A ringed planet Earth?
Fred Watson
Fred Watson
Now, a group of Earth scientists at Melbourne’s Monash University have asked the question “Did Earth ever have a ring?” And surprisingly the evidence they’ve uncovered points to an intriguing “yes”.
Their work took them to an era 466 million years ago called the Middle Ordovician, when our planet was subjected to a high rate of bombardment by meteorites and asteroids. We know this from the large number of craters that remain, and from asteroid debris that has been found in sedimentary strata across the Eurasian continent.
Until now, scientists had assumed this material came from a large asteroid that broke up in the main asteroid belt between the orbits of Mars and Jupiter, with the resulting fragments eventually finding their way to Earth. But a closer investigation reveals a different story.
Whenever we look at the history of our planet over even relatively short timescales, we must include the drift of continents by tectonic activity. We can now reconstruct this movement back to well over a billion years ago, so we know where the continents would have been in the Middle Ordovician.
It turns out that at that time, all the impact craters studied were scattered around the equator, which would not be expected if material had bombarded the Earth directly from the asteroid belt. Instead, the scientists argue, the concentration of impacts close to the equator was probably the result of a ring of debris that had originated in the gravitational disintegration of a large asteroid on a near-miss trajectory. A similar disintegration is believed to have led to the rings of Saturn, and, like those, the Earth’s ring would eventually have dissipated due to debris falling down to the planet, which explains the impact craters around the equator.
The Monash scientists have one additional piece of circumstantial evidence for the ring’s existence. Around the same time as the craters were formed, the Earth began to cool, eventually entering an ice age. Could that cooling have been due to the shading of the planet’s surface by its ring? Further research will be needed to answer this tantalising question.
