April 15, 2024

I, Science

The science magazine of Imperial College

On the 15 September 2017, after almost 20 years of unprecedented insight in to Saturn and its satellites, NASA's unmanned spacecraft, Cassini, will take it's final flight, crashing in to the surface of Saturn. In this new series, we celebrate Cassini and some of its achievements.

On June 2013 and April 2017, NASA spacecraft, Cassini, took two photos of the mysterious hexagonal atmospheric formation at Saturn’s North Pole. Similar in appearance to the patterns one might observe through a kaleidoscope, the two photos demonstrated that this formation had clearly changed in appearance between the two periods the photos were captured.

How and why did this formation drastically change in colour? What had happened to Saturn’s North Pole in the four years between the two pictures had been taken? And will it change again?

gif of Saturn's north pole blue on left, purple on right

Colour change in Saturn’s North Pole. JPL, NASA.

As can be seen from these original pictures of Saturn’s North Pole, the colour was mainly blue in 2013. Then, by April 2017, the colour had changed to a yellow shade, with darker tones, but retaining the central blue disc. Similar pictures were also taken by Cassini in 2012 and 2016, in which the same phenomenon can also be observed.

Regarding the change in colour, scientists have put forward two possible reasons. Firstly, scientists claimed that this variation may be related to seasonal change on Saturn. According to NASA, it takes Saturn around 27 years to complete an orbit around the sun. The first time Cassini arrived at Saturn, it was experiencing a long winter. During this period, there were only a small number of aerosols, which are clouds of tiny particles, inside the hexagon. After crossing through the equinox, Saturn was exposed to greater levels of sunshine. As a result, more aerosols were produced by increasing the photochemical reaction. The haze, formed by an increase in the concentration of  aerosols in the hexagon, may have then led to the difference in appearance over the 4-year period. From this explanation, we therefore infer that the colour change phenomenon is not unique, but is in fact seasonal.

Another possibility is a large movement of air over Saturn’s North Pole. Scientists believe that the regular changes of solar heating may exert an influence on the winds in this region, which may also be partly responsible for the colour change.

However, the exact reason of the colour change is hard to assess. We may, however, be able to access more answers in the coming few weeks when Cassini moves closer to Saturn and sends back higher resolution data.

Whilst the Cassini mission may now be coming to an end, it has provided us with incredible insights in to Saturn and other objects in our solar system. It’s now time for us to look forward to new and exciting missions that promise to unlock more secrets of our universe.

Yiming Chen, Junhua Ma, Chenyu Zhang – Centre for Academic English, Imperial College London

Banner image: Saturn’s Hexagon, JPL, NASA