Small lightning flashes from shallow electrical storms on Jupiter

Abstract

Lightning flashes have been observed by a number of missions that visited or flew by Jupiter over the past several decades. Imagery led to a flash rate estimate of about 4 × 10−3 flashes per square kilometre per year (refs. 1,2). The spatial extent of Voyager flashes was estimated to be about 30 kilometres (half-width at half-maximum intensity, HWHM), but the camera was unlikely to have detected the dim outer edges of the flashes, given its weak response to the brightest spectral line of Jovian lightning emission, the 656.3-nanometre Hα line of atomic hydrogen1,3,4,5,6. The spatial resolution of some cameras allowed investigators to confirm 22 flashes with HWHM greater than 42 kilometres, and to estimate one with an HWHM of 37 to 45 kilometres (refs. 1,7,8,9). These flashes, with optical energies comparable to terrestrial ‘superbolts’—of (0.02–1.6) × 1010 joules—have been interpreted as tracers of moist convection originating near the 5-bar level of Jupiter’s atmosphere (assuming photon scattering from points beneath the clouds)1,2,3,7,8,10,11,12. Previous observations of lightning have been limited by camera sensitivity, distance from Jupiter and long exposures (about 680 milliseconds to 85 seconds), meaning that some measurements were probably superimposed flashes reported as one1,2,7,9,10,13. Here we report optical observations of lightning flashes by the Juno spacecraft with energies of approximately 105–108 joules, flash durations as short as 5.4 milliseconds and inter-flash separations of tens of milliseconds, with typical terrestrial energies. The flash rate is about 6.1 × 10−2 flashes per square kilometre per year, more than an order of magnitude greater than hitherto seen. Several flashes are of such small spatial extent that they must originate above the 2-bar level, where there is no liquid water14,15. This implies that multiple mechanisms for generating lightning on Jupiter need to be considered for a full understanding of the planet’s atmospheric convection and composition.

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Fig. 1: Images from Juno SRU Jovian lightning survey.
Fig. 2: Optical energies of lightning flashes observed by the Juno SRU and past broadband visible imagers.
Fig. 3: Conceptual illustration of lightning generation above and below the 3-bar level in Jupiter’s atmosphere.

Data availability

The Juno SRU data supporting the findings of this study are available within the paper and its Supplementary Information. The Juno MWR data that support the findings of this study are available from the Planetary Data System archive (https://pds.nasa.gov/index.shtml) as ‘Juno Jupiter MWR reduced data records v1.0’ (dataset JNO-J-MWR-3-RDR-V1.0). Source data are provided with this paper.

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Acknowledgements

We thank G. Berrighi and S. Becucci of the Leonardo Finmeccanica S.p.A. (formerly Selex Galileo S.p.A) Juno SRU Team for retrieval of SRU optics and CCD quantum efficiency parameters used in the study. We thank J. E. P. Connerney for comments on the manuscript. J. Arballo is thanked for rendering of figures and tables. M. Stetson is thanked for artistic rendering of Fig. 3. We thank Y. Yair for bringing the consideration of ice–ice collision charge separation to our attention. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration; at the Observatoire de la Côte d’Azur under the sponsorship of the Centre National d’Etudes Spatiales; and at the Southwest Research Institute under contract with NASA.

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Authors

Contributions

H.N.B. led the acquisition and interpretation of SRU lightning data, wrote the manuscript with input from co-authors, and performed the SRU camera response computations. S.J.B. and T.G. contributed to the interpretation of shallow lightning atmospheric dynamics. M.J.B. contributed to the acquisition of SRU lighting data and performed the SRU observation geometry computations. J.W.A. contributed to SRU camera response computations, flash identification and mapping, and analysis of camera vignetting characteristics. A.G. computed the SRU survey area. S.K.A. and P.G.S. contributed expertise in Jovian atmospheric dynamics and composition. J.I.L. assisted with the ammonia-water thermodynamics, the lightning generation discussion and construction of Fig. 3. Y.S.A. contributed to the lightning generation discussion. A.P.I. contributed to the SRU data interpretation. S.T.B. analysed the MWR data to extract and filter MWR lighting observations. S.M.L. is the lead co-investigator of the MWR.

Corresponding author

Correspondence to Heidi N. Becker.

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The authors declare no competing interests.

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Peer review information Nature thanks Karen Aplin and Yoav Yair for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Properties of the SRU optical system.

a, Energy distribution of the camera’s PSF, shown for an image of a point source; each square represents a pixel. The scale bar indicates the percentage of the total signal. b, The combined throughput of the SRU optical system, QT (Q, CCD quantum efficiency; T, optics transmission), as a function of wavelength. Source data

Extended Data Fig. 2 Overlap of the beam of MWR antenna 1 and the SRU field of view during lightning detections.

Shown are circular 17-degree MWR antenna 1 beam contours (green and red circles) for MWR lightning detections acquired within 30 s of an example SRU lightning flash detection (inside the yellow circle). Red MWR beam contours correspond to footprint locations during the 1-s SRU image exposure (underlying black-and-white image: start time 2018-144T04:57:50.263).

Extended Data Fig. 3 Estimated spatial extent of flashes.

af, Deconvolved lightning flash signatures for six flashes (named at top centre of each panel) where a half-width at half-maximum flash intensity (HWHM) could be estimated. Colour scales show pixel signal levels in analogue-to-digital units (background signal was subtracted before deconvolution). Estimates represent the maximum possible value. The white circle indicates the maximum pixel area that can be assumed fully illuminated by flash photons given spatial resolution limitations. The estimated HWHM was generally less than the size of one pixel width. The red line in e indicates the diagonal distance of the estimated HWHM.

Extended Data Fig. 4 Morphology of signatures from optical and ionizing radiation sources.

Main panel, SRU image 12, perijove 13. Insets show magnified views of example signatures from an optical source (lightning, circled in yellow), and an ionizing radiation source (penetrating particle, circled in blue). Dimmer pixels are blue and brighter pixels are yellow. Signatures from optical sources have a more symmetric appearance, which follows the camera PSF.

Extended Data Fig. 5 SRU pixel coordinate system conversion.

Illustration of the transformation from a pixel array (numbered 1 to 512; left) to the 0 to 511 pixel coordinate system of the SRU instrument frame (right). Open and filled circles indicate the pixel locations following the parity flip (indicated by the grey arrow) of this transformation.

Extended Data Fig. 6 Reconstruction of the true profile of a flash.

Shown is an example reconstruction for SRU lightning flash 11_12_1. Colour scales show pixel signal levels in analogue-to-digital units (background signal was subtracted before deconvolution). a, Observed flash signature. b, Deconvolution solution, which is the estimated flash shape on Jupiter. The white circle indicates the maximum pixel area that can be assumed to be fully illuminated by flash photons given spatial resolution limitations. 1–2 pixels are estimated to be fully illuminated in this example. c, Result following convolution of the estimated shape with the camera PSF. d, Residual signal (a minus c).

Extended Data Fig. 7 Maximum durations of flashes observed with no TDI.

a, Deconvolved SRU flash 14_12_15. Colour scales show pixel signal levels in analogue-to-digital units, and background signal was subtracted before deconvolution. The white circles indicate a possible flash area for a steady-state source at the start (lower) and end (upper) of the exposure. The spacecraft spin direction and the direction in which the scene will smear are indicated with white arrows. The maximum possible duration is 8.1 ms (about three rows of smear along-column). b, Same as a but for SRU flash 14_12_17; maximum flash duration is 10.8 to 16.2 ms. c, Same as a but for SRU flash 17_13_4 (‘string of pearls’ flash 1); maximum duration is 5.4 ms.

Extended Data Table 1 Lightning flashes observed by the Juno SRU
Extended Data Table 2 Supplementary parameters used in flash mapping and energy calculations

Supplementary information

Supplementary Data 1

Record of MWR Antenna 1 lightning detections where the Antenna 1 beam covered regions which included SRU lightning flash locations.

Supplementary Data 2

Raw pixel data for the nine Juno SRU lightning survey images. Excel file format. Each image is contained within a separate worksheet of the Excel file. Worksheets are labelled with the perijove number and image number.

Supplementary Data 3

Excel file containing a mapping of hot pixel signal rates (DN s-1) in the SRU pixel array format. The map represents known hot pixel rates at the time of perijove 17 data analysis.

Supplementary Data 4

Raw pixel data from SRU star images collected near Juno’s apojove without motion compensation, wherein stars appear as along-column streaks. Normalized signal levels, relative to the peak signal along each streak, are also shown for each row of data. Excel file format.

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Becker, H.N., Alexander, J.W., Atreya, S.K. et al. Small lightning flashes from shallow electrical storms on Jupiter. Nature 584, 55–58 (2020). https://doi.org/10.1038/s41586-020-2532-1

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