Planetary Protection


by Rafael Moro-Aguilar

Planetary protection is a notion that presents scientific, legal, and ethical questions of the highest importance. 

It covers contamination of celestial bodies other than the Earth. Biological contamination could make it difficult to determine if life was originally present on the celestial body, hence the importance of preventing it. States must also avoid contaminating the Earth’s environment due to the introduction of extraterrestrial matter. 

According to Article IX of the Outer Space Treaty, States Parties shall avoid adverse changes and harmful contamination of both the terrestrial and space environments, and they shall adopt appropriate measures when necessary. Practical guidance for compliance is found in the COSPAR Planetary Protection Policy. However, future challenges abound, and we can expect the further evolution of planetary protection as we increase our knowledge of celestial bodies and the presence -or not- of life on them.

by Rafael Moro-Aguilar

I was led to Space Law by an early interest in Astronomy and Astronautics. I still feel fascinated by topics such as planetary protection, which is a perfect blend of International Law and Space Sciences, notably Astrobiology. Planetary protection is defined by NASA as “the practice of protecting solar system bodies from contamination by Earth life and protecting Earth from possible life forms that may be returned from other solar system bodies.” The risk of biological contamination resulting from space exploration was first raised in the 1950s by a group of distinguished American scientists, such as Joshua Lederberg and Carl Sagan. National and international institutions conducted scientific studies, and eventually this subject made its way to UNCOPUOS and was embodied in Article IX of the Outer Space Treaty. The Policy on Planetary Protection (PPP) of the Committee on Space Research (COSPAR) is developed and maintained by the international scientific community as a reference for space-faring nations to comply with Article IX. COSPAR’s PPP has evolved over time as scientists have acquired more information about the possible habitability of celestial bodies. The latest version dates from June 2020. Several space agencies have their own internal policies in order to implement PPP standards. Space probes landing on potentially inhabited places such as Mars are routinely sterilized before being launched. Also, the first Apollo astronauts to the Moon were quarantined after their return to Earth, in case they were bringing with them any kind of lunar pathogens. Adopting these measures means an increase in the costs and difficulties of space missions. However, there is a general consensus that preventing biological contamination of both celestial bodies and the Earth is in the best interest of everyone. We can expect further changes of planetary protection as new space activities are developed. Lunar exploration, sample-return missions from Mars, space mining, all this will have to adopt extreme precautions to avoid both forward and backward contamination; the latter in case we may inadvertently bring alien microbes together with the mineral samples carried to the Earth. A manned mission to Mars would be even more complicated. First of all, the original Martian environment should not be disrupted by the astronauts introducing terrestrial biological materials. Secondly, any kind of contamination of the Earth’s biosphere has to be prevented. Astronauts, equipment and samples would have to be isolated during their return trip, making what is already a very challenging mission even harder. Sound excessive? Our current predicament caused by the Covid-19 pandemics is living proof that we have to take utmost care to prevent any infections due to biological contamination.

by Leslie I. Tennen

Article IX of the Outer Space Treaty obligates states to avoid the harmful contamination of extraterrestrial environments. “Forward contamination” from biological material brought from earth could jeopardize scientific integrity in the search for extraterrestrial life. States also are to prevent “back contamination,” that is adverse changes to the earth’s environment caused by the introduction of extraterrestrial matter. State practice to prevent forward and back contamination has been to adhere to the Planetary Protection Policy (PPP) developed by the Committee on Space Research (COSPAR). The PPP applies to all space objects that travel beyond earth orbit. Specific requirements are established for the return to earth of samples of extraterrestrial matter. In addition, guidelines have been articulated for crewed missions to Mars. The substance of the PPP is recognized by all launching authorities conducting interplanetary missions, and has been incorporated into the governing regulations of NASA and ESA. The PPP began as a planetary quarantine policy which required near-sterility for interplanetary spacecraft such as Viking. The PPP is subject to continuous review and modification, and the current policy establishes standards of conduct based on a combination of target body and mission objectives. Five categories are delineated, with increasing levels of planetary protection based on their relative importance in the search for life. Missions to Category I bodies, such as the sun, have no specific protections. Category II bodies, including the moon, require only minimal documentation. Category III is for fly-by and orbiting missions to Mars, and requires that spacecraft comply with either specified decontamination levels or particular orbital parameters. Category IV applies to missions intended to land on Mars, or Titan or Enceladus. These spacecraft must meet specified requirements, and missions which will search for evidence of life are subject to more stringent decontamination obligations. Moreover, similarly strict decontamination requirements must be met for all spacecraft which will land in “special regions” of Mars, where the temperature and presence of H2O may be hospitable to sustaining life. Significant gaps exist in the policies to protect interplanetary environments, including that states have not made the COSPAR PPP applicable to private missions in their regulatory regimes. Nevertheless, the PPP has been crucial to prevent forward contamination and protect scientific integrity in the search for evidence of extraterrestrial life.