Am not asking about planetary/meteorite surfaces and am restricting myself to the interstellar medium
edit: by interstellar medium I mean, the following:
"Interstellar medium (ISM) is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space."
(copied verbatim from a google search).