Photoionization Loss of Mercury's Sodium Exosphere: Seasonal Observations by MESSENGER and the THEMIS Telescope

Autor: Jim M. Raines, R. M. Dewey, Anna Milillo, J. M. Jasinski, Neil Murphy, James A. Slavin, Leonardo Regoli, Timothy A. Cassidy, V. Mangano
Rok vydání: 2021
Předmět:
Atmospheres
Sodium
Planetary Atmospheres
Clouds
and Hazes
chemistry.chemical_element
Atmospheric Composition and Structure
Photoionization
Radiation
Planetary Geochemistry
law.invention
Ion
Telescope
Neutral Particles
Planetary Sciences: Solar System Objects
law
Research Letter
Physics::Atomic and Molecular Clusters
Planetary Sciences: Astrobiology
Ionosphere
photoionization
sodium
Planetary Sciences: Solid Surface Planets
Planetary Sciences: Fluid Planets
plasma
Mineralogy and Petrology
Physics
Electromagnetics
Planetary Atmospheres
Mercury
Plasma
exosphere
Ionization Processes
Mercury (element)
Interplanetary Physics
Planetary Mineralogy and Petrology
Geochemistry
Geophysics
chemistry
Plasmas
Physics::Space Physics
ions
Space Plasma Physics
General Earth and Planetary Sciences
Planetary Sciences: Comets and Small Bodies
Astrophysics::Earth and Planetary Astrophysics
Atomic physics
Space Sciences
Composition
Exosphere
Zdroj: Geophysical Research Letters
ISSN: 1944-8007
0094-8276
DOI: 10.1029/2021gl092980
Popis: 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 ∼1024 atoms/s from the sodium exosphere (maxima of 4 × 1024 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.
Key Points Photoionization can be a significant loss process to the sodium exosphere with peak loss estimates of 4 × 1024 atoms/sThe photoionization loss process of Mercury's sodium exosphere varies throughout the planet's orbit around the SunMore sodium is lost due to photoionization on the inbound leg (true anomaly angle of 180°–360°) of Mercury's orbit than the outbound leg
Databáze: OpenAIRE
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