Emergency procedures for the lab — like what to do in the case of fire or medical troubles — also involved breaking isolation.

“This ended up being an example of planetary protection security theater,” said Jordan Bimm, a historian of science at the University of Chicago who was not involved in Dr. Degroot’s research.

The Apollo 11 astronauts’ very return to Earth also put the planet at risk. Their vehicle, for instance, was designed to vent itself on the way down, and the astronauts were to open their hatch in the ocean.

In a 1965 memo, a NASA official stated that the agency was morally obligated to prevent potential contamination, even if it meant changing the mission’s weight, cost or schedule. But four years later, on return to Earth, the spacecraft vented anyway, and the capsule’s interior met the Pacific.