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NASA's Cassini probe orbiting Saturn. Credit: NASA / JPL-Caltech Credit: NASA / JPL-Caltech
New research emerging from the final orbits of NASA's Cassini spacecraft represents a significant advance in our understanding of Saturn's system, particularly the mysterious, never-before-seen region between the planet and its rings. Some preconceptions turn out to be false as new issues come up.
Six teams of researchers publish their work on October 5 in the journal Science, based on the conclusions of Cassini's grand finale. It was then that, while the spacecraft was running out of fuel, the mission team drove Cassini dramatically near Saturn on 22 orbits before deliberately spraying it at one time. final dive into the atmosphere in September 2017.
Knowing that Cassini's days were numbered, her mission team headed for gold. The spaceship flew where it was never designed to fly. For the first time, he surveyed Saturn's magnetized environment, traversed icy and rocky ring-shaped particles, and sniffed the atmosphere in the ditch between rings and cloud tops (1,200 km). Not only did the flight path push the spacecraft to its limits, but new discoveries show how powerful and agile the instruments were.
Many other scientific results from the grand finale are coming, but here are some of today's highlights:
- Complex organic compounds embedded in water nanograins pour out from the rings of Saturn into the upper atmosphere. The scientists saw water and silicates, but they were surprised to see also methane, ammonia, carbon monoxide, nitrogen and carbon dioxide. The composition of organic substances is different from that found on the Enceladus moon – and also different from that of the Titan moon, which means that there are at least three distinct reservoirs of organic molecules in the system of Saturn.
- For the first time, Cassini closely examined the interactions of the rings with the planet and observed particles and gases from the inner ring falling directly into the atmosphere. Some particles pick up electrical charges and spiral along magnetic field lines, falling into Saturn at higher latitudes – a phenomenon known as "ring rain". But scientists were surprised to see that others are quickly drawn into Saturn at the equator. And all of this falls rings faster than scientists thought – no less than 10,000 kilograms of material per second.
- Scientists were surprised to see what the material looked like between the rings and Saturn's atmosphere. They knew that the particles in the rings were large to small. But sampling in space has mostly revealed tiny particles of nanoscale, such as smoke, suggesting that a yet unknown process involves grinding particles.
- Saturn and its rings are even more interconnected than scientists thought. Cassini revealed a system of electric current until then unknown, which connected the rings to the top of Saturn's atmosphere.
- Scientists have discovered a new radiation belt around Saturn, close to the planet and composed of energetic particles. They found that, if the belt crossed with the innermost ring, the ring was so thin that it did not block the formation of the belt.
- Unlike all other planets with a magnetic field in our solar system, Saturn's magnetic field is almost completely aligned with its axis of rotation. The new data indicates a tilt of the magnetic field less than 0.0095 degrees. (The earth's magnetic field is tilted 11 degrees from its axis of rotation.) After all that scientists know about how planetary magnetic fields are generated, Saturn should not have any. It's a mystery that physicists will strive to solve.
- Cassini flew over the magnetic poles of Saturn, directly sampling the regions where radio broadcasts are generated. The results more than doubled the number of direct measurements of radio sources on the planet, one of the few non-terrestrial locations where scientists have been able to study a radio generation mechanism that is supposed to work in the universe as a whole.
NASA's Cassini spacecraft plunges between Saturn and its deepest rings, as part of the Mission's Grand Final. Credit: NASA / JPL-Caltech
For the Cassini mission, the science deployed from the orbits of the Grand Finale justifies more than the calculated risk of diving into the slot, careening the upper atmosphere and bypassing the edge of the inner rings, said Linda Spilker, Cassini Project Manager.
"Almost everything that was happening in this area has turned out to be a surprise," Spilker said. "It was important to go there, to explore a place we had never been before, and the expedition really paid off: the data is extremely exciting."
The analysis of Cassini data from spacecraft instruments will continue in the coming years, helping to paint a clearer picture of Saturn.
"Many mysteries remain, as we assemble the pieces of the puzzle," Spilker said. "The results of the latest Cassini orbits have proved more interesting than we could have imagined."
Some of the findings of Cassini's direct sampling: complex organic matter fall from the rings of Saturn; The particles of the inner ring take up electric charges and move along the magnetic field lines; recently discovered electric current system and radiation belt; and a closer measurement of Saturn's near-zero magnetic field inclination. Credit: NASA / JPL-Caltech
Articles published in Science are:
"Chemical interactions between Saturn's atmosphere and its rings", by J. Hunter Waite, et al.
"D-Ring dust falling into the equatorial ionosphere and the upper atmosphere of Saturn", by Donald Mitchell, et al.
"In situ collection of dust grains falling from the rings of Saturn into its atmosphere", by Hsiang-Wen Hsu, et al.
This illustration represents NASA's view of Cassini's probe during one of her last dives between Saturn and her deepest rings, as part of the Mission's Grand Final. Credit: NASA / JPL-Caltech
"An energy proton radiation belt located between Saturn and its rings", by Elias Roussos, Peter Kollmann, et al.
"The Magnetic Field of Saturn Revealed by the Cassini Grand Final", by Michele Dougherty, et al.
"The Low Frequency Saturn Radiation Source (SKR)", by Laurent Lamy, et al.
October 4, as Science publication embargo lifts, articles describing the complementary research to these results will be posted in Letters of geophysical research (GRL), a journal of the American Geophysical Union (AGU).
Explore further:
In his last days, Cassini was bathing in "the rain ring"
More information:
J.H. Waite et al. Chemical interactions between the atmosphere of Saturn and its rings, Science (2018). DOI: 10.1126 / science.aat2382
D. G. Mitchell et al. The dust grains fall from Saturn's D ring into the upper equatorial atmosphere. Science (2018). DOI: 10.1126 / science.aat2236
Hsiang-Wen Hsu et al. In situ collection of dust grains falling from the rings of Saturn into its atmosphere, Science (2018). DOI: 10.1126 / science.aat3185
E. Roussos et al. An energy proton radiation belt located between Saturn and its rings, Science (2018). DOI: 10.1126 / science.aat1962
Michele K. Dougherty et al. The magnetic field of Saturn revealed by the grand finale of Cassini, Science (2018). DOI: 10.1126 / science.aat5434
L. Lamy et al. The low frequency source of Saturn's kilometric radiation, Science (2018). DOI: 10.1126 / science.aat2027
Letters of geophysical research: agupubs.onlinelibrary.wiley.co … 8007.CASSINI_FINALE1
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