NASA | JPL-Caltech | Cassini | 2015 Sep 02
[img3="The planet Saturn, viewed by NASA's Cassini spacecraft during its 2009 equinox. Data on how the rings cooled during this time provide insights about the nature of the ring particles. (Credit: NASA/JPL/SSI)"]http://www.jpl.nasa.gov/images/cassini/ ... 667-16.jpg[/img3][hr][/hr]When the sun set on Saturn's rings in August 2009, scientists on NASA's Cassini mission were watching closely. It was the equinox -- one of two times in the Saturnian year when the sun illuminates the planet's enormous ring system edge-on. The event provided an extraordinary opportunity for the orbiting Cassini spacecraft to observe short-lived changes in the rings that reveal details about their nature.
Like Earth, Saturn is tilted on its axis. Over the course of its 29-year-long orbit, the sun's rays move from north to south over the planet and its rings, and back again. The changing sunlight causes the temperature of the rings -- which are made of trillions of icy particles -- to vary from season to season. During equinox, which lasted only a few days, unusual shadows and wavy structures appeared and, as they sat in twilight for this brief period, the rings began to cool.
In a recent study published in the journal Icarus, a team of Cassini scientists reported that one section of the rings appears to have been running a slight fever during equinox. The higher-than-expected temperature provided a unique window into the interior structure of ring particles not usually available to scientists. ...
Incomplete cooling down of Saturn’s A ring at solar equinox: Implication
for seasonal thermal inertia and internal structure of ring particles - Ryuji Morishima et al
- Icarus (online 23 June 2015) DOI: 10.1016/j.icarus.2015.06.025
arXiv.org > astro-ph > arXiv:1508.07375 > 28 Aug 2015