Space Scientists Discover a Never-Before-Seen Mechanism Fueling Huge Planetary Aurorae on Saturn

Infrared image of Saturn showing an aurora at its southern pole, captured by the Cassini spacecraft. Credit: NASA/JPL/ASI/University of Arizona/University of Leicester

Saturn’s high-altitude winds generate an extraordinary aurorae.

Leicester space scientists have discovered a never-before-seen mechanism fuelling huge planetary aurorae at Saturn.

Saturn is unique among planets observed to date in that some of its aurorae are generated by swirling winds within its own atmosphere, and not just from the planet’s surrounding magnetosphere.

At all other observed planets, including Earth, aurorae are only formed by powerful currents that flow into the planet’s atmosphere from the surrounding magnetosphere. These are driven by either interaction with charged particles from the Sun (as at the Earth) or volcanic material erupted from a moon orbiting the planet (as at Jupiter and Saturn).

This discovery changes scientists’ understanding of planetary aurorae and answers one of the first mysteries raised by NASA’s Cassini probe, which reached Saturn in 2004: why can’t we easily measure the length of a day on the Ringed Planet?

When it first arrived at Saturn, Cassini tried to measure the bulk rotation rate of the planet, that determines the length of its day, by tracking radio emission ‘pulses’ from Saturn’s atmosphere. To the great surprise of those making the measurements, they found that the rate appeared to have changed over the two decades since the last spacecraft to have flown past the planet – Voyager 2, also operated by NASA – in 1981.

Leicester PhD researcher Nahid Chowdhury is a member of the Planetary Science Group within the School of Physics and Astronomy and corresponding author for the study, published in Geophysical Research Letters.

He said: “Saturn’s internal rotation rate has to be constant, but for decades researchers have shown that numerous periodic properties related to the planet – the very measurements we’ve used at other planets to understand the internal rotation rate, such as the radio emission – tend to change with time. What’s more, there are also independent periodic features seen in the northern and southern hemispheres which themselves vary over the course of a season on the planet.

“Our understanding of the physics of planetary interiors tells us the true rotation rate of the planet can’t change this quickly, so something unique and strange must be happening at Saturn. Several theories have been touted since the advent of the NASA Cassini mission trying to explain the mechanism/s behind these observed periodicities. This study represents the first detection of the fundamental driver, situated in the upper atmosphere of the planet, which goes on to generate both the observed planetary periodicities and aurorae.

“It’s absolutely thrilling to be able to provide an answer to one of the longest standing questions in our field. This is likely to initiate some rethinking about how local atmospheric weather effects on a planet impact the creation of aurorae, not just in our own Solar System but farther afield too.”

Astronomers and planetary scientists based at the University of Leicester led a study alongside colleagues from NASA’s Jet Propulsion Laboratory (JPL), the Japan Aerospace Exploration Agency (JAXA), and the Universities of Wisconsin-Madison, Boston, and Lancaster, plus Imperial and University Colleges, London, to resolve the decades-old question.

They measured infrared emissions from the gas giant’s upper atmosphere using the Keck Observatory in Hawai’i and mapped the varying flows of Saturn’s ionosphere, far below the magnetosphere, over the course of a month in 2017.

This map, when fixed against the known pulse of Saturn’s radio aurorae, showed that a significant proportion of the planet’s aurorae are generated by the swirling pattern of weather in its atmosphere and are responsible for the planet’s observed variable rate of rotation.

Researchers believe the system is driven by energy from Saturn’s thermosphere, with winds in the ionosphere observed between 0.3 and 3.0 kilometers per second.

Simplified figure showing the direction of winds within layers of Saturn’s atmosphere. Credit: Nahid Chowdhury/University of Leicester

Dr. Tom Stallard, Associate Professor in Planetary Astronomy at the University of Leicester, added: “The University of Leicester has long been involved in measuring the effects of this new discovery – we’ve observed how the pulsing aurorae and the wobbling magnetic field lines stretching out into space highlight an apparently changing rotation rate. For two decades our researchers, along with the wider scientific community, have speculated about what might be driving these strange periodicities.

“Over the years, scientific meetings have had late-night discussions about whether the volcanic moon Enceladus might be the cause, or interactions with the thick atmosphere of the moon Titan, or perhaps interactions with Saturn’s bright rings. But recently, many researchers have focused on the possibility that it is Saturn’s upper atmosphere that causes this variability.

“This search for a new type of aurora harks back to some of the earliest theories about Earth’s aurora. We now know that aurorae on Earth are powered by interactions with the stream of charged particles driven from the Sun. But I love that the name Aurora Borealis originates from the ‘the Dawn of the Northern Wind’. These observations have revealed that Saturn has a true Aurora Borealis – the first ever aurora driven by the winds in the atmosphere of a planet.”

Dr. Kevin Baines, a JPL-Caltech-based co-author of the study and a member of the Cassini Science Team, added: “Our study, by conclusively determining the origin of the mysterious variability in radio pulses, eliminates much of the confusion into Saturn’s bulk rotation rate and the length of the day on Saturn.”

Because of the variable rotation rates observed at Saturn, scientists have been prevented from using the regular pulse of radio emission to calculate the bulk internal rotation rate. Fortunately, a novel method was developed by Cassini scientists using gravity-induced perturbations in Saturn’s complex ring system, which now seems to be the most accurate means of measuring the planet’s bulk rotational period, which was determined in 2019 to be 10 hours, 33 minutes and 38 seconds.

Reference: “Saturn’s weather-driven aurorae modulate oscillations in the magnetic field and radio emissions” by M. N. Chowdhury, T. S. Stallard, K. H. Baines, G. Provan, H. Melin, G. J. Hunt, L. Moore, J. O’Donoghue, E. M. Thomas, R. Wang, S. Miller, S. V. Badman, 28 December 2021, Geophysical Research Letters.
DOI: 10.1029/2021GL096492

This work was supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute.

AuroraGeophysicsPlanetsPopularSaturnUniversity of Leicester
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  • Babu G. Ranganathan

    Babu G. Ranganathan*
    (B.A. Bible/Biology)

    JUST BECAUSE SCIENCE CAN EXPLAIN how an airplane works doesn’t mean that no one designed or made the airplane. And just because science can explain how life or the universe works doesn’t mean there was no Designer and Maker behind them.

    Natural laws may explain how the order in the universe works and operates, but mere undirected natural laws cannot explain the origin of that order. Once you have a complete and living cell then the genetic code and biological machinery exist to direct the formation of more cells from raw materials such as amino acids and other chemicals, but how could life or the cell have naturally originated when no directing code and mechanisms existed in nature? Read my Internet article: HOW FORENSIC SCIENCE REFUTES ATHEISM.

    WHAT IS SCIENCE? Science simply is knowledge based on observation. No human observed the universe coming by chance or by design, by creation or by evolution. These are positions of faith. The issue is which faith the scientific evidence best supports.

    SCIENCE SHOWS THAT THE UNIVERSE CANNOT BE ETERNAL because it could not have sustained itself eternally due to the law of entropy (increasing and irreversible net energy decay, even in an open system). Even a hypothetical oscillating universe could not continue to oscillate eternally! Einstein’s General Theory of Relativity shows that space, matter, and time all are physical and all had a beginning. Space even produces particles because it’s actually something, not nothing. What about the Higgs boson (the so-called “God Particle”)? The Higgs boson, even if it existed, would not have created mass from nothing, but rather it would have converted energy into mass. Einstein showed that all matter is some form of energy. Even time had a beginning! Time is not eternal.

    The law of entropy doesn’t allow the universe to be eternal. If the universe were eternal, everything, including time and space (which modern science has shown are as physical as mass or matter), would have become totally entropied by now and the entire universe would have ended in a uniform heat death a long, long time ago. The fact that this hasn’t happened already is powerful evidence for a beginning to the universe.

    Popular atheistic scientist Stephen Hawking admits that the universe had a beginning and came from nothing but he believes that nothing became something by a natural process yet to be discovered. That’s not rational thinking at all, and it also would be making the effect greater than its cause to say that nothing created something. The beginning had to be of supernatural origin because science teaches us from the First Law of Thermodynamics that natural laws and processes do not have the ability to bring something into existence from nothing.

    The supernatural origin of the universe cannot be proved by science but science points to a supernatural intelligence and power for the origin and order of the universe. Where did God come from? Obviously, unlike the universe, God’s nature doesn’t require a beginning.

    The disorder in the universe can be explained because of chance and random processes, but the order can be explained only because of intelligence and design.

    Gravity may explain how the order found in the precise and orderly courses of thousands of billions of stars is maintained, but gravity cannot explain the origin of that order.

    Some evolutionary astronomers believe that trillions of stars crashed into each other leaving surviving stars to find precise orderly orbits in space. Not only is this irrational, but if there was such a mass collision of stars then there would be a super mass residue of gas clouds in space to support this hypothesis. The present level of residue of gas clouds in space doesn’t support the magnitude of star deaths required for such a hypothesis. And, as already stated, the origin of stars cannot be explained by the Big Bang because of the reasons mentioned above. It’s one thing to say that stars may decay and die into random gas clouds, but it is totally different to say that gas clouds form into stars.

    Even the father of Chaos theory admitted that the “mechanisms” existing in the non-living world allow for only very rudimentary levels of order to arise spontaneously (by chance), but not the kind or level of order we find in the structures of DNA, RNA, and proteins. Yes, individual amino acids have been shown to come into existence by chance but not protein molecules which require that the various amino acids be in a precise sequence just like the letters found in a sentence.

    Some things don’t need experiment or scientific proof. In law there is a dictum called prima facie evidence. It means “evidence that speaks for itself.”

    An example of a true prima facie would be if you discovered an elaborate sand castle on the beach. You don’t have to experiment to know that it came by design and not by the chance forces of wind and water.

    If you discovered a romantic letter or message written in the sand, you don’t have to experiment to know that it was by design and not because a stick randomly carried by wind put it there. You naturally assume that an intelligent and rational being was responsible.

    It’s interesting that Carl Sagan would have acknowledged sequential radio signals in space as evidence of intelligent life sending them, but he wouldn’t acknowledge the sequential structure of molecules in DNA (the genetic code) as evidence of an intelligent Cause. Read my popular Internet article, HOW DID MY DNA MAKE ME.

    I encourage all to read my popular Internet articles:

    NATURAL LIMITS TO EVOLUTION
    HOW FORENSIC SCIENCE REFUTES ATHEISM

    Visit my latest Internet site: THE SCIENCE SUPPORTING CREATION (This site answers many arguments, both old and new, that have been used by evolutionists to support their theory)

    Author of popular Internet article, TRADITIONAL DOCTRINE OF HELL EVOLVED FROM GREEK ROOTS

    *I have given successful lectures (with question and answer period afterwards) defending creation before evolutionist science faculty and students at various colleges and universities. I’ve been privileged to be recognized in the 24th edition of Marquis “Who’s Who in The East” for my writings on religion and science.

  • tommy2 tone

    What ever.

  • Neil Barron

    Whoopee! You can’t even acknowledge Kristian Birkeland who’s shoulders you stand on. Without all the tools you have available
    you couldn’t put a jigsaw puzzle together.

  • Dunn

    I think someone really should look up the definition of a mechanism

  • StarGaySir

    Yo Babu,
    I you are so critically acclaimed you shouldn’t have to advertise.
    Also, nothing in your statement disproves my stoner hypothesis that the whole universe is actually just a toe nail on another giant creature so massive that we can’t begin to see it. Each galaxy a cell with it’s own mysterious nucleui and simple stars as mitochondria. All communicating information to each other that we can’t grasp. All human existence, including your rambling on this article could be as insignificant to an unseen giant being, as ants crossing the sidewalk to a tourist in a foreign city.
    By giving thought and naming “nothingness” nothing, it became something. Simple as Descartes’s, “I think therefore I am.”
    Science requires one to hypothesize, analyze, prove, and/or disprove. We clicked here to read about Saturn moving, like you should move yourself into a different field of work if you can’t grasp that home boy.