The James Webb Telescope has finally discovered Saturn’s best kept secret

Saturn has become a headache for scientists since the Cassini probe in 2004 took action of its rotation speed that did not coincide with the figures accepted in the scientific community. Little by little, new data has been discovered that helps explain this inconsistency, but it has been necessary for the James Webb Space Telescope to come into play to find the definitive answer.

Cassini’s incoherence. In 2004, the Cassini probe took advantage of its visit to Saturn to measure some important dataas its rotation speed. Normally this is calculated by analyzing parameters that occur periodically, such as radio emission pulses. It is a very consolidated method, which has been used to calculate the rotation rate of many planets. With Cassini, it was expected to obtain a figure that would coincide with what the Voyager 2 probe had previously taken in 1981. However, to the surprise of the scientists who studied the data, the numbers didn’t add up.

A mysterious push. A planet cannot speed up or slow down without an external force driving it. There should be something driving those changes in rotation speed. Or, at the very least, some unknown factor that was falsifying the results. All this was a mystery until 2021, when a team of scientists from the University of Leicester published a study in which new clues were provided.

The auroras enter the scene. For a month, scientists at the University of Leicester measured infrared emissions in Saturn’s upper atmosphere. This allowed them to map a series of variable fluxes of activity in the ionosphere, the layer of the atmosphere in which ionized particles are abundant. That is, atoms that have gained or lost electrons and have acquired a negative or positive charge, respectively. These flows were related to the formation of auroras. However, there was something strange. Unlike on other planets, including Earth, a good part of these auroras were produced by the action of rotating winds within Saturn’s own atmosphere, not only by the influence of the magnetosphere.

A reminder about the auroras. The auroras are formed when charged particles interact with the atoms that make up a planet’s atmosphere, exciting them and causing the emission of light. Normally, these charged particles come from solar activity, as happens on Earth, or from volcanic eruptions on nearby moons, as happens on Jupiter. Be that as it may, they are concentrated in a region external to the planets, known as the magnetosphere. In the case of Saturn, the 2021 study showed that auroras were also forming within the planet’s own atmosphere.

On Earth, auroras are formed by solar activity

A puzzle still incomplete. The interaction of molecules and atoms in the atmosphere with charged particles does not only cause the emission of light. It also causes the emission of radiation in other regions of the spectrum. For example, radio pulses. Let us remember that these pulses are the ones that were used to measure the rotation of Saturn. The auroras could be falsifying them. These auroras, as we have seen so far, are produced by the action of rotating winds in Saturn’s own atmosphere. But where do those winds come from?

The rock star arrives. The James Webb Space Telescope is the rock star of space telescopes. A state-of-the-art instrument, capable of reaching where other telescopes could not. Therefore, thanks to him, the necessary measurements could be taken to find the origin of Saturn’s winds. Specifically, it has captured the glow caused in the infrared by a molecule in Saturn’s upper atmosphere, called trihydrogen cation.

This is very useful, because it acts as a kind of thermometer. It is very susceptible to environmental conditions, so its ionization state helps to know the surrounding temperature. By carefully analyzing its state in different regions of Saturn’s northern hemisphere, it has been possible to make a map of both temperatures and particle density.

The missing piece. The temperature and particle density patterns match those predicted in a series of computer models 10 years ago. In these models, these patterns originated when the auroras themselves acted as a heat source.

The endless cycle. What happens is this: the auroras, with all their display of light and radiation, heat the atmosphere at a specific point. This heating causes the movement of particles between points at different temperatures, generating a wind charged with electricity. This wind, in turn, propels electrically charged particles, which cause more auroras to form.

It’s a vicious circle or, as the authors of the study explaina planetary heat pump. A perfect system that feeds itself. And, of course, the mysterious external factor that upset scientists trying to measure Saturn’s rotation.

Image | NASA | Bruce Waters (Wikimedia Commons) | Vincent Guth (Unsplash)

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