Imagining Earth with a Saturn-Like Ring System

The Ordovician. This term, little known to the general public, taken from the name of a Welsh tribe, describes a period in the history of the Earth, located between 485 and 444 million years ago. It is characterized by the simultaneity of a major glaciation and a spectacular increase in asteroid impacts.

Massive impacts that would have created a ring of debris that probably lasted tens of millions of years, and that gave the Earth the appearance of Saturn. It is this ring that could have led to global cooling and even contributed to the coldest period on Earth in the last 500 million years.

A large asteroid has disrupted the Earth's climate

That's the hypothesis put forward in a new study published in the journal Earth and Planetary Science Letters and led by the team of Andy Tomkins, a professor of planetary science at Monash University in Australia. His group of researchers analyzed 21 crater sites around the world, all created by the fall of debris from a large asteroid between 488 and 443 million years ago. That corresponds to the Ordovician period.

Using computer models of how tectonic plates moved in the past, they were able to map where the craters were when they formed more than 400 million years ago. The team found that all of the craters formed on continents that floated within 30 degrees of the equator, suggesting they were created by debris from a single large asteroid that broke up after slicing past Earth.

Craters all linked

“Under normal circumstances, asteroids hitting Earth can strike at any latitude, randomly, as we see with craters on the Moon, Mars and Mercury,” Tomkins writes in an article published in The Conversation. “So it is extremely unlikely that all 21 craters from this period would have formed near the equator if they were not linked together.”

These researchers also claim that this chain of craters corresponds to a ring of debris orbiting the Earth. A ring similar to those that generally form above the equator of the planets, as is the case with those surrounding Saturn, Jupiter, Uranus and Neptune.

A ring of debris in orbit

The same study found that the asteroid that created the ring was about 7.8 miles (12.5 kilometers) wide. Once it broke up as it approached Earth, its fragments “wandered” around before settling in a ring of debris orbiting Earth's equator, Tomkins said.

“Over millions of years, material from this ring gradually fell to Earth, creating the peak of meteorite impacts observed in the geological record,” Tomkins continued in a university statement. “We also see that sedimentary rock layers from this period contain extraordinary amounts of meteorite debris.”

Still some gray areas…

If Earth had a Saturn-like ring around its equator, that ring would have had a significant impact on our planet's climate, according to the new study. Because Earth's axis is tilted relative to its orbit around the Sun, the ring would have cast a shadow on parts of our planet's surface, potentially causing global cooling.

While they acknowledge that this remains unclear, the researchers speculate that such an event could have contributed to the dramatic cooling of our planet 465 million years ago: “We don't know what the ring would have looked like from Earth, or how much light it would have blocked, or how much debris would have had to be in the ring to cool the Earth,” Tomkins tells New Scientist.