The conditions under which the aurora borealis appears on Earth and on Jupiter are very different. Sun is questionable for Earth. For Jupiter, it’s the volcanic activity of its moon Io.
On the left, we have a representation of Jupiter’s auroras, and on the right, a representation of Earth’s auroras And of course, the Earth is about 10 times bigger, otherwise it would seem very insignificant compared to its big sister.
These are 3D representations, but based on real satellite data. In addition to visible and familiar surfaces, the polar aurora has been added, represented in blue. These auroras were observed in ultraviolet wavelengths by the Juno probe for Jupiter and the IMAGE satellite for Earth.
It’s important to explain how we create our science communication images and explain that no, you wouldn’t see these stars if you could observe these stars with the naked eye to avoid misunderstandings. It is not, of course, a question of deception, as opposed to showing what is there, but which our senses hide from us.
How does the aurora appear?
Auroras result from the impact of charged particles (usually electrons) at the top of a planet’s atmosphere. Following this effect, atoms and molecules in the atmosphere emit light in a series of wavelengths (of color, if you will) that are specific to them. These auroras are called “polar” because the planet’s magnetic field directs these charged particles from the magnetosphere toward the polar regions. In the north we have the aurora borealis and in the south the aurora australis.
A planet’s magnetosphere is a “bubble” in space, where the movement of charged particles is controlled by the planet’s magnetic field rather than the Sun’s. Most of the particles in a magnetosphere simply rotate around the magnetic field lines and oscillate along them. But a whole series of events, such as excitation by different waves, the presence of electric currents or even “magnetic reconnection” can precipitate particles in the polar atmosphere and create auroras. Auroras therefore form a picture of the movement of particles in this magnetosphere.
Radically different magnetospheres between Earth and Jupiter
Earth is very sensitive to variations in the solar wind. In particular, when the magnetic field of the solar wind and the Earth’s magnetic field are aligned, but in opposite directions, in front of the magnetosphere, a phenomenon called magnetic reconnection occurs, which allows solar particles to rush into the Earth’s magnetosphere.
Jupiter’s magnetosphere is mainly populated by volcanic particles from its moon Io. These electrons and sulfur and oxygen ions are then carried by the planet’s magnetic field and start spinning at the same speed as Jupiter’s rotation, accumulating in Io’s orbit and forming what is known as “Io’s torus”. These particles will then slowly escape, causing waves, electric currents and magnetic reconnection processes.
So it is clear that the magnetospheres of Earth and Jupiter do not work in the same way. Therefore, Jupiter’s aurora is very different from Earth’s aurora.
Understanding the planets by studying their auroras
Take for example the stretch to the left of Jupiter’s aurora. This is called the auroral imprint of the IO. It is caused by the eddies that Io creates in the torus that it has created itself.
On the other hand, there is a structure that is almost identical in the two images: it is this strange shape in the shape of an eye, right below Jupiter and below for Earth. These are called “dawn storms” on Jupiter and “auroral substorms” on Earth. Both are caused by sudden reorientation of the trailing part of the magnetosphere (magnetotail). Indeed, although for completely different reasons, one due to material ejected from the IO and the other due to the solar wind, the two magnetospheres can accumulate mass and energy in this magnetotail, until it ruptures and releases large amounts of particles in the auroral as well. region
This practice is called comparative astronomy, and it makes it possible, as we have just seen, to isolate universal phenomena from the specific characteristics of each planet. By observing these distant planets, we learn almost as much about these extraterrestrial worlds as we do about our own planet.
Bertrand Bonfond, FNRS qualified researcher, University of Liège
This article is republished from The Conversation under a Creative Commons license. Read the original article.