The rings of Saturn are one of the most spectacular sights in the Solar System and one of the most photographed. Despite the interest they garner, astronomers still puzzle over how the rings formed and why they have survived.
One clue is that Saturn’s rings sit within the Roche limit, the theoretical distance at which gravitational tidal forces from the parent planet would tear apart any ordinary moon.
Indeed, that has turned out to be a common feature of other rings. In 1977, astronomers discovered rings around Uranus and two years later the Voyager 1 spacecraft spotted a ring around Jupiter. Astronomers have since discovered rings around Neptune, around the dwarf planet Haumea and around Chariklo, a small body orbiting between Saturn and Uranus. All of these rings also sit within the Roche limit.
Which is why the discovery of rings around the dwarf planet Quaoar is such a surprise. ...
