The recent documentary “Spaceship Earth” mentions the 1972 science-fiction film “Silent Running”, directed by Douglas Trumbull.
The premise may seem preposterous. The Earth has become the usual dystopian wasteland, and all the flora are in a space colony (not exactly an O’Neill Cylinder). They are domes in an orbit around Saturn (although Titan would be nearby).
Then commander Freeman Lowell (Bruce Dern) receives an order to destroy the botanical colonies.
The film is short for its kind (89 min) and was available in wide-screen formats. I vaguely remember seeing it in a dollar house, I think, near Bailey’s Crossroads (where I live now, ironically), during a period in my life when I worked for the Navy and had returned to the DC area.
Picture is from the Botanical Garden near the Capitol, Washington DC, late Nov., 2018