Measurement of Jupiter’s asymmetric gravity field

Abstract

The gravity harmonics of a fluid, rotating planet can be decomposed into static components arising from solid-body rotation and dynamic components arising from flows. In the absence of internal dynamics, the gravity field is axially and hemispherically symmetric and is dominated by even zonal gravity harmonics J that are approximately proportional to q, where q is the ratio between centrifugal acceleration and gravity at the planet's equator. Any asymmetry in the gravity field is attributed to differential rotation and deep atmospheric flows. The odd harmonics, J, J, J, J and higher, are a measure of the depth of the winds in the different zones of the atmosphere. Here we report measurements of Jupiter's gravity harmonics (both even and odd) through precise Doppler tracking of the Juno spacecraft in its polar orbit around Jupiter. We find a north-south asymmetry, which is a signature of atmospheric and interior flows. Analysis of the harmonics, described in two accompanying papers, provides the vertical profile of the winds and precise constraints for the depth of Jupiter's dynamical atmosphere.

Dynamo Action in the Steeply Decaying Conductivity Region of Jupiter‐Like Dynamo Models

“…Since the wind dynamics is tied to density variations, the gravity signal can help to constrain their depth. A recent analysis by Kaspi et al (), based on the equatorially antisymmetric gravity moments J 3 to J 9 measured by the Juno mission (Iess et al, ), concludes that the wind speed must be significantly reduced at about 3,000 km depth, which corresponds to about 0.96 r J . This conclusion is supported by new interior models based on Juno data (Guillot et al, ).…”

Jovian Auroral Ion Precipitation: X‐Ray Production From Oxygen and Sulfur Precipitation

“…Since arrival, Juno has arguably uncovered more questions than it has answered, although its discoveries have been numerous. In its time spent at Jupiter, Juno has put greater constraints on the gravitational field (Folkner et al, ; Iess et al, ), measured a magnetic field with substantial complexity (Connerney et al, , ; Moore et al, ), and returned images of Jupiter detailing the intricate features seen in the cloud tops (Orton et al, ; Sánchez‐Lavega et al, ). Most importantly to this paper, Juno has been able to measure heavy ions above the polar caps that indicate they are precipitating into the top of the atmosphere (Clark, Mauk, Haggerty, et al, ; Clark, Mauk, Paranicas, et al, ; Haggerty et al, ), potentially producing Jupiter's dynamic X‐ray aurorae.…”

A deeper look at Jupiter

“…T he evolution of cooperation hinges on the benefits of cooperation being shared among those who cooperate 1 . On page 242, Santos et al 2 investigate the evolution of cooperation using computer-based modelling analyses, and they identify a rule for moral judgements that provides an especially powerful system to drive cooperation.…”

“…In particular, is the planet's interior as dynamic as its surface? In three papers [1][2][3] in this issue, scientists have used small signatures in the gravitational field of Jupiter to address these questions and to potentially revolutionize our understanding of the internal dynamics of such gas-giant planets.…”

“…Iess et al 1 (page 220) tracked the acceleration of the Juno spacecraft in its close elliptical orbit around Jupiter by monitoring the change in frequency, known as the Doppler shift, of radio waves sent back to Earth. Tiny anomalies in these signals revealed details about the mass distribution of Jupiter.…”