Planetary protection

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A Viking lander being prepared for dry heat sterilization – this remains the "Gold standard"[1] of present-day planetary protection. The Viking spacecraft were heat=treated for 30 hours at 112 °C, nominal 125 °C (five hours at 112 °C was considered enough to reduce the population tenfold even for enclosed parts of the spacecraft, so this was enough for a million-fold reduction of the originally low population).[2]
NASA's introduction to planetary protection: First video on overview page of the NASA Office of Planetary Protection

Planetary protection is a guiding principle in the design of missions to other celestial bodies aiming to prevent biological contamination of the target, and also to protect humans and the biosphere of Earthfrom extraterrestrial biology in the case of sample-return missions. Planetary protection reflects both the unknown nature of the space environment and the desire of the scientific community to preserve the pristine nature of celestial bodies until they can be studied in detail.[3][4]

There are two types of interplanetary contamination. Forward contamination is the transfer of viable organisms from Earth to another celestial body. Back contamination is the transfer of extraterrestrial organisms, if such exist, back to the Earth's biosphere.

History[edit | hide | hide all]

The potential problem of lunar and planetary contamination was first raised at the International Astronautical Federation VIIth Congress in Rome in 1956.[5]

In 1958[6] the U.S. National Academy of Sciences (NAS) passed a resolution stating, “The National Academy of Sciences of the United States of America urges that scientists plan lunar and planetary studies with great care and deep concern so that initial operations do not compromise and make impossible forever after critical scientific experiments.” This led to creation of the ad hoc Committee on Contamination by Extraterrestrial Exploration (CETEX), which met for a year and recommended that interplanetary spacecraft be sterilized, and stated, “The need for sterilization is only temporary. Mars and possibly Venus need to remain uncontaminated only until study by manned ships becomes possible”.[7]

In 1959, planetary protection was transferred to the newly formed Committee on Space Research (COSPAR). COSPAR in 1964 issued Resolution 26 affirming that:

the search for extraterrestrial life is an important objective of space research, that the planet of Mars may offer the only feasible opportunity to conduct this search during the foreseeable future, that contamination of this planet would make such a search far more difficult and possibly even prevent for all time an unequivocal result, that all practical steps should be taken to ensure that Mars be not biologically contaminated until such time as this search has been satisfactorily carried out, and that cooperation in proper scheduling of experiments and use of adequate spacecraft sterilization techniques is required on the part of all deep space probe launching authorities to avoid such contamination.[8]

Signatories of the Outer Space Treaty - includes all current and aspiring space faring nation states. By signing the treaty, these nation states have all committed themselves to planetary protection.
  Signed only
  Not signed

In 1967, the US, USSR, and UK ratified the United Nations Outer Space Treaty. The legal basis for planetary protection lies in Article IX of this treaty:

"Article IX: ... States Parties to the Treaty shall pursue studies of outer space, including the Moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose...[9][10]

This treaty has since been signed and ratified by 104 nation states. Another 24 have signed but not ratified. All the current space-faring nation states have both signed and ratified it. Amongst nations with space faring aspirations, some have not yet ratified: the United Arab Emirates, Syria and North Korea have signed but not yet ratified.[11]

The Outer Space Treaty has consistent and widespread international support, and as a result of this, together with the fact that it is based on the 1963 declaration which was adopted by consensus in the UN National Assembly, it has taken on the status of customary international law. The provisions of the Outer Space Treaty are therefore binding on all states, even those who have neither signed nor ratified it.[12]

For forward contamination, the phrase to be interpreted is "harmful contamination". Two legal reviews came to differing interpretations of this clause (both reviews were unofficial). However the currently accepted interpretation is that “any contamination which would result in harm to a state’s experiments or programs is to be avoided”. NASA policy states explicitly that “the conduct of scientific investigations of possible extraterrestrial life forms, precursors, and remnants must not be jeopardized”.[13]

COSPAR recommendations and categories[edit | hide]

The Committee on Space Research (COSPAR) meets every two years, in a gathering of 2000 to 3000 scientists,[14] and one of its tasks is to develop recommendations for avoiding interplanetary contamination. Its legal basis is Article IX of the Outer Space Treaty [15] (see history below for details).

Its recommendations depend on the type of space mission and the celestial body explored.[16] COSPAR categorizes the missions into 5 groups:

  • Category I: Any mission to locations not of direct interest for chemical evolution or the origin of life, such as the Sun or Mercury. No planetary protection requirements.[17]
  • Category II: Any mission to locations of significant interest for chemical evolution and the origin of life, but only a remote chance that spacecraft-borne contamination could compromise investigations. Examples include the Moon, Venus, and comets. Requires simple documentation only, primarily to outline intended or potential impact targets, and an end of mission report of any inadvertent impact site if such occurred.[17]
  • Category III: Flyby and orbiter missions to locations of significant interest for chemical evolution or the origin of life, and with a significant chance that contamination could compromise investigations e.g., Mars, Europa, Enceladus. Requires more involved documentation than Category II. Other requirements, depending on the mission, may include trajectory biasing, clean room assembly, bioburden reduction, and if impact is a possibility, inventory of organics.[17]
  • Category IV: Lander or probe missions to the same locations as Category III. Measures to be applied depend on the target body and the planned operations. "Sterilization of the entire spacecraft may be required for landers and rovers with life-detection experiments, and for those landing in or moving to a region where terrestrial microorganisms may survive and grow, or where indigenous life may be present. For other landers and rovers, the requirements would be for decontamination and partial sterilization of the landed hardware."[18]
Missions to Mars in category IV are subclassified further:[16]
  • Category IVa. Landers that do not search for Martian life - uses the Viking lander pre-sterilization requirements, a maximum of 300,000 spores per spacecraft and 300 spores per square meter.
  • Category IVb. Landers that search for Martian life. Either the complete lander or the life detection systems must be sterilized to at least to the Viking post-sterilization biological burden levels of 30 spores total per spacecraft. If only the subsystem that acquires and analyses the samples is sterilized in this way, then there needs to be a method to prevent recontamination of the sterilized systems or the samples [an example here might be a drill that can drill down to a potential habitat for present day life]
  • Category IVc. Any component that accesses a Martian special region where terrestrial organisms are likely to propagate, or interpreted to have a high potential for existence of extamt Martian life forms.[19] (see below) must be sterilized to at least to the Viking post-sterilization biological burden levels of 30 spores total per spacecraft.
  • Category V: This is further divided into unrestricted and restricted sample return.
  • Unrestricted Category V: samples from locations judged by scientific opinion to have no indigenous lifeforms. No special requirements.
  • Restricted Category V: (where scientific opinion is unsure) the requirements include: absolute prohibition of destructive impact upon return, containment of all returned hardware which directly contacted the target body, and containment of any unsterilized sample returned to Earth.

For Category IV missions, a certain level of biological burden is allowed for the mission. In general this is expressed as a 'probability of contamination', required to be less than one chance in 10,000[20][21] of forward contamination per mission, but in the case of Mars Category IV missions (above) the requirement has been translated into a count of Bacillus spores per surface area, as an easy to use assay method.[17][22]

More extensive documentation is also required for Category IV. Other procedures required, depending on the mission, may include trajectory biasing, the use of clean rooms during spacecraft assembly and testing, bioload reduction, partial sterilization of the hardware having direct contact with the target body, a bioshield for that hardware, and, in rare cases, complete sterilization of the entire spacecraft.[17]

For restricted Category V missions, the current recommendation[23] is that no uncontained samples should be returned unless sterilized. Since sterilization of the returned samples would destroy much of their science value, current proposals involve containment and quarantine procedures. For details, see Containment and quarantine below. Category V missions also have to fulfill the requirements of Category IV to protect the target body from forward contamination. (COSPAR,2020, COSPAR Policy on Planetary Protection : 2)

Category I[edit | hide]

“not of direct interest for understanding the process of chemical evolution or the origin of life.” [24]

  • Io, Sun, Mercury, undifferentiated metamorphosed asteroids

Category II[edit | hide]

… where there is significant interest relative to the process of chemical evolution and the origin of life, but where there is only a remote1 chance that contamination carried by a spacecraft could compromise future investigations.

1: “Remote” here implies the absence of environments where terrestrial organisms could survive and replicate, or a very low likelihood of transfer to environments where terrestrial organisms could survive and replicate. [25][24][26]

  • Callisto, comets, asteroids of category P, D, and C, Venus,[27] Kuiper belt objects (KBO) < 1/2 size of Pluto.

Provisional Category II[edit | hide]

These are likely to be Category II but may be Category III.

  • Ganymede, Titan, Triton, the Pluto-Charon system, and other large KBOs (> 1/2 size of Pluto),[28] Ceres,

For Pluto and Charon, they state that more research is needed, because there is a remote possibility that the tidal interactions could maintain some water reservoir below the surface.

Similar considerations to the ones for Pluto and Charon apply to other larger KBOs.

Triton is insufficiently well understood at present to say it is definitely devoid of liquid water. The only close up observations to date are those of Voyager 2.

In a detailed discussion of Titan, scientists concluded that there was no danger of contamination of its surface, except short term adding of negligible amounts of organics.

However, Titan could have a below surface water reservoir that communicates with the surface, and if so, this could be at risk of contamination.

In the case of Ganymede, it has strong evidence for a subsurface ocean. The question is, given that its surface shows pervasive signs of resurfacing, is there any communication with its subsurface ocean?

They found no known mechanism by which this could happen, and the Galileo spacecraft found no evidence of cryovolcanism. Initially, they assigned it as Priority B minus, meaning that precursor missions are needed to assess its category before any surface missions. However, after further discussion they provisionally assigned it to Category II. This means that no precursor missions are required, though this could still be revised again, depending on future research.

If there is cryovolcanism on Ganymede or Titan, the undersurface reservoir is thought to be 50 – 150 km below the surface. They were unable to find a process that could transfer the surface melted water back down through 50 km of ice to the under surface sea.[29]

This is why both Ganymede and Titan were assigned a reasonably firm provisional Category II, but pending results of future research.

Icy bodies that show signs of recent resurfacing need further discussion and might need to be assigned to a new category depending on future research. This approach has been applied, for instance, to missions to Ceres. The planetary protection Category is subject for review during the mission of the Ceres orbiter (Dawn) depending on the results found.[30]

Category III / IV[edit | hide]

These are category III for orbiters and category IV for landers.

“…where there is a significant chance that contamination carried by a spacecraft could jeopardize future exploration.” We define “significant chance” as “the presence of niches (places where terrestrial microorganisms could proliferate) and the likelihood of transfer to those places.” [25][24]

  • Mars because of possible surface habitats.
  • Europa because of its subsurface ocean.
  • Enceladus because of evidence of water plumes.

Category V[edit | hide]

Unrestricted Category V: “Earth-return missions from bodies deemed by scientific opinion to have no indigenous life forms.”[24]

Restricted Category V: "Earth-return missions from bodies deemed by scientific opinion to be of significant interest to the process of chemical evolution or the origin of life."[24]

In the category V for sample return the conclusions so far are:[24]

  • Restricted Category V: Mars, Europa, Enceladus.
  • Unrestricted Category V: Venus, the Moon.

with others to be decided.

Other objects[edit | hide]

If there has been no activity for 3 billion years, it will not be possible to destroy the surface by terrestrial contamination, so can be treated as Category I. Otherwise, the category may need to be reassessed.

Mars special regions[edit | hide]

A special region on Mars is a region classified by COSPAR where terrestrial organisms are likely to propagate, or interpreted to have a high potential for existence of extant Martian life forms.[19][31][32]. Based on current understanding, this includes any region with a high enough temperature for Earth organisms to propagate (above -18°C), and with water in a form accessible to them (water activity higher than 0.6) [33], both requirements to be satisfied simultaneously.

Other environmental factors such as the perchlorates and other chemistry [34], ionizing radiation[35]., UV radiation[36], and low atmospheric pressure[37] are not used to restrict special regions, because some Earth microbes tolerate them. The presence of multiple environmental factors simultaneously is also not used to restrict special regions because of the existence of polyextremophiles that can withstand multiple simultaneous extreme conditions[38].

In principle native Martian life could have additional capabilities, and so, be able to propagate at lower temperatures or with lower water activity (one suggestion is a mixture of water and hydrogen peroxide as internal solvent in the cells[39] ). However, since these capabilities are unknown, they are not used to determine special regions.

The requirements also apply to spacecraft induced special regions. Missions need to study these in the planning phase, for instance the potential to create them through impact or sources of thermal energy foreign to Mars[19]. If a hard landing risks biological contamination of a special region, it has to be sterilized sufficiently to prevent this (COSPAR category IVc)[19].[40][19].

Missions need to study their potential to create Spacecraft-Induced special regions during the planning phase and take action to make sure they are not inadvertently created. Spacecraft also need to avoid special regions if not sterilized sufficiently to prevent contaminating them[40]. The risk of spacecraft induced special regions needs to be evaluated separately for each mission, taking account of the spacecraft and the landing ellipse[19].

There are currently no confirmed special regions. However there are many uncertain regions such as the recurring slope lineae. These are treated as special regions for the purposes of planetary protection, until more is known[41].

Catherine Conley, NASA's Planetary protection officer[2] at the time, explains why the spacecraft we send to Mars are sterilized, 33 seconds into this video

Third video on overview page of the NASA Office of Planetary Protection.

“So we have to do all of our search for life activities, we have to look for the Mars organisms, without the background, without the noise of having released Earth organisms into the Mars environment”

See also

Revisions of the definition of a special region[edit | hide]

The definition of a special region has been revised several times. In the 2006 study it was implicit that a special region must be defined by warm enough temperatures combined with sufficient water activity. If the Mars surface is mapped using those requirements alone and requiring them to overlap, the map would be blank [42]. The only place where habitats could occur for the 2006 report were deep below the surface, or perhaps places like the gully systems where water could be exposed to the surface dynamically from the subsurface.

However the 2014 study finds that though the temperature and water activity conditions are not present simultaneously, often they are present at the same location on the surface within a 24 hour period of each other due to the extreme day - night cycles on Mars. That then makes it possible that terrestrial biology could bridge the gap (e.g. retain the water through to warmer temperatures in the same day). For instance at the Curiosity and Viking sites temperatures in the daytime are regularly high enough for replication and at night relative humidity was above 0.6 and nearly always close to 1.0, and since both conditions occur in the same 24 hour period, there may be a way for organisms to connect the favorable aspects of these different periods through biotic adaptation [43]

The report remarks that they didn't have any evidence yet that terrestrial organisms could bridge that gap, and they had some evidence that suggested it might be unbridgeable. However where the atmospheric pressure is above the triple point of water, precipitation that reaches the ground could melt and provide a temporary habitat. Also some materials such as clays, and the organisms themselves could retain more water than the soil itself. It also remarks on the potential occurrence of small-scale habitats, especially in the subsurface, not detectable with space instruments either existing or planned.

Before the 2014 report was published, both NASA and ESA took steps to have it reviewed independently. This 2015 review concurred with 29 findings of the original report. They did not support one of them and proposed modifications to 15 others[41]. The 2015 review comittee in their report[44] said that they believe that some important aspects were not covered in the previous report[45]. For instance:

  • The possibility of terrestrial contamination blown in the Martian dust.

Although UV radiation would sterilize life quickly, this can be attenuated by the dust. Also the life can occur in larger cell chains, clumps or aggregates, and the cells in the interior of these aggregates can be protected from UV.

The review says that research so far is not sufficient to answer the question and that the possibility of this form of contamination could be confirmed or rejected in terrestrial Mars simulation chambers[46]

  • The ability of multi-species microbial communities to alter dispersed small-scale habitats.

Cells in biofilms are embedded in a matrix of externally produced substances (such as polysaccharides, proteins, lipids and DNA) and adjust environmental parameters to make them more habitable[47]. There are many examples of small-scale and even microscale communities on Earth including biofilms only a few cells thick. Microbes can propagate in these biofilms despite adverse and extreme surrounding conditions.

  • microscale habitats that can't be detected from orbit.

The 2014 report briefly considers these. The 2015 review expands on this topic, and says that to identify such potential habitats requires a better understanding of the temperature and water activity of potential microenvironments on Mars, for instance in the interior of craters, or microenvironments underneath rocks. These may provide favourable conditions for establishing life on Mars even when the landscape-scale temperature and humidity conditions would not permit it. [48]

  • Ice close to the surface needs to be taken account of for spacecraft induced special regions.

The 2014 report looked at distributions of ice and concluded that ice in the tropics is buried too deep to be a consideration[49]

However the 2014/5 review corrected this due to evidence of ice present at depths of less than one meter in pole-facing slopes[50]

  • Utility of maps

The 2014 report[19] provided a map of regions of Mars where there may be ice below the surface as well as potential RSL's. The 2015 review however said that such maps are most useful if accompanied by cautionary remarks on their limitations, as they are subject to change with new discoveries and because of the potential for microhabitats[44].

Caution on use of maps[edit | hide]

The committees for the 2014/5 revisions caution that maps of regions with higher or lower probability to host special regions should be accompanied by cautionary remarks on their limitations. Any such map can only represent the current state of konwledge, which is incomlete and subject to change as new information is obtained. [51]

Instead each mission needs to be considered on a case by case basis using all the available data. They give the example of Schiaparelli where, for example, all HiRISE images of the landing site were inspected for the possible presence of RSL's. [52]

For more details about the characterization of Mars special regions for purposes of planetary protection see:

See also

Planetary categorizations of solar system objects[edit | hide]

Some targets are easily categorized. Others are assigned provisional categories by COSPAR, pending future discoveries and research.

The 2009 COSPAR Workshop on Planetary Protection for Outer Planet Satellites and Small Solar System Bodies covered this in some detail. Most of these assessments are from that report, with some later refinements. This workshop also gave more precise definitions for some of the categories:[25][53]

The Coleman-Sagan equation[edit | hide]

The aim of the current regulations is to keep the number of microorganisms low enough so that the probability of contamination of Mars (and other targets) is acceptable. It is not an objective to make the probability of contamination zero.

The aim is to keep the probability of contamination of 1 chance in 10,000 of contamination per mission flown.[20] This figure is obtained typically by multiplying together the number of microorganisms on the spacecraft, the probability of growth on the target body, and a series of bioload reduction factors.

In detail the method used is the Coleman-Sagan equation.[54]



= the number of microorganisms on the spacecraft initially
= Reduction due to conditions on spacecraft before and after launch
= Probability that microorganisms on the spacecraft reach the surface of the planet
= Probability that spacecraft will hit the planet - this is 1 for a lander
= Probability of microorganism to be released in the environment when on the ground, usually set to 1 for crashlanding.
= Probability of growth. For targets with liquid water this is set to 1 for sake of the calculation.

Then the requirement is

The is a number chosen by Sagan et al., somewhat arbitrarily. Sagan and Coleman assumed that about 60 missions to the Mars surface would occur before the exobiology of Mars is thoroughly understood, 54 of those successful, and 30 flybys or orbiters, and the number was chosen to endure a probability to keep the planet free from contamination of at least 99.9% over the duration of the exploration period.[21]

Critiques[edit | hide]

The Coleman Sagan equation has been criticised because the individual parameters are often not known to better than a magnitude or so. For example, the thickness of the surface ice of Europa is unknown, and may be thin in places, which can give rise to a high level of uncertainty in the equation.[55][56] It has also been criticised because of the inherent assumption made of an end to the protection period and future human exploration. In the case of Europa, this would only protect it with reasonable probability for the duration of the period of exploration.[55][56]

Greenberg has suggested an alternative, to use the natural contamination standard - that our missions to Europa should not have a higher chance of contaminating it than the chance of contamination by meteorites from Earth.[57][58]

As long as the probability of people infecting other planets with terrestrial microbes is substantially smaller than the probability that such contamination happens naturally, exploration activities would, in our view, be doing no harm. We call this concept the natural contamination standard.

Another approach for Europa is the use of binary decision trees which is favoured by the Committee on Planetary Protection Standards for Icy Bodies in the Outer Solar System under the auspices of the Space Studies Board.[20] This goes through a series of seven steps, leading to a final decision on whether to go ahead with the mission or not.[59]

Recommendation: Approaches to achieving planetary protection should not rely on the multiplication of bioload estimates and probabilities to calculate the likelihood of contaminating Solar System bodies with terrestrial organisms unless scientific data unequivocally define the values, statistical variation, and mutual independence of every factor used in the equation.

Recommendation: Approaches to achieving planetary protection for missions to icy Solar System bodies should employ a series of binary decisions that consider one factor at a time to determine the appropriate level of planetary protection procedures to use.

Laws for a restricted category V sample return[edit | hide]

Although the forwards direction is only covered by the Outer Space Treaty there are many other laws that protect us in the backwards direction of a sample returned from Mars (say) to Earth. Margaret Race looked in detail at the legal processes that would have to be completed before we can return a sample from Mars to Earth, even to a purpose built receiving facility.

Before a sample return, we have to accomplish, in this order

  • Several years: Formal environment impact statement for NEPA + laws on quarantine to be enacted, involving broad public consultation. The average length of time for an EIS in the twelve months ending 30th September 2016 was 46 months (see the DOE's Lessons Learned Quarterly Report).
  • Several years: Presidential review of potential large scale effects on the environment. This has to be done after all the other domestic legislation is completed.
  • Can be done alongside the other work: International treaties to be negotiated and domestic laws of other countries

This covers only a few of the main points

In more detail, summary of Margaret Race's findings[60]:

She found that under the National Environmental Policy Act (NEPA) (which did not exist in the Apollo era) a formal environment impact statement is likely to be required, and public hearings during which all the issues would be aired openly. This process is likely to take up to several years to complete.

During this process, she found, the full range of worst accident scenarios, impact, and project alternatives would be played out in the public arena. Other agencies such as the Environment Protection Agency, Occupational Health and Safety Administration, etc, may also get involved in the decision making process.

The laws on quarantine will also need to be clarified as the regulations for the Apollo program were rescinded. In the Apollo era, NASA delayed announcement of its quarantine regulations until the day Apollo was launched, so bypassing the requirement for public debate - something that would be unlikely to be tolerated today.

It is also probable that the presidential directive NSC-25 will apply which requires a review of large scale alleged effects on the environment and is carried out subsequent to the other domestic reviews and through a long process, leads eventually to presidential approval of the launch.

Then apart from those domestic legal hurdles, there are numerous international regulations and treaties to be negotiated in the case of a Mars Sample Return, especially those relating to environmental protection and health. She concluded that the public of necessity has a significant role to play in the development of the policies governing Mars Sample Return}}

Containment and quarantine for restricted Category V sample return[edit | hide]

In the case of restricted Category V missions, Earth is protected through quarantine of sample and astronauts, and sample containment.

In the case of a Mars sample return, missions would be designed so that no part of the capsule that encounters the Mars surface is exposed to the Earth environment.

One way to do that is to enclose the sample container within a larger outer container from Earth, in the vacuum of space. The integrity of any seals is essential and the system must also be monitored to check for the possibility of micro-meteorite damage during return to Earth.[61][62][63][64]

The recommendation of the ESF report is that [23]

“No uncontained Mars materials, including space craft surfaces that have been exposed to the Mars environment should be returned to Earth unless sterilised"

..."For unsterilised samples returned to Earth, a programme of life detection and biohazard testing, or a proven sterilisation process, shall be undertaken as an absolute precondition for the controlled distribution of any portion of the sample.”

No restricted category V returns have been carried out in recent times.

During the Apollo program the sample returns were regulated through the Extra-Terrestrial Exposure Law. This was rescinded in 1991, so new legislation would need to be enacted. The Apollo era quarantine procedures are of interest as the only attempt to date of a return to Earth of a sample that, at the time, was thought to have a remote possibility of including extraterrestrial life.

Samples and astronauts were quarantined in the Lunar Receiving Laboratory.[65] The methods used would be considered inadequate for containment by modern standards.[66] Also the lunar receiving laboratory would be judged a failure by its own design criteria as the sample return didn't contain the lunar material, with two failure points during the Apollo 11 return mission, at the splashdown and at the facility itself.

However the Lunar Receiving Laboratory was built quickly with only two years from start to finish, a time period now considered inadequate. Lessons learned from it can help with design of any Mars sample return receiving facility.[67]

Design criteria for a proposed Mars Sample Return Facility, and for the return mission, have been developed by the American National Research Council,[68] and the European Space Foundation.[69] They concluded that it could be based on biohazard 4 containment but with more stringent requirements to contain unknown microorganisms possibly as small as or smaller than the smallest Earth microorganisms known, the ultramicrobacteria. The ESF study also recommended that it should be designed to contain the smaller gene transfer agents if possible, as these could potentially transfer DNA from martian microorganisms to terrestrial microorganisms if they have a shared evolutionary ancestry. It also needs to double as a clean room facility to protect the samples from terrestrial contamination that could confuse the sensitive life detection tests that would be used on the samples.

Before a sample return, new quarantine laws would be required. Environmental assessment would also be required, and various other domestic and international laws not present during the Apollo era would need to be negotiated.[60]

Decontamination procedures[edit | hide]

For all spacecraft missions requiring decontamination, the starting point is clean room assembly in US federal standard class 100 cleanrooms. These are rooms with fewer than 100 particles of size 0.5 µm or larger per cubic foot. Engineers wear cleanroom suits with only their eyes exposed. Components are sterilized individually before assembly, as far as possible, and they clean surfaces frequently with alcohol wipes during assembly. Spores of Bacillus subtilis was chosen for not only its ability to readily generate spores, but its well-established use as a model species. It is a useful tracker of UV irradiation effects because of its high resilience to a variety of extreme conditions. As such it is an important indicator species for forward contamination in the context of planetary protection.

For Category IVa missions (Mars landers that do not search for Martian life), the aim is to reduce the bioburden to 300,000 bacterial spores on any surface from which the spores could get into the Martian environment. Any heat tolerant components are heat sterilized to 114 °C. Sensitive electronics such as the core box of the rover including the computer, are sealed and vented through high-efficiency filters to keep any microbes inside.[70][71][72]

For more sensitive missions such as Category IVc (to Mars special regions), a far higher level of sterilization is required. These need to be similar to levels implemented on the Viking landers, which were sterilized for a surface which, at the time, was thought to be potentially hospitable to life similar to special regions on Mars today.

In microbiology, it is usually impossible to prove that there are no microorganisms left viable, since many microorganisms are either not yet studied, or not cultivable. Instead, sterilization is done using a series of tenfold reductions of the numbers of microorganisms present. After a sufficient number of tenfold reductions, the chance that there any microorganisms left will be extremely low.[original research?]

Dry heat sterilization[edit | hide]

The two Viking Mars landers were sterilized using dry heat sterilization. After preliminary cleaning to reduce the bioburden to levels similar to present day Category IVa spacecraft, the Viking spacecraft were heat-treated for 30 hours at 112 °C, nominal 125 °C (five hours at 112 °C was considered enough to reduce the population tenfold even for enclosed parts of the spacecraft, so this was enough for a million-fold reduction of the originally low population).[2]

Revised figures as used in 2017 extend the range up to 200 C using various formulae, see table 1 of the 2017 survey article by Shirey et al, "An Overview of Surface Heat Microbial Reduction as a Viable Microbial Reduction Modality for Spacecraft Surfaces."[73]. For encapsulated surfaces the formula for 2-3 decimal reductions are:

  • Range 116 to 125 °C, Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "":): {\displaystyle 5*0.5* 10^{((125 –T) / 15)}} hours. Figures are not given for temperatures below 116 °C, but if the formla is extrapolated down to the Viking temperatures, that makes it 18 hours for a 2-3 decimal reductions[74] and just short of ten hours at 116 °C[75]
  • Range 125 to 140 °C, Failed to parse (syntax error): {\displaystyle 5*0.5* 10^{((125 –T) / 21)}} hours. Example, at 140 °C it's [76] = 0.48 hours
  • Range 140 to 200 °C, Failed to parse (syntax error): {\displaystyle 5*0.5* 10^{((140 –T) / (23*T/140))}} hours. Example, at 200 °C it's [77] = 0.037 hours or about 2 minutes 14 seconds.

A million fold reduction is achieved with 350 °C for 1 hr. and 500 °C for 0.5 secs[73]

Challenge of modern materials[edit | hide]

Modern materials however are often not designed to handle such temperatures, especially since modern spacecraft often use "commercial off the shelf" components. Problems encountered include nanoscale features only a few atoms thick, plastic packaging, and conductive epoxy attachment methods. Also many instrument sensors cannot be exposed to high temperature, and high temperature can interfere with critical alignments of instruments.[2]

New methods[edit | hide]

As a result, new methods are needed to sterilize a modern spacecraft to the higher categories such as Category IVc for Mars, similar to Viking.[2] Methods under evaluation, or already approved, include[78]:

  • Vapour phase hydrogen peroxide - effective, but can affect finishes, lubricants and materials that use aromatic rings and sulfur bonds. This has been established, reviewed, and a NASA/ESA specification for use of VHP has been approved by the Planetary Protection Officer, but it has not yet been formally published.[79]
  • Ethylene oxide - this is widely used in the medical industry, and can be used for materials not compatible with hydrogen peroxide. It is under consideration for missions such as ExoMars.
  • Gamma radiation and electron beams have been suggested as a method of sterilization, as they are used extensively in the medical industry. They need to be tested for compatibility with spacecraft materials and hardware geometries, and are not yet ready for review.
  • Supercritical carbon dioxide snow (Mars) - is most effective against traces of organic compounds rather than whole microorganisms. Has the advantage though that it eliminates the organic traces - while other methods kill the microorganisms, they leave organic traces that can confuse life detection instruments. Is under study by JPL and ESA.

Some other methods are of interest as they can sterilize the spacecraft after arrival on the planet.[citation needed]

Heat sterilization at higher temperatures with modern components, 200 - 300°C, or 500°C[edit | hide]

In the NASA Venus Technology Plan (2010)[80], they explore ideas for a rover to operate at Venus surface temperatures for long periods of time. One option is to cool it to 200 - 300°C. Another is to design it to run at 500°C with no cooling. For the first option, they say (page 16)

1) Medium-Temperature Semiconductor-Based Electronics: Medium-temperature (200–300°C) electronics are not only technically less difficult than electronics that operate at Venus surface temperatures but also have terrestrial commercial applications. A broad set of component options, including microprocessor and memory devices exist.

Sauders et al have done work on an "automation rover" that could function at up to 500 C using a mixture of mechanical components, as in the early mechanical ballistic computers, and electronics, and have suggested using this for sterile rovers.[81].

An automaton rover could be subjected to much higher contamination control procedures than traditional rovers. It could be baked at extremely high temperatures, irradiated, and subjected to multiple chemical baths to kill any bacteria. Thus, automatons would be valuable in highly contamination control sensitive environments, like collecting samples from the dark, water streaks on Mars. In this type of situation, the automaton would likely be working in tandem with a traditional Mars rover.

Brian Wilcox is working on a 100% sterile probe to descend into the Europan ocean. [82]. It would be deployed from a less sterile lander and it would be sterilized by keeping it at a temperature of 500°C throughout the journey out to Europa. In his abstract he says

A central thesis of this work is that we must start by addressing the Planetary Protection constraints, and not to try to add them on at the end. Specifically, all hardware in the probe would be designed to survive heat sterilization at 500 °C for extended periods, as required to meet the COSPAR 1-in-10,000 probability per mission of biological contamination of the ocean

The NASA press release says[83]

To ensure no Earth microbes hitched a ride, the probe would heat itself to over 900 degrees Fahrenheit (482 degrees Celsius) during its cruise on a spacecraft. That would kill any residual organisms and decompose complex organic molecules that could affect science results.

Bioburden detection and assessment[edit | hide]

The spore count is used as an indirect measure of the number of microorganisms present. Typically 99% of microorganisms by species will be non-spore forming and able to survive in dormant states[citation needed], and so the actual number of viable dormant microorganisms remaining on the sterilized spacecraft is expected to be many times the number of spore-forming microorganisms.

One new spore method approved is the "Rapid Spore Assay". This is based on commercial rapid assay systems, detects spores directly and not just viable microorganisms and gives results in 5 hours instead of 72 hours.[2]

Challenges[edit | hide]

It is also long been recognized that spacecraft cleaning rooms harbour polyextremophiles as the only microbes able to survive in them.[84][85][86][87] For example, in a recent study, microbes from swabs of the Curiosity rover were subjected to desiccation, UV exposure, cold and pH extremes. Nearly 11% of the 377 strains survived more than one of these severe conditions.[87]

This does not mean that these microbes have contaminated Mars. This is just the first stage of the process of bioburden reduction. To contaminate Mars they also have to survive the low temperature, vacuum, UV and ionizing radiation during the months long journey to Mars, and then have to encounter a habitat on Mars and start reproducing there. Whether this has happened or not is a matter of probability. The aim of planetary protection is to make this probability as low as possible. The currently accepted target probability of contamination per mission is to reduce it to less than 0.01%, though in the special case of Mars, scientists also rely on the hostile conditions on Mars to take the place of the final stage of heat treatment decimal reduction used for Viking. But with current technology scientists cannot reduce probabilities to zero.[original research?]

New methods[edit | hide]

Two recent molecular methods have been approved[2] for assessment of microbial contamination on spacecraft surfaces.[71][88][when?]

  • Adenosine triphosphate (ATP) detection - this is a key element in cellular metabolism. This method is able to detect non cultivable organisms. It can also be triggered by non viable biological material so can give a "false positive".
  • Limulus Amebocyte Lysate assay - detects lipopolysaccharides (LPS). This compound is only present in Gram-negative bacteria. The standard assay analyses spores from microbes that are primarily Gram-positive, making it difficult to relate the two methods.

Impact prevention[edit | hide]

This particularly applies to orbital missions, Category III, as they are sterilized to a lower standard than missions to the surface. It is also relevant to landers, as an impact gives more opportunity for forward contamination, and impact could be on an unplanned target, such as a special region on Mars.

The requirement for an orbital mission is that it needs to remain in orbit for at least 20 years after arrival at Mars with probability of at least 99% and for 50 years with probability at least 95%. This requirement can be dropped if the mission is sterilized to Viking sterilization standard.[89]

In the Viking era (1970s), the requirement was given as a single figure, that any orbital mission should have a probability of less than 0.003% probability of impact during the current exploratory phase of exploration of Mars.[90]

For both landers and orbiters, the technique of trajectory biasing is used during approach to the target. The spacecraft trajectory is designed so that if communications are lost, it will miss the target.

Issues with impact prevention[edit | hide]

Despite these measures[which?] there has been one notable failure of impact prevention. The Mars Climate Orbiter which was sterilized only to Category III, crashed on Mars in 1999 due to a mix-up of imperial and metric units. The office of planetary protection stated that it is likely that it burnt up in the atmosphere, but if it survived to the ground, then it could cause forward contamination.[91]

Mars Observer is another Category III mission with potential planetary contamination. Communications were lost three days before its orbital insertion maneuver in 1993. It seems most likely it did not succeed in entering into orbit around Mars and simply continued past on a heliocentric orbit. If it did succeed in following its automatic programming, and attempted the manoeuvre, however, there is a chance it crashed on Mars.[citation needed]

Three landers have had hard landings on Mars. These are Schiaparelli EDM lander, the Mars Polar Lander, and Deep Space 2. These were all sterilized for surface missions but not for special regions (Viking pre-sterilization only). Mars Polar Lander, and Deep Space 2 crashed into the polar regions which are now treated as special regions because of the possibility of forming liquid brines.

Controversies[edit | hide]

Meteorite argument[edit | hide]

Alberto G. Fairén and Dirk Schulze-Makuch published an article in Nature recommending that planetary protection measures need to be scaled down. They gave as their main reason for this, that exchange of meteorites between Earth and Mars means that any life on Earth that could survive on Mars has already got there and vice versa.[92]

Robert Zubrin used similar arguments in favour of his view that the back contamination risk has no scientific validity.[93][94]

Rebuttal by NRC[edit | hide]

The meteorite argument was examined by the NRC in the context of back contamination. It is thought that all the Martian meteorites originate in relatively few impacts every few million years on Mars. The impactors would be kilometers in diameter and the craters they form on Mars tens of kilometers in diameter. Models of impacts on Mars are consistent with these findings.[95][96][97]

Earth receives a steady stream of meteorites from Mars, but they come from relatively few original impactors, and transfer was more likely in the early Solar System. Also some life forms viable on both Mars and on Earth might be unable to survive transfer on a meteorite, and there is so far no direct evidence of any transfer of life from Mars to Earth in this way.

The NRC concluded that though transfer is possible, the evidence from meteorite exchange does not eliminate the need for back contamination protection methods.[98]

Impacts on Earth able to send microorganisms to Mars are also infrequent. Impactors of 10 km across or larger can send debris to Mars through the Earth's atmosphere but these occur rarely, and were more common in the early Solar System.[citation needed]

Proposal to end planetary protection for Mars[edit | hide]

In their 2013 paper "The Over Protection of Mars", Alberto Fairén and Dirk Schulze-Makuch suggested that space agencies no longer need to protect Mars, essentially using Zubrin's meteorite transfer argument.[99] This was rebutted in a follow up article "Appropriate Protection of Mars", in Nature by the current and previous planetary protection officers Catherine Conley and John Rummel.[100][101]. The debate continues in articles in Astrobiology journal in 2017[102][103], 2018[104][105] and 2019[106]

Critique of Category V containment measures[edit | hide]

The scientific consensus is that the potential for large-scale effects, either through pathogenesis or ecological disruption, is extremely small.[68][107][108][109][110] Nevertheless, returned samples from Mars will be treated as potentially biohazardous until scientists can determine that the returned samples are safe. The goal is to reduce the probability of release of a Mars particle to less than one in a million.[108]

The International Committee Against Mars Sample Return[111] agree with the assessment of low probability of large-scale effects, but consider the proposed containment measures insufficient, given the possible severity of the worst-case scenario. They come to this conclusion partly as a result of considerations of human error and the novelty of the mission proposal. Consequently, they advocate much more in situ research before undertaking a Mars Sample Return (MSR).[111][112]

Proposal for extension of protection to non-biological considerations[edit | hide]

A COSPAR workshop in 2010, looked issues to do with protecting areas from non biological contamination.[113][114] They recommended that COSPAR expand its remit to include such issues.

Recommendations of the workshop include:

Recommendation 3 COSPAR should add a separate and parallel policy to provide guidance on requirements/best practices for protection of non-living/nonlife-related aspects of Outer Space and celestial bodies

Ideas for doing this suggested since the workshop include protected special regions, or "Planetary Parks"[115] to keep regions of the Solar System pristine for future scientific investigation, and also for ethical reasons.

Proposal to extend time scale for contamination prevention[edit | hide]

This is about whether the aim is to make sure that any contamination is contained (for instance on or in the spacecraft) for some fixed future time frame like a century, or whether exploration should be done in such a way that contamination is contained indefinitely.

Astrobiologist Christopher McKay has argued that until we have better understanding of Mars, our explorations should be biologically reversible.[116][117] For instance if all the microorganisms introduced to Mars so far remain dormant within the spacecraft, they could in principle be removed in the future, leaving Mars completely free of contamination from modern Earth lifeforms.

In the 2010 workshop one of the recommendations for future consideration was to extend the period for contamination prevention to the maximum viable lifetime of dormant microorganisms introduced to the planet.

"'Recommendation 4.' COSPAR should consider that the appropriate protection of potential indigenous extraterrestrial life shall include avoiding the harmful contamination of any habitable environment —whether extant or foreseeable— within the maximum potential time of viability of any terrestrial organisms (including microbial spores) that may be introduced into that environment by human or robotic activity."[114]

In the case of Europa, a similar idea has been suggested, that it is not enough to keep it free from contamination during our current exploration period. It might be that Europa is of sufficient scientific interest that the human race has a duty to keep it pristine for future generations to study as well. This was the majority view of the 2000 task force examining Europa, though there was a minority view of the same task force that such strong protection measures are not required.

"One consequence of this view is that Europa must be protected from contamination for an open-ended period, until it can be demonstrated that no ocean exists or that no organisms are present. Thus, we need to be concerned that over a time scale on the order of 10 million to 100 million years (an approximate age for the surface of Europa), any contaminating material is likely to be carried into the deep ice crust or into the underlying ocean."[118]

Protecting objects beyond the Solar System[edit | hide]

The proposal by the German physicist Claudius Gros, that the technology of the Breakthrough Starshot project may be utilized to establish a biosphere of unicellular organisms on otherwise only transiently habitable exoplanets,[119] has sparked a discussion,[120] to what extent planetary protection should be extended to exoplanets.[121][122]

Claudius Gros he also considers the possiblity of young oxygen rich planets. M-dwarf planets may have oxygen levels, from the dissociation of water, of many bars. This might sterilize the planet of any emerging primitive life, but be suitable for oxygen using Earth life. If so, he argues that it might be ethically acceptable to seed it with microbes that initiate a new biosphere there in probes that would get there thousands of years from now. The need to preserve it for scientific study, he argues, is not as relevant as for solar system bodies, because of the long timescales to get there and likely development of computer simulations to study evolution at early stages like that. The missions should value higher life and abort if any are detected from orbit. If the planet already has prokaryotes then he suggests that this may be ethically acceptable[123].

For terrestrial life it is customto attribute value nearly exclusively to complex life, viz to animals and plants. Killinga few billion bacteria while brushing teeth does not cause, to give an example, moralheadaches The situation changes however when it comes to extrasolar life, for which wemay attribute value also to future evolutionary pathways. This is a delicate situation.Is it admissible to bring eukaryotes to a planet in a prokaryotic state, superseding suchindigenous life with lifeforms having the potential to develop into complex ecologies ... Endowing a selected number of exoplanetswith the possibility to evolve higher life forms would in this case not interfere with theevolution of yet simple life forms on potentially billions of other planets.

See also[edit | hide]

References[edit | hide]

  1. Assessment of Planetaryabou Protection and Contamination Control Technologies for Future Planetary Science Missions, Jet Propulsion Laboratory, January 24, 2011
    3.1.1 Microbial Reduction Methodologies:

    "This protocol was defined in concert with Viking, the first mission to face the most stringent planetary protection requirements; its implementation remains the gold standard today."

  2. 2.0 2.1 2.2 2.3 2.4 2.5 Assessment of Planetary Protection and Contamination Control Technologies for Future Planetary Science Missions see Section 3.1.2 Bio-burden Detection and Assessment. January 24, JPL, 2011
  3. Tänczer, John D. Rummel; Ketskeméty, L.; Lévai, G. (1989). "Planetary protection policy overview and application to future missions". Advances in Space Research. 9 (6): 181–184. Bibcode:1989AdSpR...9..181T. doi:10.1016/0273-1177(89)90161-0. PMID 11537370. Retrieved 2012-09-11. 
  4. Portree, David S.F. (2 October 2013). "Spraying Bugs on Mars (1964)". Wired. Retrieved 3 October 2013. 
  5. NASA Office of Planetary Protection. "Planetary Protection History". Retrieved 2013-07-13. 
  6. Preventing the Forward Contamination of Mars (2006) - Page 12
  7. Preventing the Forward Contamination of Mars
  8. Preventing the Forward Contamination of Mars - p12 quotes from COSPAR 1964 Resolution 26
  9. Full text of the Outer Space Treaty Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies Archived 2013-07-08 at the Wayback Machine. - See Article IX
  10. Centre National d’Etudes Spatiales (CNES) (2008). "Planetary protection treaties and recommendations". Retrieved 2012-09-11. 
  11. "Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies". United Nations Office for Disarmament Affairs. Retrieved 2013-04-18. 
  12. Meishan Goh, Gérardine; Kazeminejad, Bobby (2004). "Mars through the looking glass: an interdisciplinary analysis of forward and backward contamination". Space Policy. 20 (3): 217–225. doi:10.1016/j.spacepol.2004.06.008. ISSN 0265-9646. More crucially, because of the consistent and widespread international support for its fundamental tenets, and the fact that it was based on an earlier 1963 Declaration adopted by consensus in the United Nations General Assembly [43], the principles enshrined in the Outer Space Treaty have taken on the status of customary international law [44]. They are therefore binding on all states, even those that have neither signed nor ratified the Outer Space Treaty 
  13. Preventing the Forward Contamination of Mars, page 13 Summarizes this para in the book:

    A policy review of the Outer Space Treaty concluded that, while Article IX "imposed international obligations on all state parties to protect and preserve the environmental integrity of outer space and celestial bodies such as Mars," there is no definition as to what constitutes harmful contamination, nor does the treaty specify under what circumstances it would be necessary to "adopt appropriate measures" or which measures would in fact be "appropriate"

    An earlier legal review, however, argued that "if the assumption is made that the parties to the treaty were not merely being verbose" and "harmful contamination" is not simply redundant, "harmful" should be interpreted as "harmful to the interests of other states," and since "states have an interest in protecting their ongoing space programs," Article IX must mean that "any contamination which would result in harm to a state’s experiments or programs is to be avoided"

    Current NASA policy states that the goal of NASA’s forward contamination planetary protection policy is the protection of scientific investigations, declaring explicitly that "the conduct of scientific investigations of possible extraterrestrial life forms, precursors, and remnants must not be jeopardized"

  14. COSPAR scientific assemblies
  15. Preventing the Forward Contamination of Mars ( 2006 ) - Page 13
  16. 16.0 16.1 COSPAR PLANETARY PROTECTION POLICY (20 October 2002; As Amended to 24 March 2011)
  17. 17.0 17.1 17.2 17.3 17.4 COSPAR’s Planetary Protection Policy (as of 2017)
  18. "Mission Design And Requirements". Office of Planetary Protection. 
  19. 19.00 19.01 19.02 19.03 19.04 19.05 19.06 19.07 19.08 19.09 19.10 19.11 19.12 19.13 19.14 19.15 19.16 Rummel, J.D., Beaty, D.W., Jones, M.A., Bakermans, C., Barlow, N.G., Boston, P.J., Chevrier, V.F., Clark, B.C., de Vera, J.P.P., Gough, R.V. and Hallsworth, J.E., 2014. A new analysis of Mars “special regions”: findings of the second MEPAG Special Regions Science Analysis Group (SR-SAG2).
  20. 20.0 20.1 20.2 Planetary Protection Standards for Icy Bodies in the Outer Solar System - about the Committee on Planetary Protection Standards for Icy Bodies in the Outer Solar System
  21. 21.0 21.1 Carl Sagan and Sidney Coleman Decontamination Standards for Martian Exploration Programs, Chapter 28 from Biology and the Exploration of Mars: Report of a Study edited by Colin Stephenson Pittendrigh, Wolf Vishniac, J. P. T. Pearman, National Academies, 1966 - Life on other planets
  22. Keeping it clean
  23. 23.0 23.1 Mars Sample Return backward contamination – Strategic advice and requirements Archived 2013-08-19 at the Wayback Machine.- foreword and section 1.2
  24. 24.0 24.1 24.2 24.3 24.4 24.5 "Planetary Protection Categories (click on highlighted text for Planetary Protection Categories". Office of Planetary Protection. NASA’s Planetary Protection policy calls for the imposition of controls on contamination for certain combinations of mission type and target body. There are five categories for target body/mission type combinations. The assignment of categories for specific missions is made by the NASA Planetary Protection Officer based on multidisciplinary scientific advice. The five categories are
    • Category I includes any mission to a target body, which is not of direct interest for understanding the process of chemical evolution or the origin of life. No protection of such bodies is warranted and no Planetary Protection requirements are imposed.
    • Category II includes all types of missions to those target bodies where there is significant interest relative to the process of chemical evolution and the origin of life, but where there is only a remote chance that contamination carried by a spacecraft could jeopardize future exploration. The requirements are only for simple documentation. This documentation includes a short Planetary Protection plan, which is required for these missions, primarily to outline intended or potential impact targets; brief pre-launch and post-launch analyses detailing impact strategies; and a post-encounter and end-of-mission report providing the location of inadvertent impact, if such an event occurs.
    • Category III includes certain types of missions (typically a flyby or orbiter) to a target body of chemical evolution or origin-of-life interest or for which scientific opinion holds that the mission would present a significant chance of contamination which could jeopardize future biological exploration. Requirements consist of documentation (more involved than that for Category II) and some implementing procedures, including trajectory biasing, the use of clean rooms (Class 100,000 or better) during spacecraft assembly and testing and possibly bioburden reduction. Although no impact is generally intended for Category III missions, an inventory of bulk constituent organics is required if the probability of inadvertent impact is significant.
    • Category IV includes certain types of missions (typically an entry probe, lander or rover) to a target body of chemical evolution or origin-of-life interest or for which scientific opinion holds that the mission would present a significant chance of contamination, which could jeopardize future biological exploration. Requirements include rather detailed documentation (more involved than that for Category III), bioassays to enumerate the burden, a probability of contamination analysis, an inventory of the bulk constituent organics and an increased number of implementing procedures. The latter may include trajectory biasing, the use of clean rooms (Class 100,000 or better) during spacecraft assembly and testing, bioload reduction, possible partial sterilization of the hardware having direct contact with the taget body, and a bioshield for that hardware, and, in rare cases, a complete sterilization of the entire spacecraft. Subdivisions of Category IV (designated IVa, IVb or IVc) address lander and rover missions to Mars (with or without life detection experiments) and missions landing or accessing regions on Mars, which are of particularly high biological interest.
    Category V pertains to all missions for which the spacecraft, or a spacecraft component, returns to Earth. The concern for these missions is the protection of the Earth from back contamination resulting from the return of extraterrestrial samples (usually soil and rocks). A subcategory called "Unrestricted Earth Return" is defined for solar system bodies deemed by scientific opinion to have no indigenous life forms. Missions in this subcategory have requirements on the outbound (Earth to target body) phase only, corresponding to the category of that phase (typically Category I or II). For all other Category V missions, in a subcategory defined as "Restricted Earth Return," the highest degree of concern is expressed by requiring the absolute prohibition of destructive impact upon return; the need for containment throughout the return phase of all returning hardware, which directly contacted the target body or unsterilized material from the body; and the need for containment of any unsterilized samples collected and returned to Earth. Post-mission, there is a need to conduct timely analyses of the returned unsterilized samples, under strict containment, and using the most sensitive techniques. If any sign of the existence of a nonterrestrial replicating organism is found, the returned sample must remain contained unless treated by an effective sterilization procedure. Category V concerns are reflected in requirements that encompass those of Category IV plus a continuous monitoring of mission activities, studies, and research in sterilization procedures and containment techniques.
      line feed character in |quote= at position 386 (help)
  25. 25.0 25.1 25.2 COSPAR Workshop on Planetary Protection for Outer Planet Satellites and Small Solar System Bodies European Space Policy Institute (ESPI), 15–17 April 2009
  26. COSPAR (2020). "COSPAR Policy on Planetary Protection". 
  27. Assessment of Planetary Protection Requirements for Venus Missions -- Letter Report
  28. COSPAR Final
  29. COSPAR Workshop on Planetary Protection for Titan and Ganymede
  30. Catharine Conley Planetary Protection for the Dawn Mission, NASA HQ, Jan 2013
  31. COSPAR. (2011)COSPAR Planetary Protection Policy[20October 2002, as amended to 24 March 2011], COSPAR,Paris.
  32. Planetary protection for ExoMars, ESA

    !The ExoMars mission is classified as Planetary Protection Category IVb based on the mission objectives to search for life on Mars and in agreement with the COSPAR Planetary Protection Policy. The ExoMars mission does not intend to access a Mars special region.

    (A special region is considered to be "... a region within which terrestrial organisms are likely to propagate, or a region which is interpreted to have a high potential for the existence of extant Martian life forms. Given current understanding, this applies to regions where liquid water is present or may occur." (Reference: COSPAR 2002 & 2005, NASA, 2005))"

  33. (see section 7.1.1. Recommended organism-based parameters defin-ing the limits of life, and the requirements for Mars Special Regions, page 940 of[19])

    Conditions on the surface of Mars areoften described as being cold and dry (along with dusty andcratered). As it happens, those conditions are critical to the ability of terrestrial organisms to replicate in any environment. If it is too cold (or too hot) or too dry, terrestrial microbes will not replicate. Thus we define the basic parameters of a Special Region (without margin) as a location where

    (1) the temperature (T) is 255 K (-18°C) or above (Finding 3-1) and
    (2) water activity (aw) is above 0.60 (Finding 3-4).


    While it can be shown that organisms can be more sensitive to aw than the accuracy of measurement suggested by a value of 0.60, the practicality of measuring water activity at the same accuracy as an organism senses it has not yet been established.

    Under the definition adopted by MEPAG in 2006, ‘‘if a martian environment can simultaneously exceed the threshold conditions of-20°C and aw over 0.5, propagation may be possible’’ (italics added). Both of those parameters in 2006 had margin placed on them, to lower the temperature as well as the water activity required for describing a location as an Uncertain region, which could be expected to host microbial life if it were introduced therein.

    With equivalent margin added, the basic parameters of a Special Region would describe a location where(1) the temperature (T) is 250 K (-23°C) or above and(2) water activity (aw) is above 0.50.

  34. (see section 2.1, page 891 of[19]).

    Finding 2-1: Modern martian environments may contain molecular fuels and oxidants that are known to support metabolism and cell division of chemolithoautotrophic microbes on Earth

  35. (see 3.6. Ionizing radiation at the surface page 891 of[19]).

    Finding 3-8: From MSL RAD measurements, ionizing radiation from GCRs at Mars is so low as to be negligible. Intermittent SPEs can increase the atmospheric ionization down to ground level and increase the total dose, but these events are sporadic and last at most a few (2–5)days. These facts are not used to distinguish Special Regions on Mars.

    Over a 500-year time frame, the martian surface could be estimated to receive a cumulative ionizing radiation dose of less than 50 Gy, much lower than the LD90 (lethal dose where 90% of subjects would die) for even a radiation-sensitive bacterium such as E. coli (LD90 of ~200–400 Gy)

  36. (see 3.5. Ultraviolet radiation on the surface of Mars page 901 of[19]).

    Finding 3-7: The martian UV radiation environment is rapidly lethal to unshielded microbes but can be attenuated by global dust storms and shielded completelyby<1 mm of regolith or by other organisms.

  37. (see 3.4.3. Pressure of[19]).

    Finding 3-6: Most terrestrial bacteria tested fail to grow below 2500 Pa. However, a small subset of bacteria havenow been identified that can reproduce (on rich hydratedagar media) in a ‘‘martian’’ atmosphere (anoxic, CO2)ataverage martian pressure (700 Pa) and 0°C. This fact isnot used to distinguish Special Regions on Mars.

  38. (see 3.7. Polyextremophiles: combined effects of environmental stressors of[19]).

    Finding 3-9: The effects on microbial physiology of more than one simultaneous environmental challenge are poorly understood. Communities of organisms may be able totolerate simultaneous multiple challenges more easily than individual challenges presented separately. What little is known about multiple resistance does not affect our current limits of microbial cell division or metabolism in response to extreme single parameters.

  39. Houtkooper, Joop M.; Dirk Schulze-Makuch (2007-05-22). "A Possible Biogenic Origin for Hydrogen Peroxide on Mars". International Journal of Astrobiology. 6 (2): 147. arXiv:physics/0610093Freely accessible. Bibcode:2007IJAsB...6..147H. doi:10.1017/S1473550407003746. 
  40. 40.0 40.1 Section 8. Summary of [19]

    Thus, during the planning phases, missions will study their own potential to create Spacecraft-Induced SpecialRegions by the presence of a lander itself or by non-nominaloperations during the descent phase and will take action toensure that Special Regions are not inadvertently created.Robotic spacecraft will need to avoid Special Regions if they are not clean enough to avoid contaminating those regions. Although current requirements are the same as those met by the Viking missions of the mid-1970s, no spacecraft sent to Mars since that time has been clean enough to enter a Special Region

  41. 41.0 41.1 Mars Special Regions Redefined NASA Appel Knowledge Services News Digest
  42. (see page 941 of[19])
  43. Referring to the Viking and Curiosity (MSL) landing sites they say (page 941 of[19])

    ... where in some seasons the temperature required for microbial replication was regularly reached during the driest part of the day, whereas at night, when the temperature was too low for replication, the relative humidity at the site was above 0.6 and nearly always close to 1.0. The non-overlap of the required values for a Special Region is reflected in Finding 4-12, but the fact that both could be reached within the same 24 h period, regularly, suggests that there may be a way for organisms to connect the favorable aspects of those periods across a bridge of biotic adaptation.

  44. 44.0 44.1 44.2 44.3 44.4 44.5 44.6 44.7 44.8 Board, S.S., European Space Sciences Committee and National Academies of Sciences, Engineering, and Medicine, 2015. Review of the MEPAG report on Mars special regions. National Academies Press.
  45. Chapter 2: The Assessment of the Potential of Terrestrial Lifeforms to Survive and Proliferate on Mars in the Next 500 Years, from [44]
  46. In chapter 2 of [44]:

    A potential problem with designating Special Regions on Mars is that viable microorganisms that survive the trip to Mars could be transported into a distant Special Region by atmospheric processes, landslides, avalanches (although this risk is considered minimal), meteorite impact ejecta, and lander impact ejecta. In addition to dilution effects, the flux of ultraviolet radiation within the martian atmosphere would be deleterious to most airborne microbes and spores. However, dust could attenuate this radiation and enhance microbial viability. In addition, for microbes growing not as single cells but as tetrades or larger cell chains, clusters, or aggregates, the inner cells are protected against ultraviolet radiation. Examples are methanogenic archaea like Methanosarcina, halophilic archaea like Halococcus, or cyanobacteria like Gloeocapsa. This is certainly something that could be studied and confirmed or rejected in terrestrial Mars simulation chambers where such transport processes for microbes (e.g., by dust storms) are investigated. The SR-SAG2 report does not adequately discuss the transport of material in the martian atmosphere.

  47. In chapter 2 of [44]:

    where the cells are embedded in a self-produced extracellular matrix consisting of polysaccharides and proteins, which includes other macromolecules such as lipids and DNA. These so-called extrapolymeric substances (EPS) provide protection against different environmental stressors (e.g., desiccation, radiation, harmful chemical agents, and predators). Biofilms are highly organized structures that enable microbial communication via signaling molecules, disperse cells and EPS, distribute nutrients and release metabolites, and facilitate horizontal gene transfer.

    The majority of known microbial communities on Earth are able to produce EPS, and the protection provided by this matrix enlarges their physical and chemical limits for metabolic processes and replication. EPS also enhances their tolerance to simultaneously occurring multiple stressors and enables the occupation of otherwise uninhabitable ecological niches in the microscale and macroscale. The presence of EPS within a microbial community has implications for several aspects of the SR-SAG2 report, including the physical and chemical limits for life, the dimension of habitable niches versus the actual resolution capability of today’s instruments in Mars orbit, colonization of brines, and tolerance to multiple stressors. In extreme cold and salty habitats (e.g., brines of sea ice and cryopegs in permafrost), EPS has been found to be an excellent cryoprotectant

  48. In chapter 2 of [44]:

    There are many examples of small-scale and microscale environments on Earth that can host microbial communities, including biofilms, which may only be a few cell layers thick. The biofilm mode of growth, as noted previously, can provide affordable conditions for microbial propagation despite adverse and extreme conditions in the surroundings. On Earth, the heterogeneity of microbial colonization in extreme environments has become more obvious in recent years. To identify Special Regions across the full range of spatial scales relevant to microorganisms, a better understanding of the temperature and water activity of potential microenvironments on Mars is necessary. For instance, the interior of the crater Lyot in the northern mid-latitude has been described as an optimal microenvironment with pressure and temperature conditions that could lead to the formation of liquid water solutions during periods of high obliquity (Dickson and Head 2009). Craters, and even microenvironments underneath and on the underside of rocks, could potentially provide favorable conditions for the establishment of life on Mars, potentially leading to the recognition of Special Regions where landscape-scale temperature and humidity conditions would not enable it.

  49. [19]

    SR-SAG2 Finding 5-3: Depths to buried ice deposits in the tropics and mid-latitudes are considered to be >5 m.

  50. Chapter: 3 Martian Geological and Mineralogical Features Potentially Related to Special Regions, SNOW, ICE DEPOSITS, AND SUBSURFACE ICE of [44]

    Revised Finding 5-3: In general, depths to buried ice deposits in the tropics are considered to be >5 m. However, there is evidence that water ice is present at depths of <1 m on pole-facing slopes in the tropics and mid latitudes. Thus, a local detailed analysis for a particular area is necessary to determine if it could be a Special Region.

  51. chapter 5 of [44]

    In general, the review committee contends that the use of maps to delineate regions with a lower or higher probability to host Special Regions is most useful if the maps are accompanied by cautionary remarks on their limitations. Maps that illustrate the distribution of specific relevant landforms or other surface features can only represent the current (and incomplete) state of knowledge for a specific time—knowledge that will certainly be subject to change or be updated as new information is obtained.

  52. chapter 5 of [44]

    In the case of Schiaparelli, for example, all available data for the proposed site in Meridiani Planum were analyzed to determine if Special Regions existed within the landing ellipse. In particular, all HiRISE images were inspected for the possible presence of RSL.

  53. COSPAR power point type presentation, gives good overview of the detailed category decisions Archived 2013-10-19 at the Wayback Machine.
  54. edited by Muriel Gargaud, Ricardo Amils, Henderson James Cleaves, Michel Viso, Daniele Pinti Encyclopedia of Astrobiology, Volume 1 page 325
  55. 55.0 55.1 Richard Greenberg, Richard J. Greenberg Unmasking Europa: the search for life on Jupiter's ocean moon ISBN 0387479368
  56. 56.0 56.1 Paul Gilster Europa: Thin Ice and Contamination
  57. B. Randall Tufts, Richard Greenberg Infecting Other Worlds Archived 2016-10-18 at the Wayback Machine., American Scientist, July 2001
  58. Europa the Ocean Moon, Search for an Alien Biosphere, chapter 21.5.2 Standards and Risks
  59. Committee on Planetary Protection Standards for Icy Bodies in the Outer Solar System; Space Studies Board; Division on Engineering and Physical Sciences; National Research Council Assessment of Planetary Protection Requirements for Spacecraft Missions to Icy Solar System Bodies ( 2012 ) / 2 Binary Decision Trees
  60. 60.0 60.1 Race, M.S., 1996. Planetary protection, legal ambiguity and the decision making process for Mars sample return. Advances in Space Research, 18(1-2), pp.345-350. Cite error: Invalid <ref> tag; name "race" defined multiple times with different content
  61. Designing a Box to Return Samples From Mars, 2013
  62. Office of Planetary Protection: Mars Sample Quarantine Protocol Workshop
  63. Mars sample return mission concept study (for decadal review 2010)
  64. Proof of concept of a Bio-Containment System for Mars Sample Return Mission
  65. Richard S. Johnston, John A. Mason, Bennie C. Wooley, Gary W. McCollum, Bernard J. Mieszkuc BIOMEDICAL RESULTS OF APOLLO, SECTION V, CHAPTER 1, THE LUNAR QUARANTINE PROGRAM Archived 2013-07-17 at the Wayback Machine.
  66. Nancy Atkinson How to Handle Moon Rocks and Lunar Bugs: A Personal History of Apollo’s Lunar Receiving Lab, Universe Today, July 2009. See quote from: McLane who lead the group that designed and built the Lunar Receiving Facility:

    "The best that I hear now is that the techniques of isolation we used wouldn’t be adequate for a sample coming back from Mars, so somebody else has a big job on their hands."

  67. The Quarantine and Certification of Martian Samples - Chapter 7: Lessons Learned from the Quarantine of Apollo Lunar Samples, Committee on Planetary and Lunar Exploration, Space Studies Board
  68. 68.0 68.1 Assessment of Planetary Protection Requirements for Mars Sample Return Missions (Report). National Research Council. 2009. 
  69. European Science Foundation - Mars Sample Return backward contamination - strategic advice Archived 2016-06-02 at the Wayback Machine. July, 2012, ISBN 978-2-918428-67-1
  70. In-situ Exploration and Sample Return: Planetary Protection Technologies JPL - Mars Exploration Rovers
  71. 71.0 71.1 Office of Planetary Protection (August 28, 2012). "Office of Planetary Protection - Methods and Implementation". NASA. Archived from the original on September 29, 2012. Retrieved 2012-09-11. 
  72. Benton C. Clark (2004). "Temperature–time issues in bioburden control for planetary protection". Advances in Space Research. 34 (11): 2314–2319. Bibcode:2004AdSpR..34.2314C. doi:10.1016/j.asr.2003.06.037. 
  73. 73.0 73.1 Shirey, T. Brian, James N. Benardini, and Wayne Schubert. "An Overview of Surface Heat Microbial Reduction as a Viable Microbial Reduction Modality for Spacecraft Surfaces." 47th International Conference on Environmental Systems, 2017
  74. 5*0.5*10^((125-112)/15) - Google calculator
  75. 5*0.5*10^((125-116)/15) - Google calculator
  76. 5*0.5*10^((125-140)/21) - Google calculator
  77. 5*0.5* 10^((140 –200) / (23*200/140))) - Google calculator
  78. Pugel, DE Betsy, J. D. Rummel, and Catharine Conley. "Brushing your spacecraft's teeth: A review of biological reduction processes for planetary protection missions." In Aerospace Conference, 2017 IEEE, pp. 1-10. IEEE, 2017.
  79. Fei Chen, Terri Mckay, James Andy Spry, Anthony Colozza, Salvador Distefano, Robert Cataldo Planetary Protection Concerns During Pre-Launch Radioisotope Power System Final Integration Activities - includes the draft specification of VHP sterilization and details of how it would be implemented. Proceedings of Nuclear and Emerging Technologies for Space 2013. Albuquerque, NM, February 25–28, 2013 Paper 6766
  80. NASA Venus Technology Plan (2010)
  81. Sauder, Jonathan, Evan Hilgemann, Michael Johnson, Aaron Parness, Jeffrey Hall, Jessie Kawata, and Kathryn Stack. "Automation Rover for Extreme Environments." (2017)
  82. Wilcox, B.H., Carlton, J.A., Jenkins, J.M. and Porter, F.A., 2017, March. A deep subsurface ice probe for Europa. In Aerospace Conference, 2017 IEEE (pp. 1-13). IEEE.
  83. NASA press release, 2017, NASA Tests Robotic Ice Tools
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  85. Ghosh S, Osman S, Vaishampayan P, Venkateswaran K (2010). "Recurrent isolation of extremotolerant bacteria from the clean room where Phoenix spacecraft components were assembled". Astrobiology. 10: 325–35. Bibcode:2010AsBio..10..325G. doi:10.1089/ast.2009.0396. PMID 20446872. Extremotolerant bacteria that could potentially survive conditions experienced en route to Mars or on the planet's surface were isolated with a series of cultivation-based assays that promoted the growth of a variety of organisms, including spore formers, mesophilic heterotrophs, anaerobes, thermophiles, psychrophiles, alkaliphiles, and bacteria resistant to UVC radiation and hydrogen peroxide exposure 
  86. Webster, Guy (6 November 2013). "Rare New Microbe Found in Two Distant Clean Rooms". NASA. Retrieved 6 November 2013. 
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  88. A. Debus (2004). "Estimation and assessment of Mars contamination". Advances in Space Research. 35 (9): 1648–1653. Bibcode:2005AdSpR..35.1648D. doi:10.1016/j.asr.2005.04.084. PMID 16175730. 
  89. Preventing the Forward Contamination of Mars ( 2006 ) Page 27 (footnote to page 26) of chapter 2 Policies and Practices in Planetary Protection
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  93. Robert Zubrin "Contamination From Mars: No Threat", The Planetary Report July/Aug. 2000, P.4–5
  94. transcription of a tele-conference interview with Robert Zubrin conducted on March 30, 2001 by the class members of STS497 I, "Space Colonization"; Instructor: Dr. Chris Churchill
  95. O. Eugster, G. F. Herzog, K. Marti, M. W. Caffee Irradiation Records, Cosmic-Ray Exposure Ages, and Transfer Times of Meteorites, see section 4.5 Martian Meteorites LPI, 2006
  97. Tony Irving Martian Meteorites - has graphs of ejection ages - site maintained by Tony Irving for up to date information on Martian meteorites
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  99. Fairén, A.G. and Schulze-Makuch, D., 2013. The overprotection of Mars. Nature Geoscience, 6(7), p.510.
  100. Conley, C.A. and Rummel, J.D., 2013. Appropriate protection of Mars. Nature Geoscience, 6(8), p.587.
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  115. 'Planetary Parks' Could Protect Space Wilderness by Leonard David,’s Space Insider Columnist, January 17, 2013
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