Why the cheese on the moon is green

In 1991, as Apollo 12 Commander Pete Conrad reviewed the transcripts of his conversations relayed from the moon back to Earth, the significance of the only known microbial survivor of harsh interplanetary travel struck him as profound:

"I always thought the most significant thing that we ever found on the whole...Moon was that little bacteria who came back and lived and nobody ever said [anything] about it."


Microbes one of the simplest organisms in the biosphere. Having evolved over billions of years they retained the mechanisms to retain life in the harshest environments ,and to “resurrect” when environmental conditions and adequate nutrients become available.

The Earth looked remarkably different when bacteria first colonized the oceans and land. Oxygen was scarce. To many early plants, cyanobacteria and anaerobic bacteria, oxygen was a poison. The thin ozone layer that currently shields intense solar radiation was largely unformed. Bacteria, originating under global conditions very different from our present day, can be thought to be space travelers already: over time the generational records of microbes have sampled swings in environment here on earth that rival the differences between today's Earth and some of the more hospitable planetary outposts. The growing list of space-hardiness conditions include:

Vacuum conditions, with bacteria taken down to near zero pressure and temperature, provided suitable care is exercised in the experimental conditions.

Pressure, with viable bacteria after exposure to pressures as high as 10 tonnes per square centimeter (71 tons/sq-in). Colonies of anaerobic bacteria have recently been recovered from depths of 7 km (4.2 mi) or more in the Earth's crust.

Heat. Archaebacteria that can withstand extreme heat have been found thriving in deep-sea hydrothermal vents and in oil reservoirs a mile underground

Radiation, including viable bacteria recovered from the interior of an operating nuclear reactor. In comparison to space, each square meter on Earth is protected by about 10 tons of shielding atmosphere.

Long preservation, including bacteria revived and cultured after some 25 million years of encapsulation in the guts of a resin-trapped bee.

The Surveyor probes were the first U.S. spacecraft to land safely on the Moon. In November, 1969, the Surveyor 3 spacecraft's microorganisms were recovered from inside its camera that was brought back to Earth under sterile conditions by the Apollo 12 crew.

The 50-100 organisms survived launch, space vacuum, 3 years of radiation exposure, deep-freeze at an average temperature of only 20 degrees above absolute zero, and no nutrient, water or energy source. (The United States landed 5 Surveyors on the Moon; Surveyor 3 was the only one of the Surveyors visited by any of the six Apollo landings. No other life forms were found in soil samples retrieved by the Apollo missions or by two Soviet unmanned sampling missions, although amino acids - not necessarily of biological origin - were found in soil retrieved by the Apollo astronauts.)

Space historians will recall that the journey to the stars has more than one life form on its passenger list: the names of a dozen Apollo astronauts who walked on the moon and one inadvertent stowaway, a common bacteria, Streptococcus mitis, the only known survivor of unprotected space travel. As Marshall astronomers and biologists met recently to discuss biological limits to life on Earth, the question of how an Earth bacteria could survive in a vacuum without nutrients, water and radiation protection was less speculative than might first be imagined.