Telescope throws new light on Saturn’s rings

Saturn as observed by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 on June 20, 2019.

The latest view of Saturn from the Hubble Space Telescope captures exquisite details of the structure of the ring system and other atmospheric details that could earlier only be captured by visiting spacecraft.

One such intriguing feature is the long-lasting hexagon-shaped structure circling the planet’s north pole. This pattern, which NASA’s Voyager 1 spacecraft first discovered during its flyby in 1981, is caused by a high-speed jet stream. The “hexagon” is so large that four earths could fit inside its boundaries. (There is no similar structure at Saturn’s south pole.)

Saturn’s appearance changes with its seasons, which occur because Saturn’s equator is tilted at 27 degrees with respect to the plane of its orbit around the sun, similar to the earth’s 23.5 degrees that cause the earth’s seasons. This new Saturn image was taken during summer in the planet’s northern hemisphere. Seasons on Saturn last more than seven years.

The amber colours in this image come from summer smog-like hazes, produced in photochemical reactions driven by solar ultraviolet radiation. Below the haze lie clouds of ammonia ice crystals, as well as deeper, unseen lower-level clouds of ammonium hydrosulphide and water. Saturn’s trademark ring system is now tilted toward the earth, giving viewers a magnificent look at its bright, icy structure. The high resolution of Hubble’s Wide Field Camera 3 has enabled the telescope to capture the numerous ringlets and the fainter inner rings.

Dutch astronomer Christiaan Huygens first identified the rings as a separate phenomenon in 1655, but he also thought they were a continuous disk encircling the planet. Today, we know the rings are mostly made of pieces of ice, with sizes ranging from tiny grains to giant boulders, and that they constantly move around the planet in an intricate cosmic dance.

The age of Saturn’s ring system continues to be debated. What is more intriguing is what cosmic catastrophe could have formed the rings. Additional clues came in as NASA’s Cassini spacecraft plunged into Saturn’s atmosphere on September 15, 2017, which marked the end of the mission. During its final orbits, Cassini measured the mass of the ring system as merely 1/1000th the mass of earth’s moon. Some astronomers have interpreted this low mass to mean that the rings may only be 100 million years old, a fraction of Saturn’s age.