A new form of aurora from Jupiter

Aurora is a phenomenon in which particles carried by the solar wind collide with the planet’s atmosphere and emit light. It is already known that such a light spectacle can also be seen on Jupiter, but this time a completely new type of aurora was observed.

Data observed by NASA’s Jupiter spacecraft, Juno, using ultraviolet spectroscopy, confirms that the aurora rings are spreading at a tremendous rate in the North Pole. According to a paper published in the Journal of Geophysical Research: Space Physics, the annular aurora appearing at Jupiter’s North Pole spreads like a smoke ring at a speed of 3.3 to 7.7 km/sec, reaching a diameter of up to 2,000 km. I did it. The research team calls this ultraviolet light emission in a ring shape.

The position of ultraviolet light that is unfolded in the shape of a ring is slightly shifted from the North Pole because the axis of Jupiter’s rotation and magnetic field are inclined by 10 degrees. The newly discovered faint ultraviolet light appears to occur tens of thousands of kilometers from Jupiter’s surface, possibly where the Jupiter’s magnetosphere collides with the solar wind. The solar wind is a supersonic flow of particles from the sun. It is known that the solar wind reaching Jupiter causes some interaction with the magnetic field of Jupiter, but it has not been elucidated in detail yet.

Earth’s aurora also occurs where the magnetosphere and solar wind collide. In the case of the earth, the solar wind that hits the geomagnetic first flows toward the earth along the magnetic field line. There is a weak magnetic field on the Earth’s side, and because the solar wind flows here, particles accumulate more and more, and this area is called a plasma sheet.

The particles accumulated on the plasma sheet flow along the magnetic field to the Earth’s poles. Therefore, when it collides with the atmosphere, the particles emit light and the aurora shines.

A similar thing to Earth is happening on Jupiter, but the difference is the number of orders of magnitude in the magnetic field. Jupiter has the strongest magnetic field among the planets in the solar system, and the surface force is known to be ten times Earth. Also, Jupiter’s rotation cycle is 10 hours. It is believed to affect the movement of magnetosphere particles because it orbits the fastest among the planets in the solar system.

As confirmed this time, the ring-shaped aurora is officially a phenomenon called Kelvin-Helmholtz instability. Significant speed is essential for this to form, and this special aurora formation is believed to be due to the effect of Jupiter’s enormous magnetic field and rotational speed on the particles in the plasma sheet. However, detailed analysis has not been made yet.

The Jupiter probe Juno has been orbiting Jupiter since 2016 and has been observing Jupiter’s magnetic field and aurora, and has been sending more detailed data to Earth than the Hubble Space Telescope. This time, thanks to the UV spectrometer mounted on Juno, it has led to the discovery of a new aurora that has not yet been observed. Probably, the appearance of a rare aurora that can never be seen on Earth is quite interesting in that the way similar phenomena appear depending on the planetary environment. Related information can be found here.