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First Observations of Anomalous Cosmic Rays in to 36 Solar Radii

Rankin, J. S. and McComas, D. J. and Leske, R. A. and Christian, E. R. and Cohen, C. M. S. and Cummings, A. C. and Joyce, C. J. and Labrador, A. W. and Mewaldt, R. A. and Posner, A. and Schwadron, N. A. and Strauss, R. D. and Stone, E. C. and Wiedenbeck, M. E. (2021) First Observations of Anomalous Cosmic Rays in to 36 Solar Radii. Astrophysical Journal, 912 (2). Art. No. 139. ISSN 0004-637X. doi:10.3847/1538-4357/abec7e.

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NASA's Parker Solar Probe mission continues to travel closer to the Sun than any prior human-made object, with an expected closest approach of <10 solar radii (<0.046 au) by 2024. On board, the Integrated Science Investigation of the Sun instrument suite makes unprecedented in situ measurements of energetic particles in the near-Sun environment. The current low level of solar activity offers a prime opportunity to measure cosmic rays closer to the Sun than ever before. We present the first observations of anomalous cosmic rays in to 36 solar radii (0.166 au), focusing specifically on helium. Our results indicate a strong radial intensity gradient of ~25 ± 5%/au over energies of ~4 to ~45 MeV/nuc. These values are larger than prior observations, further out in the heliosphere, and come at a unique time in our understanding and modeling of particle transport and acceleration, particularly as both Voyagers have crossed the heliopause and IBEX has accumulated a full solar cycle of observations. Thus, continued measurements of cosmic rays by Parker Solar Probe will play a critical role in linking past observations with our present knowledge and significantly advancing our understanding of cosmic ray transport in the heliosphere.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemData
https://spdf.gsfc.nasa.govRelated ItemData
Rankin, J. S.0000-0002-8111-1444
McComas, D. J.0000-0001-6160-1158
Leske, R. A.0000-0002-0156-2414
Christian, E. R.0000-0003-2134-3937
Cohen, C. M. S.0000-0002-0978-8127
Cummings, A. C.0000-0002-3840-7696
Joyce, C. J.0000-0002-3841-5020
Labrador, A. W.0000-0001-9178-5349
Mewaldt, R. A.0000-0003-2178-9111
Schwadron, N. A.0000-0002-3737-9283
Strauss, R. D.0000-0002-0205-0808
Stone, E. C.0000-0002-2010-5462
Wiedenbeck, M. E.0000-0002-2825-3128
Additional Information:© 2021. The American Astronomical Society. Received 2021 February 2; revised 2021 March 2; accepted 2021 March 3; published 2021 May 13. This work was supported as a part of the Integrated Science Investigation of the Sun on NASA's Parker Solar Probe mission, under contract NNN06AA01C. The IS⊙IS data and visualization tools are available to the community at; data are also available via the NASA Space Physics Data Facility ( We thank the SOHO/EPHIN team at Christian-Albrechts-Universität zu Kiel for making their data publicly available and Patrick Kühl and Bernd Heber for their guidance as well as their thorough documentation of the level 3 data product. We also gratefully acknowledge the support provided by Michigan State University's National Superconducting Cyclotron Laboratory, Texas A&M University's Cyclotron Institute, and the Lawrence Berkeley National Laboratory's 88 inch Cyclotron Laboratory during EPI-Hi's calibration and testing. Parker Solar Probe was designed, built, and is now operated by the Johns Hopkins Applied Physics Laboratory as part of NASA's Living with a Star (LWS) program. Support from the LWS management and technical team has played a critical role in the success of the Parker Solar Probe mission. We thank all the scientists and engineers who have worked hard to make PSP a successful mission.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Subject Keywords:Cosmic rays; Solar wind; Heliosphere; Solar energetic particles; Solar physics; Solar cycle; Quiet sun; Particle astrophysics; Interplanetary magnetic fields; Plasma astrophysics; Interplanetary particle acceleration; Pickup ions
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Cosmic rays (329); Solar wind (1534); Heliosphere (711); Solar energetic particles (1491); Solar physics (1476); Solar cycle (1487); Quiet sun (1322); Particle astrophysics (96); Interplanetary magnetic fields (824);
Record Number:CaltechAUTHORS:20210518-084408052
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Official Citation:J. S. Rankin et al 2021 ApJ 912 139
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109167
Deposited By: Tony Diaz
Deposited On:19 May 2021 18:48
Last Modified:19 May 2021 18:48

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