The meaning of planetary protection has been evolving and expanding since it was first conceived in the 1960s. In general, it refers to preventing harm to planets and their environments by human activity. This can include protecting planet surfaces from contamination by Earth life or vice versa; preventing the impact of space debris; and safeguarding natural resources.
There are two main types of planetary protection: forward contamination, which is the transfer of terrestrial organisms to other solar system bodies, and backward contamination, which is the return of extraterrestrial material (including possible pathogens) to Earth. A third category, mutual contamination, covers when both forward and backward contamination could occur simultaneously (e.g., during a sample return mission).
Most missions sent beyond Earth’s orbit are subject to some level of planetary protection requirements set by international treaties such as the Outer Space Treaty and the Agreement on the Rescue of Astronauts, Return of Space Objects. The Committee on Space Research (COSPAR) is responsible for developing planetary protection policy recommendations that are used by national space agencies when planning their missions.
Planetary protection measures have been applied to all U.S. interplanetary spacecraft since 1967, starting with NASA’s Mariner 4 mission to Mars. These policies were formalized with the creation of NASA’s Office of Planetary Protection in 1968. Over time, COSPAR’s guidelines have become more stringent as we have learned more about potentially habitable environments in our solar system and beyond. For example, special care is now taken to avoid contaminating moons like Europa that may harbor life in subsurface oceans.
As we continue exploring our solar system and look toward future missions to Mars and other destinations, it is important that we maintain a high standard for planetary protection. By doing so, we can ensure that our search for life beyond Earth is not compromised – and that any life we do find has not been contaminated by us