Occurrence rate of ultra-low frequency waves in the foreshock of Mercury increases with heliocentric distance

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https://www.nature.com/articles/s41467-021-26344-2

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https://doi.org/10.1038/s41467-021-26344-2
 http://hdl.handle.net/11603/23859

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
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UMBC Physics Department

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Author/Creator ORCID

https://orcid.org/0000-0001-9210-0284

Date

2021-11-19

Type of Work

journal articles
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Citation of Original Publication

Romanelli, N., DiBraccio, G.A. Occurrence rate of ultra-low frequency waves in the foreshock of Mercury increases with heliocentric distance. Nat Commun 12, 6748 (2021). https://doi.org/10.1038/s41467-021-26344-2

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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract

Studies of Mercury’s foreshock have analyzed in detail the properties of ultra-low frequency waves. However, an open question remains in regards to understanding favorable conditions for these planetary foreshocks waves. Here, we report that 0.05–0.41 Hz quasi monochromatic waves are mostly present under quasi-radial and relatively low intensity Interplanetary Magnetic Field, based on 17 Mercury years of MESSENGER Magnetometer data. These conditions are consistent with larger foreshock size and reflection of solar wind protons, their most likely source. Consequently, we find that the wave occurrence rate increases with Mercury’s heliocentric distance. Detection of these waves throughout Mercury’s highly eccentric orbit suggests the conditions for backstreaming protons are potentially present for all of Mercury’s heliocentric distances, despite the relatively low solar wind Alfvén Mach number regime. These results are relevant for planetary magnetospheres throughout the solar system, and the magnetospheres of exoplanets, and provide knowledge of particle acceleration mechanisms occurring inside foreshocks.