Several months passed with the grandiose completion of the Cassini mission. Worked in the Saturn system for about 13 years, the probe died in dense clouds of the gas giant. But the information collected by him continues to be analyzed and to supply new information about this wonderful world. It was these data that enabled Jan-Erik Wahlund of the Swedish Institute of Space Physics and his co-authors from Europe and the USA to discover the unexpected influence that the rings of Saturn have on its ionosphere.
Of course, there is no surface, as such, near the gas planet, and conditionally it assumes such a height, the pressure at which is equal to the pressure of the earth’s atmosphere – this is approximately 60,300 km from the center of Saturn. Its ionospherebegins another 300 km higher and stretches to 5000 km (on Earth its height is about 60 to 1000 km). This is an extremely rarefied region, most of the particles in which are ionized by the ultraviolet radiation of the Sun and cosmic rays.
In the ionosphere of Saturn, Cassini entered on April 27, 2017 and moved along it with long spirals, registering the situation with an onboard RPWS tool kit. Measuring the distribution of the density of ions and electrons, he showed that under the rings A and B (the most massive and dense ones), it varies markedly. About this Vakhlund and his colleagues tell in an article published by the journal Science . According to them, large rings can strongly shield cosmic radiation, so the plasma concentration in their shadow decreases.
At the same time, the authors note that in the shadow of massive rings, the content of ions does not fall too much. This they connect with the influence of not so large inner ring D, which is also irradiated from space. Ionized water molecules from it get into the ionosphere, maintaining a certain level of its stability even in the shadow of rings A and B. The idea of the existence of such a “rain with rings” on Saturn was first heard in the 1980s, and now finds a remarkable confirmation.