Both photographs were taken when the planet was at opposite ends of its elliptical orbit.
How are the images of Mars in ultraviolet?
In the first image that was captured in July of last year, you can see the Argyre basin, one of the deepest craters on Mars (it can be seen near the lower left of the planet).
The crater appears filled with atmospheric hazewhile the deep canyons of Valles Marineris (at top left) They appear full of clouds. That huge white patch you see to the south is the polar cap.
The scientists were able to determine that Mars loses a large amount of hydrogen on those dates, something that can be explained by the warming of the southern summer and because dust storms carry water vapor to high altitudes.
The second photograph was obtained in January of this year, when the planet was at its furthest point from the solar orbit. The purple layers that you see are made up of ozone molecules, while the white or bluish areas are the haze and clouds that are on the planet.