{"id":234,"date":"2017-05-26T08:19:44","date_gmt":"2017-05-26T08:19:44","guid":{"rendered":"https:\/\/staffblogs.le.ac.uk\/leicester-to-jupiter\/?p=234"},"modified":"2025-02-26T13:28:19","modified_gmt":"2025-02-26T13:28:19","slug":"junos-first-observations-of-jupiter-are-revealing-a-giant-world-that-is-defying-our-expectations","status":"publish","type":"post","link":"https:\/\/staffblogs.le.ac.uk\/leicester-to-jupiter\/2017\/05\/26\/junos-first-observations-of-jupiter-are-revealing-a-giant-world-that-is-defying-our-expectations\/","title":{"rendered":"Juno\u2019s first observations of Jupiter are revealing a giant world that is defying our expectations"},"content":{"rendered":"

[This is an extended version of an article that first appeared on the Conversation<\/a>]<\/em><\/p>\n

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Last month, planetary scientists from around the world met at the European Geophysical Union (EGU) conference in Vienna, and were treated to the first glimpse of long-awaited results from NASA\u2019s Juno spacecraft. The atmosphere was one of surprise, excitement, and elation that this mission was starting to deliver new insights into the Solar System\u2019s largest planet, ten months after its nerve-wracking arrival. But the main message was one of confusion: Juno is forcing scientists to re-evaluate their understanding of Jupiter, throwing out old theories, and making way for something new. It certainly makes this an exciting time to be a Jupiter scientist!<\/p>\n

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Jupiter’s south pole from Juno. \u00a0Credits: NASA\/JPL-Caltech\/SwRI\/MSSS\/Betsy Asher Hall\/Gervasio Robles<\/p><\/div>\n

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These first findings from Juno are published today in Science, and are supported by a whole host of new Jupiter papers published in a special collection of Geophysical Research Letters. Juno arrived at Jupiter in July 2016<\/a>, and began a long, looping first orbit that took it far out from the planet before zipping back in for its first scientific close-up on August 27th. These close encounters are called \u2018perijoves\u2019, and last a short few hours as the solar-powered spacecraft flies from the north pole to the south pole, zipping within 4000 km of the equatorial clouds and beneath Jupiter\u2019s most intense and damaging radiation belts. The challenge presented by Jupiter is extreme \u2013 Juno detected impacts and the resulting clouds of plasma from fast dust grains hitting the spacecraft, making the solar panels into enormous dust detectors. Despite this, it seems that the radiation damage so far is less than expected, meaning that Juno\u2019s instruments might survive much longer than we\u2019d hoped. Today, despite initial problems<\/a> with Juno\u2019s engine and spacecraft software, the mission has settled into a regular pattern of close perijoves every 53.5 days \u2013 the sixth such flyby happened on May 19th, the seventh will be on July 11th. But the new findings reported today are from that very first glimpse on August 27th, and everywhere we look, we find a planet that is defying our expectations.<\/p>\n

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Chaos at the poles<\/strong><\/p>\n

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Credit: NASA\/SWRI\/MSSS\/Gerald Eichst\u00e4dt\/Se\u00e1n Doran<\/a><\/p><\/div>\n

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If you\u2019ve ever been lucky enough to see Jupiter through a telescope, you\u2019ll be familiar with the organised, striped structure of whiter zones and dark brown belts. These colourful bands are bordered by powerful jet streams whizzing east and west around the planet. On Saturn, the Cassini spacecraft has shown that this organised, banded structure persists all the way to the poles, with one of the most poleward jets showing a strange hexagonal wave pattern encircling a hurricane-like polar cyclone. But Jupiter\u2019s poles are different. Gone is the organised structure of jets. There\u2019s no evidence for hexagons or any other polygonal waves. And instead of one cyclone, we see multitudes, surrounded by a whole host of chaotic and turbulent features. With the ability to see structures as small as 50km, Juno\u2019s camera has revealed numerous bright cyclones of a variety of appearances \u2013 some appear sharp, some have clear spirals, some are fluffy and diffuse, and the largest is some 1400 km across. That\u2019s about the same distance between London and Majorca. These bright storms sit on top of dark background clouds, giving the appearance of \u2018floating\u2019 on a dark sea, and it\u2019ll be some time until we understand the lifetimes and motions of these storms. But it is clear that our Earth-based view of striped Jupiter is biased, and that chaos reigns at Jupiter\u2019s poles.<\/p>\n

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One particular feature stands out in those images \u2013 a polar cloud so high that is it catching the dying rays of sunlight at dusk. Standing some 60 km above the surrounding clouds (that\u2019s the distance from London to Reading, for context), the icy particles comprising this cloud are still reflecting sunlight despite being on Jupiter\u2019s nightside. This points to the strong forces at work shaping Jupiter\u2019s atmosphere, and hints at three-dimensional structure that is hard to see from Earth.<\/p>\n

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Mysteries in the deep<\/strong><\/p>\n

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Initial results from Juno’s microwave radiometer, showing a plume of ammonia over the equator: Credits: NASA\/JPL-Caltech\/SwRI<\/p><\/div>\n

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One of Juno\u2019s key strengths is the ability to peer through the overlying shroud of ammonia clouds, to probe the deep atmosphere down to ~350 km or so for the first time. We\u2019ve never been able to see this deep before, so even the first observations from Juno\u2019s microwave instrument provide a treasure trove of new insights. These show that the banded structure that we see at the cloud-tops is really just the tip of the iceberg \u2013 Jupiter exhibits banding all the way down to ~350km, much deeper than what we\u2019ve generally thought of as Jupiter\u2019s \u2018weather layer\u2019 in the upper few tens of kilometres. What\u2019s more, that structure isn\u2019t the same all the way down \u2013 it varies with depth, indicating a large, complex circulation pattern.<\/p>\n

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Another surprise came when scientists tried to replicate the brightness they observed in the microwave \u2013 these observations reveal the distribution of ammonia gas, one of Jupiter\u2019s key cloud-forming species, and which was expected to be well mixed (i.e., drenched) below the topmost clouds. That idea has been turned on its head \u2013 the ammonia concentration is much less than expected. Intriguingly, much of the ammonia is concentrated into an equatorial plume, rising from the depths of Jupiter to the cloud-tops due to some powerful upwelling force. We\u2019ve known that ammonia is enhanced at Jupiter\u2019s equator for some time (we can measure this from Earth), but we never knew how deep this column went. It\u2019s important to remember that this is only one location on Jupiter, and that Earth-based infrared observations suggest that the plume may not be this strong elsewhere around Jupiter\u2019s equator, but could be \u2018patchy\u2019. Only with more perijove passes will we begin to understand the strange dynamics of Jupiter\u2019s tropics.<\/p>\n

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Exploring the Gravity and Magnetic Fields<\/strong><\/p>\n

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The surprises didn\u2019t stop here. Juno can probe even deeper into the planet by monitoring small tweaks to the spacecraft\u2019s orbit by the gravity field of Jupiter\u2019s interior. Ultimately, these will be used to assess whether Jupiter possesses a well-defined core, but that cannot be done from a single perijove pass \u2013 at the moment, the measurements are inconsistent with any previous model, and possibly hint at a \u2018fluffy\u2019 core dispersed out to half of Jupiter\u2019s radius, rather than being a well-defined core. Jupiter\u2019s interior appears to be anything but uniform. We have to remember that scientists have spent years developing models of the interior of Jupiter based on sparse data taken from great distances \u2013 Juno is now testing these models to the extreme because it is flying so close, sampling the gravity field in a region that we\u2019ve never been able to access before.<\/p>\n

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