Ancient Earth May Have Had Its Own Saturn-Like Ring System

Earth may have had a Saturn-like system of rings in the distant past, according to a recent study that suggests that our home planet may have possessed such a magnificent feature. Typically associated with the Solar System’s large outer planets, the temporary presence of these rings may explain not only an unusual period of meteor bombardment that occurred nearly half a billion years ago, but also why Earth went through a sudden period of extensive global cooling, an even that, in turn, triggered a mass extinction event.
Published by researchers from Australia’s Monash University, the study found that Earth received nearly two dozen major meteor impacts over a geologically-short period of time between 485.4 million to 443.8 million years ago, called the Ordovician impact spike. Aside from such a large number of impacts occurring over such a comparatively short span of time—the period itself lasted less than 42 million years, less than two-thirds the time between the extinction of the dinosaurs and now—all of these impacts occurred within 30 degrees of the Earth’s equator.

“It’s statistically unusual that you would get 21 craters all relatively close to the equator,” explained lead author Andrew Tomkins, a geologist and professor of Earth and planetary sciences. “It shouldn’t happen. They should be randomly distributed.”

Such a pattern suggests that the objects, consisting of rocky meteors called L chondrites, had come from a band of debris circling the planet around the equator, most likely in the form of a planetary ring. Tomkins’s team estimates that the parent object of these meteors was an asteroid that was a minimum of 10.5 kilometers in diameter, although the study points out that it would have been much larger because most of the resulting debris “would be ejected from Earth’s orbit during break-up and disk evolution.”

They proposed that about 466 million years ago this asteroid was caught by the Earth’s gravitational field and in doing so passed too close to the planet, causing it to break up from the stresses generated by Earth’s tidal forces. The resulting debris eventually settled into a ring that spread from an altitude of 15,800 kilometers (9,818 miles) out to 35,786 kilometers (22,237 miles) above the surface.

This can be visualized as a Saturn-like ring with an inner edge starting a little more than one planetary width above the Earth’s surface, with an outer edge that extends out by another one-and-a-half widths; overall, this structure would be nearly 84,400 kilometers (52,444 miles) across—that’s 6.6 times wider than the Earth itself, or nearly one-tenth the way to the Moon.

Without knowing the density of the debris, it would be difficult to say what this ring would have looked like from the surface, but even at the sparse end of the team’s estimates it should have been visible at night.

“If you were on the night side of the Earth looking up, and the sunlight is shining on the rings, but not on you, that would make it probably quite interestingly visible—it would be quite spectacular,” Tomkins illustrated. The presence of the ring may have lasted somewhere between 20 million and 40 million years, steadily disappearing as the material that formed it either rained down on the surface or escaped the planet’s orbit.

The researchers also hypothesize that the shadow of the ring may have blocked enough sunlight to have caused a severe drop in global temperatures, triggering planet-wide glaciation that marked the Hirnantian global icehouse period, along with a mass extinction event that saw the end of approximately 85 percent of all marine life.

“The paper presents a pleasing idea that ties together a few mysteries,” astrophysicist Vincent Eke, an associate professor with Durham University’s Institute for Computational Cosmology, stated in an email to CNN. Although not involved in the study, Eke went on to say that “the subsequent debris from such an event (a potential ring) could account for these three observations,” referring to the odd distribution of the impact craters, the presence of the debris from the meteors that formed them, and the resulting sudden shift in global climate.

It’s also hypothesized that Mars may one day acquire its own ring, after its innermost moon, Phobos, ventures too close to the planet and disintegrates from the tidal forces it would encounter, something that Eke says might happen in the next 100 million years. “Thankfully, for the development of life on Earth, these types of (events) are rare at the current time!”