Latest Evidence that Saturn and Its Rings Are Young
A new set of post-Cassini papers has to deal with observational facts: Saturn and its rings cannot last billions of years.
Science Magazine just added to the growing body of post-Cassini literature analyzing 13 years’ worth of data gathered by the legendary Saturn orbiter. During the last 22 “high-dive” orbits in 2017, Cassini had unprecedented opportunities to sample the space between the rings and the planet. Here are some of the surprising findings being reported.
Hsu et al, “In situ collection of dust grains falling from Saturn’s rings into its atmosphere” (Science). A “ring rain” of nanoparticles detected by the Cosmic Dust Analyzer (CDA) puts an upper limit of 400 million years on the rings.
Mitchell et al, “Dust grains fall from Saturn’s D-ring into its equatorial upper atmosphere” (Science). Atmospheric drag is ejecting dust from the D-ring analogous to “sawdust ejected from a circular saw as it cuts through wood.” They believe the process “plays a role in slowing the fall of the dust through the atmosphere,” but sawdust does not normally evolve back into wood.
Waite et al, “Chemical interactions between Saturn’s atmosphere and its rings” (Science). This paper, with co-author Jeff Cuzzi, a ringmaster most of his professional life, cannot support billion-year rings. Water is falling into the planet from the rings at a rate of up to 45,000 kilograms per second. Other compounds are also flowing off the rings into Saturn, as measured by the Ion and Neutral Mass Spectrometer (INMS). Here’s the team’s conclusion:
The large mass of infalling material has implications for ring evolution, likely requiring transfer of material from the C ring to the D ring in a repeatable manner. The infalling material can affect the atmospheric chemistry and the carbon content of Saturn’s ionosphere and atmosphere.
Here’s the operative quote about ages: not millions of years, but thousands?
The mass of Saturn’s C ring is ~1018 kg, about 0.03 times the mass of Saturn’s moon Mimas. Therefore, if we use the mass influx inferred from the INMS measurements (4800 to 45,000 kg s–1), we calculate a lifetime of 700,000 to 7 million years for the C ring. Yet this only reflects today’s influx. The current influx is directly from the D ring rather than the C ring, which must be the ultimate supplier because the mass of the D ring [likely no more than 1% of the C ring mass] can maintain current loss rates for only 7000 to 66,000 years—a very short amount of time in terms of solar history. It is unclear whether the C ring can lose 1% of its mass into the D ring by viscous spreading over that time period.
Although viscous spreading of the C ring is likely not the cause of mass transfer to the D ring, occasional transfer of ~1% of the mass of the C ring into the D ring region via a large ring-tilting event is feasible. These ring-tilting events involve a stream of planet-orbiting rubble crossing the ring plane somewhere in the C or D rings. The C ring provides the ultimate source, containing enough mass to last (at current influx rates) about 5% of the time that the rings themselves have existed (~200 million years). The D ring could be repopulated sporadically by large impact events such as those that tilted the D and C ring plane. Once enough small particles are brought into the D ring region, exospheric drag would quickly drain them into the planet, as observed by Cassini.
Notice that keeping the rings old (“repopulated”) requires an appeal to the old-age standby explanation: impacts. The number of lucky impacts needed to keep the rings billions of years old, however, stretches credibility.
Perry et al, “Material Flux From the Rings of Saturn Into Its Atmosphere” (Geophysical Research Letters). This team measured the flow of nanometer-sized particles from the rings that are swept up by Saturn’s atmosphere and dragged into the planet. The predicted flux was wrong, and had to be revised upward significantly. It’s “exciting” to be wrong by a factor of a hundred, isn’t it?
Surprisingly, the flux is a hundred times larger than past predictions, and at least half of the material is hydrocarbon, which comprises less than 5% of the water ice‐dominated rings. Cassini’s data also show that the influx varies at least a factor of 4 and may be linked to clumps that appeared in 2015 on D68, the ringlet on the inner edge of the rings. These newly discovered particles and processes alter the evolutionary landscape of the rings and provide an exciting, rich field for future research aimed at understanding the origin and history of the rings.
How This Came Across in the Popular Press
Leah Crane, “Cassini revealed three big surprises before diving into Saturn” (New Scientist). Can Ms Crane bring herself to criticize planetary scientists who got things so wrong? On the subject of Saturn’s magnetic field, she comes close:
The magnetic fields of planets in our solar system are all tilted to some extent – Neptune’s is off by a whopping 47 degrees. But Saturn’s magnetic field seems to be perfectly straight, and our current theories of how these fields are generated suggests that should be impossible.
“If you don’t have a tilt, you would expect the magnetic field to start dying away, but as we got in really close with the Grand Finale orbits, we saw that it is not,” says Michele Dougherty at Imperial College London.
Michele is a dignified and accomplished woman on the Cassini team, but she was wrong on this point. She was wrong on another point, too (as were all the Cassini scientists). Once again, they are excited about being wrong:
Even the seemingly empty space between Saturn’s surface and its rings is more exciting than we thought. “There’s this connection between the rings and the upper atmosphere of Saturn that we just didn’t think would be there,” says Dougherty. “That was a complete surprise.”
Crane goes on to compare the amount of infalling material (dust, ice and gas), measured to be about 45,000 kg (22,000 pounds) per second, this way:
That’s the equivalent of about 1800 cars falling into Saturn every minute – such a downpour may mean that the rings are disappearing faster than we thought.
A little math helps picture this. How much material should have been lost in Saturn’s assumed lifetime? 4.5 x 104 kg/s times 86,400 sec/day times 365 days/year times 4.5 x 109 years: if this has been going on for the age of the solar system, Saturn’s rings would have lost 24 x 1021 kg of material by now. In plain English, that’s a whopping 6,500 billion billion kilograms, or 4,800 million billion cars! That’s close to 240 times the entire mass of the rings. Is that credible?
Groundbreaking Science Emerges from Ultra-Close Orbits of Saturn (Jet Propulsion Laboratory). Will JPL apologize for getting it so wrong? Don’t count on it. Scientists must always look good to the public, because they are the high priests of knowledge in our culture.
Scientists can’t be blamed for things that could not be measured or detected before, obviously, but much of what was taught about Saturn and its rings for decades has just been tossed out the window. The press release mentions “surprise” four times. How about that magnetic field? Haven’t students of geophysics been taught that a dynamo in the core generates the field? That’s been falsified, at least in the case of Saturn; “That might mean that Saturn produces its magnetic field differently from the other planets in our solar system,” Crane said. Actually, it might mean that the theory for generating magnetic fields is wrong for all planets. Philosophers of science look askance at special pleading.
That’s not the only mystery or surprise, either. The whole mission was a string of surprises:
- According to everything scientists know about how planetary magnetic fields are generated, Saturn should not have one. It’s a mystery that physicists will be working to solve….
- But scientists were surprised to see that others [particles] are dragged quickly into Saturn at the equator. And it’s all falling out of the rings faster than scientists thought — as much as 22,000 pounds (10,000 kilograms) of material per second.
- Scientists were surprised to see what the material looks like in the gap between the rings and Saturn’s atmosphere. They knew that the particles throughout the rings ranged from large to small. But the sampling in the gap showed mostly tiny, nanometer-sized particles, like smoke, suggesting that some yet-unknown process is grinding up particles….
Indeed, says project scientist Linda Spilker, “Almost everything going on in that region turned out to be a surprise.” No shame, though; “the data is tremendously exciting.”
Now what? “Many mysteries remain, as we put together pieces of the puzzle,” Spilker said. “Results from Cassini’s final orbits turned out to be more interesting than we could have imagined.”
In all these surprises, mysteries, and falsifications, one thing is never called into question by secular planetary scientists: the assumed age of the solar system. That figure—the Law of the Misdeeds and Perversions—cannot be altered.
Instead of hiding their heads in shame, they are excited about being way off. So what is the likely impact of the revised estimates? Saturn’s rings are young. Plug that into your story of “understanding the origin and history of the rings.” The ramifications are likely to ripple across the solar system, all the way to Earth.