Earth Might Have Been a Ringed Planet, Like Saturn

Saturn, as seen by Cassini

17 September 2002

Earth may once have been surrounded by temporary rings of debris, much like Saturn, according to a new computer model that finds the rings might have cast parts of the planet into a twilight glow all day long.

The idea is not new, but the fresh modeling adds weight to the plausibility of an asteroid impact kicking up a sea of orbiting debris, and it considers how the rings would have cooled Earth's climate.

The new model, based on Saturns B-ring scaled down to Earth-size, was produced by Peter Fawcett of the University of New Mexico and Mark Boslough of the U.S. Department of Energys Sandia National Laboratories. It is based on climate models that had already been developed.

The scientists said a ring might form with a glancing blow, in which a space rock and the debris it carves from the planet ricochet into the atmosphere.

An expanding vapor cloud causes some of the debris to go into orbit. Over time, it collapses into a plane that matches Earth's equator. The ring then lasts from about 100,000 years to perhaps 1 million years at most.

Fawcett told the debris ring would have cooled the planet by blocking or reducing the amount of sunlight received in the tropics and subtropics. The rest of the planet would cool, too, because less heat would be transported from tropical regions to higher latitudes. That would mean fewer storms farther north.

The work is speculative, the researchers say, but there is some evidence they might be on the right track.

Geologic records reveal a layer of melted meteorite material thought to be associated with an asteroid impact 35.5 million years ago. Some 100,000 years of cooler global temperatures followed.

"This cooling is longer than one would expect from a large impact alone, so we hypothesized that a temporary ring might have formed," Fawcett said. "The jury is still out on this though."

Had there been any humans on the planet to survive the impact and witness the rings, it's hard to say exactly what they would have seen. But Boslough has some ideas, based on an assumption that the rings would have been semi-transparent, like Saturn's.

"For a person in the shadow of a reasonably opaque ring, it would be dark like twilight or a heavy overcast," he said. "The ring would be scattering light in addition to blocking it. I think the most spectacular view would be after sunset or before sunrise, when the sky is dark but parts of the sunlit ring would be brightly visible in the sky."