MRO has been observing Mars for 6 Mars Years (MY), each of which lasts for 687 Earth days.
Shown here is an impact crater on the north polar ice cap, which contains an icy deposit on the crater floor.
These inter-crater ice deposits shrink and expand or change shape or surface texture from year to year, In this animation, we can see the appearance of this crater fill in MY 29 (2/2008), 30 (8/2010), 31 (7/2012), 33 (2/2016), 34 (1/2018), and 35 (12/2019).
