Here’s a good reason to take a look at Saturn, which drops in the southwest just after dark. The first sight of Saturn in a telescope can be a life-changing experience.
The fact that I’m still writing this weekly column after 34 years of keyboarding is a testament to my soft jaw amazement when I first saw Saturn’s rings at the age of 12.
In the decades I have hosted school programs at Perkins Observatory, I have shown the rings to thousands of elementary school children. Their reactions were invariable: rapid inspiration and slow expiration. “Oh. Wowwww.” That “Oh wow” was the air I breathed and the food that sustained me through long, painful days and many sleepless nights.
The rings were as much of a revelation to me as they were to Christiaan Huygens when he saw them as one ring in 1659. Previously, Galileo had seen two bumps on either side of the planet and proclaimed that ” the farthest planet has a triple form. . “Huygens’ more advanced telescope has shown that Saturn” is surrounded by a thin, flat ring, which does not touch anywhere. “
For centuries, astronomers could not find another planet so endowed.
The visible part of this ring is enormous. Saturn is gigantic at 75,000 miles across. We now know that the Huygens Ring spans approximately 220,000 miles. It would just fit between Earth and its moon.
Still, he looked extremely thin. Its inclination varies from our point of view as Saturn revolves around the sun. Huygens knew that the ring would eventually appear “in front” to observers a few years later. When astronomers then observed it, the rings were thin enough that they completely disappeared for a few days.
Huygens had explained Galileo’s bumps but raised three other puzzling puzzles. Why was Saturn the only planet surrounded by a ring? What was it made of? How did it come to this?
The mystery was compounded when, in 1675, Giovanni Cassini pointed his much improved telescope at Saturn and saw that the ring were, in fact, rings.
These days, it doesn’t take much of an amateur telescope to see the most obvious gap in the ring, which is called Cassini’s division in honor of the astronomer. Since then, using technologically superior telescopes and even a planetary orbiter aptly named Cassini, astronomers have discovered that the ring is made up of more than 100,000 loops.
Even the Cassini division is not at all a real gap. Inside are several weak subdivisions, including a loop named after the great Huygens himself.
As the number of rings increased, so did astronomers’ curiosity about their composition. In 1659, James Clerk Maxwell proved that the rings could not be strong.
They had to revolve around Saturn. Otherwise, the enormous gravity of the planet would drag them down. However, when turning, strong rings would tear.
According to Maxwell, it must be countless particles, mostly tiny, all in independent orbits around the planet.
Such claims are difficult to prove. To date, neither telescopes nor orbiters can resolve rings into their component particles. It took over 200 years to demonstrate, albeit indirectly, that Maxwell was right.
Indeed, Saturn has up to a billion billion moons orbiting it. Most of them are the size of dust or sand. Few are the size of mountains on Earth. The bright rings that we can see in amateur telescopes stretch from just 4,300 miles to about 50,000 miles from Saturn’s surface.
Astronomers estimate that if all the particles in the ring were grouped together, they would form a Saturnian moon only 30 to 40 miles wide. Considering the enormous reach of the ring system, they must be extremely thin. In some places, they are only a few hundred meters thick.
And yet, they glow so bright that even a casual observer will notice they are brighter than Saturn’s surface. Only ice of various varieties – mainly water ice – explain such luminosity.
Astronomers still argue over the origin of the rings. Ring theorists roughly fall into two camps: the early ringers, who say the rings were present soon after Saturn was formed, and the late ringers, who believe the rings were formed in the last hundreds of millions. years.
The starting point of the current controversy is the work of the 19th century astronomer Edouard Roche.
He proposed that the rings were once a moon of Saturn that spiraled around the planet. When the moon, which Roche nicknamed Veritas, came within 2.5 Saturnian rays, a distance known as the Roche limit, it was torn apart by Saturn’s considerable gravity.
Some early ringers speculate that the rings are made up of particles that have not merged into Saturnian moons. Its supporters include astronomers Robin Canup and Sébastien Charnoz. They claim that the rings were present soon after the formation of Saturn.
The rocky material in the ring was massive enough to attract more material to itself, and in this way some of Saturn’s moons formed.
Subsequently, gravitational interactions with Saturn’s other moons knocked them out of the rings. So the rings we see now are just frozen scraps.
Early ring theorists also argue that an early moon of Saturn was struck by an asteroid-like object quite early in Saturn’s life. Such an event could have happened at any time in Saturn’s history, of course. However, such impacts were more likely when many objects crashed into planets and their moons.
This period, dubbed the Late Bombing Period, occurred about four billion years ago. We see evidence of LBP in the Moon’s many old craters.
Current evidence leans toward late formation, possibly because Saturn’s gravity stripped one of the moons of its icy outer covering as the moon spiraled into Saturn. Alternatively, the ring’s creator object could have been an asteroid or a comet that got too close to Saturn’s oscillation.
The last ringers have a powerful argument for their theory. The icy particles of the rings appear to be shiny and pure. If the rings had formed early, the ice should have darkened as they were battered by rocky micrometeorites and solar radiation, both of which tend to darken the ice over time.
Saturn will always have almost invisible rings as micrometeorites bombard its outer moons and release a thin cloud of dusty debris into orbit. This is the case with the Phoebe Ring, which was only discovered in 2009 by NASA’s Spitzer infrared space telescope. The ring is a fine mixture of dust-sized particles of mostly icy materials.
The ring continues to form just inside the orbit of Phoebe, one of Saturn’s furthest moons. As meteorites large and small pound Phoebe’s already battered surface, the cloud of dusty debris spreads in a thin ring. As long as Phoebe exists, this ring will survive.
However, if late ring theorists are correct, the shiny rings we see today could be a passing phase in Saturn’s long life.
It is still possible that these are ancient and permanent installations that are billions of years old. More likely, they could be very young – a speck in Saturn’s eye that Saturn’s gravity will eventually wash away as the planet pulls the larger particles inward.
The particles in the ring slowly spiral towards Saturn due to their relative proximity to a massive, gravitationally powerful planet. Estimates of Saturn’s absorption rate vary, but the message is clear.
Find a telescope and point it at Saturn and its rings. In 100 million years or so, it will be too late to see them.
If that sounds like a long time, think about the age of Saturn. Like all planets in the solar system, it formed around 4.5 billion years ago. One hundred million years would equal about a year and a half in a 70-year human life.
In this relatively short period of time, all that will be left is a thin, almost invisible ring-shaped cloud of dirty, icy dust, which meteoric impacts will continually replenish from one or more of Saturn’s outer moons.
Over the centuries, the Battle of the Ring has raged, and still, astronomers are uncertain.
During my tenure at Perkins, many of my temporary students were frustrated by the lack of certainty on this and many other astronomical questions.
I would always say something like this:
When you look at the rings, you are looking at one of the greatest mysteries in astronomy. Revel in this uncertainty. Maybe you or someone from your generation will be the one to discover the definitive answer. Mankind has yet to crown the Lord of the Rings.
Tom Burns is the former director of the Perkins Observatory in Delaware.