Mars Ozone Mapping with MAVEN IUVS

Abstract:

Ozone (O₃) on Mars is a product of the CO₂ photolysis by ultraviolet radiation. It is destroyed with a timescale of less than ~1 hour during the day by the H, OH, and HO₂ radicals. This tight coupling between O₃ and HO_x species makes ozone a sensitive tracer of the odd hydrogen chemistry that stabilizes the CO₂ atmosphere of Mars, and ozone measurements offer a powerful constraint for photochemical models. Ozone is also expected to be anti-correlated to water vapour, the source of hydrogen radicals HO_x. At high latitudes in winter, the absence of H₂O prevents the production of HO_x and the chemical lifetime of ozone may increase up to several days. In these conditions, the ozone column abundance usually reaches its largest values of the Martian year and ozone turns into a measurable tracer of the polar vortex dynamics.

The Imaging Ultraviolet Spectrograph (IUVS) is one of nine science instruments aboard the Mars Atmosphere and Volatile and Evolution (MAVEN) spacecraft. In the apoapse imaging phase, the spacecraft motion carries the IUVS lines-of-sight across the Martian disk while the scan mirror is used to make transverse swaths. This observation mode allows mapping the ozone vertically-integrated column from its signature in the solar ultraviolet flux backscattered by the surface and the atmosphere.

This paper will present an overview of the first year of ozone mapping by IUVS. We will describe in particular the last Mars northern winter (2015) when the largest ozone columns have been observed since the beginning of the MAVEN mission. The data will be compared to prior Earth-based observations and to the SPICAM and MARCI ozone datasets. We will also test our quantitative understanding of the Martian ozone by comparing the IUVS observations to our three-dimensional model with photochemistry.