Explore the vast range of titles available.

The determination of Jupiter’s odd gravitational harmonics by the Juno spacecraft reveals that the observed jet streams extend to about three thousand kilometres below the cloud tops. 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 J 3 , J 5 , J 7 and J 9 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. The depth to which Jupiter’s observed east–west jet streams extend has been a long-standing question 1 , 2 . Resolving this puzzle has been a primary goal for the Juno spacecraft 3 , 4 , which has been in orbit around the gas giant since July 2016. Juno’s gravitational measurements have revealed that Jupiter’s gravitational field is north–south asymmetric 5 , which is a signature of the planet’s atmospheric and interior flows 6 . Here we report that the measured odd gravitational harmonics J 3 , J 5 , J 7 and J 9 indicate that the observed jet streams, as they appear at the cloud level, extend down to depths of thousands of kilometres beneath the cloud level, probably to the region of magnetic dissipation at a depth of about 3,000 kilometres 7 , 8 . By inverting the measured gravity values into a wind field 9 , we calculate the most likely vertical profile of the deep atmospheric and interior flow, and the latitudinal dependence of its depth. Furthermore, the even gravity harmonics J 8 and J 10 resulting from this flow profile also match the measurements, when taking into account the contribution of the interior structure 10 . These results indicate that the mass of the dynamical atmosphere is about one per cent of Jupiter’s total mass.

The determination of Jupiter’s even gravitational moments by the Juno spacecraft reveals that more than three thousand kilometres below the cloud tops, differential rotation is suppressed and the gas giant’s interior rotates as a solid body. 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 J 3 , J 5 , J 7 and J 9 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. Jupiter’s atmosphere is rotating differentially, with zones and belts rotating at speeds that differ by up to 100 metres per second. Whether this is also true of the gas giant’s interior has been unknown 1 , 2 , limiting our ability to probe the structure and composition of the planet 3 , 4 . The discovery by the Juno spacecraft that Jupiter’s gravity field is north–south asymmetric 5 and the determination of its non-zero odd gravitational harmonics J 3 , J 5 , J 7 and J 9 demonstrates that the observed zonal cloud flow must persist to a depth of about 3,000 kilometres from the cloud tops 6 . Here we report an analysis of Jupiter’s even gravitational harmonics J 4 , J 6 , J 8 and J 10 as observed by Juno 5 and compared to the predictions of interior models. We find that the deep interior of the planet rotates nearly as a rigid body, with differential rotation decreasing by at least an order of magnitude compared to the atmosphere. Moreover, we find that the atmospheric zonal flow extends to more than 2,000 kilometres and to less than 3,500 kilometres, making it fully consistent with the constraints obtained independently from the odd gravitational harmonics. This depth corresponds to the point at which the electric conductivity becomes large and magnetic drag should suppress differential rotation 7 . Given that electric conductivity is dependent on planetary mass, we expect the outer, differentially rotating region to be at least three times deeper in Saturn and to be shallower in massive giant planets and brown dwarfs.

Precise Doppler tracking of the Juno spacecraft in its polar orbit around Jupiter is used to determine the planet’s gravity harmonics, showing north–south asymmetry caused by atmospheric and interior flows. 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 J 3 , J 5 , J 7 and J 9 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. 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 2 n that are approximately proportional to q n , where q is the ratio between centrifugal acceleration and gravity at the planet’s equator 1 . Any asymmetry in the gravity field is attributed to differential rotation and deep atmospheric flows. The odd harmonics, J 3 , J 5 , J 7 , J 9 and higher, are a measure of the depth of the winds in the different zones of the atmosphere 2 , 3 . 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 4 , 5 , provides the vertical profile of the winds and precise constraints for the depth of Jupiter’s dynamical atmosphere.

The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions (“boomlets”). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a resolution of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05 %. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers—multiple rotations about the spacecraft x and z  axes—to characterize spacecraft fields and/or instrument offsets in flight.

Jupiter’s upper atmosphere is considerably hotter than expected from the amount of sunlight that it receives 1 – 3 . Processes that couple the magnetosphere to the atmosphere give rise to intense auroral emissions and enormous deposition of energy in the magnetic polar regions, so it has been presumed that redistribution of this energy could heat the rest of the planet 4 – 6 . Instead, most thermospheric global circulation models demonstrate that auroral energy is trapped at high latitudes by the strong winds on this rapidly rotating planet 3 , 5 , 7 – 10 . Consequently, other possible heat sources have continued to be studied, such as heating by gravity waves and acoustic waves emanating from the lower atmosphere 2 , 11 – 13 . Each mechanism would imprint a unique signature on the global Jovian temperature gradients, thus revealing the dominant heat source, but a lack of planet-wide, high-resolution data has meant that these gradients have not been determined. Here we report infrared spectroscopy of Jupiter with a spatial resolution of 2 degrees in longitude and latitude, extending from pole to equator. We find that temperatures decrease steadily from the auroral polar regions to the equator. Furthermore, during a period of enhanced activity possibly driven by a solar wind compression, a high-temperature planetary-scale structure was observed that may be propagating from the aurora. These observations indicate that Jupiter’s upper atmosphere is predominantly heated by the redistribution of auroral energy. High-resolution observations confirm that Jupiter’s global upper atmosphere is heated by transport of energy from the polar aurora.

Jupiter’s magnetosphere is often presented as a template for fast-rotating magnetospheres. Distinct from Earth-like, solar wind-driven magnetospheres, it contains an extended magnetodisk encircling the planet. Although the magnetodisk has been studied since the 1970s, its stability and non-equilibrium dynamics remain poorly understood. Here, we present observational evidence for the role of plasma pressure anisotropy-driven instabilities, including the mirror, cyclotron, and firehose instabilities, in these processes. Data from the Juno mission, supported by theoretical analysis, indicate that these instabilities determine the marginal equilibrium states towards which the magnetodisk plasma tends to evolve after being disturbed. Detailed analyses particularly highlight the role of firehose instability, which acts as a key mechanism to dissipate free energy produced by Fermi acceleration during magnetic dipolarizations. Our observations thus suggest that pressure anisotropy-driven instabilities govern the non-equilibrium evolution of the Jovian magnetodisk following disturbances, offering insights into the physics of Jupiter’s magnetodisk and magnetosphere. Jupiter’s magnetodisk mediates mass, momentum, and energy exchange between Jupiter’s atmosphere, ionosphere, magnetosphere, and moon tori. Here, the authors show that pressure anisotropy-driven instabilities regulate its nonequilibrium dynamics.

In July 2016, NASA’s Juno mission becomes the first spacecraft to enter polar orbit of Jupiter and venture deep into unexplored polar territories of the magnetosphere. Focusing on these polar regions, we review current understanding of the structure and dynamics of the magnetosphere and summarize the outstanding issues. The Juno mission profile involves (a) a several-week approach from the dawn side of Jupiter’s magnetosphere, with an orbit-insertion maneuver on July 6, 2016; (b) a 107-day capture orbit, also on the dawn flank; and (c) a series of thirty 11-day science orbits with the spacecraft flying over Jupiter’s poles and ducking under the radiation belts. We show how Juno’s view of the magnetosphere evolves over the year of science orbits. The Juno spacecraft carries a range of instruments that take particles and fields measurements, remote sensing observations of auroral emissions at UV, visible, IR and radio wavelengths, and detect microwave emission from Jupiter’s radiation belts. We summarize how these Juno measurements address issues of auroral processes, microphysical plasma physics, ionosphere-magnetosphere and satellite-magnetosphere coupling, sources and sinks of plasma, the radiation belts, and the dynamics of the outer magnetosphere. To reach Jupiter, the Juno spacecraft passed close to the Earth on October 9, 2013, gaining the necessary energy to get to Jupiter. The Earth flyby provided an opportunity to test Juno ’s instrumentation as well as take scientific data in the terrestrial magnetosphere, in conjunction with ground-based and Earth-orbiting assets.

Jupiter exhibits peculiar multiwavelength auroral emissions resulting from the electromagnetic interactions of Io, Europa, and Ganymede with the magnetospheric plasma flow. Characterizing the faint auroral footprint of the fourth Galilean moon, Callisto, has always been challenging because of its expected weakness and its proximity to Jupiter’s bright main aurora. Here, we report on unusual magnetospheric conditions that led to an equatorward shift of Jupiter’s main auroral oval unveiling the auroral footprints of the four Galilean moons in a single observation. Remote observations by the Juno spacecraft reveal a double-spot structure, characteristic of the footprints of the other three moons, with a maximum ultraviolet brightness of 137 ± 15 kR. Concurrent observations within Callisto’s flux tube reveal field-aligned electrons with a characteristic energy of 10 keV, depositing an energy flux of 55 mW.m -2 in Jupiter’s atmosphere. The electron properties are consistent with the triggering of radio emissions with intensities lower than 5 × 10 -18 W.m -2 .Hz -1 . The detection of the auroral footprint of Jupiter’s moon Callisto is challenging, but a shift in Jupiter’s bright main auroral oval could provide an opportunity for potential detections. Here, the authors show observation of the ultraviolet footprint of Callisto using Juno spacecraft data, benefiting from such opportunity.

The Juno Magnetic Field investigation (MAG) characterizes Jupiter’s planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ∼20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of ’s three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno’s massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 × 10 6  nT per axis) with a resolution of ∼0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of view and also provides a continuous record of radiation exposure. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors, and residual spacecraft fields and/or sensor offsets are monitored in flight taking advantage of Juno’s spin (nominally 2 rpm) to separate environmental fields from those that rotate with the spacecraft.

On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter, passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter's poles show a chaotic scene, unlike Saturn's poles. Microwave sounding reveals weather features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow low-latitude plume resembling a deeper, wider version of Earth's Hadley cell. Near-infrared mapping reveals the relative humidity within prominent downwelling regions. Juno's measured gravity field differs substantially from the last available estimate and is one order of magnitude more precise. This has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter's core. The observed magnetic field exhibits smaller spatial variations than expected, indicative of a rich harmonic content.