Open AccessModeling MESSENGER observations of calcium in Mercury's exosphere
Author(s) -
Burger Matthew H.,
Killen Rosemary M.,
McClintock William E.,
Vervack Ronald J.,
Merkel Aimee W.,
Sprague Ann L.,
Sarantos Menelaos
Publication year - 2012
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2012je004158
Subject(s) - exosphere , mercury (programming language) , vaporization , astrobiology , solar wind , sputtering , physics , atomic physics , ion , plasma , computer science , thin film , quantum mechanics , thermodynamics , programming language
The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MESSENGER spacecraft has made the first high‐spatial‐resolution observations of exospheric calcium at Mercury. We use a Monte Carlo model of the exosphere to track the trajectories of calcium atoms ejected from the surface until they are photoionized, escape from the system, or stick to the surface. This model permits an exploration of exospheric source processes and interactions among neutral atoms, solar radiation, and the planetary surface. The MASCS data have suggested that a persistent, high‐energy source of calcium that was enhanced in the dawn, equatorial region of Mercury was active during MESSENGER's three flybys of Mercury and during the first seven orbits for which MASCS obtained data. The total Ca source rate from the surface varied between 1.2 × 10 23 and 2.6 × 10 23 Ca atoms s −1 , if its temperature was 50,000 K. The origin of this high‐energy, asymmetric source is unknown, although from this limited data set it does not appear to be consistent with micrometeoroid impact vaporization, ion sputtering, electron‐stimulated desorption, or vaporization at dawn of material trapped on the cold nightside.