This discovery changes scientists understanding of planetary aurorae and responses among the first mysteries raised by NASAs Cassini probe, which reached Saturn in 2004: why cant we quickly measure the length of a day on the Ringed Planet?
When it first got to Saturn, Cassini attempted to determine the bulk rotation rate of the planet, that figures out the length of its day, by tracking radio emission pulses from Saturns environment. To the terrific surprise of those making the measurements, they found that the rate appeared to have actually changed over the two years considering that the last spacecraft to have flown past the planet– Voyager 2, likewise operated by NASA– in 1981.
Leicester PhD scientist Nahid Chowdhury is a member of the Planetary Science Group within the School of Physics and Astronomy and corresponding author for the research study, released in Geophysical Research Letters.
He said: “Saturns internal rotation rate has to be constant, however for decades scientists have actually revealed that numerous regular residential or commercial properties connected to the world– the extremely measurements weve utilized at other planets to comprehend the internal rotation rate, such as the radio emission– tend to change with time. Whats more, there are also independent regular functions seen in the northern and southern hemispheres which themselves vary throughout a season in the world.
” Our understanding of the physics of planetary interiors informs us the real rotation rate of the world cant alter this quickly, so something unusual and unique need to be taking place at Saturn. Numerous theories have actually been touted considering that the advent of the NASA Cassini mission trying to explain the mechanism/s behind these observed periodicities. This study represents the very first detection of the essential driver, located in the upper environment of the world, which goes on to produce both the observed planetary periodicities and aurorae.
” Its absolutely thrilling to be able to supply an answer to among the longest standing concerns in our field. This is likely to initiate some reassessing about how regional climatic weather effects on a world impact the development of aurorae, not just in our own Solar System however further afield too.”
Astronomers and planetary scientists based at the University of Leicester led a research study along with colleagues from NASAs 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 fix the decades-old question.
They measured infrared emissions from the gas giants upper atmosphere using the Keck Observatory in Hawaii and mapped the varying circulations of Saturns ionosphere, far below the magnetosphere, over the course of a month in 2017.
This map, when fixed versus the known pulse of Saturns radio aurorae, showed that a substantial proportion of the worlds aurorae are produced by the swirling pattern of weather condition in its atmosphere and are responsible for the worlds observed variable rate of rotation.
Scientists think the system is driven by energy from Saturns thermosphere, with winds in the ionosphere observed in between 0.3 and 3.0 kilometers per second.
Simplified figure showing the instructions of winds within layers of Saturns atmosphere. Credit: Nahid Chowdhury/University of Leicester
Dr. Tom Stallard, Associate Professor in Planetary Astronomy at the University of Leicester, included: “The University of Leicester has actually long been associated with determining the results of this new discovery– weve observed how the pulsing aurorae and the wobbling magnetic field lines stretching out into space highlight an apparently altering rotation rate. For 2 decades our researchers, together with the broader clinical community, have hypothesized about what may be driving these strange periodicities.
” Over the years, scientific conferences have had late-night conversations about whether the volcanic moon Enceladus might be the cause, or interactions with the thick atmosphere of the moon Titan, or perhaps interactions with Saturns bright rings. But just recently, numerous researchers have actually concentrated on the possibility that it is Saturns upper environment that triggers this irregularity.
” This search for a new kind of aurora returns some of the earliest theories about Earths aurora. We now understand that aurorae on Earth are powered by interactions with the stream of charged particles driven from the Sun. But I enjoy that the name Aurora Borealis originates from the the Dawn of the Northern Wind. These observations have actually revealed that Saturn has a real Aurora Borealis– the very first aurora driven by the winds in the atmosphere of a world.”
Dr. Kevin Baines, a JPL-Caltech-based co-author of the research study and a member of the Cassini Science Team, added: “Our research study, by conclusively identifying the origin of the mystical irregularity in radio pulses, removes much of the confusion into Saturns bulk rotation rate and the length of the day on Saturn.”
Because of the variable rotation rates observed at Saturn, researchers have been avoided from utilizing the regular pulse of radio emission to calculate the bulk internal rotation rate. Fortunately, a novel method was established by Cassini researchers utilizing gravity-induced perturbations in Saturns complex ring system, which now appears to be the most accurate methods of measuring the worlds bulk rotational period, which was figured out in 2019 to be 10 hours, 33 minutes and 38 seconds.
Reference: “Saturns weather-driven aurorae modulate oscillations in the electromagnetic field and radio emissions” by M. N. Chowdhury, T. S. Stallard, K. H. Baines, G. Provan, H. Melin, G. J. Hunt, L. Moore, J. ODonoghue, 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.
Infrared picture of Saturn revealing an aurora at its southern pole, captured by the Cassini spacecraft. Credit: NASA/JPL/ASI/ University of Arizona/University of Leicester
Saturns high-altitude winds create an extraordinary aurorae.
Leicester area scientists have discovered a never-before-seen mechanism fuelling big planetary aurorae at Saturn.
Saturn is unique among worlds observed to date in that a few of its aurorae are created by swirling winds within its own environment, and not just from the planets surrounding magnetosphere.
At all other observed worlds, including Earth, aurorae are only formed by powerful currents that flow into the worlds atmosphere from the surrounding magnetosphere. These are driven by either interaction with charged particles from the Sun (as at the Earth) or volcanic product erupted from a moon orbiting the planet (as at Jupiter and Saturn).
” Our understanding of the physics of planetary interiors tells us the real rotation rate of the planet cant change this rapidly, so something distinct and strange should be taking place at Saturn.” This search for a new type of aurora harks back to some of the earliest theories about Earths aurora. We now know that aurorae on Earth are powered by interactions with the stream of charged particles driven from the Sun. I love that the name Aurora Borealis stems from the the Dawn of the Northern Wind. These observations have actually exposed that Saturn has a real Aurora Borealis– the very first ever aurora driven by the winds in the environment of a planet.”