Image credit: NASA/ESA

Astronomers have watched Jupiter produce X-ray auroras for forty years, but they did not know how they were produced, only that they occurred when ions collided with the atmosphere.

Now a team led by University College London (UCL) and the Chinese Academy of Sciences has discovered that X-ray flares are triggered by the periodic vibrations of Jupiter’s magnetic field lines.

These vibrations create waves of plasma (ionized gas) that send heavy ion particles “surfing” along magnetic field lines until they crash into the planet’s atmosphere, releasing energy in the form of X-rays.

Ions are transported by waves of plasma
The discovery was published this Friday by Science Advances and accounts for the observations of an international group of astronomers who combined data from NASA’s Juno satellite, which orbits the planet, with simultaneous X-ray measurements from the XMM-Newton observatory of the European Space Agency, in the orbit of the Earth.

One of the study’s co-authors, William Dunn of the UCL has pointed out that they now know that these ions are transported by waves of plasma, an explanation that had not been proposed before, although a similar process occurs in the Earth’s aurora itself.

Therefore, it could be “a universal phenomenon, present in many different environments of space,” Dunn has conjectured.

The phenomenon occurs every 27 minutes
X-ray auroras occur at Jupiter’s north and south poles, often with clockwork regularity: During the observation used to obtain data, the planet produced bursts of X-rays every twenty-seven minutes.

The charged ionic particles that hit the atmosphere originate from volcanic gas that pours into space from the giant volcanoes of Io, one of Jupiter’s moons.

This gas is ionized, that is, its atoms are stripped of electrons, due to collisions in the immediate environment of Jupiter, forming a kind of plasma donut that surrounds the planet.

The study’s lead author, Zhonghua Yao of the Chinese Academy of Sciences, stressed that now that they have identified this “fundamental process” of charged particles “surfing” plasma waves, there is a much better chance of studying it in the future.

The same situation could occur on other planets and exoplanets
Similar processes could also occur, the researcher estimated, on Saturn, Uranus, Neptune and, probably, on exoplanets.

While on Jupiter the magnetic field is filled with sulfur and oxygen ions that are expelled by the volcanoes of Io, on Saturn the moon Enceladus launches water into space, filling the planet’s magnetic field with ions from the water group.

The process observed on Jupiter bears great similarity to ionic auroras that occur on Earth, where the ion responsible is a proton, which comes from a hydrogen atom, but the process is not energetic enough to create X-rays.