How NASA Planetary Protection Works

Look at that lovely panoramic shot of Apollo 16's landing site on April 23, 1972. What if a microbe had hitched a ride from these lunar highlands to Earth aboard the shuttle? See pictures of space exploration.
Image courtesy NASA

In 1972, the Apollo 16 mission returned to Earth with 731 rock and soil samples taken from the lunar central highlands, which they eventually sent to labs around the world. One of those labs was buried beneath Area 51, the top-secret military installation located in southern Nevada. There, a team of geologists and astrobiologists recovered spores of unknown origin from a rock's surface and stored the reproductive structures for further study.

The peculiar spores remained dormant until 1974, when they suddenly germinated, infecting dozens of lab workers and producing symptoms similar to those caused by the Ebola virus. The outbreak, known as the Crenshaw Episode after the first person to contract the mysterious illness, claimed seven lives until lab authorities could contain the microbes and prevent further infection.


Now the good news: We lied. The preceding story, at least the part about the Crenshaw Episode, is a complete fabrication. And the bad news: It's based on events that really could happen.

In fact, NASA created the Planetary Protection Office in the 1960s to consider scenarios just like these. Seriously? NASA really spends hard-earned taxpayer money to study extraterrestrial bugs? You bet. And it's not just because agency officials fret over a lunar or Martian microbe wiping out Earth's population. They're also worried about what our germs could do if they gained a toehold on another planet. A few transplanted bacteria might confound future searches for life or, worse, kill any indigenous organisms.

Yes, sir, humans have been mulling over this issue for decades. By the time John F. Kennedy delivered his "we choose to go to the moon" speech in 1962, scientists had already discussed the issue in September 1956, when the International Astronautical Federation convened its seventh congress in Rome.

Almost exactly a year later, the Soviet Union launched Sputnik, ushering in the space race and moving the concept of lunar and planetary contamination from a vague possibility to a sudden and frightening reality.


Sterile Beginnings: The History of Planetary Protection

Although astronomers and astrobiologists discussed planetary protection as early as 1956, they didn't really mobilize until 1958. In the spring of that momentous year, the National Academy of Sciences created the Space Science Board to study the scientific aspects of the human exploration of space.

By June, the academy, based on the board's recommendations, shared its concerns about contamination with the International Congress of Scientific Unions (ICSU), hoping to make the issue a global concern. What did the ICSU do? Form a committee on Contamination by Extraterrestrial Exploration (CETEX) to evaluate whether human exploration of the moon, Venus and Mars could lead to contamination. The CETEX folks reasoned that terrestrial microorganisms would have little hope of surviving on the moon, but that they might be able to eke out an existence on Mars or Venus. As a result, CETEX recommended that humans send only sterilized space vehicles, including orbiters that could have accidental impacts, to those planets.


By the fall of 1958, the ICSU decided it was time to form yet another planetary protection committee. This one, known as the Committee on Space Research, or COSPAR, eventually came to oversee the biological aspects of interplanetary exploration, including spacecraft sterilization and planetary quarantine. COSPAR replaced CETEX. Got that?

At the same time, NASA was being born in the United States. In 1959, Abe Silverstein, NASA's director of Space Flight Programs, made the U.S. space agency's first formal statements about planetary protection:

The National Aeronautics and Space Administration has been considering the problem of sterilization of payloads that might impact a celestial body. ... As a result of the deliberations, it has been established as a NASA policy that payloads which might impact a celestial body must be sterilized before launching.

That same year, planetary protection responsibilities bounced around within NASA like an orphaned child. They were delegated first to the Office of Life Sciences and then to the Office of Space Science and Applications. In 1963, within that office's Biosciences Programs, the Planetary Quarantine Program began and eventually oversaw several Apollo mission activities, such as shielding moon rocks from terrestrial contamination and protecting Earth from lunar wee beasties, if they existed.

In 1976, the Planetary Quarantine Program became the Office of Planetary Protection, and the PQ Officer became the Planetary Protection Officer (PPO). Today, the PPO is still a major player when it comes to shaping NASA missions. He or she consults with internal and external advisory committees and then provides guidance on, well, just about everything, from how a spacecraft must be assembled to how samples from other celestial bodies are collected, stored and returned to Earth.

As you can imagine, the mission teams don't always love the PPO because his or her recommendations make their jobs harder. But then again, who cares? The PPO has a very profound -- and a profoundly difficult -- task, which is to protect life in the galaxy at all costs.


Microbes Coming and Going (or Forward and Back Contamination)

Before you can contemplate contamination, you have to get a little heavy and define life in a strictly biological sense. What is it? Is the organic life we see on Earth the same kind we can expect on a planet in another galaxy?

Well, in the solar system immediately surrounding our home planet, life probably does obey similar biological and physical principles. If Mars, for example, possessed an Earth-like atmosphere and liquid water billions of years ago, then you might expect that carbon-based life forms might have evolved there, too. Indeed, some scientists speculate that life on Earth came from Mars (the ultimate example of planetary contamination!). The idea is that meteorites knocked loose from our red neighbor traveled across space and smacked our young, just-developing planet. These meteorites might have carried the "seeds" of organic life, which nestled into Earth's warm, watery bosom and began the evolutionary journey to produce the vast diversity of species we know today.


Another important development in defining life has been the study of weird and exotic organisms on Earth. Biologists refer to these creatures as extremophiles: organisms that thrive in extreme conditions, such as strong acid, low oxygen or extremely high temperatures. Apparently, Dr. Ian Malcolm, the wry mathematician in "Jurassic Park," had it right when he said, "life finds a way." There may be no place on this planet, even environments poisonous to higher organisms, where highly specialized microorganisms can't live quite comfortably. And if life finds a way in Earth's extreme environments, then it stands to reason that it could do the same in the harsh conditions found on Mars or even Venus.

This logic forms the foundation of planetary protection and drives its two main priorities: to prevent forward and back contamination. Forward contamination occurs when Earth-based microbes hitch a ride on a NASA rocket (or a NASA astronaut), land on another body in the solar system and, once there, decide to stick around. In fact, to a hardy microbe, Martian soil represents just one more extreme environment to which it must adapt. The reverse could happen just as easily. In back contamination, an extraterrestrial bug, hunkered down in the barren soil of its home planet, could attach to an astronaut's boot, journey to Earth and start living large in its new, five-star resort.

NASA designs its planetary protection program to prevent either type of contamination. How it manages that awesome feat is up next.


NASA's Approach to Planetary Protection

NASA's planetary protection office classifies missions into five different categories, depending on the threat of forward or back contamination.

Considering a single person has more bacteria on her body than there are people in the United States and considering a single NASA rocket or probe is a hands-on project for thousands of workers, it might seem like a fool's errand to try to decontaminate a spacecraft [source: Hurst and Reynolds]. Then again, skeptics scoffed at the idea of sending humans to the moon and returning them safely. To tackle these complex scenarios, NASA planners do what they always do: they break the problem down and make sure each small piece has an adequate solution.

For planetary protection, this meticulous process begins by defining the mission in terms of the target body (let's say Mars), the type of encounter (land and operate an unmanned rover named Curiosity) and the specific goals (figure out whether Mars could have supported life by doing lots of chemical analysis on Martian samples).


Because each type of mission presents unique contamination challenges, the Planetary Protection Officer determines specific requirements based on the current scientific knowledge and input from advisory bodies. He or she passes these requirements to the engineers and planners, who must incorporate them as they build, test and develop mission components. In NASA's current policy, the officer will classify a mission into one of five categories, each with its own planetary protection requirements (see table).

Up next, we'll see how NASA battles all those contamination risks.


Earthly Microbes Not Welcome: Reducing Forward Contamination Risks

That engineer is sporting cleanroom casual at NASA's Jet Propulsion Laboratory.
Image courtesy NASA

Remember how NASA first asked those biologists at Fort Detrick to develop effective methods for decreasing the number of microorganisms on outbound spacecraft -- what insiders refer to as bioburden reduction? Well, as more missions came online, we got better at planetary protection. For example, NASA officials implemented strict crew quarantine rules for the early Apollo missions because they didn't know whether or not lunar microbes existed. After early testing of lunar samples, however, scientists determined that the moon never harbored life, so crew quarantine procedures were out the window after the third Apollo voyage.

The Viking missions of the mid-1970s were just as important for planetary protection as the Apollo ones, and led to the development of many techniques still used today.


  • Cleanrooms and microbial barriers. NASA workers built Viking components in bug- and dust-free rooms known as cleanrooms. These rooms live up to their name by way of laminar airflow systems, which keep air moving in one direction along parallel flow lines and at uniform velocity. As the air moves, superfine filters trap dust, bacteria and other debris that might otherwise settle on the surface of equipment. All cleanrooms receive ratings based on how well they do their jobs. The lower the rating, the cleaner the facility. Class 10 rooms, for example, have fewer than 10 particles per cubic foot. NASA required Viking components to be built in Class 100 cleanrooms [source: NASA Office of Planetary Protection].
  • Protective clothing. Before workers can step in a cleanroom, they must don special clothing from head to toe. These garments include hoods, masks, gloves and bunny suits, full-body suits like those made famous by Intel in the late 1990s. The clothing prevents workers from depositing hair or bacteria into the cleanroom environment.
  • Sterilization. After the Fort Detrick experiments, NASA selected dry-heat sterilization as the preferred technique for the Viking landers. In essence, dry-heat sterilization requires putting the fully assembled spacecraft in a giant oven and baking it at 233 degrees Fahrenheit (112 degrees Celsius) for 30 hours. Before workers bake the vessel, they encase it in a large ceramic sheath -- something resembling CorningWare -- to help protect delicate components. An alternate method, used since Viking, relies on vaporized hydrogen peroxide, which can be applied at lower temperatures, yet still kills microbes effectively.

Of course, the techniques we've covered so far only decrease the bioburden on a spacecraft's metallic surfaces. NASA also worries about something known as encapsulated burden -- bacteria buried deep inside nonmetallic spacecraft material. If an orbiter or lander accidentally strikes its target, something known as an inadvertent impact in NASA-speak, these encapsulated microbes could be released, foiling the mission's planetary protection efforts.

To safeguard against this happening, mission planners employ a technique called trajectory biasing. Here's how it works: First, flight engineers aim the spacecraft so it will miss its target by hundreds or even thousands of kilometers. Then, after launch, they track the vessel carefully and, as they get more confident that it's on course and responding well, they begin correcting the trajectory slowly over time. If they ever lose contact with the spacecraft and can no longer control it, they know it will be far less likely to make an inadvertent impact with the target body.

Earth-return missions use all of these techniques for the outbound trip. The inbound trip requires a couple of steps to make sure returning astronauts or samples don't contaminate Earth's biosphere.


Alien Microbes Not Welcome: Reducing Back Contamination on Apollo 11

You're looking at the three Apollo 11 astronauts, plus a member of the recovery team, all clad in their BIGS after the astronauts were extracted from the command module.
Image courtesy NASA/Newsmakers

When NASA set its sights on the moon in the 1960s, no one knew if lunar dust held exotic life forms or not. What if a nasty bug lived on our nearest celestial neighbor? And what if said bug made it back to Earth and upset the planet's delicate ecological balance? These weren't just concerns of the U.S. space program. Nope, author Michael Crichton posed them, too.

In May 1969, just two months before Apollo 11 would carry the first humans to walk on another celestial body, Crichton published "The Andromeda Strain," a cautionary tale about dangerous microorganisms carried to Earth on a spacecraft. The best-seller ignited fears about the consequences of a space mission contaminating our planet. NASA, of course, had already worked hard to develop stringent planetary protection guidelines by then, but it redoubled its efforts to help soothe public concerns.


Like we talked about, NASA ultimately would deem the moon incapable of supporting life and ease its planetary protection guidelines around lunar missions, but the early Apollo program, especially Apollo 11, models how the space agency has minimized previous back contamination risks. NASA's approach addressed three main concerns: the returning spacecraft, the astronauts and any samples carried back. Let's start with the astronauts.

When the Columbia Command Module splashed down in the Pacific Ocean on July 24, 1969, a recovery crew jumped from a helicopter to the floating spacecraft. After attaching a flotation collar to the craft and inflating rafts, one of the crew members opened the hatch to the module, passed over three biological isolation garments (BIGs) and quickly resealed the hatch. This crew member also wore one of the suits to prevent contamination during the hand-off.

Once the astronauts sealed themselves safely within their protective garments, the command module hatch was reopened, and they climbed aboard one of the rafts. All three astronauts received a bleach-based sponge bath and then waited as the member of the recovery crew wiped down the hatch and the exhaust vents of the command module with iodine solution. Then the people on the helicopter hoisted the astronauts out of the water and carried them to the deck of the USS Hornet. After an elevator ride down to lower decks, they exited and walked to the mobile quarantine facility (MQF), a sealed chamber that would be their home for several days.

The ship transported the facility, with the Apollo crew sealed inside, to Honolulu. Then an airplane carried it to Houston, where a waiting truck whisked the astronauts to the Lunar Receiving Laboratory, or LRL. On July 27, the astronauts walked from the MQF through a sealed tunnel into the lab's crew reception area. The astronauts remained under quarantine in Houston until Aug. 10, while a team of doctors monitored their health and watched for possible infections. When none developed, they were deemed healthy and free of lunar pathogens.


Planetary Protection on Apollo 11

Hey, um, Neil, quick thing before you go: Try not to bring back any killer lunar microbes, OK?
Central Press/Getty Images

Once the astronauts were safely ensconced in the MQF, the recovery crew worked to get the Columbia Command Module aboard the Hornet. A ship's crane lifted the spacecraft from the water and placed it on an elevator. Then it was lowered to the same deck as the MQF. There, a plastic tunnel was placed between the command module and the quarantine facility so lunar samples and film shot during the mission could be transferred to the MQF without fear of contamination. On July 30, the spacecraft arrived in Houston at the LRL, where recovery engineers removed and bagged all of the equipment for quarantine. Then they wiped the interior with disinfectant, heated it to 110 degrees Fahrenheit (43 degrees Celsius) and filled it with formaldehyde gas for 24 hours. As a precaution, the recovery crew also remained quarantined along with the Apollo astronauts.

What happened to the samples? Handlers removed them from the MQF using decontamination locks. Then they also made their way back to the LRL. They arrived in airtight suitcases known as Apollo Lunar Sample Return Containers, or ALSRCs. Handlers at the lab sterilized the outside of the suitcases by first exposing them to ultraviolet light and then washing them in peracetic acid, a biocide typically used in food and beverage environments. After rinsing them with sterile water, handlers passed the ALSRCs through a vacuum lock into the main vacuum chamber glove box. All early testing on the lunar samples took place within the glove box, which served as an airtight barrier to keep any microbes from escaping. By August 1969, after intense biological and chemical analysis, LRL officials declared the lunar samples free of lunar microorganisms and released them from quarantine.


That may sound like a lot of precautions, but some have argued that the planetary protection efforts used by NASA for Apollo 11 were futile at best. After all, when the Columbia Command Module splashed into the Pacific Ocean, no safeguards were in place to capture a pesky microbe that might have somehow survived re-entry into Earth's atmosphere. And analysis of the lunar samples was halted at one point when workers feared that the vacuum chamber glove box might have a leak. What if the moon did indeed support life? And what if one of those lunar life forms shook free from the Columbia spacecraft, settled to the ocean floor and colonized? Is that pure science fiction? Or perhaps an inevitable reality as we, spacefaring humans that we are, explore more and more of our vast, mysterious universe?

Author's Note

Do a little research on planetary protection, and you're going to encounter Michael Crichton's "The Andromeda Strain." But if you want a campier take on the subject, pick up (or download) the 1982 flick "Creepshow." In it, there's a story called "The Lonesome Death of Jordy Verrill," which stars Stephen King in the eponymous role. Jordy is a farmer who finds a meteorite and thinks it's his golden ticket. Unfortunately, the meteorite carries alien spores that turn the poor guy into a walking weed. It's not a happy ending, but it's an interesting take on planetary protection.

Related Articles


  • COSPAR Planetary Protection Policy. Oct. 20, 2002, amended Mar. 24, 2011.
  • Hurst, William C. and A. Estes Reynolds. "Food, Hands and Bacteria." University of Georgia College of Agriculture and Environmental Sciences. Mar. 19, 2010. (Feb. 20, 2012)
  • Irion, Robert. "Did Life on Earth Come from Mars." Discover Magazine. Aug. 1, 2001. (Feb. 20, 2012)
  • Jha, Alok. "Martian meteorite contains pockets of the red planet's atmosphere." The Guardian. Feb. 8, 2012. (Feb. 20, 2012)
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  • Weed, William Speed. "Are We Ready for Alien Bugs?" Discover Magazine. March 1, 2003. (Feb. 20, 2012)