Remote observations of the solar photospheric light scattered by electrons (the K-corona) and dust (the F-corona or zodiacal light) have been made from the ground during eclipses1 and from space at distances as small as 0.3 astronomical units2,3,4,5 to the Sun. Previous observations6,7,8 of dust scattering have not confirmed the existence of the theoretically predicted dust-free zone near the Sun9,10,11. The transient nature of the corona has been well characterized for large events, but questions still remain (for example, about the initiation of the corona12 and the production of solar energetic particles13) and for small events even its structure is uncertain14. Here we report imaging of the solar corona15 during the first two perihelion passes (0.16–0.25 astronomical units) of the Parker Solar Probe spacecraft13, each lasting ten days. The view from these distances is qualitatively similar to the historical views from ground and space, but there are some notable differences. At short elongations, we observe a decrease in the intensity of the F-coronal intensity, which is suggestive of the long-sought dust free zone9,10,11. We also resolve the fine-scale plasma structure of very small eruptions, which are frequently ejected from the Sun. These take two forms: the frequently observed magnetic flux ropes12,16 and the predicted, but not yet observed, magnetic islands17,18 arising from the tearing-mode instability in the current sheet. Our observations of the coronal streamer evolution confirm the large-scale topology of the solar corona, but also reveal that, as recently predicted19, streamers are composed of yet smaller substreamers channelling continual density fluctuations at all visible scales.
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The code used in the WISPR pipeline and analysis is available as part of the SolarSoft library (https://sohowww.nascom.nasa.gov/data/software.html).
The PSP Science Data Management Plan (https://sppgway.jhuapl.edu/docs/data/7434-9101_Rev_A.pdf) requires that all science data from the first two orbits with calibrations must be released to the public within six months of downlink of the first orbit. In addition to this data type, we will be releasing background subtracted images, videos, and lists of events. Furthermore, the data must be delivered to the appropriate NASA/GSFC facility and integrated into the Virtual Observatory. Thus, the data is available from 12 November 2019. A complete archive is maintained at NRL (https://wispr.nrl.navy.mil) and will be publicly available at least during the full mission lifetime. A copy of the WISPR data will be located at the NASA/GSFC SDAC facility (https://umbra.nascom.nasa.gov) and integrated into the Virtual Solar Observatory.
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We acknowledge the efforts of the PSP operations team in operating the mission and the WISPR team in developing and operating the instrument. We are grateful to R. Pinto (IRAP) for providing the Multi-VP magnetohydrodynamics simulations of the background solar wind used in Extended Data Fig. 3. R.A.H, A.V., R.C.C., C.E.DF., B.G., J.R.H., P.H., A.K.H., C.M.K., P.C.L., J.L., M.L., N.E.R., D.G.S., G.S. and A.F.T. acknowledge support from the NASA Parker Solar Probe Program Office. N.M.V. is supported through the NASA Heliophysics Internal Scientist Funding Model. A.P.R., A.K. and N.P. acknowledge financial support from the ERC for the project SLOW_SOURCE - DLV-819189. P.L.L. acknowledges financial support from Centre National d’Etudes Spatiales. P.R. acknowledges support by the BELSPO /PRODEX. V.B. acknowledges the support of the Coronagraphic German and US Solar Probe Plus Survey (CGAUSS) project for WISPR by the German Aerospace Center (DLR) under grant 50OL1901 as a national contribution to the Parker Solar Probe mission.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Peer review information Nature thanks Manuela Temmer and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
Extended Data Fig. 1 Comparison of observations and synthetic observations from magnetohydrodynamics model.
a, An image from the inner WISPR telescope taken on 3 November 2018 at 06:55:41 ut. The field of view (of both panels) is 40°× 40° with the Sun 13.5° to the left. Two distinct sets of bright streamer rays are marked by red arrows. They are separated by a darker region marked by a blue arrow. The technique employed to remove the background F-corona in the WISPR image has artificially enhanced this dark region. The streamer rays located northwards of the dark region (top red arrow) are brighter than the rays situated southwards of the dark region (bottom red arrow). b, A synthetic white-light image produced from three-dimensional simulations of the solar wind by the MULTI-VP magnetohydrodynamics code using a Wilcox Solar Observatory photospheric magnetogram33. The three-dimensional density cubes produced by running the MULTI-VP code were processed by a white-light rendering code computing the brightness of the corona in the WISPR field of view from the heliocentric position of Parker Solar Probe. The MULTI-VP numerical model and the procedure to produce white-light images have been detailed33. The star field from the new Hipparchus astrometric catalogue34 was added to the simulated image in b for comparison with the WISPR image in a.
Extended Data Fig. 2 Latitude versus time maps—observations and modelling.
HEEQ, Heliocentric Earth Equator. a, A representation of WISPR inner telescope images in the form of a latitude versus time map. This map provides a summary of the temporal and spatial variability of coronal rays observed during the first encounter. We note that such fine structure along the streamer belt has been observed before19,28. We identify in these maps the main streamer rays already seen in Extended Data Fig. 1 (the same blue and red arrows are shown here). During the period of super and corotation (5 to 9 November 2018), bright coronal rays drift in latitude away from the equator (green arrows). This is also visible in Supplementary Video 2. b, An equivalent map to a obtained from the WISPR synthetic images based on the MULTI-VP three-dimensional density cubes shown in Extended Data Fig. 1b. These medium-resolution simulations reproduce the time-varying aspect of the main streamer including their fading during perihelion (5 to 7 November). c, MULTI-VP high-resolution simulation results for the period 5 to 9 November 2018 based on 2-degree resolution magnetograms produced by the Air Force Data Assimilative Photospheric Flux (ADAPT) model35. The colour table has been saturated in these maps to enhance the features. The solar wind simulations reveal the finer striated structure of the corona and the coronal rays migrating poleward as observed by WISPR (green arrows). A search in the simulation data cubes reveals that these faint rays are separate from the brighter streamer rays. They form in the simulation as a result of considerable variability in the properties of the magnetic fields along which the slow solar wind forms. Since the prescribed coronal heating is scaled to the magnetic field properties this drives different mass flux along different flux tubes. We interpret the coronal rays marked by the top red arrows as resulting from the main streamer and the rays situated southwards (bottom red arrow) as resulting of a pseudo-streamer.
Extended Data Fig. 3 Modelling of a CME as a 3D flux rope.
a, An image from the inner WISPR telescope taken on 1 November 2018 at 19:30:50 ut during the passage of a pristine CME. Clear substructures are discernible in the WISPR image. The field of view is 40° × 40° with the Sun 13.5° to the left. A bright ring at the outer contour/boundary of the CME is indicated by a blue arrow. A striking feature of this CME event is the presence of a dark circular core located at the centre of the CME event and indicated by a red arrow. b, The same image as in a but with the results of a three-dimensional flux rope fit superimposed. This figure proposes an interpretation for the different features observed by WISPR based on our current understanding of the appearance of CMEs imaged in white light. The magnetic field lines (computed from solutions of the Grad–Shafranov equation) of the CME are traced inside this flux rope. The bright ring (blue arrow) corresponds to plasma located on the boundary of the flux rope where the poloidal magnetic field lines of the CME are adjacent to the ambient solar wind plasma. The dark core (red arrow) marks the location where strong toroidal (axial) magnetic fields dominate the plasma locally. Detailed modelling of the event will be presented in a future dedicated publication. We acknowledge the use of the Wilcox Solar Magnetograms used in this paper, obtained from the website at http://wso.stanford.edu.
Video of the combined WISPR telescopes for the first PSP encounter period. The encounter 1 observations from 1–10 November 2018 encompass the period when PSP is within 0.25 AU from the Sun. The cadence of the video is at the cadence of the outer telescope which is longer than that of the inner telescope. The cadence varies throughout the encounter due to the number of images per day that were taken. The background, consisting mostly of the F-corona, has been removed. The grid lines are in the HPLN-ARC coordinate system. The radial range of the video extends from 13.5o to 108o.
Video of the WISPR-I telescope for the second PSP encounter period. The encounter observations encompass the period when PSP is within 0.25 AU from the Sun. The background, consisting mostly of the F-corona, has been removed. The cadence varies throughout the encounter due to the number of images per day that were taken. The grid lines are in the HPLN-ARC coordinate system. The radial range of the video extends from 13.5o to 108o from the Sun.
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Howard, R.A., Vourlidas, A., Bothmer, V. et al. Near-Sun observations of an F-corona decrease and K-corona fine structure. Nature 576, 232–236 (2019). https://doi.org/10.1038/s41586-019-1807-x
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