NASA's Cassini spacecraft has completed the first of its ring-grazing orbits and snapped stunning images of the strange hexagon-shaped jet stream at Saturn's northern pole.
With less than a year left to go in its mission, Cassini's new orbits mark the start of special maneuvers that could offer scientists fresh insight into the evolution of the planet's moons and iconic rings.
Cassini's cameras captured the latest images of the giant hexagon on Dec. 2 and 3, a few days after the spacecraft first began its new orbit on Nov. 30. Each side of that six-sided figure is about as wide as Earth. At the center, a giant storm swirls on the north pole. It's a surprising structure, surrounded by Saturn's smoother rings, and scientists have long wondered how it maintains its shape. (Saturn's larger cousin, Jupiter, has no such shape at its northern pole.)
One of the strangest things about this hexagon is the fact that it's been around for decades: It was first spotted by NASA's Voyager mission in the 1980s.
"It's still an interesting puzzle," Linda Spilker, Cassini's project scientist, told the Los Angeles Times shortly before the ring-grazing orbits began. "How could this jet stream keep this six-sided shape and rotate as a unit for such a long time?"
The maneuvers send the spacecraft above the gas giant's northern atmosphere and allow it to skim just past unexplored outer edges of the main rings, sensing dust and gas particles along the way.
The 20 ring-grazing orbits, each about seven days long, are just the preamble to Cassini's final chapter: 22 grand finale orbits, starting in April. During these passes the spacecraft will come within about 1,012 miles of the planet's cloud tops, and will also shoot through the gap between the rings and the planet, a move that will allow scientists to calculate the mass of both structures separately.
Cassini will end its mission in dramatic fashion, plunging into the planet's thick atmosphere, sending back data until the signal is finally lost.
