1. Introduction; why quarantines? Mars and Europa
Quarantine is from the Latin quadragina, forty. The original definition is “…a period of forty days during which an arriving vessel suspected of carrying contagious disease is detained in port in strict isolation…” (Guralnik, 1970). Quarantines have been used throughout history to protect against disease spread: smallpox, bubonic plague, or rabies, and they are still applicable today.
Human history is filled with instances of harmful plants, animals, and diseases being inadvertently or deliberately introduced into a new locale with disastrous results. The destructive effects of rabbits brought to Australia or gypsy moths brought to North America are two examples of good intentions gone awry. The deliberate use of smallpox to exterminate native populations in the Americas is a gruesome example of “germ warfare” (Diamond, 1997).
But what does this have to do with space travel? A lot! While the Earth is the only known place harboring life, there are locales in the Solar System that have the potential for at least microbial life. The growing appreciation of the hardiness of life on the Earth makes it quite possible that Mars and Europa, in particular, may be home to life. It is now known that microbial life on Earth can exist at exist at extremes of temperature from above 1000 C to far below zero. Life forms can live in highly acidic or alkaline conditions and be resistant to very high pressures and extreme radiation levels (Gross, 2001).
Life is very unlikely on Mercury, Venus, comets, asteroids, the gas giants, and most of their frigid moons. Titan and Enceladus are interesting because Titan has a dense atmosphere and contains large amounts of organic compounds but is extremely cold. Enceladus has cryovolcanism with potential subsurface liquid water. The conditions existing on Mars or in the subsurface ocean of the Jovian satellite Europa could probably support many hardy terrestrial life forms (Rummel, 2001). Mars has considerable polar ice and subsurface ice, probably once had liquid water on its surface, and even today may have subsurface water that occasionally briefly flows onto the surface (Rummel, 2001). The composition of Europa and other Jovian and Saturnian satellites is still being debated, but it is quite possible there is a large subsurface ocean on Europa that occasionally breaks through a thin surface crust of ice. It is an exciting place to look for life (Lunine, 2004). Thus, it is not unreasonable to expect alien life may exist in a limited number of places in the Solar System.
2. Forward and backward contamination
The possible discovery of life elsewhere presents us with three great dilemmas. First, what are the sociological implications of such a discovery? That discussion is beyond the scope of this essay and is better examined elsewhere. On a more practical basis, our first concrete dilemma is how do we assure ourselves we are not mistaking a terrestrial contaminant for an actual alien life form? And our second concrete dilemma is what happens if we bring it back home? Bringing a terrestrial life form to another planet is forward contamination and bringing an alien form back to Earth is backward contamination.
With our admittedly zero knowledge of alien life forms, the only safe approach for space exploration is to impose severe restrictions to prevent these contaminations. In other words, we need to impose planetary quarantine or planetary protection. For example, the Galileo mission ended with an intentional entry into Jupiter’s atmosphere on September 21, 2003 to avoid the risk of a crash onto and contamination of Europa (Barengoltz, 2005).
3. Protecting the Planets
Quarantine standards were adopted as early as 1958 by the International Council of Scientific Unions (ICSU), and the U.S. National Academy of Sciences (NAS) proposed specific planetary quarantine standards in the period of 1958-1960 (Rummel, 2001). ISCU established the Committee on Space Research (COSPAR) to define acceptable levels of contamination on an outbound spacecraft. The United Nations Outer Space Treaty of 1967 specified exploration of other Solar System bodies would be done in a fashion “…so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter” (Rummel, 2001). In response to this treaty, NASA established a Planetary Quarantine Office which evolved into the Planetary Protection Office. ICSU through COSPAR continues to provide a venue for international discussion on planetary protection. Planetary protection activities for NASA are currently managed by the Science Mission Directorate at NASA Headquarters (NASA, 2006). The Space Studies Board of NAS also provides independent advice on all aspects of space science.
3a. The Apollo Moon missions
The Apollo Moon missions represent the only serious US effort so far to prevent backward contamination of the Earth. At that time, the quarantine procedures for the Apollo missions were directed through the manned spaceflight organization. The Planetary Quarantine Office was only concerned with returned samples from robotic missions. The Astronauts from both the Apollo 11 and Apollo 12 crews were quarantined for 30 days after their arrivals back on Earth . The Moon rocks they brought back were examined in the Lunar Receiving Laboratory (LRL) which attempted to keep the samples in a vacuum as they were being biologically contained and examined. This proved to be quite difficult and vacuum containment is not recommended for evaluation of future samples from Solar System exploration (Wood, 2001). Extensive life-detection and biohazard protocols were followed in the quarantine of the Astronauts and the study of the Moon rocks. Nothing alive or dangerous was found, and quarantines were not continued for the remaining Apollo missions (Rummel, 2001).
Besides Moon rocks, the November 1969 Apollo 12 mission also brought back pieces of the robotic Surveyor 3 probe from the Moon. The probe had been on the Moon two years. Viable streptococcus mitus spores were found from a swab of the Surveyor’s camera case. These spore were assumed to have traveled with the Surveyor probe to the Moon. Such spores are well known to withstand a vacuum, and they were in a location in the robotic probe that protected them from temperature extremes. there is, however, a possibility the spores were a simple laboratory contamination back on Earth (Oberg, 1996). The present NASA policy considers the Moon to be without life and to be effectively a part of the Earth (Rummel, 2001).
3b. The 1976 Viking missions
The 1976 Viking landers successfully operated on the surface of Mars for 8½ months searching for life. Because they detected no organic compounds with the gas chromatograph/mass spectrometer (GS/MS), the search for life was considered unsuccessful but much interesting surface data and atmospheric data was gathered (Gross, 2001; Lunine, 2004). To prevent contamination of Mars by terrestrial organisms, each lander was thoroughly cleansed and then baked in an oven until reaching a temperature of 1100C. One-third the cost for the Viking missions involved their decontamination prior to launch.
The Viking results were interpreted at that time as showing the surface of Mars would not likely support Earth life. Our present understanding of the extreme range of conditions that life can adapt to calls this interpretation into question (Koike, 1996). Nevertheless, since the Viking days, subsequent Martian landers not specifically designed to search for life, such as the 1996 Pathfinder mission, no longer undergo heat treatment. All Mars landings still must undergo a thorough Viking-like cleansing, and any mission searching for life is still subject to a full heat treatment (Rummel, 2001).
Heat treatment is time-consuming and stressful on delicate electronic equipment. Moreover, the continued discovery of extremophile organisms raises the question as to whether we can guarantee complete sterilization of a spacecraft prior to its launch (Gross, 2001). We can not, but heating spacecraft equipment to just above 1000C is probably a reasonable compromise that preserves delicate equipment while killing those organisms most likely to be present.
3c. The quarantine and certification of Mars samples
Any missions undertaken by NASA or other space agencies for returning Solar System samples back to Earth are examined closely before launch for their potential backward contamination of the Earth. Samples returned from asteroids or comets, such as the Genesis and Stardust missions, are considered to be of very low risk. Currently, only the Mars sample return missions are felt to have any possibility for biological back contamination (Rummel, 2001).
“The Quarantine and Certification of Martian Samples” is a report of the National Research Council (NRC) released in 2001 (Wood, 2001). It details recommendations for the study of samples returned from Mars. It recommends the facility handling the samples be the most stringent type of containment facility available, the type designated BSL-4 (biosafety laboratory, level 4), the same type of facility that would study highly infectious diseases, such as Ebola virus (Wood, 2001). The NRC also recommends experience gained from the design and use of the LRL should be incorporated in the facility for handling Mars samples. While the facility would be under the auspices of NASA, NRC feels it should be physically associated with an ongoing containment facility with BSL-4 capabilities, such as the Centers for Disease Control and Prevention in Atlanta, Georgia.
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