NASA has one primary Planetary Protection Point of Contact (PoC) at this time. For more information, contact the PoC below.

As presented in the December 2015 Planetary Protection Subcommittee meeting, and pending final approval, the Mars 2020 (M2020) project will be designated a Category V Restricted Earth Return mission, while the outbound leg will be required to comply to Category IVb constraints at the subsystem level. Accordingly, certain clarifications to NPR 8020.12, Planetary Protection Provisions for Robotic Extraterrestrial Missions will apply to M2020. Examples clarifications include

(Note: The following language is comprised of direct quotes from the policy.)

Sections 5.3.2.3c and 5.3.2.5c

• Due to the presence of a radiothermal generator (RTG) used to power the M2020 rover, the M2020 project shall ensure that candidate landing sites exclude the following from the post-parachute-opening 3-sigma landing ellipse:
• Locations with ice or hydrated minerals at depths of <5 meters (based on MSL impact calculations), for which exposure to an RTG could cause liquid to be liberated sufficient to mobilize a particle of <50 nm in size,
• Special Regions as formally defined in NPR 8020.12D Section 5.3.2.5 or as modified by mutual agreement prior to launch, pending evaluation of the definition rendered by the 2014-15 MEPAG/SSB/ESF evaluations, and subject to review by the NASA Planetary Protection Subcommittee,
• Transient Special Regions created by the presence of an RTG on the rover are included in these constraints: their absence shall be demonstrated by test and analysis.
• In addition to the standard reviews, the final candidate landing sites shall undergo an independent review, organized by the PPO, as part of the pre-launch landing site selection process and prior to the preparation and presentation of landing site options to the Science Mission Directorate Associate Administrator.
• Later access to previously identified locations, via either vertical or horizontal mobility of rover elements, shall be prohibited.

Sections 5.3.2.5a

• Clarifications to the Special Regions include a lower temperature limit of -28˚C, reevaluation of the 500 year timescale for limits, and a focus on regions “including dark streaks”.

Section 5.3.2.2

• Caching hardware involved in acquisition, delivery, and storage of samples intended for Earth return shall be
• Cleaned to a level of <300 heat resistant ‘spores’/m²,
• Enclosed in a physical biobarrier,
• And subjected to a validated bioburden reduction process the achieves at least 4-orders of magnitude of microbial reduction.
• The physical biobarrier that prevents recontamination shall not be opened until operations at Mars.
• Example acceptable contamination limits while conducting operations on Mars include:
• <1 viable Earth organism per cached sample,
• 100 ppb TOC baseline (Tier 1 & 2 compounds),
• And 40 ppb TOC threshold (Tier 1 & 2 compounds).

Section 5.3.3.2

• The M2020 project shall ensure that Mars samples intended for possible future return are not contaminated by terrestrial organic compounds or viable organisms at levels above those specified below, through final deposition of sample tubes on Mars:
• The probability that a single viable organism is introduced into each sample shall be less than the limit obtained by multiplying the internal surface area of a sealed sample tube, in m², by the Viking post-sterilization surface bioburden limit of 0.03 viable organisms per m²,
• Terrestrial organic contamination shall be limited to levels below <1 ppb of any Tier 1 organic compound per sample; <10 ppb Total Organic Carbon per sample,
• And sample tubes shall be designed for opening after return to Earth in a manner that prevents additional contamination of samples during extraction.

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.

In 2013, Japan formed the Japanese Aerospace Exploration Agency (JAXA) Planetary Protection Safety Review Board after many years of commitment to Planetary Protection and expected future space exploration missions. For the Hayabusa I and II missions, JAXA worked with NASA to ensure compliance to Committee on Space Research Planetary Protection policy.

The European Space Agency (ESA) is committed to the responsible exploration of the solar system and works closely with NASA in the practice and development of Planetary Protection policy. The Planetary Protection Officer for ESA is Dr. Gerhard Kminek. The ESA Planetary Protection-related documents include 

• ESSB-ST-U-001 (Issue 1): ESA planetary protection requirements
• ECSS-Q-ST-70-53C: Material and hardware compatibility tests for sterilization processes
• ECSS-Q-ST-70-55C: Microbial examination of flight hardware and cleanrooms
• ECSS-Q-ST-70-56C: Vapour phase bioburden reduction for flight hardware
• ECSS-Q-ST-70-57C: Dry heat bioburden reduction for flight hardware
• ECSS-Q-ST-70-58C: Bioburden control of cleanrooms

Internationally, technical aspects of Planetary Protection are developed through deliberations by the Committee on Space Research (COSPAR), part of the International Council of Science, which consults with the United Nations in this area. The COSPAR Panel on Planetary Protection develops and makes recommendations on Planetary Protection policy to COSPAR, which may adopt them as part of the official COSPAR Planetary Protection Policy.

The United Nation’s (U.N.) Office of Outer Space Affairs (UNOOSA) is responsible for promoting international cooperation in the peaceful uses of outer space. UNOOSA serves as the secretariat for the U.N. General Assembly’s only committee dealing exclusively with international cooperation in the peaceful uses of outer space: the U.N. Committee on the Peaceful Uses of Outer Space, known as COPUOS. In respect to Planetary Protection, Article IX of the 1967 U.N. Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Bodies states that all countries party 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.”

Planetary Protection controls on the forward contamination are intended to preserve the planetary record of natural processes on these bodies by preventing human-caused microbial introductions that could interfere with future astrobiological investigations.

For Category I, typically missions to Mercury and those of heliophysical interest are considered to be of no direct interest for understanding the process of chemical evolution and do not require planetary protection controls. However, reassessment of the Planetary Protection concerns for Mercury are underway due to the recent discovery of water ice and organics by the MESSENGER mission. Further, for heliophysical missions, assignment to Category II may be warranted if planetary bodies of concern may be impacted. Missions to Venus and Earth’s moon are typically assigned as Category II missions. Though some scientists have speculated that microbial life might be able to survive in the atmosphere of Venus, the consensus is that the environment of Venus is too harsh to support life as we know it, and Planetary Protection is currently not a major concern for that planet.

While some of the moons of Jupiter and Saturn are considered good sites for astrobiological investigation, the consensus is that the environments of Jupiter and Saturn themselves are not suited to supporting life as we know it, and Planetary Protection is currently not a major concern for these gas giants. Likewise, Planetary Protection is not a major concern for the other outer planets Uranus, Neptune and Pluto and many of the satellites of the outer planets. This same assessment also applies to comets and asteroids.

The most stringent requirements are those for Mars; Jupiter’s moons Europa, Ganymede, and Callisto; and Saturn’s moons of Titan and Enceladus due to the great potential for studying the origin, evolution and distribution of life on these bodies. For Mars, the requirements are based upon orbital lifetime constraints for Category III missions and numerical bioburden constraints for the Category IV missions. For the Jovian and Saturn moons, the primary planetary protection focus is on the probability of contamination of a liquid water body.

Comets reside in the so-called Kuiper belt, a region in space beyond the orbit of Neptune, or the Oort cloud, a region far beyond Pluto. Comets are believed to be the oldest, most primitive bodies in the solar system, containing remains of the original material from which the sun and the planets formed. Scientists speculate that they may contain some of the basic biochemical building blocks of life. Comets are known to contain stores of water ice, and scientists believe they may have delivered water (ice melted by impacts) to Earth billions of years ago, making life on this planet possible. Water does not exist in liquid form on comets, however, and the scientific consensus is that comets cannot support life as we know it.

Asteroids, most of which are located in a region of space between Mars and Jupiter, are also believed to be remnants of the original material from which solar system bodies formed. The scientific consensus is that asteroids are not likely to support life as we know it. The National Research Council’s Space Studies Board has thus concluded that no special containment is needed for returned samples of interplanetary dust, comets and some asteroids (depending on their compositional type). See “Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies: Framework for Decision Making” for details.

Visit the Solar System Exploration for more information.

Titan and Enceladus — two of Saturn’s 47 known moons — are of biological interest to space scientists.

About one tenth the size of Titan, Saturn’s moon Enceladus is the brightest body in the solar system because its surface reflects almost 100 percent of the sunlight that strikes it. Enceladus has a varied terrain; some areas have craters, while other areas have none, indicating that major resurfacing events have taken place in the geologically recent past. The surface of Enceladus has fissures, plains, corrugated terrain and other crustal deformations, indicating that the interior of the moon may be liquid today. Scientists suggest that Enceladus may be heated by a tidal mechanism similar to Jupiter’s moons.

Cassini observations have revealed a water vapor plume in the southern polar region of Enceladus, hinting that this moon might have liquid water and making it a possible new candidate for astrobiological research.

As the largest moon of Saturn, Titan is the only planetary satellite in our solar system known to have a substantial and permanent atmosphere — though it is nothing like the atmosphere of Earth. The atmosphere of Titan, at a temperature of 94 Kelvin (290 degrees below zero Fahrenheit), is rich with nitrogen and methane. The interaction of this atmosphere with solar ultraviolet radiation could generate saturated and unsaturated hydrocarbons as well as nitriles, through methane photolysis. These products could condense as aerosols and reach the surface, where some could liquefy while others take solid form.

Observations of Titan have indicated that it may have lakes or oceans of liquid hydrocarbons on its surface in addition to frozen deposits of these compounds. Some scientists have speculated that, over billions of years, impacts on the surface of Titan could have melted frozen surface materials, yielded water, and thus enabled chemical reactions that could possibly produce amino acids. Since prebiotic organic chemistry is considered a possibility on Titan, this planetary satellite is considered a good target for astrobiological investigation.

Observations fromNASA’sCassiniSaturn Orbiter have revealed that the dark equatorial regions, previously observed on Titan and thought to be possible liquid hydrocarbon oceans, are seas of sand dunes similar to those found on Earth. The sand may have formed through bedrock erosion caused by liquid methane rain. Another theory is that the sand may come from organic solids produced by photochemical reactions in Titan’s atmosphere. Observations from the European Space Agency’s Huygens Probe during its descent through Titan’s atmosphere have shown gullies, streambeds and canyons there, along with ice pebbles and possible methane or ethane ground fog on surface. The surface is darker than originally thought, consisting of a mixture of water and hydrocarbon ice. The scientific consensus is that Titan’s methane is not a product of biological activity.

Visit NASA's websites for Saturn’s moons and Solar System Exploration for more information.

Spacecraft observations have revealed that Jupiter’s moons Europa, Ganymede and Callisto are all covered with water ice. Most recently, observations of these three planetary satellites by the Galileo spacecraft have indicated that they may all have liquid water oceans beneath their icy crusts. The presence of liquid water makes these bodies good targets for astrobiological exploration. Europa is an especially promising target for astrobiological investigation. A National Research Council task force has reported that “hydrothermal systems are likely to have operated within a few hundred kilometers of Europa’s surface at some point in its history.” (See“ Preventing the Forward Contamination of Europa.”)

Scientists speculate that hydrothermal activity could have occurred on Ganymede as well at some point in its history. While Callisto differs from Europa and Ganymede in some important respects, it also appears to have a subsurface liquid water ocean. Prudence dictates taking precautions to avoid contamination of Europa, Ganymede and Callisto in order to ensure preservation of the record of natural processes on these bodies. Planetary Protection considerations are thus a key component of planning for NASA’s future missions to further explore Eurpoa or Jupiter’s other icy satellites.

Visit the NASA website for Jupiter’s moons and Solar System Exploration for more information.

Jupiter is the fifth planet from the sun and the largest planet within the solar system. It is two and a half times as massive as all of the other planets in the solar system combined. Jupiter — along with Saturn, Uranus and Neptune — is classified as a gas giant. The planet Jupiter is primarily composed of hydrogen with a small proportion of helium; it may also have a rocky core of heavier elements under high pressure.

Jupiter is considered to be of significant interest relative to the process of chemical evolution and the origin of life, however, the chance that contamination carried by a spacecraft could compromise future investigations is considered to be remote. Therefore, Planetary Protection is not a major concern for missions to this planet. Accordingly, missions to Jupiter be assigned to Category II.

Visit NASA's websites for Jupiter and Solar System Exploration for more information.

Mars is a primary target in the search for evidence of extraterrestrial life, past or present. This planet appears to possess all of the materials and some of the environments associated with life on Earth. While the surface of Mars is now cold and dry, some scientists believe that conditions on the planet may have been much like those on Earth early in solar system history (though others speculate that Mars may have been cold and dry in this early period). And Mars subsurface conditions are now, and may always have been, quite different than those on the Martian surface.

In recent years, NASA’s Mars Global Surveyor (MGS) and Mars Odyssey spacecraft have made observations that show evidence of plentiful water ice. More recently,NASA’s Mars Exploration Rovers,Spirit and Opportunity, and the European Space Agency’s Mars Express orbiter have collected evidence of past liquid water on the planet’s surface. Some scientists claim observations also reveal signs of possibly recent liquid water flows on the surface of Mars. Others speculate that Mars may have been cold and dry, as it appears to be today, for billions of years. Scientists have long considered, as well, that liquid water may have existed, and may still exist today, beneath the surface of Mars. They have also explored the possibility of interplanetary transfer of microbial life from Mars to Earth or Earth to Mars. Such transfers could have resulted from the high-velocity ejection of soil and rock caused by planetary impacts of comets and other small bodies early in the history of the solar system, when such events were frequent. Planetary Protection considerations for missions to Mars are thus substantial, and sterilization requirements for spacecraft landing on Mars are strict. Planetary Protection requirements for MGS and Mars Odyssey are intended to ensure that the orbiting spacecraft do not inadvertently drop out of orbit and crash onto Mars after their missions are completed. Planetary Protection requirements for the Mars Exploration Rovers are intended to ensure that these landers did not transport Earth microbes to the surface of Mars.

Planetary Protection techniques that may be applied to spacecraft bound for Mars include clean manufacturing processes for spacecraft components and the use of cleanroom techniques during spacecraft assembly, test and launch operations. Biological contamination loads may be reduced by methods such as alcohol wiping, dry heat microbial reduction and hydrogen peroxide sterilization. Radiation treatment is an option for spacecraft components that can tolerate it, and newer molecular-level contamination detection methods may also be employed to characterize biological loads. Cultivation-based microbial assays are still the standard forward contamination control method, in part because of the lack of comparability with molecular methods and also because of additional personnel, training and requirements associated with molecular methods. These newer methods are attractive, however, because a biological load measurement that could take three days to complete using a microbial cultivation assay could be made in less than one hour using a molecular detection method.

Missions to Mars may be designated Category III, IVa, IVb or IVc for Planetary Protection purposes, depending on their aims. Mars orbiters such as MGS and Mars Odyssey are classified Category III and subject to biological burden limits or orbital lifetime requirements to ensure against inadvertent contamination of the planet in the event of a crash. Mars landers not carrying instruments designed to search for evidence of extant Martian life are designated Category IVa and subject to biological contamination limits: their biological burden is restricted to a level no greater than the Viking-lander pre-sterilization level.

Mars landers carrying instruments designed to search for evidence of extant Martian life are designated Category IVb and subject to more stringent sterilization requirements: The entire landed system must be sterilized at least to Viking Lander post-sterilization biological burden levels or to levels of biological burden reduction driven by the nature and sensitivity of the particular life-detection experiments, whichever are more stringent — or, alternatively, subsystems to be used in acquiring, delivering and analyzing Martian samples for in-situ life detection experiments must be sterilized to these levels, and a method of preventing recontamination of sterilized subsystems and contamination of material to be analyzed must be in place.

Mars lander missions intended to explore so-called “special regions,” areas where liquid water is present or likely to occur — even if they are not designed to carry life-detection instruments — are designated Category IVc and subject to stringent sterilization requirements, in whole or in part, determined by the parameters of the mission, such as landing method, landing site or rover mobility.

Visit NASA's websites for Mars and Solar System Exploration for more information.

The timeline of lunar exploration from 1959 to 2013 includes Luna 1, which performed a flyby in 1959, and LADEE and Chang’e3, which orbited and landed on the moon, respectively. Scientists have found no evidence of liquid water on the moon and none of the more than 2,000 samples of lunar material brought back to Earth by six Apollo missions yielded any evidence of past or present lunar biological activity. Thus, the current scientific consensus is that the potential for indigenous life on the moon is negligible, and that forward and back contamination resulting from lunar exploration are not concerns. (See the National Research Council’s Space Studies Board report,“Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies: Framework for Decision Making.”)

Claims have been made that a terrestrial microbe was transported to the moon aboard the Surveyor 3 robotic lunar lander, survived in a dormant state for more than two and a half years on the lunar surface, and proved to be still viable upon return to Earth. Apollo 12 astronauts retrieved the Surveyor 3 camera from the surface of the moon and brought it back to Earth for analysis. Laboratory examination of this returned hardware at NASA’s Manned Spacecraft Center (now Johnson Space Center) included efforts to culture possible microbes on the hardware. Some researchers involved in the laboratory examinations claimed they found a viable terrestrial microbe — specifically,Streptococcus mitis bacteria — embedded in this hardware, but others have argued that the microbial life they found was a result of contamination introduced during the laboratory examination.

Visit the NASA websites for the Earth’s Moon and Solar System Exploration for more information. 

The most stringent Planetary Protection requirements apply to missions that will be returning samples to Earth from solar system bodies that are considered potential sites for life. The first “restricted Earth return” mission, requiring strict containment of extraterrestrial samples brought back to this planet, may be NASA’s first Mars sample return mission, tentatively planned for the second decade of this century. Samples will have to be completely contained before the sample return vehicle leaves the surface of Mars, and containment will have to be maintained throughout the trip from Mars to Earth’s surface.

Returned samples will have to be housed in a Bio-Safety Level 4 (BSL-4) biocontainment laboratory. (BSL-4 is the U.S. government’s designation for the strictest level of biological containment.) No Martian samples may be released from this facility until they pass an extensive battery of tests designed to detect any evidence of past or present biological activity. NASA has drafted a Mars sample return protocol specifying procedures for containment and handling. Samples of extraterrestrial materials returned to Earth from bodies that are not considered suitable sites for life will not be required to meet containment requirements beyond those required to protect the scientific value of the samples.

Visit NASA’s Science Mission Directorate website for more information about Earth science at NASA.

In size, mass and composition, Venus is similar to Earth. On Venus, however, surface temperatures are over 450 degrees Celsius (842 degrees Fahrenheit), atmospheric pressure is 90 times that on Earth and there is no water. The atmosphere of Venus is made up mainly of carbon dioxide and contains sulfuric acid.

Some scientists have speculated that microbial life might be able to survive in the atmosphere of Venus. The Space Studies Board (SSB) of the National Research Council has considered the possibility of atmospheric venutian life and concluded that the environment of Venus is too harsh to support life as we know it. Planetary Protection is therefore currently not a major concern for missions to this planet. Nonetheless, the SSB recommended that missions to Venus be assigned to Category II.

Visit NASA's websites for Venus and Solar System Exploration for more information.

The history and development of Planetary Protection has been chronicled in many texts and articles. The following are a brief timeline of key events and selected references. 

Selected References

• When Biospheres Collide: A History of NASA’s Planetary Protection Programs, Sept. 14 2011, Michael Meltzer
• The Planetary Quarantine Program: Origins and Achievements, 1956-1973
• Scientific Concern Over Possible Contamination
• Planetary Protection for Icy Moons: updating the SSB Europa Report