They almost never went to planets where they couldn’t breathe the atmosphere, because Rose disliked spacesuits, but eventually they came to an airless planet that the Doctor looked so eager to explore that Rose told him he should. He practically bounced to the wardrobe and came back in an orange spacesuit that looked familiar to Rose.
“Hang on.” She stopped him before he could bound past her, studying the “SB6” on the badge. “Is this…?”
“Oh.” He looked down sheepishly. “Yeah. I…Call it a keepsake.”
“You sentimental sweetheart,” she said, and kissed him.
The Doctor never did explore the planet.