The formation of "recurring slope lineae" is a fascinating process on Mars that we're just beginning to investigate, and one that we've imaged before in Palikir Crater.
These RSLs show up in the spring and fade in the winter. Their presence might be due to briny water, and it opens up the door to taking a fresh look at other possible RSL candidates. This observation was done to accomplish just that: to re-image a previously photographed area that might confirm if this a candidate for RSL.
When HiRISE re-images an area, we try to match the exact lighting as before, in order to see any differences. Along with a stereo pair and resulting anaglyph, our understanding of the terrain is more complete.
Photo credit: NASA/JPL/University of Arizona