Page "Foundation and Earth" Paragraph 7

They next go to Melpomenia, the third and final Spacer coordinate they have.

They find that the atmosphere has become depressurized to a few thousandths of normal atmospheric pressure.

Wearing space suits, they enter a library, and find a statue, as well as writings with the coordinates of all of the Spacer worlds.

While departing Melpomenia, they notice a carbon-dioxide-feeding moss has begun feeding off insignificant leakages in their space suits.

Barely recognizing this before stepping on their fully pressurized ship — which would have likely been disastrous — they set their blasters to minimum power to fry it off, and then set the ship to heavy UV-illumination before stepping on board.

This disinfection procedure kills any trace of the moss, preventing it from spreading to other worlds.