Saturn's hexagon
Saturn's hexagon is a persistent approximately hexagonal cloud pattern around the north pole of the planet Saturn, located at about 78°N.[1][2][3] The sides of the hexagon are about 14,500 km (9,000 mi) long,[4][5][6][7] which is about 2,000 km (1,200 mi) longer than the diameter of Earth.[8] The hexagon may be a bit more than 29,000 km (18,000 mi) wide,[9] may be 300 km (190 mi) high, and may be a jet stream made of atmospheric gases moving at 320 km/h (200 mph).[4][5][10] It rotates with a period of 10h 39m 24s, the same period as Saturn's radio emissions from its interior.[11] The hexagon does not shift in longitude like other clouds in the visible atmosphere.[12]
Saturn's hexagon was discovered during the
Discovery
Saturn's polar hexagon was discovered by David Godfrey in 1987[14] from piecing together fly-by views from the 1981 Voyager mission,[15][16] and was revisited in 2006 by the Cassini mission.[17]
Cassini was able to take only
After its discovery, and after it came back into the sunlight, amateur astronomers managed to get images showing the hexagon from Earth, even with modest-sized telescopes.[20][self-published source?]
Color
Between 2012 and 2016, the hexagon changed from a mostly blue color to more of a golden color.
Explanations for hexagon shape
One hypothesis, developed at Oxford University, is that the hexagon forms where there is a steep
Other researchers claim that lab studies exhibit vortex streets, a series of spiraling vortices not observed in Saturn's hexagon. Simulations show that a shallow, slow, localized meandering jetstream in the same direction as Saturn's prevailing clouds are able to match the observed behaviors of Saturn's hexagon with the same boundary stability.[24]
Developing barotropic instability of Saturn's North Polar hexagonal circumpolar jet (Jet) plus North Polar vortex (NPV) system produces a long-living structure akin to the observed hexagon, which is not the case of the Jet-only system, which was studied in this context in a number of papers in literature. The NPV, thus, plays a decisive dynamical role to stabilize hexagon jets. The influence of moist convection, which was recently suggested to be at the origin of Saturn's NPV system in the literature, is investigated in the framework of the barotropic rotating shallow water model and does not alter the conclusions.[25]
A 2020 mathematical study at the California Institute of Technology, Andy Ingersoll laboratory found that a stable geometric arrangement of the polygons can occur on any planet when a storm is surrounded by a ring of winds turning in the opposite direction to the storms itself, called an anticyclonic ring, or anticyclonic shielding.[26][27] Such shielding creates a vorticity gradient in the background of a neighbor cyclone, causing mutual rejection between the cyclones (similar to the effect of beta-drift). Although apparently shielded, the polar cyclone on Saturn cannot hold a polygonal pattern of circumpolar cyclones such as Jupiter's due to the bigger size and slower wind speed of Saturn's polar cyclone, so the side-adjacent vortices and deep barotropic instability (Cassini's wind speed measurements preclude shallower barotropic instability at least at the time of the Cassini encounter), or possibly baroclinic instabilities remain as the most viable explanations for Saturn's sustained hexagon.[28]
See also
References
- .
- S2CID 45574015.
- New York Times. Retrieved August 6, 2014.
- ^ S2CID 130345071.
- ^ PMID 30177694.
- ^ Imster, Eleanor (12 August 2014). "The Eye of Saturn". Earth & Sky. Retrieved 13 September 2018.
- ^ Williams, Matt (10 May 2017). "Saturn's Hexagon Will be the Star of the Cassini Finale". Universe Today. Retrieved 13 September 2018.
- ^ "New images show Saturn's weird hexagon cloud". NBC News. December 12, 2009. Retrieved December 5, 2013.
- oblate spheroid, the radius of such an hexagon may be a bit greater than its side length (ie, 14,500 km), making the width (diameter) a bit greater than 29,000 km.
- ^ Wall, Mike (4 September 2018). "Bizarre Hexagon on Saturn May Be 180 Miles Tall". Space.com. Retrieved 4 September 2018.
- S2CID 19965347.
- .
- Bibcode:2002DPS....34.1307S. Archived from the originalon September 5, 2008.
- ISSN 0019-1035.
- S2CID 26837742.
- PMID 32513703.
- ^ "Saturn's Strange Hexagon". NASA. March 27, 2007. Retrieved May 1, 2013.
- ^ "Saturn's Mysterious Hexagon Emerges From Winter Darkness". NASA. December 9, 2009. Archived from the original on April 24, 2016. Retrieved May 1, 2013.
- ^ Staff (December 4, 2013). "NASA's Cassini Spacecraft Obtains Best Views of Saturn Hexagon". Jet Propulsion Laboratory (NASA). Retrieved December 5, 2013.
- ^ Fletcher, Leigh (January 31, 2013). "Saturn's Hexagon Viewed from the Ground". Planetary Wanderings.
- ^ a b Staff (October 21, 2016). "Changing Colors in Saturn's North". NASA. Retrieved December 26, 2016.
- ^ .
- ^ a b Lakdawalla, Emily (May 4, 2010). "Saturn's hexagon recreated in the laboratory". Planetary.org. Retrieved 2014-02-07.
- .
- S2CID 59473881.
- ^ "Scientists solve mystery of Jupiter's polygon storms". Sky News. Retrieved 2020-09-25.
- PMID 32900956.
- S2CID 236096014.
External links
- Cassini Video of Saturn's Hexagon on YouTube
- Saturn Revolution 175, Cassini images, November 27, 2012
- Saturn’s Strange Hexagon – In Living Color! – Universe Today
- Edge of the hexagon from Planetary Photojournal
- Saturn's Hexagon Comes to Light, APOD January 22, 2012
- In the Center of Saturn's North Polar Vortex, Astronomy Picture of the Day – December 4, 2012
- Video of hexagon's rotation from NASA
- NASA's Cassini Spacecraft Obtains Best Views of Saturn Hexagon (December 4, 2013)
- Animated vortex view (TPS)
- Hexagon image
- Saturn's Hexagon Replicated In Laboratory, video
- Hexagon Changes Color (October 21, 2016)