A video currently making the rounds on the Web ponders an intriguing astronomical scenario: What if Earth had rings, as Saturn does?

If the animation below, by YouTube user Roy Prol, is to be believed (and it seems to jibe with related imaginings, such as one in a NASA educator guide about Saturn [pdf]), rings would be a stunning addition to Earth's sky, day or night. And Prol's video shows that rings would make a heck of a nice backdrop for photographers of terrestrial landmarks (for example, Paris's Eiffel Tower, Rio's Christ the Redeemer, Australia's Ayers Rock) around the globe.

But such a ring, if it were to suddenly appear, might not be all good news. Decades ago, John O'Keefe of the NASA Goddard Space Flight Center ventured that Earth may have had a ring system similar to Saturn's for a brief period. In a 1980 paper in Nature, O'Keefe pointed to climatic data indicating colder winters at the end of the Eocene epoch some 34 million years ago along with showers of tektites, glassy rocks of mysterious origin, at around the same time. O'Keefe's theory held that tektites that missed the Earth in this bombardment were captured into a ring system that may have persisted for millions of years, casting a winter shadow across Earth's surface and contributing to a late Eocene die-off of many marine organisms such as plankton and mollusks.

If Earth may have once had rings, why doesn't it now? Two reasons come to mind, says planetary ring scientist Linda Spilker of the NASA Jet Propulsion Laboratory in Pasadena, Calif. The first is the massive moon that drives our tides and helps stabilize Earth's tilttwo effects that make our planet so habitable. "The tidal pull from our moon would be very good at disrupting and dissipating any sort of ring," Spilker says. "Second, the solar perturbations (tidal pull from the sun) are much larger at Earth, and the terrestrial planets, than they are at Jupiter and outward." Those forces would break up a ring, Spilker adds, and the push from solar photons and streaming charged particles in the solar wind would disturb small constituents in Earth-centric rings as well.