INTRODUCTION
Planetary biosecurity, also called 'planetary protection' is concerned with protecting the ecosphere of a planet, of avoiding the introduction of foreign organisms from one planet or moon to another. The purpose of terrestrial biosecurity is two-fold: to avoid contaminating another planet or moon with organisms from Earth during exploration of that body, and to avoid back-contamination of the Earth in the case of sample return missions.
The first aim is to prevent the introduction of terrestrial organisms from Earth that might mask the presence of life on the body being explored. The second aim is to prevent the introduction to the Earth of dangerous alien organisms (xenobiology) that could cause disease in the terrestrial ecosystem.
It should be noted that planetary biosecurity can also be concerned with maintaining population health through the control of disease in populations and the maintenance of appropriate food stocks and good hygiene to ensure population survival. Such biosecurity has nothing to do with extraterrestrial biology and is undoubtedly the greater threat. The term planetary protection does not usually concern itself with this latter problem of biosecurity.
OVERVIEW
The diagram below indicates the various aspects of space planetary biosecurity, its goals and the actions that can be taken to assure such security.
Planetary protection is thus the managing of contact between terrestrial life and organic material from celestial bodies in order to:
1) Prevent disruption of the scientific study of these bodies
HISTORY
1956 Lunar and Planetary contamination issue raised at the International Astronautical Federation in their 7th congress in Rome
1958 US National Academy of Sciences passed a resolution to avoid biological contamination in lunar and planetary exploration
1959 Planetary Protection was placed under the Committee on Space Research (COSPAR)
1964 COSPAR issued resolution 26 urging countries to avoid biological contamination of planets during space exploration
1967 US, USSR and UK ratified the UN Outer Space treaty which committed them to conduct space exploration to avoid contamination of celestial bodies & Earth
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THE SCOPE OF LIFE
The original classification of life was by kingdom - originally five but now expanded to six kingdoms.
A more recent classification uses three domains in what is termed the phylogenetic classification. Archaea is a recently discovered domain of 'extremophile bacteria' that could be very relevant to life beyond the Earth.
Many definitions of life exist although there is no general agreement on any of them as they all fall short for some aspects of life. Viruses do not get included in many classifications of life as they only ‘become alive’ within the cells of other life forms.
This lack of a comprehensive definition of life is even more surprising as humans generally have an immediate recognition of what things are alive, even organisms observed through a microscope. There are some exceptions.
No definition is very useful in experiments to determine the presence of life, particularly robotic experiments which are often fooled by non-organic processes. We will see this in the Mars Viking life experiments.
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The forms of life most likely to survive space travel Anthrax bacterial spores are shown at right. |
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The size of life is important in the detection and evaluation of life forms. Relative sizes of terrestrial biological cells and their components are show below.
SPECULATED ABODES OF LIFE
Speculated abodes of life in the solar system are shown below:
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EARTH LUNAR MARS EUROPA ENCELADUS CALLISTO TITAN GANYMEDE CERES PLUTO VENUS |
Y Ubiquitous – wherever water is present X Not after the Apollo Missions (no water?) ? Active Investigation ? Speculation (subsurface ocean) ? Speculation (water geysers seen) ? Speculation (subsurface ocean) ? Speculation (enhanced by Cassini Mission) ? Speculation (subsurface water?) ? Speculation (subsurface water?) ? Speculation after New Horizons (surface ice) ? Phosphine in atmosphere (60km altitude) |
PLANETARY PROTECTION MISSION CATEGORIES
NASA has defined five categories by which all interplanetary missions can distinguished for planetary protection purposes.
Mission Type - Flyby, Orbiter or Lander
Mission Target - Sun, Mercury, some Asteroids, Io
Category I mission targets are basically those that are considered extremely unlikely to support life or contribute to our understanding of life processes in the Solar System. The Sun and Mercury are considered too hot although some science fiction writers have speculated about life living in the twilight zone, in the polar regions. Arthur C Clarke also speculated about 'life' being ejected from the Sun in a short story called "Out of the Sun".
Mission Type - Flyby, Orbiter or Lander
Mission Target - Venus, Luna, Comets, some Asteroids, Jupiter, Saturn, Uranus, Neptune
Category II mission targets are presumed to be of secondary interest in studies of life, but are still thought to be of sufficient interest that simple steps should be taken to avoid the remote risk of forward contamination by terrestrial organisms.
Mission Type - Flyby or Orbiter
Mission Target - Mars, Jovian moons Europa, Ganymede and Callisto
Category III mission targets are those believed able to contribute to our understanding of life development and life processes. Because these missions have a potential for impact on the target surfaces, precautions such as clean room assembly, trajectory biasing and possibly bioburden reduction should be taken.
Mission Type - Probe, Lander or Rover
Mission Target - Mars
Category IV missions are those which are designed to operate on the surface of Mars, which is believed to be the solar system body most likely to support life or the development of life. Planetary protection measures should include clean room assembly, trajectory biasing, sterilisation and detailed documentation of all mission procedures
Mission Type - Earth return
Mission Target - Any
Category V missions are split into unrestricted and restricted missions. Unrestricted missions are those only concerned with forward contamination. Restricted missions are those concerned with both forward and backward contamination. Restricted missions will require the strictest procedures to reduce biological contamination on both the direct and return sections of the journey - specifically maximum sterilisation efforts
THE COLEMAN-SAGAN EQUATION
The Coleman Sagan equation was devised to quantify the probability of contaminating another planetary body by Earth microorganisms, and was published by Michael Coleman and Carl Sagan in 1965. The equation is written:
Nc = the expected contaminating microbial number
N(0) = the initial number of microbes on the spacecraft
R Reduction due to conditions on spacecraft before and after launch
Ps = Probability that microbes on the spacecraft reach the planet surface
Pt = Probability that spacecraft will hit the planet - this is 1 for a lander
Pr = Probability of microbe environmental release (=1 for crashlanding)
Pg Probability of microbe growth. For targets with liquid water Pg=1
For planetary protection acceptability Nc should be less than 0.0001
DETECTION OF LIFE
It has not yet proven possible to define life in such a way that a definitive measurement can be made to determine if life is present in a planetary sample.
The detection of life through a remote automated procedure is not at all easy. Most proposed protocols will allow a determination of no life, but alternative hypotheses will usually call into question a positive result.
The only life detection experiments that have been sent to the surface of a planet are the three experiments carried by each of the two Martian Viking landers. Although they successfully touched down on the Martian surface and did some impressive science, the life detection portion of the mission was something of a fiasco — with conflict, controversy and ultimately quite a bit of confusion.
Clearly, scientists did not yet know enough about how to search for life beyond Earth and the confounding results pretty much eliminated life-detection from NASA’s missions for decades.
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On Earth microscopy can often be used to give a definitive answer as to the presence of life. Incubation and examination are also used.
This technician is taking a prelaunch swab |
PLANETARY PROTECTION IN INTERNATIONAL SPACE LAW
 | Outer Space Treaty (OST – 1967) [ OST Article IX ] |
PLANETARY PROTECTION OFFICERS (NASA)
In the final analysis it is people who control what actually happens to implement planetary protocols. NASA employs a Planetary Protection Officer (PPO) who has a staff to plan the implementation of appropriate protocols, and to monitor and test for compliance.
 Longtime NASA PPO Dr Catherine(Cassie) Conley |
 Current PPO Dr J Nick Berndini |
PROCEDURES - DECONTAMINATION
Various procedures have been used to carry out planetary protection protocols.
Forward protection requires that microbial loads introduced to a planetary surface be kept below a certain value. This is accomplished by:
Reverse protection (of Earth) requires containment and sterilisation
SPACECRAFT ASSEMBLY - CLEAN ROOMS
Nearly all spacecraft are assembled in clean rooms, even the many satellites for which Planetary Protection is not required. This is because the elimination of contaminants drastically increases the reliability of space systems.
Clean room specifications only require the total particulate matter to conform to the specified standard. To determine whether the microbial load also confirms to the Planetary Protection standard, biological assay must also be made. This are usually done by swabbing clean room surfaces, incubating the material for an appropriate period of time and then counting the microbial colonies.
Recently a more intensive investigation has been conducted into the presence of Archaea in clean rooms. This has revealed a ubiquitous presence of these extremophiles in both NASA and ESA clean rooms. Humans seem to be the vector!
APOLLO LUNAR MISSIONS - PLANETARY PROTECTION
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The Apollo manned missions to the Moon were concerned with both forward and reverse planetary protection. The main problem with any manned mission is that humans cannot be sterilised. This adds an uncontrollable dimension to PP. Apollo missions 11, 12 and 14 subjected the returning astronauts to 21 days quarantine from first exposure to lunar material. |
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The assumptions made for lunar planetary protection were:
NASA was concerned with both toxins and replicative material that might be returned to Earth
TOXINS
REPLICATIVE MATERIAL (“LIFE”)
The transportation of the lunar material from Apollo capsule splashdown to the receiving facilities at the NASA Johnson Space Center in Houston, Texas is shown in the illustration below.
The Lunar Receiving Laboratory at the Johnson Space Center is shown in the aerial view below. Both lunar specimens and lunar astronauts were transferred here under strict quarantine.
The prime purpose of this laboratory was to provide a place for testing returned astronauts and lunar material for the possible presence of agents that might be infectious or toxic to man, animals or plants. It was the goal of the laboratory to provide safety clearance for lunar samples within a period of 30 days – providing no deleterious materials were found.
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The three most important tasks at the Lunar Receiving Laboratory were Protection, Isolation and Testing (shown below)/
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VIKING MISSIONS TO MARS - PLANETARY PROTECTION
Two Viking spacecraft were sent to Mars in the mid 1970’s. Because these were non-return missions, only forward contamination was considered. A combination of heat sterilisation and containment within an outer vessel were used to keep terrestrial microorganisms from the Martian surface.
 Viking 1 enroute to Mars |
 Viking 1 deploys lander |
 Firing rockets for soft landing |
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Viking 1 fully deployed on Martian Surface (simulation) at left View of Martian Surface (right) |
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The Viking spacecraft was assembled within a clean room. The lander was placed within an outer container and loaded into an oven where it was subject to dry-heat sterilisaton at 120 degrees C for 30 hours. Although modern electronics can be similarly sterilised at even higher temperatures, to do so will result in a decrease in equipment reliability.
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OVERVIEW OF VIKING MISSIONS TO MARS
VIKING LIFE DETECTION EXPERIMENTS
The size of this biology experiment package was limited to a volume of less than one cubic foot. It was limited by the lander volume, by the aeroshell size and shape, by the launch vehicle throw mass and by the non-availability of a Saturn V launch vehicle.
Four experiments were carried aboard each Viking lander to try and detect if life is present on Mars. The Gas Exchange experiment shared the Gas Chromatograph Mass Spectrometer which was used to identify a large range of chemicals in the Martian soil. The two release experiments used the carbon 14 isotope which can be readily detected from its radiation.
The Labelled Release experiment gave a definite positive result, whereas the other three experiments gave either a nil or ambiguous result. Scientific discussions following analysis of the results led a majority of scientists to believe that the results could be explained by inorganic chemical reactions. Not everyone agreed with these, including the two scientists who ran the Labelled Release experiment.
The confusion and dissension which surrounded the Viking life detection results led NASA to omit life detection experiments aboard Mars landers for many decades.
More recent reanalysis of the Viking results has changed the opinion of some researchers and the most we can really say is that they did not produce a useful result.
The inability of the Viking Mars life experiments to reach a definite conclusion on the presence or absence of planetary life points to a fundamental flaw in Planetary Protection itself. It you can’t determine the presence or absence of life, you can’t protect it!
NATURAL INTERPLANETARY CROSS CONTAMINATION
Meteoroids are continually crossing interplanetary space and frequently collide with the Earth and other planetary bodies. These small pieces of matter may have come from asteroids or comets. We have recently come to realise that they can also be ejected into space from planets during impact events.
Until recently it had been thought the impact events throwing material from a planet’s surface into space would involve such high accelerations and high temperatures that any life forms could not survive such events. However, recent research, including mathematical modelling of such events has shown that there are conditions that are not subject to such life-destroying conditions, and that the physics of impact events does not totally exclude the possibility of transfer of life forms from one planet to another due to ‘natural’ causes.
Deserts (such as the Nullabor) and Antarctica have proven fertile grounds for the recovery of meteorites. The Allan Hills in Antarctica has resulted in a large number of finds. One particular meteorite ALH84001 from this area was studied by Dr David McKay at the NASA Marshall Space Flight Center. The meteorite was an SNC class which are believed to originate from Mars due to their oxygen isotope ratios. McKay produced an electron microscope image of a feature in the meteorite that looked like a fossilised bacterium. Current opinion is that this structure was not produced by a life form.
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Above from left to right: the Allan Hills area in Antarctica, the meteorite in question ALH84001 (the first meteorite found in the Allan Hills area in 1984) and at the right a microscopic section of the meteorite showing a segmented feature that looks like a life-form but is considerably smaller than terrestrial life of similar appearance.
ARE WE TOO LATE?
Planetary contamination may already have occurred for a number of reasons:
EXPANDING PLANETARY PROTECTION HORIZONS
Nearly all discussion of planetary protection is based on the assumption that any life form will be similar to life forms we are familiar with on Earth – ie it will be based around carbon and more specifically, around DNA and/or RNA molecules. And in particular, it will require a water environment of some type to exist. This may be too restrictive, and we may need to leave the biologists and venture into science fiction.
REFERENCES
COSPAR Planetary Protection Policy (pdf)
COSPAR
NASA Planetary Protection Web Page
NASA
Australian Space Academy
