Measurement of Jupiter’s asymmetric gravity field

[BjarneModerator Super Nova]

Measurement of Jupiter’s asymmetric gravity field

Editorial Summary

Probing the depths of Jupiter

The Juno mission set out to probe the hidden properties of Jupiter, such as its gravitational field, the depth of its atmospheric jets and its composition beneath the clouds. A collection of papers in this week’s issue report some of the mission’s key findings. Jupiter’s gravitational field varies from pole to pole, but the cause of this asymmetry is unknown. Rotating planets that are squashed at the poles like Jupiter can have a gravity field that is characterized by a solid-body component, plus components that arise from motions in the atmosphere. Luciano Iess and colleagues use Juno’s Doppler tracking data to determine Jupiter’s gravity harmonics. They find that the north–south asymmetry arises from atmospheric and interior wind flows. To determine the depths of these flows, Yohai Kaspi and colleagues analyse the odd gravitational harmonics and find that the J3, J5, J7 and J9 harmonics are consistent with the jets extending deep into the atmosphere, perhaps as far as 3,000 kilometres. They conclude that the mass of Jupiter’s dynamical atmosphere is about one per cent of Jupiter’s total mass. The composition of Jupiter beneath its turbulent atmosphere remains a mystery. If different parts of a spinning object rotate at different rates, then the object probably has a fluid composition. Tristan Guillot and colleagues study the even gravitational harmonics and find that, below a depth of about 3,000 kilometres, Jupiter is rotating almost as a solid body. The atmospheric zonal flows extend downwards by more than 2,000 kilometres, but not beyond 3,500 kilometres, as is also the case with the jets.

Jeg har desværre kun adgang til dette sammendrag af artiklerne i Nature. Målinger af Jupiters gravitationsfelt viser, at de atmosfæriske jetstrømme strækker sig næsten ned til 3000 kilometers dybde. Jupiter roterer som et stift legeme under 3000 km.

[nightskyDeltager Neutron star]

Den bedste on-line artikel omkring alle 4 artikler i Nature jeg har kunnet finde. Ikke for teknisk, George Dvorsky har lavet denne fine artikel.
https://gizmodo.com/the-juno-spacecraft-is-revealing-some-astounding-things-1823579625

Ellers er der Juno missionens hjemmeside, hvor man deler alle Juno data med amatører som os, og vi kan give indspark til Juno teamet.

[BjarneModerator Super Nova]

Ja. Det er en fin ikke-teknisk oversigt. Kendskabet til Jupiters indre findes ved at bestemme de sfærisk harmoniske koefficienter Jn for gravitationspotentialet. De ulige koefficienter, J1,J3,j5,…, bestemmer asymmetrien mellem nord og syd omkring ækvator. De skyldes jetstrømme i atmosfæren. De lige koefficienter, J2,J4,J6,…, bestemmer den rotationssymmetriske del af massefordelingen. Man kan sammenligne de lige koefficienter med beregnede værdier for forskellige modeller for massetæthedens forløb mod centrum. Jeg ved ikke, hvor langt man er kommet på den front.

[Forfatter]

Indlæg