A weird hexagon-shaped vortex that formed above Saturn's north pole is much taller than scientists previously thought, a new study using data gathered by an instrument aboard the Cassini spacecraft has revealed.
The bizarre 20,000-mile wide jet stream of air moves at a speed of about 200 mph and surrounds a smaller circular vortex. Scientists regarded the hexagon as a lower-atmospheric phenomenon that occurs within the clouds of the planet's troposphere.
It turns out, however, that the unusual vortex is taller than scientists had previously thought. Analysis of data gathered by the Cassini mission revealed that the structure actually stretches about 180 miles above the clouds up into the stratosphere layer of the ringed planet's atmosphere.
The hexagon at the north pole has been around for at least 38 years. It was spotted by NASA's Voyager 1 and Voyager 2 when they flew by Saturn in the 1980s.
Scientists have been studying the sharp-cornered feature for decades, but they only started to get a more detailed look at the structure in 2004 when the Cassini spacecraft began its orbit around the ringed planet.
It was winter in Saturn's northern hemisphere at the start of the mission, so Cassini's observations were initially restricted to the troposphere for a decade. The extremely low temperatures in the stratosphere compromised measurements made by the spacecraft's Composite Infrared Spectrometer (CIRS) instrument. The CIRS could not make observations up in the northern stratosphere, where the temperature was 20 degrees Celsius too cold to gather reliable measurements.
Cassini had to wait for summer for more reliable observations. Since one Saturnian year is equivalent to about 30 years on Earth, winters are long and the high-altitude regions of the planet's north pole were left unexplored for many years.
Saturn began to warm in 2009 when the planet started to emerge from its northern winter. Researchers were finally able to use the CIRS to study the northern stratosphere for the first time in 2014.
The warmer temperature has allowed Leigh Fletcher, from the University of Leicester in the U.K., and colleagues to study the polar vortex in infrared light. Analysis of the new observations revealed more details about the hexagon high above the clouds.
"As the polar vortex became more and more visible, we noticed it had hexagonal edges, and realised that we were seeing the pre-existing hexagon at much higher altitudes than previously thought," Fletcher said in a statement from ESA.
Fletcher and colleagues published their findings in the journal Nature Communications on September 3.