The four giant planets of our solar system - Jupiter, Saturn, Uranus and Neptune - have all got a system of rings. While Saturn’s icy rings have turned out to be iconic, those of the others were discovered much later. We’ll be looking into the rings of the largest of these four planets this week, their components and how they came into existence.
Though we have known about Saturn’s rings for over four centuries now, it has been only about four decades since we found out about Jupiter’s rings. Both, however, have a Galileo connection. While Saturn’s rings were observed by Galileo in 1610 and studied there on, Jupiter’s rings were first observed by the Voyager space probe in the 1970s and then thoroughly researched by the Galileo orbiter in the 1990s.
The Jovian ring system has four main components to it: very faint outer rings that are almost sewn together to form a pair of gossamer rings; a flat main ring that is exceptionally thin and relatively bright; and a thick inner ring called the halo. While much of the rings have a reddish colour in visible and near-infrared light, the halo is either neutral or blue in colour.
The doughnut-shaped halo is between 20,000 and 40,000 km in overall thickness, even though most of the materials lie within 100 km of the ring plane. Its shape is believed to be the effect of electromagnetic forces within Jupiter’s magnetosphere acting on the particles making up the ring. The flat main ring is only 6,500 km wide while the gossamer rings are over 50,000 km wide.
Unlike Saturn’s rings, Jupiter’s rings are made up of dust and not ice. While this was known, it was only in 1998 that the reason behind this was discovered by people in different institutions working together. It is now understood that these rings are created by the dust thrown off by high-velocity impacts of cosmic bodies on Jupiter’s moons.
Images and observations from Galileo space probe not only showed that the ring particles mimic the orbits of their mother moon, but also that they move into orbit around Jupiter after impact with the moons as the gravity of these small moons is so weak. It is for this reason that Adrastea, with the weakest gravity, contributes the maximum for the rings.
It can be seen that the gossamer rings actually outline the orbits of the moon Amalthea and Thebe and the main ring was produced by the moons Metis and Adrastea, which almost share the same orbit. The halo, as said earlier, is made up of particles from the main ring that interact with the magnetic field of Jupiter.
Scientists and astronomers are interested in the rings of Jupiter because they believe that these can be utilised as dynamic laboratories that would help us understand the formation of the solar system billions of years ago. And that might one day help us come to terms with the evolution of the universe.
ganesh.a.s@thehindu.co.in
