Saturn's famous hexagon, a structure on the planet's north pole has changed its color from blue to gold over the last four years. The cause is still unknown, and researchers are working to figure it out.
The hexagon, a six-sided jet stream, is about 32 000 km (20 000 miles) wide, and about 100 km (60 miles) deep, immersed in the Saturn's dense atmosphere.
Research, conducted by NASA's Voyager and Cassini spacecraft, shows the structure rotates at its center at almost the same rate the planet rotates on its axis. A jet stream of air, swirling along the hexagon's rim, is moving eastward at 321 km/h (200 mph). Due to its size and movement, it's likely produced by a giant hurricane at the center of the Saturn's north pole. The storm was likely around for decades, and perhaps even centuries, according to estimates.
Although the scientists have managed to explain what the structure is, they're still quite puzzled about how it got there, and have come up with numerous possible explanations.
"Scientists have bandied about a number of explanations for the hexagon’s origin. For instance, water swirling inside a bucket can generate whirlpools possessing holes with geometric shapes. However, there is, of course, no giant bucket on Saturn holding this gargantuan hexagon," said Charles Q. Choi from Space.com.
These two natural color images from NASA's Cassini spacecraft show the changing appearance of Saturn's north polar region between 2012 and 2016. Image credit: NASA/JPL-Caltech/Space Science Institute/Hampton University
Another puzzle to solve is the apparent change in hexagon's color, as the Cassini spacecraft reported two different colors in the period between November 2012 and September 2016.
According to NASA's explanation, the change may be due to a change in Saturn's seasons. Its year is as long as 29 Earth's years, so the planet switches the seasons every seven years. A change from a bluish to a more golden hue could be caused by an increased production of photochemical hazes in the atmosphere as the north pole approaches summer solstice in May 2017.
Other effects, for examples changes in atmospheric circulation, may also have some impact, as the seasonally shifting patterns of solar heating probably influence the winds in the polar regions.
Video credit: NASA/JPL-Caltech/SSI/Hampton University/University of Arizona
"Inside the hexagon, there are fewer large haze particles and a concentration of small haze particles, while outside the hexagon, the opposite is true," Kunio Sayanagi, a Cassini imaging team associate at Hampton University.
"The hexagonal jet stream is acting like a barrier, which results in something like Earth's Antarctic ozone hole."
In the period between November 1995 and August 2009, in the time of a polar winter, Saturn's north polar atmosphere became clear of aerosols produced by photochemical reactions, and the hexagon was of a clear blue color. Over the last three years, aerosols were produced inside the hexagon, and around the north pole, which resulted in hazy and golden appearance of the polar atmosphere.
However, the theory, for now, remains only an educated guess, until more evidence is gathered.
Featured image credit: Natural color image from NASA's Cassini spacecraft showing the appearance of Saturn's north polar region in September 2016. Image credit: NASA/JPL-Caltech/Space Science Institute/Hampton University