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NASA’s Cassini Watches Storm Choke on Its Own Tail.
“Call it a Saturnian version of the Ouroboros, the mythical serpent that bites its own tail. In a new paper that provides the most detail yet about the life and death of a monstrous thunder-and-lightning storm on Saturn, scientists from NASA’s Cassini mission describe how the massive storm churned around the planet until it encountered its own tail and sputtered out. It is the first time scientists have observed a storm consume itself in this way anywhere in the solar system.
“This Saturn storm behaved like a terrestrial hurricane - but with a twist unique to Saturn,” said Andrew Ingersoll, a Cassini imaging team member based at the California Institute of Technology, Pasadena, who is a co-author on the new paper in the journal Icarus. “Even the giant storms at Jupiter don’t consume themselves like this, which goes to show that nature can play many awe-inspiring variations on a theme and surprise us again and again.”
Earth’s hurricanes feed off the energy of warm water and leave a cold-water wake. This storm in Saturn’s northern hemisphere also feasted off warm “air” in the gas giant’s atmosphere. The storm, first detected on Dec. 5, 2010, and tracked by Cassini’s radio and plasma wave subsystem and imaging cameras, erupted around 33 degrees north latitude. Shortly after the bright, turbulent head of the storm emerged and started moving west, it spawned a clockwise-spinning vortex that drifted much more slowly. Within months, the storm wrapped around the planet at that latitude, stretching about 190,000 miles (300,000 kilometers) in circumference, thundering and throwing lightning along the way. ”
St. Elmo’s fire
‘Everything is in flames—the sky with lightning—the water with luminous particles, and even the very masts are pointed with a blue flame…’ wrote Charles Darwin while aboard the Beagle. He was describing of a fascinating natural phenomenon that sailors have seen for thousands of years—a sudden glow atop a ship’s mast near the end of a thunderstorm, which many sailors believed to be a sign of salvation from St. Elmo. ‘St. Elmo’s Fire’ is a weather phenomenon that behaves a bit like lightning because it’s plasma—i.e. ionised air that emits a glow—and it’s similarly created in thunderstorms, when the air is electrically charged and there’s a significant charge imbalance in the air. However, lightning is a movement of electricity between clouds and ground, while St. Elmo’s Fire is a spark between the air and a charged object, such as the mast of a ship, a church steeple, or an aeroplane wing. These charged, pointed objects discharge electrical energy when the voltage in the air gets high enough, and the imbalance between the discharge and the air causes atoms of gas molecules (the nitrogen and oxygen of our atmosphere) to tear apart. Negatively-charged electrons move away from positively-charged protons, creating ionised air that emits light. Since the discharge usually lasts several minutes, it creates a constant blue glow—different gases glow different colours when they become plasmas, and nitrogen and oxygen glow blue. Interestingly, St. Elmo’s Fire behaves somewhat like a plasma globe: a pilot once reported that the phenomenon occurred on the windshield of her plane while flying through a storm cloud, and when she touched the windshield, blue plasma streaked out to meet the tips of her fingers.
