Classic scifi cover illustrator Frank Kelly Freas created iconic alien landscapes and creatures for many of the most popular stories of the 1950s, 60s and 70s. This is the 1973 cover for DAW Books' Testament XXI by Guy Snyder.
And this pulpy, beautiful painting is an unpublished picture of mining on one of Jupiter's moons. I love the idea of the regular old Earth tractor, improbably parked on this rocky terrain beneath the gas giant. According to journalist Pat English from Squirrelbasket, Freas said of this painting, "That Jupiter is recognisable is the only concession to astronomical accuracy here."
via Squirrelbasket (Thanks, John Marr!)