A Complex System
Jupiter is a gas giant with a big atmosphere. And this atmosphere is mostly hydrogen (the most abundant element in the Universe) at 90%, with the remaining 10% being helium (although there’s a small amount of other molecules like ammonia, sulphur, methane and water vapour in there).
However, all this gas doesn’t make one big uniform soup: it makes layers, varying by temperature and pressure, from the troposphere at 50km above the ‘surface’ at -160ºC to -100ºC (creating the characteristic bands of cloud visible from Earth); to the stratosphere at up to 320km high with temperatures similar to the troposphere; to the thermosphere (where the aurora occur) at up to 1,000km high and with hot temperatures of 725ºC.
Some may have noticed that the values for the heights are relatively low (in fact, similar to that of Earth’s) and yet Jupiter is a lot bigger than Earth. The reason is that the lower boundary of an atmosphere is defined by having the same atmospheric surface pressure as on Earth (1 bar) [1]. The ‘surface’ in fact extends much much further, but is made of liquified and solidified substances like hydrogen (usually in gaseous form on Earth) because of the intense pressures down there [2].
As well being made of complex layers, the atmosphere is also made of beautifully defined bands. They could be made up of gaseous plumes containing sulphur and phosphorus, moved by the Coriolis effect (the spin of a planet deflecting the direction of wind and water, creating things such as the Gulf Stream on Earth [3]), stronger than on Earth since 1 Jovian day is just 10 hours. This makes extremely fast jet streams separated into light and dark belts [2]; 9 to be exact [4]. And, with little to cause friction because of the absence of a solid surface like on Earth, the winds can get even faster, with some reaching 539km/h at the equator [2].
However, these facts and figures on wind speed could only be calculated because of the clouds in Jupiter’s troposphere, leaving out the stratosphere, until now. The comet Shoemaker-Levy 9 smashed into Jupiter back in 1994 created new molecules which have been carried along by the Jovian winds ever since, and recently studied using the Atacama Large Millimetre/Submillimetre Array (ALMA) at the European Southern Observatory (ESO) in Chile. A team of French astronomers discovered the presence existence of strong jet streams close to the aurorae near Jupiter’s poles, with truly astronomical sizes of 900km in height, 4 times the diameter of Earth and 1,450km/h in wind speed: more than double the maximum in the seemingly measly maximum in the troposphere [15].
Animation of stratospheric winds at the Jovian south pole. Credit: ESO/L. Calçada & NASA/JPL-Caltech/SwRI/MSSS, CC BY 4.0
The Great Red Spot
These winds can then create storms, like on Earth, but far far worse, creating a tapestry of colours across the whole of the Jovian atmosphere. There is, however, one that trumps them all: the Great Red Spot.
It’s a cyclone-like storm known as an anticyclone (swirling around a high pressure core, as opposed to the low pressure cores found on Earth [7]) that started at least 300 years ago (when it was first observed), whipping up speeds of up to 680km/h (with the threshold for a cyclone being only 119km/h and the fastest surface wind speed on Earth being only 407.5km/h [5]) in an area which could fit 2-3 scale pictures of Earth. “What’s the secret to a long life?” you may ask. Well, on Earth cyclones are generally dissipated by the lack of fuel (water) and friction caused by hitting land. However, this doesn’t happen on Jupiter with no land to cut the fuel of anticyclones [6].
As well as this, another reason has recently been investigated by researchers, in the form of cyclonic cannibalism: the spot sucks up smaller ones around it, visibly making it smaller by chipping away at it, but inflicting the spot with only superficial wounds: much of the 200km deep storm is in fact unaffected. Moreover, the anticyclone rotated quicker after taking a bite from its neighbours, suggesting it was absorbing their energy and maintaining it (even though the anticyclone has been mysteriously shrinking for at least 150 years) [8][9][10].
The Great Red Spot imaged by Voyager 1. Credit: NASA
Lights Show
But the Jovian atmosphere isn’t all about wind: with the title of the largest continuous structure in the Solar System (apart from the Sun’s vast heliosphere) and at 20,000 times the strength of Earth’s, Jupiter’s magnetosphere stems from its metallic liquid hydrogen outer core that creates a magnetic field when flowing. However, as well as its size, this field is quite different from Earth’s, with two south poles (one near the actual south pole and one near the equator, called the ‘great blue spot’, blue since negative charge is generally denoted by blue) and a confused north pole, where positively charged magnetic field lines don’t have fixed negative counterparts (apart from one section right at the magnetic north pole) [11][12][13].
However, there is one beautiful similarity with Earth in the form of the Jovian aurorae: spectacular iridescent blue rings of fire cover the north and south poles, made of unimaginably high energy electrons, up to 400,000 electron volts (10 to 30 times more energetic than terrestrial aurorae). Moreover, source is different, with Earth’s coming from the solar wind’s interaction with its magnetosphere (magnetic field), whilst Jupiter’s comes from particles escaping its volcanic moon Io which then ionise like solar wind particles on Earth.
Recently, another difference between terrestrial and Jovian aurorae was found in the form of a contrast between daytime and nighttime aurorae. Illuminated to by NASA’s Juno spacecraft, the daytime aurorae give out at least 10 times as much energy as its nighttime counterpart: something that couldn’t be seen from Earth since the nightside is never visible [14].
Ultra Violet pole aurorae seen by Juno of Jupiter compared with Earth's.
Credit: NASA/JPL Caltech/SwRI/UVS/STScI/MODIS/WIC/IMAGE/ULiège
Jupiter still holds many secrets up its sleeve, with much more to learn about its atmosphere and magnetosphere, let alone other equally interesting features it has such as its thin rings and moons, so we’ve got much more to look forward to in the coming years.
by George Abraham, ADAS member.
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Click here to watch a video of a simulation by ESO of the stratospheric winds at Jupiter’s poles.
Click here to watch a simulation of Jupiter’s magnetosphere, including the peculiar ‘great blue spot’.
Click here to see a video by NASA’s Juno team of Jupiter’s cloud belts sped up to show the violent weather system in action.
Click here to see the evolution of the aurorae from nighttime to daytime by NASA, JPL-Caltech, SwRI, UVS, and the University of Liège.
Click here to look at an interactive model of Jupiter using NASA’s Eyes software (online)
References
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"Great Red Spot". NASA Juno. Archived from the original on 20th March 2021.
"Jupiter's Great Red Spot may survive by gobbling up smaller storms". Space.com. Archived from the original on 20th March 2021.
"Jupiter's Great Red Spot feeds on smaller storms". Science Daily. Archived from the original on 20th March 2021.
"Jupiter's Great Red Spot is a ruthless cannibal that devours smaller storms". Live Science. Archived from the original on 20th March 2021.
"Jupiter's Magnetosphere". NASA Solar System Exploration. Archived from the original 20th March 2021.
"Jupiter's Magnetosphere". LASP. Archived from the original on 20th March 2021.
"Jupiter's Weird Magnetic Field Gets Even Weirder". Space.com. Archived from the original on 20th March 2021.
"Jupiter's Aurorae Present a Powerful Mystery". NASA. Archived from the original on 20th March 2021.
"NASA's Juno Reveals Dark Origins of One of Jupiter's Grand Light Shows". NASA JPL. Archived from the original on 20th March 2021.
"Powerful stratospheric winds measured on Jupiter for the first time". ESO. Archived from the original on 20th March 2021.
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