⊚ The Changing Rings of Saturn

Saturn takes 29 years to orbit the Sun.

The view we see of it rings changes during this time for the same reason we have seasons. Like the Earth, Saturn is on a tilt. 

Saturn

Image of Saturn’s changing rings by Kevin Parker

When you take your telescope out to view Saturn this winter, you might notice something a bit different compared to previous years.  The rings will be spectacular as always, but they’ll appeared tilted away from us.  Fast forward to May 2025 and the rings will appear edge on to us and to almost have vanished from view.

The Earth spins on its axis tilted back at an angle of approx. 23 degrees.  Around the middle of the year the Northern hemisphere is pointed towards the Sun and experiences longer days and warmer weather. The Southern Hemisphere is exactly opposite. It’s pointed away from the Sun, the days are shorter and weather cooler.   You might have heard the days when the Earth is at the maximum “tilt” during these periods as the Winter and Summer “Solstice”.

On a day between Winter Solstice and the Summer Solstice the Earth is spinning exactly upright. The Sun will appear directly overhead and the days will be the same length everywhere on the planet. All these effects are caused by the Earth’s tilt.  From a planet somewhere else in the Solar System the Earth would appear to slowly tilt backwards and forwards throughout the year as the seasons here change.

Other Solar System planets tilt as well – especially Saturn

The Earth is not the only planet in the Solar System to obit the Sun on a tilt.  Mars orbits on a 25 degree tilt. Venus and Jupiter have only a small tilt of about 3 degree tilt meaning there’s almost no seasons on those planets.  Neptune is tilted at nearly 30 degree and Uranus orbits at a tilt of some 98 degrees.  This tilt is so large it’s possible the planet was impacted by another large body in the early development of Solar System.

However without careful observation it’s hard to detect these tilts.  Saturn on the other hand has a tilt of almost 27 degree and the changes it goes through during each year on Saturn are obvious from Earth through even a small telescope.

Saturn’s magnificent rings surround its equator and tilt with the planet. We see them from Earth as we orbit the Sun in line with Saturn and most other planets in he Solar System.  This means Saturn’s rings are tilted towards us at the most during it winter and summer Solstice when the planet it tilted the most.

Saturn takes roughly 29 years to orbit the Sun, Saturn’s rings are at their widest and most spectacular roughly every 15 and a half years.  The last one occurred in 2009.

Image of Saturn during Solstice by Damien Peach

At the time of writing, June 2022, Saturn is heading towards its Equinox. This will occur in 2025. It will be orbiting upright and not on a tilt. From our point of view, Saturn’s rings will almost disappear! Over the follow years Saturn’s ring will again tilt towards us again as the gas giant planet continues its orbit around the Sun and be at their best in 2040.

Science during Saturn’s Equinox

While Saturn’s rings are hard to see during Equinox, their edge on the Sun position offers some unique opportunities for scientists explore them further.

These are images taken by the Cassini–Huygens mission from above Satern looking down on the rings. The small features have been lit from the Sun, in much the same way we see long shadows during early morning on dusk.

Left: small-scale dynamical features known as ‘propellers’ are disturbances in the rings created by moonlets. The propeller seen here in Saturn’s A Ring was imaged on 21 February 2017 (image scale is 207 m/pixel). The width of the gap is estimated to be about 2 km, with a tiny central moonlet thought to be driving the feature.

Middle: the exquisite details of vertical structures in the rings was revealed at equinox. They are driven by gravitational perturbations of nearby moons, with the peaks rising to about 2.5 km above the plane of the rings. The image shows a 1200 km long section imaged on 26 July 2009, and the image scale is 2 km/pixel.

Left: ‘spokes’, features that rotate along with the rings like the spokes in a wheel, were seen to appear and disappear with the seasons. This image shows the radial markings as the planet approached equinox in August 2009 (image scale is 30 km/pixel).

 

 

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