Aug 20, 2015: Cassini's Final Close Views of Dione - A pockmarked, icy landscape looms beneath NASA's Cassini spacecraft in new images of Saturn's moon Dione taken during the mission's last close approach to the small, icy world. (Image Advisory can be found here.)
July 6, 2011
Sacre bleu! Our great good fortune to be in orbit around Saturn has won us an unprecedented view of a dramatic and startling meteorological phenomenon: the rapid and violent onset of a massive, hissing, lightning-producing storm in the northern Saturnian hemisphere that has raged for the last seven months, with no end in sight.
The first indications that a major storm had erupted were intense electrostatic emissions, the usual accompaniment to lightning flashes, detected by Cassini's Radio and Plasma Wave experiment on December 5, 2010. Also that day, by coincidence, our cameras sighted a bright white cloud at approximately 35 degrees north latitude. A few days later, after notification by Cassini scientists, amateur observers all around the globe got into the act and helped document the development of what became a gargantuan storm that, by late January 2011, had wrapped completely around the planet because of the pronounced wind shear at the storm's latitude. And Cassini was there to record this major Saturnian event in detail ... a space exploration first!
That such a phenomenon would occur at 35 degrees northern latitude during northern spring is puzzling and remarkable. Since we arrived at Saturn seven years ago, and while the sun shone on the southern hemisphere during southern summer, Cassini observed only 10 lightning storms and they all erupted in a region around 35 degrees southern latitude that we imaging scientists dubbed `Storm Alley' for obvious reasons. (On Earth and on Jupiter, lightning storms are far more frequent and smaller than anything we've yet observed on Saturn.) The first such storm in this region, initially heard in July 2004 and finally seen in September the same year, was the famed Dragon Storm.
And now that the seasons have advanced and the sun is currently shining in the north, the region of major storm activity and intense electrostatic discharges is mirrored in the north at the same distance from the equator. Why this symmetry should exist we haven't a clue at the moment. But you can be sure that our atmospheric scientists are going to be noodling this one out for quite some time!
And they will also be puzzling over the enormous level of gorgeous detail seen in our false-color images, from the structure and stratigraphy of the clouds in the head of the storm to the appearance of a string of several bluish ovals seen in the portion of the storm to the south that has wrapped around the planet and overtaken the storm's head.
One might think that after years in orbit around Saturn, we are now accustomed to great big happenings and fantastic spectacles. But far from it. It is the shock of the unexpected, the intense mind-grabbing, eye-popping, soul-stirring thrill of seeing the unseen that gets us every time. And, as all of you well know, that is what this glorious, history-making exploration of Saturn and its magnificent realm is all about.
Carolyn Porco Cassini Imaging Team Leader Director, CICLOPS Boulder, CO