A solution to the mystery of Jupiter’s X-ray auroras

Scheme of Jupiter's X-ray auroras
An article published in the journal “Science” reports a study on the planet Jupiter’s auroras that offers a solution to the mystery of X-ray emissions. A team of researchers obtained the crucial information thanks to data collected by ESA’s XMM-Newton space telescope and NASA’s Juno space probe. That allowed them to understand how ions are transported by the electromagnetic waves present in the Jovian magnetic field to the planet’s atmosphere, with which they collide to generate the auroras.

Jupiter’s auroras have been observed for a long time, including X-ray ones. Their examination indicates that these X-ray emissions are triggered by charged particles, ions, colliding with Jupiter’s atmosphere. However, the mechanism that carried the ions to the atmosphere remained a mystery. New clues came from observations conducted from Earth’s orbit by the XMM-Newton space telescope and from Juno’s orbit by the Juno space probe, which arrived there on July 4, 2016.

Zhonghua Yao of the Beijing Academy of the Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, lead author of this research, has been involved in studies of Jupiter’s magnetic field for quite some time. Together with other colleagues, he examined the characteristics of Jupiter’s magnetic field noting the differences compared to what happens with the Earth’s auroras.

With his team, Zhonghua Yao conducted simulations that indicated that Jupiter’s pulsating X-ray auroras could be linked to closed magnetic fields, in which magnetic field lines come out of the planet at a pole and reconnect to the planet at the other pole. Closed magnetic fields are generated inside the planet, extend for millions of kilometers into space and then come back. These conclusions were published in April 2021 in an article again in “Science”.

The researchers found that pulsating X-ray auroras are generated by fluctuations in Jupiter’s magnetic field. The planet spins and drags its magnetic field, which is directly hit by the solar wind particles and compressed. These compressions heat the particles trapped in the magnetic field and this triggers a phenomenon called electromagnetic ion cyclotron (EMIC) waves in which the particles are directed along the field lines.

Crucial data came from observations conducted in 2017. The Juno space probe detected magnetic field compression with the generation of electromagnetic ion cyclotron waves and subsequently an ion pulse traveling along the field line. A few minutes later, the XMM-Newton space telescope observed an X-ray explosion.

The image (Yao/Dunn/ESA/NASA) shows a scheme of Jupiter’s pulsating X-ray auroras. Magnetic field lines carry ionized atoms into the planet’s atmosphere generating auroras. On the top left, the XMM-Newton space telescope near the Earth. On the right side the Juno space probe.

This process of generating Jupiter’s X-ray auroras can be extended to other places, starting with the other gas planets in the solar system. The identified process is similar to the one that generates ion auroras on Earth, where the ion is hydrogen and therefore a single proton, and the energies are much lower than those of the Jovian auroras.

It will now be possible to conduct targeted analyzes of the data collected to conduct other studies of Jupiter’s auroras, to look for them on other planets and also in other places in the cosmos where there may be electromagnetic ion cyclotron waves.

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