Aurorae discovered on all four major moons of Jupiter

jupiter aurora art

A team of astronomers using the W. M. Keck Observatory in Hawaii has discovered that aurorae at visible lengths appear on all four of Jupiter’s major moons, namely Io, Europa, Ganymede, and Callisto. The discovery was made using the High-Resolution Echelle Spectrometer (HIRES) at the Keck Observatory, as well as other high-resolution spectrographs at the Large Binocular Telescope and Apache Point Observatory.

The observations were made in Jupiter’s shadow, where the moons were nearly invisible, making the aurorae the only indication that the team had pointed the telescopes in the right direction. The aurorae were caused by Jupiter’s strong magnetic field, which causes the gas giant to act like a giant dynamo.

The findings were published in two research papers, one titled “The Optical Aurorae of Europa, Ganymede, and Callisto” and the other titled “Io’s Optical Aurorae in Jupiter’s Shadow.” The lead authors of the papers are Katherine de Kleer, a professor at Caltech, and Carl Schmidt, an astronomy professor at Boston University.

The Galilean moons all show the same oxygen aurora visible in Earth’s polar skies. However, gases on Jupiter’s moons are much thinner, causing a deep red color to glow nearly 15 times brighter than the familiar green light. At Europa and Ganymede, oxygen also lights up in infrared wavelengths, just a little redder than the human eye can see, which is the first occurrence of this phenomenon seen in the atmosphere of a body other than Earth.

Io, the innermost of Jupiter’s major moons, is the most fascinating of the four moons in terms of aurorae. It has volcanic plumes of gas and dust that can reach hundreds of kilometers in height. These plumes contain salts like sodium chloride and potassium chloride, which break down to produce additional colors. Sodium gives Io’s aurora the same yellowy-orange glow that we see in urban streetlamps. The new measurements also show potassium aurora at Io in infrared light, which has not been detected anywhere else previously.

The different colors of aurorae indicate what these moons’ atmospheres are likely made up of. According to de Kleer, “we find that molecular oxygen, just like what we breathe here on Earth, is likely the main constituent of the icy moon atmospheres.” The new measurements show minimal evidence for water, fueling an active scientific debate over whether the atmospheres of Jupiter’s moons feature significant water vapor.

The discovery of aurorae on all four major moons of Jupiter is a significant contribution to our understanding of the Galilean moons and adds a new dimension to what is already a golden age for Jupiter fans, thanks to NASA’s Juno mission and the upcoming James Webb Space Telescope.

The scientists hope that their findings will provide insight into the atmospheric chemistry and magnetic fields of the moons, as well as potentially revealing new information about the possibility of water and the conditions necessary for life.

Aurorae on Jupiter were first discovered by the Voyager 1 spacecraft in 1979. The Pioneer 10 and 11 spacecraft also provided important data on Jupiter’s aurorae in the 1970s. Since then, many missions have studied Jupiter’s aurorae, including the Galileo spacecraft, which orbited Jupiter from 1995 to 2003, and the Juno spacecraft, which has been orbiting Jupiter since 2016.


1 Io’s Optical Aurorae in Jupiter’s Shadow – Schmidt et al. – The Planetary Science Journal – February 16, 2023 – DOI 10.3847/PSJ/ac85b0 – OPEN ACCESS

2 The Optical Aurorae of Europa, Ganymede, and Callisto – de Kleer et al. – The Planetary Science Journal – February 16, 2023 – DOI 10.3847/PSJ/acb53c – OPEN ACCESS

3 New Aurorae Detected On Jupiter’s Four Largest Moons – W.M. Keck Observatory – February 16, 2023

Featured image: Aurora on Jupiter (artist’s representation). Credit: The Watchers

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One Comment

  1. Auroras are still complete mystery under current physics. In fact, even NASA is acknowledging that Jupiter’s Auroras Present a Powerful Mystery https://www.nasa.gov/feature/jpl/jupiter-s-aurora-presents-a-powerful-mystery However, I am not surprised that auroras are mysteries under current physics. But, the phenomenon of aurora is not the only mystery. The most important physics facts about our own solar system are still mysteries and will remain mysteries for ever as long as gravity is still considered as the dominant force. Because in reality, gravity is the weakest force among all the manifestations of the supreme force that rules the cosmos. In other words, without understanding this supreme force and its manifestations, all physical phenomena will be explained relying on the force of gravity. And, since gravity has only a very limited role in the dynamic processes and almost no role in the energy processes, the most important scientific facts will remain mysteries. Finally, I would like to bring to your attention that Earth’s aurora shows infinitely important fact, but surely the gravity dominated physics cannot explain it or rather know it.

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