Analysis mode.
The blue is a heatmap of whatever geo or bio feature is on the planet. In probe firing mode you can cycle through the individual things and see the map change - i.e. Bacteria/shrubs/cactoid/whatever.
It starts as a low rez bitmap overlaid on the planet and resolves more dense as you get closer*. Pale blue is sparse, darker blue you can't move for tripping over the things (except bacteria patches, damn hard to find them). Clear is nothing to be found.
It actually does work pretty well and I've been finding all manner of plants with it.
*Not sure if this is intentional as for me the planet terrain LOD is similar and really janky with it's step changes as you approach, and really obvious the planets are tile skinned. Plus the 'wait, there was a canyon there visible from orbit. Where's it gone?'