Spatial distribution of oxygen and hydrogen upper atmospheres of Mars as observed by Hisaki and MAVEN/IUVS

Simultaneous observations of the upper atmosphere of Mars were conducted by the EXtreme ultraviolet spectrosCope for ExosphEric Dynamics (EXCEED) instrument on the Hisaki spacecraft and the Imaging Ultraviolet Spectrograph (IUVS) on the Mars Atmospheric and Volatile EvolutioN (MAVEN) spacecraft. Hisaki is an earth-orbiting satellite that carries the EXtreme ultraviolet spectrosCope for ExosphEric Dynamics (EXCEED) instrument, and it was launched in September 2013 to study the dynamics of the exosphere and plasma around the solar system bodies such as Jupiter, Venus, and Mars. IUVS has been observing the upper atmosphere of Mars since MAVEN arrived at Mars in September 2014 after its launch in November 2013.

In this study we report an observation result of oxygen 130.4 nm and hydrogen Lyman-beta emissions from the Martian upper atmosphere performed by the Hisaki spacecraft from the end of August to the end of September in 2016. We estimated an average disk intensity of these emissions by assuming the photons mainly came from disk illuminating area. We confirmed that the brightness of the 130.4 nm emission was reasonably consistent but Lyman-beta seemed stronger compared to previous studies [1, 2, 3, 4, 5]. We also examined the spatial distribution of these emissions along the slit of EXCEED. The Lyman-beta emission appeared a broader spatial distribution than the oxygen's spatial distribution, although both spatial distributions are affected by the pointing accuracy of Hisaki.

These results suggest that the main illuminating area for 130.4 nm is similar to the Martian disk size but one for Lyman-beta is larger than that. To confirm this, we examine the brightness of the main illuminating area of oxygen 130.4 nm using the MAVEN/IUVS disk scan data obtained near apoapsis and then estimate the size of the main illuminating area of Lyman-beta. This will provide the global spatial distribution of hydrogen atmosphere around Mars.

1. Feldman et al., 2000, AJ, 538, 395

2. Krasnopolsky and Feldman, 2002, Icarus, 160, 86

3. Feldman et al., 2011, Icarus, 214, 394

4. Deighan et al., 2015, GRL, 42, 9009

5. Jain et al., 2015, GRL, 42, 9023