Saturn’s rings are arguably one of the most widely recognized features of our solar system. While Saturn isn’t the only planet that has a ring system (Jupiter, Neptune and Uranus also have rings), the sixth planet from the sun does have the most prominent and spectacular rings, visible from Earth on clear nights with the aid of a bit of telescopic magnification.
Back in December, we also learned something interesting about Saturn’s ring system: that it may be much younger than we once thought, having appeared more recently than the dinosaurs.
Luciano Iess of the Sapienza University of Rome told Astronomy.com that “A catastrophic event like a collision looks to me the most obvious explanation, but there may be problems with that too… The origin of the rings has to be put in the broader context of the dynamics of the Saturnian system.” Iess went on to cite colleagues of his “that even [think] the inner moons of Saturn are young, and they are migrating inward.”
Recent astronomical studies helped us determine the youth of Saturn’s rings. Since the physical matter which composes them constitutes fairly low mass, astronomers guess that the rings are between 10 and 100 million years old (Saturn, on the other hand, is believed to be almost 4.5 billion years old). Iess told Astronomy.com that measurements going all the way back to Voyager and Cassini were highly suggestive that the planet’s rings came much later.
Knowing that the most prominent planetary ring system in our celestial neighborhood was a recent addition, it has caused some to ask whether Earth itself might have at one time had rings, too.
This was precisely the idea proposed by Danish astronomer Kaare Rasmussen of the National Museum in Copenhagen in the early 1990s, who argued that in the past 2800 years Earth may have had rings on as many as 16 separate occasions.
According to am April 1991 article in New Scientist by John Gribben, Rasmussen “carried out a survey of all reports of meteorite falls, fireballs and showers of shooting stars from 800 BC to 1750 AD. He then carried out a statistical analysis of the data. He discovered that there were many distinct periods of intense activity.” Based on this, Rasmussen noted that these active periods peaked coinciding with high meteoritic activity, during which time he believed that rings formed as a result of a comet or asteroid being caught in Earth’s orbit. Subsequent decreases in meteoritic activity might have indicated periods of ring stability, followed by a return to activity as particles from the particulate ring were decelerated by Earth’s upper atmosphere and began to shower down upon the Earth.
Some interesting observational data exists from the last couple of centuries that suggests Earth could have had asteroids trapped in its orbit even more recently. In 1907, the June 12 edition of the Edmonton Bulletin featured an article on a colorful character by the name of E. Stone Wiggins, a Canadian astronomer who claimed to have spotted a second moon in orbit around the Earth:
“In 1882,” says Prof. Wiggins, “I discovered another moon. It is now at that point of its orbit nearest the earth… I knew this moon existed because our visible moon showed a disturbing force in her revolutions around the earth, for which astronomers could not account.
“In 1884 I published a letter in the New York Tribune claiming the discovery, giving the evidence of trustworthy persons in Michigan who declared to me that the sun was eclipsed on May 16 of that year, the sky being perfectly cloudless and when our visible moon was in another quarter of the heavens and therefore could not possibly eclipse the sun. This dark moon has an immense carbon atmosphere in which the dun develops little or no light; but it has often been seen by persons who happened to be in the range of incidence of its reflected light.”
It’s not impossible that a fairly large object could enter Earth’s orbit for a period of time, thus resulting in what astronomers have called a “moonlet” (see my article here for more on this), or as Kaare Rassmussen suggested in the 1990s, maybe even a ring system around Earth for a period of time.
At his Bad Astronomy blog, Phil Plait addressed the question of whether a ring system might ever form around Earth, to which he said, “could Earth have rings? Sure!” Plait continues:
“It’s unclear exactly how Saturn (or the other four outer giant planets) got their rings, but there is more than one mechanism to create them. A small moon could get hit by an asteroid or comet, shattering it. An impact on the Earth itself, if it were big enough, could create rings (the impact that formed the Moon billions of years ago may have done just that). That would kinda suck for us, though. Saturn’s moon Enceladus has geysers which may resupply the planet’s A and E rings.”
As Plait points out, at some point in Earth’s past the impact that led to the formation of our Moon might have actually caused Earth to have a ring system, as Rassmussen suggests (although these rings would have existed much earlier than Rassmussen’s estimate of the last 2800 years). So if this is the case, why doesn’t Earth have a ring system now?
The problem with ring systems is that much of their composition is formed from ice particulates. As Fraser Cain, publisher of Universe Today and co-host of Astronomy Cast explains, “The problem with icy rings is that the Earth orbits too closely to the Sun. There’s a specific point in the Solar System known as the ‘frost line’ or ‘snow line’. This is the point in the Solar System where deposits of ice could have survived for long periods of time. Any closer and the radiation from the Sun sublimates the ice away.”
So Earth’s proximity to the Sun, in other words, makes it physically difficult for icy rings to remain for long periods, as with more distant planets in our solar system.
It’s not impossible that Earth may have had rings at some point in the past, or in the unfortunate event of an asteroid impacting the moon, or even the Earth, that our planet could have rings again someday. In the event that it ever does, let’s just hope it’s not the result of an armageddon-inducing space rock smashing us to bits in the process. In the meantime, if you’ve ever wondered what a ring system around our planet might look like from here on Earth, check out Ron Miller’s conceptual artwork that illustrates this idea.