Juno Celebrates a Year at Jupiter

Home , Gravity Science (Juno), JunoCam, UVS (Juno)

PUBLISHED: 4 JULY 2017 | VOLUME: 1 | ARTICLE NUMBER: 0178 mission control Juno celebrates a year at Jupiter NASA’s Juno mission to Jupiter has just returned its early science results after spending a year orbiting the ‘King of the Solar System’. Principal Investigator Scott Bolton summarizes what we have learnt.

aunched in August 2011, NASA’s closer to the planet than any previous Jupiter Energetic Juno spacecraft arrived at its target, Particle Detector measurements and revealed higher-order LJupiter, on 4 July 2016. Its unique polar Instrument (JEDI) terms of the magnetic field that drop orbit provided our first up-close view of Gravity off rapidly with distance. The magnetic Science the largest planet in the Solar System. Microwave field is both stronger and more spatially Although only at the early stages of Juno’s JunoCam and Radiometer complex1,5 than previously modelled. (MWR) original mapping strategy, the mission has Ultraviolet Imaging How this insight contributes to our Spectrometer (UVS) Plasma Waves already provided us with a view of Jupiter (hidden) Instrument understanding of the planetary dynamo that shatters decades-old concepts of how will depend on observations from future giant planets work. Juno’s closest approach perijove passes. Jovian Auroral Magnetometers (MAG) varies from orbit to orbit, but stays within Distributions and Advanced Stellar A primary objective of the Juno mission 3,500–8,000 km of the cloud tops. With an Experiment (JADE) Compass (ASC) is to combine remote sensing of Jupiter’s orbital period of approximately 53 days, aurora with the firstin situ measurements the spacecraft screams past the planet, of the particles and fields over the polar passing over both poles in only 2 hours. An artist’s impression of the Juno spacecraft regions. Early results show that Juno The highly elliptical trajectory carries with its science instruments. Jovian Infrared passed through the high-latitude regions Juno away from Jupiter’s harsh radiation, Auroral Mapper (JIRAM) is not shown. where particles were beamed along the reaching a distance of nearly 8 million Image: NASA/JPL-Caltech. magnetic field6, but, surprisingly, did not kilometres (113 Jovian radii) before detect the field perturbations associated returning. The result is a series of 32 close with the expected field-aligned electrical flybys, providing essentially a complete abundance changes significantly at depths currents. The lack of evidence of strongly map of Jupiter by arranging each close pass corresponding to 30 bars or more, with accelerated downward electron beams is at a different Jovian longitude. a deep band feature of high abundance puzzling; it appears that Jupiter’s auroral Juno (pictured) is equipped to penetrating down over 350 km, just processes are not as similar to Earth’s as investigate Jupiter’s interior and polar north of the Jovian equator. Jupiter’s deep previously thought. Rather, upward loss magnetosphere. To avoid contamination atmosphere clearly revealed an unexpected cones, suggestive of diffusive aurora, from the spacecraft field, Juno’s discovery1,2 : beneath the cloud tops, giant are reported7. magnetometers (MAG) are located at the planets are not uniform in composition Juno’s survey of Jovian radio emissions end of one of the solar arrays. They are or temperature. This new paradigm sheds provides the first opportunity to pass co-located with a set of non-magnetic doubt on the concept of using in situ directly through the radio-source regions star cameras (ASC) that are capable of probes to determine the global abundances at Jupiter8. Kilometric, hectometric and detecting any movement of the arrays. of elements in the giant planets — decametric emissions were all observed. The Gravity Science experiment uses the necessary for constraining planetary Juno seemingly passed through as many high-gain antenna at both X-band and formation theories. Juno’s discoveries as six sources of auroral radio emissions

Ka-band frequencies that eliminate effects will compel a revised strategy if we are to during the close pass over Jupiter’s poles. ❐ from interplanetary and Jovian plasma obtain this information with confidence in environments. The six-channel Microwave the future. SCOTT J. BOLTON is at the Southwest Radiometer (MWR) probes Jupiter’s deep Juno’s initial observations of Jupiter’s Research Institute, 6220 Culebra Road, atmosphere beneath the visible cloud gravitational and magnetic fields have San Antonio, Texas 78238, USA. tops. Juno’s polar orbit is ideal to explore yielded significant insights as well. The e-mail: [email protected] Jupiter’s magnetosphere and aurora, early gravity field measurements — characterizing the charged particles and obtained by tracking the Doppler shift of References plasma waves responsible for stimulating Juno’s radio signal acquired by the NASA 1. Bolton, S. J. et al. Science 356, 821–825 (2017). the aurora (with Waves, JADE and JEDI) Deep Space Network — hint that the core 2. Li, C. et al. Geophys. Res. Lett. http://dx.doi. org/10.1002/2017GL073159 (2017). while simultaneously imaging both in the structure is not what was expected. Instead 3. Kaspi, Y. et al. Geophys. Res. Lett. http://dx.doi. ultraviolet (UVS) and infrared (JIRAM). of seeing evidence of a compact core, or org/10.1002/2017GL073629 (2017). Extensive ground-based observations no core, the data appear more consistent 4. Wahl, S. M. et al. Geophys. Res. Lett. http://dx.doi. org/10.1002/2017GL073160 (2017). complement the measurements from with a large, possibly diffuse or fuzzy core. 5. Moore, K. M. et al. Geophys. Res. Lett. http://dx.doi. the spacecraft. There are indications of deep internal org/10.1002/2017GL073133 (2017). Juno’s first views beneath the clouds motions, raising new possibilities for how 6. Connerney, J. E. P. et al. Science 356, 826–832 (2017). show a seemingly complex world with giant planets form and evolve3,4. 7. Allegrini, F. et al. Geophys. Res. Lett. http://dx.doi. org/10.1002/2017GL073180 (2017). atmospheric composition that varies The magnetic field observations from 8. Kurth, W. S. et al. Geophys. Res. Lett. http://dx.doi. with depth and latitude. The ammonia Juno’s first perijove were obtained much org/10.1002/2017GL072889 (2017).