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Photoionization Loss of Mercury's Sodium Exosphere: Seasonal Observations by MESSENGER and the THEMIS Telescope
Author(s) -
Jasinski Jamie M.,
Cassidy Timothy A.,
Raines Jim M.,
Milillo Anna,
Regoli Leonardo H.,
Dewey Ryan,
Slavin James A.,
Mangano Valeria,
Murphy Neil
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2021gl092980
Subject(s) - exosphere , photoionization , sodium , physics , ion , mercury (programming language) , ionization , materials science , quantum mechanics , computer science , programming language , metallurgy
We present the first investigation and quantification of the photoionization loss process to Mercury's sodium exosphere from spacecraft and ground‐based observations. We analyze plasma and neutral sodium measurements from NASA's MESSENGER spacecraft and the THEMIS telescope. We find that the sodium ion (Na + ) content and therefore the significance of photoionization varies with Mercury's orbit around the Sun (i.e., true anomaly angle: TAA). Na + production is affected by the neutral sodium solar‐radiation acceleration loss process. More Na + was measured on the inbound leg of Mercury's orbit at 180°–360° TAA because less neutral sodium is lost downtail from radiation acceleration. Calculations using results from observations show that the photoionization loss process removes ∼10 24 atoms/s from the sodium exosphere (maxima of 4 × 10 24 atoms/s), showing that modeling efforts underestimate this loss process. This is an important result as it shows that photoionization is a significant loss process and larger than loss from radiation acceleration.