Unexpected energetic particle observations near the Sun by Parker Solar Probe and Solar Orbiter

Creators: Malandraki, O. E.; Cohen, C. M. S.; Giacalone, J.; Mitchell, J. G.; Chhiber, R.; McComas, D. J.; Rodríguez-Pacheco, J.; Wimmer-Schweingruber, R. F.; Ho, G. C.

Abstract

Solar energetic particles (SEPs) from suprathermal (few keV) up to relativistic (∼few GeV) energies are accelerated at the Sun in association with solar flares and coronal mass ejection-driven shock waves. Although our knowledge of the origin, acceleration, and transport of these particles from close to the Sun through the interplanetary medium has advanced dramatically in the last 40 years, many puzzles have still remained unsolved due to the scarcity of in situ measurements well inside 1 AU. Furthermore, energetic particle intensity enhancements associated with high-speed streams or stream interaction regions (SIRs) have been routinely observed at interplanetary spacecraft near Earth orbit since the 1960s. Since only a small sample of SIR events were observed by the Helios spacecraft inside 1 AU, additional observations well inside 1 AU were also needed to further investigate the energization and transport effects of SIR-associated ions and to compare with expectations from contemporary SIR-associated particle acceleration and transport models and theories. The Solar Orbiter (SolO) and Parker Solar Probe (PSP) pioneering missions have been providing unprecedented measurements of energetic particles in the near-Sun environment. This review presents the unexpected observations of SEP and SIR-related ion events as measured by the PSP/IS⊙IS and SolO/EPD experiments, which revealed surprises that challenge our understanding.

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Acknowledgement

Parker Solar Probe was designed, built, and is operated by the Johns Hopkins Applied Physics Laboratory as part of NASA's Living with a Star (LWS) program (Contract No. NNN06AA01C). We thank everyone that helped make the IS⊙IS instrument suite and PSP mission possible. The IS⊙IS data and visualization tools are available to the community at https://spacephysics.princeton.edu/missions-instruments/isois. Solar Orbiter is a mission of international cooperation between ESA and NASA, operated by ESA. Javier Rodríguez-Pacheco acknowledges the financial support by the Spanish Ministerio de Ciencia, Innovacón y Universidades FEDER/MCIU/AEI Projects ESP2017-88436-R and PID2019-104863RB- I00/AEI/10.13039/501100011033 and by the European Union's Horizon 2020 research and innovation program under Grant No. 101004159 (SERPENTINE). Robert F. Wimmer-Schweingruber thanks the German Space Agency (Deutsches Zentrum für Luft- und Raumfahrt) for their support of Grant No. 50OT2002. Rohit Chhiber acknowledges support from NASA Grant Nos. 80NSSC18K1648 and 80NSSC22K1020, and the PSP/IS⊙IS project (Contract No. NNN06AA01C) via a subcontract to the University of Delaware from Princeton University (SUB0000165).

Contributions

Olga E. Malandraki: Writing – original draft (equal); Writing – review & editing (equal). Christina M. S. Cohen: Writing – original draft (equal); Writing – review & editing (equal). Joe Giacalone: Writing – original draft (equal); Writing – review & editing (equal). John G. Mitchell: Writing – original draft (equal); Writing – review & editing (equal). Rohit Chhiber: Writing – original draft (equal); Writing – review & editing (equal). David J. McComas: Writing – original draft (equal); Writing – review & editing (equal). Javier Rodríguez-Pacheco: Writing – original draft (equal); Writing – review & editing (equal). Robert F. Wimmer-Schweingruber: Writing – original draft (equal); Writing – review & editing (equal). George C. Ho: Writing – original draft (equal); Writing – review & editing (equal).

Data Availability

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

Conflict of Interest

The authors have no conflicts to disclose.

Additional Information

Special Collection: Plasma Physics of the Sun in Honor of Eugene Parker

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