Earth may once have worn a ring like Saturn's
About 466 million years ago, craters from a burst of meteor strikes seem to have clustered in a band around Earth's equator. A 2024 study reads that pattern as the fallout of a ring of asteroid debris that circled the planet for some 40 million years, possibly chilling the climate.
According to that proposal, a large asteroid passed close enough for Earth's gravity to strip away much of its material, which settled into orbit. The ring may have shaded the surface enough to help trigger the Hirnantian glaciation, the coldest spell of the past 450 million years.
Rings are far from rare. All four giant planets have them. Galileo first glimpsed Saturn's in 1610, though Christiaan Huygens was the first to describe them correctly as a disk, in 1655; they are mostly water ice, with particles from micrometres to metres across. Voyager 1 revealed Jupiter's faint, dusty rings in 1979. Astronomers found Uranus's in 1977, and 13 dark, narrow rings are now known there. Neptune's five main rings, hinted at for decades, were confirmed by Voyager 2 in 1989, and between 20 and 70 percent of their material is dust. Minor planets can carry rings too, detected when they pass in front of stars.
Thick rings can arise in several ways: leftover disk material too close to a planet to clump into moons, wreckage from a moon shattered by a collision, or a moon torn apart by tides after straying inside the Roche limit, the distance within which a planet's pull overwhelms a body's own gravity. Fainter rings grow from dust knocked off moons by meteoroids, or, for Saturn's E ring, from icy material erupting out of a moon. Small shepherd moons keep some ring edges crisp, nudging stray particles back, flinging them away or absorbing them.
Mars may get its turn. Its moon Phobos circles faster than the planet spins, and its orbit is decaying. In about 50 million years it should break apart, and the resulting ring could eventually gather into a new moon, a cycle that may have happened several times before.
Source: Ring system
