The Hot Oxygen Corona of Mars: Observations by MAVEN IUVS
Résumé
Observation of the Martian hot oxygen corona is an important but difficult measurement in planetary science. These energetic oxygen atoms are thought to be primarily produced by dissociative recombination of O2+ in the planet's ionosphere. While the corona is dominated by gravitationally bound particles, the fraction capable of escaping the planet is expected to be the major pathway for oxygen escape from Mars at the present time. Thus, observing the hot oxygen corona provides valuable insight into the planet’s atmospheric evolution. Up until now, characterization of this population has been elusive due to its extremely tenuous nature. We present here altitude profiles of the hot oxygen corona collected by the MAVEN IUVS instrument as part of its investigation of atmospheric escape from Mars. These measurements confirm the presence of this long anticipated feature of the Martian exosphere, and offer an invaluable way of probing the mechanisms driving escape of atomic oxygen at the present day. Correlation with MAVEN EUVM measurements suggests a relationship between coronal density and solar photoionizing flux, supporting the expectation that dissociative recombination in the ionosphere is the primary source of hot oxygen at Mars. The quality and quantity of the dataset provides valuable constraints for the coronal modeling community, and preliminary comparison of the observed gross structure with a Monte Carlo model is presented.