Planetary Protection of Outer Solar System (PPOSS) - promoting responsible space exploration

With the arrival of Europeans in the New World during the fifteenth century, a variety of epidemic diseases decimated the indigenous population of the Americas. More recently, the introduction of non-native species, such as zebra mussels, in different locations around the world is causing devastating effects on local natural environments and economies. Certainly, transporting biological material from one location to another on Earth is not always harmless.

Humanity is pushing the boundaries to go deeper into space exploration, and preserving other worlds as they exist in their natural states is necessary to address fundamental questions about the origin and evolution of life. To this end, planetary protection encompasses our attempts to minimise the actual transfer of microorganisms (biological contamination) or organic matter (organic contamination) on other planets. A variety of astrobiology research has shown how microbes can survive the journey through space, and consequently spread, if conditions are favorable for them. Thus, the scope of planetary protection is:

  1. to protect our investment in scientific investigations related to the origin and distribution of life in order to avoid false positives that can mask the detection of extraterrestrial life; 
  2. to protect the Earth and its biosphere from potential harmful extraterrestrial matter carried by a spacecraft returning from an interplanetary mission. 

We humans are inexorably attracted to the exploration of other planets in our solar system and we are witnessing a sort of renaissance in space exploration today. The space exploration landscape is being reshaped by the emerging private sector, which is trying to make space accessible to people on Earth, and is even speculating about colonizing Mars. Also, several new countries are launching programs and actively competing to achieve scientific and technological progress for space exploration. Furthermore, with the increasing evidence of presence of liquid water (a prerequisite of all extant life) in planets beyond Mars, the number of potential habitable environments is increasing. Under this scenario, the issue of contaminating other planets, and preventing Earth contamination from space return missions, is more and more important and relevant. 

The first spaceflight missions to implement planetary protection measurements were the Ranger missions in 1960s. Their objective was to acquire the first close-up images of the Moon’s surface. Since then, significant efforts have been made to sterilize spacecraft that enter into contact with the surface of any planetary body and also to ensure that orbiting spacecraft will not impact areas of particular interest for scientific research related to the origins of life. Maintaining and promulgating planetary protection policy recommendations at the international level are under the mandate of the Committee on Space Research (COSPAR) and current recommendations can be consulted here. This interdisciplinary scientific body promotes scientific research in space at an international level, while providing a forum open to all scientists for the discussion of matters related to space research. To date, COSPAR has identified five categories of planetary protection requirements depending on the target body (Table 1). Such requirements have a focus in planets close to the Sun, and in particular Mars. However, an increased number of missions to more distant planetary bodies are currently under development, in relation with which there is significant scientific interest in studying chemical evolution and the origin of life. 

Table 1. COSPAR planetary protection mission categories.

For example, one of the moons of Jupiter, Europa, is covered by an icy crust and there is tantalizing evidence that suggests the presence of a subsurface salty ocean (Fig. 1). Enceladus, one of Saturn’s moons, is also the source of strong geysers ejecting plumes of water and ice, rich in compounds such as hydrogen, carbon dioxide, ammonia and methane (Fig. 2). Exploring these icy moons poses new scientific challenges for planetary protection, and identifying innovative solutions is necessary. 

Figure 1. Illustration of Europa’s subsurface ocean with Jupiter on the right. Copyright: NASA/JPL-Caltech.

Figure 2. An illustration showing plume activity on Enceladus. Copyright: NASA/JPL-Caltech.

The Planetary Protection of Outer Solar System (PPOSS) project tackles the science, technology and policy-making components related to biological and organic contamination of planetary bodies beyond Mars (outer solar system), in particular icy moons. This intensive three year programme (2016-2018) will provide an international platform and forum where science, industry and policy actors will meet to nurture and catalyse discussions, exchange of knowledge and produce policy recommendations on the matter of planetary protection. The main objectives of the PPOSS project are:

  • describe the state of the art and good practice for implementing planetary protection requirements, and identify good practices and lessons to be learnt.
  • identify scientific challenges, scientific requirements and knowledge gaps related to planetary protection of outer solar systems bodies, including small solar system bodies.
  • develop an European engineering roadmap for the industry sector.
  • review the international outer solar system planetary protection regulation structure and categorisation, suggest improvements.
  • facilitate the dissemination of knowledge related to planetary protection. 

The PPOSS consortium is represented by the European Science Foundation (Project Coordinator, France), COSPAR (France), German Aerospace Center (Germany), Eurospace (France), Imperial College London (United Kingdom), National Institute for Astrophysics (Italy) and Space Technology Ireland Ltd (Ireland). 2016 has been a busy first year for the PPOSS project. Two workshops have already been hosted to compile a handbook that describes the state-of-the-art of planetary protection as well as good practices and lessons learnt from past missions. These events attracted a variety of experts in planetary protection, some of them whom have been involved with the topic since the first missions to Mars in the 1970’s. More recently, a one-week workshop was carried out to identify scientific requirements and knowledge gaps to implement planetary protection requirements in future space exploration missions to the outer solar system. This workshop gathered a panel of scientific experts from Europe, USA and Japan with representatives of their respective national space agencies. Scientific challenges to prevent biological and organic contamination in future space missions were discussed and the main findings will be published along the current year. Stay tuned for more PPOSS posts!

Further information

The PPOSS project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 687373.

PPOSS project website


The views expressed by the authors of the Science Connector Blog articles do not necessarily represent the views of the European Science Foundation as a whole, or of its members.

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