Earlier in 2013, NASA’s Cassini orbiter
captured a stunning photo (above) of a mysterious storm on Saturn. This storm,
known only as the hexagon, is roughly 20,000 miles (32,000
km) from edge to edge — more than twice the width of the Earth, or around the
same size as its interstellar anticyclonic buddy, Jupiter’s Great Red Spot.
Until now, we’ve known very little about the storm, other than it’s been stuck
to Saturn’s north pole for at least 30 years (and probably much longer). Now,
however, thanks to a high-resolution video of the hexagon captured by Cassini,
we have a much better idea of the science behind this massive and enigmatic
hurricane.
The video, embedded above as an animated GIF,
consists of eight frames captured over a 10-hour period in December 2012 (for
whatever reason — resource constraints, transmission speed, prioritization —
NASA has only just finished processing the images). Each frame is actually
fashioned out of 16 individual images — four shots, each captured with four
different spectral filters. The filters are the important bit, as they allow
Cassini to see a wide range of colors, from ultraviolet, to visible, to
infrared light. The resulting image is actually false-color, to accentuate
various features of the hurricane — further down the story you can see a
true-color image of what you would see if you were actually orbiting Saturn.
In the video, the eye of the hurricane (the middle)
is situated over Saturn’s north pole. The eye is about 50 times larger than the
average hurricane eye here on Earth. The pinky-red blobs are separate vortices,
which rotate independently of the hexagon and main hurricane (which always spin
counterclockwise). The oval in the bottom right corner of the hexagon is about
2,200 miles across — or about twice the size of the largest hurricane to ever
sweep our own planet. The hexagon is really damn big. The hexagon
weather system has existed for at least 30 years (it was first observed by the
Voyager mission in 1981), but it has probably been there for
centuries. Just like Jupiter’s Great Red Spot, we’re not entirely sure how or
why Saturn’s hexagon continues to persist, when Earth-borne hurricanes
(fortunately) die out fairly rapidly.
The video also clearly shows the hexagon’s
“wall,” which is actually a barrier formed by the polar jet stream — a fast,
narrow jet of air that forms due to the planet’s various regions of low and
high pressure in the atmosphere.
Incidentally, all of these views are only
possible because spring has finally arrived on Saturn. While Cassini has been
in orbit around Saturn since 2004, there has only really been enough illumination
for imaging of the north pole since 2009 — and Cassini only moved itself into a
polar orbit in 2012. As Saturn approaches its summer solstice in 2017, NASA
should be able to get some even better imagery of the hexagon.
