What is NASA planning for the Cassini spacecraft towards the end of its activity
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Flash of light
In an infrared animation film produced on the basis of photographs of a large storm that occurred between January 2011 and March 2012 in the Northern Hemisphere, a very large flash of light is seen. When clouds erupt in a storm in the turbulent troposphere, heat waves travel hundreds of kilometers upwards and deposit their energy there in the configuration of two light beacons of hot air in the stratosphere. These beacons moved around Saturn in a westerly direction. The larger one moved faster and surrounded the smaller one until they merged for a short period of time into gigantic dimensions, larger than the red spot of Jupiter. This vortex was only visible in infrared and circled Saturn for 120 days. It was estimated that it would disappear by the end of 2013 (1).
A huge storm
The monitoring of this storm is done using the Xsini spacecraft and telescopes from Earth. Due to its size, the storm received the name great spring time storm. Tracing its development in December 2010 from the moment cloud swirling began deep in the atmosphere to hundreds of kilometers above the clouds in the stratosphere, the two pockets of warm air mentioned earlier - the beacons - later merged into a vortex that has been moving around the Northern Hemisphere since mid-2011. It was estimated that the storm's waves played an important role in moving the energy throughout the atmosphere. The temperature measured in the vortex was 221 degrees Kelvin more than the surrounding temperature of 70-80 degrees Kelvin, and its length at its peak was 62,000 km, about 1/4 of the circumference of Saturn in the middle latitudes. The storm observed at that time in the troposphere in visible light has almost completely subsided. From July 2011 the vortex slowly began to shrink and cool down. It was estimated that it would disappear within a few years. It was estimated that the weather in the lower part of the atmosphere has a great influence on the upper layers, hundreds of kilometers upwards as happens in the Earth's atmosphere (2).
The storm cycle
Once in one Saturnian year (30 Earth years) a massive storm occurs that affects the atmosphere on a global scale. These storms are known as great white spots. The first storm was observed in 1876 and the sixth in 2010. The storm started as a small, bright white cloud in the mid-latitudes of the Northern Hemisphere. It grew rapidly and remained active for more than 7 months. During this period, white clouds mixed with each other until a vortex ring was obtained that had an area of thousands of millions of square kilometers. The wind speed reached 500 km/h. Computer mathematical models showed that the focus of this storm is deep in the atmosphere, 300 km above the clouds that are visible in visible light. The storm transports very large amounts of water vapor-moist gas to the highest places in the atmosphere, forming clouds visible in visible light, and large amounts of energy are released. This energy comes into violent contact with the dominant winds of Saturn and creates storms with a speed of 500 km/h. Despite the strength of the storm, it cannot overcome winds that blow regularly in the same direction, similar to storms on Earth, and yet the contact is violent (3).
It turned out that Saturn can bring up different materials from a depth of more than 160 km from the atmosphere. The storm on Saturn acts like Earth's smaller convection currents. In places where air and water vapor are pushed into the upper layers of the atmosphere and manifest in huge surges of thunderstorms. These storms raise the particles of the clouds similar to volcanoes that raise materials from the depths and they are visible outside the atmosphere(4).
With its eruption, the storm grew rapidly and reached a width of 15,000 km in visible light. Its dimensions were so enormous that even amateur astronomers could observe it. in their telescopes. The storm looked like a large white spot dancing along the face of Saturn. The most important findings from all the information gathered from the Cassini and terrestrial observations show that the particles at the top of this storm are made of three types of materials, water ice, ammonia ice and another material. It could be ammonium hydrosulfide. The observations are consistent with the differentiation of different clouds of different types located next to each other. The researchers hypothesize that there are three layers of clouds in Saturn's atmosphere, water clouds at the bottom, ammonium sulfide clouds in the middle and ammonia clouds at the top, just below the haze of the upper edge of the troposphere made of an unknown substance that mixes everything below. The presence of water ice supports the hypothesis that super storms are driven by the condensation of water, 200 km below the visible cloud layer. This water rises up by strong convection currents that form at the bottom of the atmosphere. The water vapor condenses and freezes as it rises. As they rise over time, they become covered with volatile substances such as ammonium hydrosulfide and ammonia as the temperature drops (5).
Towards the end of the Cassini's mission
The plan they are thinking about for Cassini's operation in 2016 is to raise it above the North Pole outside the F ring, sample the plume of water from Enceladus' geysers, and then it will skip over the rings, enter an orbit between Saturn and its innermost ring, and make 22 orbits around Saturn until the end of its operation (6).
Sources
1. PIA16190 : Infrared hotspots in a monster Saturn storm
http://photohournal.jpl.nasa.gov/PIA16190
2. "Saturn giant storm reveals the planet's churning atmosphere" 26.10.2012
http://www.spacedaily.com/reports/Saturn_Giant_Storm_Reveals_The_Planet_ Churning_ Atmosphere_999.html
3. "Mystery of the gigantic storm on Saturn" 24.6.2013
http://www.sciencedaily.com/releases/2013/06/130634075753.htm
4. "Massive storm in Saturn throws water ice high in atmosphere" 3.9.2013
http://www.spacedaily.com/reports/Massive_Storm_In_Saturn_Throws_Water_Ice _High_ In _Atmosphere_999.html
5. "Massive storm pulls water ammonia ices from Saturn's depths" 13.9.2013
http://www.spacedaily.com/reports/Massive_Storm_Pulls_Water_Ammonia_Ices _From _Saturn_depths_999.html
6. "Cassini names final mission phase its ground finale" 30.6.2014
http://saturn.jpl.nasa.gov/news/cassinifeatures20140630
