecules glow blue.
That’s why an aurora often looks like a wave, or a curtain being blown by the wind. That is precisely what’s happening, except the curtain is our atmosphere and the wind comes all the way from the Sun.
The real question is, how does this match up with the stunning auroras recently discovered on Jupiter?
The Auroras of Jupiter
The Voyager I mission actually saw the auroras of Jupiter for the first time back in 1979, it wasn’t until the 1990s that researchers realized that there was far more going on than first expected, and that the auroras were much bigger than first believed. The Hubble Space Telescope took images of Jupiter in the ultraviolet spectrum, and saw that the emanating light was actually thousands of times brighter than initially thought.
The Chandra X-Ray Observatory further revealed that the majority of the aurora was actually in the form of X-rays, which are invisible to the human eye. Believe it or not, those X-ray auroras were larger than our entire planet!
Unlike on Earth, where the auroras come and go based on the strength of the solar wind, the auroras on Jupiter never stop! The auroras on Jupiter are not derived purely from the solar wind, as they are on Earth, although intense solar storms can cause the Jovian auroras to be stronger than normal.
The Electrically Charged Giant
First of all, Jupiter has an incredibly powerful spin. You can fit 1,321 Earths inside of Jupiter, and yet the planet whips its entire weight around the axis every 10 hours. The planet’s powerful magnetic field is also spun wildly at that speed, which creates an incredibly large amount of electricity. In fact, the poles of Jupiter generate about 10 million volts of electricity.
Similar to the magnetosphere of Earth, this electrically charged region interacts with all the particles nearby, pulling them into the huge voltage storm. When those particles are violently dragged towards the surface of the planet, the electrons are stripped away from the particles, and then the particles take those electrons back as they slow down and approach the surface. During this extremely rapid charge exchange reaction, a huge amount of X-rays are spewed out into the space around Jupiter’s poles.
While normal particles from the atmosphere are consumed in this process, there is also a relatively constant supply of other particles that are spewed into Jupiter’s orbit. Io, one of the Galilean volcanic moons of the planet, is extremely violent, kicking out oxygen and sulfur from the hundreds of volcanoes on the surface. Those volcanic outpourings gradually make their way into the range of Jupiter’s polar regions, resulting in a near-constant X-ray glow around the poles as those particles have their electrons stripped and then returned to them.
On July 4, 2016, NASA’s Juno spacecraft arrived in Jupiter’s orbit, and some of the first high-definition in-space images of the planet were taken. This close-up view of Jupiter, and the more than 35 orbits of the planet that this spacecraft will make, should certainly give us even more insight into the mysteries of that great Jovian planet.