diff --git a/TODO.md b/TODO.md
index 41ce840..fc0b201 100644
--- a/TODO.md
+++ b/TODO.md
@@ -143,3 +143,9 @@ Mars themes in all generic segment generators.
 In showEditor mode, the Open level-select dialog currently only loads the
 selected level into the editor. It should also load the level into the game
 (MODE_PLAY) so test-playing reflects the newly opened file.
+
+## Mars Surface atmosphere particles
+Mars Surface levels should have ambient floating particles (dust motes, fine
+sand) drifting across the screen to sell the atmosphere. Could tie into the
+existing wind system — particles drift with the wind direction. Should be
+subtle, low-alpha, and layered behind/in front of the player for depth.