Jupiter, the largest planet in our solar system, has always been a source of fascination for astronomers and skywatchers alike. Its immense size and striking appearance make it a captivating subject for study. However, there is one aspect of Jupiter that has puzzled scientists for quite some time - its aureoles. These luminous rings surrounding the planet have raised intriguing questions about their origin and characteristics.
Aureoles, or diffraction coronae, are not uncommon phenomena in the atmosphere. They are typically observed around the Sun and Moon, caused by the scattering of light by dust and aerosol particles. These coronae appear as colored rings, resulting from the overlap of individual and differently sized aureoles. However, the aureoles around Jupiter present two distinct puzzles that have yet to be fully explained.
The first puzzle lies in the size of Jupiter's aureoles. Unlike the smaller aureoles observed around the Sun and Moon, Jupiter's aureoles appear to be much larger. If they are not simply the central part of a larger aureole, they must be produced by significantly larger particles. Scattering theory provides some insight into this mystery. By considering Jupiter's equatorial diameter and the image scale, scientists estimate that the scattering particles responsible for the aureoles are approximately 0.5 mm in size.
The second puzzle revolves around the vertical elongation of Jupiter's aureoles. While circular aureoles are commonly observed, the elongated shape seen around Jupiter is unusual. This non-circularity implies the presence of oriented non-spherical particles. One possibility is the presence of ice crystals in high cirrus clouds. These crystals, naturally aligned in plate and column shapes, would scatter light in a horizontally elongated manner, resulting in vertically elongated aureoles.
To further investigate these puzzles, astronomers have conducted observations under various sky conditions. Cirrus clouds, as well as altostratus and altocumulus clouds, have been present during some of these observations. However, the absence of halos associated with the scattering of light by ice crystals suggests that there may be other factors at play.
In order to unravel the Jovian puzzle, more observations are needed, along with careful documentation of sky conditions. It would be particularly interesting to capture images of aureoles simultaneously from both high and low altitude objects. By comparing the circularity of the aureoles produced by these objects, scientists may gain valuable insights into the nature of Jupiter's aureoles.
In conclusion, Jupiter's aureoles remain a captivating enigma for scientists. The larger size and vertical elongation of these luminous rings present intriguing challenges in understanding their formation. While ice crystals in high cirrus clouds offer a possible explanation, further investigations are required to fully comprehend the mysteries surrounding Jupiter's aureoles. Through continued observations and meticulous analysis, we may one day unlock the secrets of these celestial phenomena and gain a deeper understanding of the majestic planet that is Jupiter.
Jovian Puzzle ~ Tamás Ladányi (site, TWAN) imaged Jupiter with its four Galilean moons (left to right Callisto, Europa, Io and Ganymede) on Aug 23, 2010. Surrounding Jupiter is an aureole that is distinctly elongated in the vertical direction. More pictures below. All images ©Tamás Ladányi, shown with permission.
Larger aureoles occur around the Sun and Moon. Those are produced by light scattered by dust and aerosol. They can be regarded as diffraction coronae from very small particles with a wide range of sizes. The usual coloured rings are blurred away by the overlap of individual and different sized coronae.
The Jupiter aureoles present two puzzles. Firstly their size. Unless they are merely the very bright central part of a larger aureole (unlikely from their appearance and colour fringe), they must be produced by much larger bodies than their solar or lunar counterparts. We can get a rough idea of the particle size from scattering theory. Jupiter's mighty equatorial diameter of 11.2 Earths subtended 48.5 seconds of arc. That provides an image scale and gives the aureole 'diameter' of about 0.1° in the top image. The scattering particles were of the order of 0.5 mm across!
The second puzzle is the vertical elongation. Vertically elongated planet aureoles are real. They have been seen before around bright Venus by Doug Zubenel, Tamás Ladanyi and Monika Landy-Gyebnar. A non-circular aureole or corona implies oriented non-spherical particles. Pollen grains produce them as in this picture of Lunar and Venusian coronae. But pollen grains do not come in 0.5 mm sizes.
Another possibility is ice crystals in high cirrus. Plate and column crystals are naturally aligned and to light from an object low in the sky (Jupiter was only 21° high in the top image and 18° at right) would appear as horizontally elongated scattering objects. These would produce the required vertically elongated aureoles.
The sky had cirrus in the top image with perhaps some altostratus/altocumulus. However the Moon was out and we might expect crystals of that size to produce halos ~ none were seen. Cirrus was also present at right.
The lower sequence, taken over a period with different cloud crossing Jupiter, shows that the aureole presence, size and shape is cloud related.
More observations are needed with careful note of the sky conditions. It would be interesting to image aureoles near simultaneously from high and low altitude objects. Those from the high object should always be circular.
This second aureole was
imaged on August 29, 2010.
Below is a sequence of images taken on the same night showing the variation in aureole size and shape as clouds passed over.
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