Planetary Rings Defy Long Ages

Models of the origin of planetary rings are simulations based on fictions. Real physics cannot keep them billions of years old.

Theory vs Realism

Researchers at Kobe University claim to have an explanation for planetary rings, Science Daily reports. Their supercomputer model accounts for the difference in composition of Saturn’s icy rings, compared to the rocky rings at Uranus and Neptune. The model, however, published in Icarus, relies on two doubtful assumptions. One is the Late Heavy Bombardment (LHB), which we reported on 9/13/16 is coming under fire. It could be a fiction based on poor data analysis of lunar craters. But even if it happened, the model requires heavy doses of luck. Roaming Kuiper Belt Objects would have to come close enough to a planet’s sphere of influence to be captured and disrupted without plunging into the planet or whizzing by at high speed. Appealing to the Late Heavy Bombardment also incurs a timing penalty, taking place far too early to account for the youthful appearance of the rings today. Without a more recent and plausible supply of candidate objects, this latest model seems to reduce to the Stuff Happens Law, for which no empirical evidence of such events is available. No wonder the authors begin, “The origin of rings around giant planets remains elusive.”

Here are two examples of ring systems that cannot be as old as their planets.

Saturn

The rings of Saturn are labeled by letters. Starting from the planet, they are D, C, B, A, F, G, and E. Farther out is the wide, diffuse Phoebe ring. News about the C ring, the second to innermost of the main rings, shows it cannot be very old. In Icarus, leading planetary ring specialists published latest findings about the contamination fraction of the C ring, and found it quite low: only about 1-2%. This number should be substantially higher if the rings are old. Since these facts fly in the face of old ages, the scientists had to concoct an auxiliary hypothesis to keep Saturn billions of years old.

Despite considerable study, Saturn’s rings continue to challenge current theories for their provenance. Water ice comprises the bulk of Saturn’s rings, yet it is the small fraction of non-icy material that is arguably more valuable in revealing clues about the system’s origin and age. Herein, we present new measurements of the non-icy material fraction in Saturn’s C ring, determined from microwave radiometry observations acquired by the Cassini spacecraft. Our observations show an exceptionally high brightness at near-zero azimuthal angles, suggesting a high porosity of 70–75% for the C ring particles. Furthermore, our results show that most regions in the C ring contain about 1–2% silicates. These results are consistent with an initially nearly pure-ice ring system that has been continuously contaminated by in-falling micrometeoroids over ∼15–90 million years, using the currently accepted value of the micrometeoroid flux at infinity of ∼4.5 × 10−17 g cm⁻² s⁻¹, and assuming that the C ring optical depth and surface density has not changed significantly during that time… We also find an enhanced abundance of non-icy material concentrated in the middle C ring….

We propose several models to explain the radially varied non-icy material contamination. Our preferred model is that the C ring has been continuously polluted by meteoroid bombardment since it first formed, while the middle C ring was further contaminated by an incoming Centaur, a rocky object torn apart by tides and ultimately broken into pieces that currently reside in the middle C ring. If correct, the spatial extent of the enhanced non-icy material fraction suggests that the Centaur was likely to be captured and integrated into the rings perhaps as recently as ∼10–20 million years ago.

Centaurs are comet-like asteroids orbiting between Jupiter and Neptune. 90 million years is an upper limit on how long the C ring has been contaminated; it could be 1/6 of that (15 million), or less, if contamination was not steady. It should be noted that the longest age offered in this model, 90 million years, is just 2% of the assumed age of Saturn. What happened after 98% of the planet’s lifetime to create this extra ring? The lower age, 10 million years, is 0.22% of the assumed age. That’s when their model calls for a sudden influx of silicates from the imaginary Centaur just 10-20 million years ago. Any longer than that, and the material should have spread out throughout the ring.

Reverse Engineering

How can rings rotate the wrong way around a planet? That’s what scientists are wondering about an exoplanet orbiting J1407, a giant planet or brown dwarf. Elizabeth Howell describes the puzzle in Space.com.

A strange and colossal ring system around an alien planet is apparently stuck in reverse, circling opposite to the planet’s own orbit around its parent star. While the arrangement appears unstable, new calculations show the rings could remain for at least 100,000 years.

That’s thousands, not billions. Even if these rings could orbit in reverse for a hundred thousand years, that doesn’t explain how they got stuck in reverse. “The researchers said they next plan to examine how the ring structure was created, and how it evolves.” PhysOrg says,

Rings that turn in this sense (retrograde rings) are not common. Therefore the researchers suspect that there has been a catastrophe that caused the rings (or the planet) to turn the other way around.

Confirmation of this phenomenon will have to await further observation, since it was detected indirectly by two astronomers watching eclipses. If confirmed, it seems reminiscent of the broad Phoebe ring that orbits around Saturn the wrong way along with the outermost moon Phoebe (10/07/09). Since none of Saturn’s rings fit neatly within the current paradigm that the solar system is 4.5 billion years old (3/19/10, 2/04/16), planetary scientists are forced to come up with auxiliary hypotheses to explain their origin.

In other Saturn news, the BBC reports that the north polar hexagon has changed color since 2012. It may be a seasonal effect as Saturn approaches its summer solstice. The additional sunlight could change the production of suspended particles – aerosols – that refract light differently.

The best observations of Saturn’s rings in Cassini’s whole mission will begin soon. For the mission’s “Grand Finale,” flight engineers are setting the spacecraft onto a highly inclined orbit beginning November 30, that by April will make it dive between Saturn and the D ring. Assuming the craft survives this daring move, it should provide the highest-resolution images of the rings from above and below the ring plane (see animation at above link of how this will look). The mission will end with Cassini’s final plunge into the planet on September 15, 2017.

Micrometeoroid impact rate is only one factor that destroys rings. Ring particles are also destroyed through a process called sputtering, where charged particles erode their surfaces. Also, rings tend to spread out through collisions, and get dragged into the planet. Even sunlight pressure can create orbital drag.

In my occasional conversations with leading ring specialists at JPL, they readily admitted that Saturn’s rings look a lot younger than Saturn. One of them also confessed that he preferred keeping them old for philosophical reasons. He didn’t like the idea that we are living in a special time when the rings are visible on earth. It would make humans look exceptional.

I would probably still be working at JPL well into 2017 on the Cassini mission had I not been fired for sharing DVDs about intelligent design. Click here for a summary of what happened. (DC)