NASA's efforts in planetary protection seek to preserve planetary conditions for future exploration of biological constituents and to protect Earth and its biosphere from potential extraterrestrial sources of contamination. Both to preserve future scientific opportunities and to comply with existing U.S. treaty obligations, particularly the 1967 Space Treaty, NASA is committed to exploring space while avoiding the biological contamination of other solar system bodies and protecting Earth against potential harm from materials returned from space. Under the provisions of NASA Policy Document (NPD) 8020.7 and the lower-tier document NASA Policy Guidebook (NPG) 8020.12, which places responsibility for implementing planetary protection policy with the associate administrator for space science, NASA maintains a planetary protection program to evaluate objectives. The associate administrator delegates the management of NASA policy to a planetary protection officer (PPO). One other salient feature of the current NASA directives is that NASA is required to seek the advice of internal and external advisory groups in implementing planetary protection policy, most notably from the Space Studies Board of the National Research Council.

For each solar system body that might be explored, NASA's requirements may range from no further action (in the case of missions to bodies not of interest with respect to life or chemical evolution) to a variety of mission constraints, including careful record keeping, a requirement for altering spacecraft trajectories to avoid hitting a planet unintentionally, or even heat or gas treatment of a spacecraft to kill the biological organisms it may carry. For returned spacecraft, depending on the target of exploration there may be no additional constraints or there may be constraints as severe as a requirement to quarantine the returned spacecraft and even sterilize its contents.

Constraints on spacecraft involved in solar system exploration missions depend on the nature of the mission and the identity of the target body (or bodies) to be explored. No strict set of procedures are in place for a given solar system body. Instead, individual missions are placed into different categories depending on the concern for the target of the mission and the type of mission envisioned.

The restrictions and categories given in Table D.1 are shown as they were presented in reports on NASA's planetary protection policy (DeVincenzi and Stabekis, 1984; DeVincenzi et al., 1996), with minor modifications in wording as embodied in NPG 8020.12, and current thinking on the status of Europa (personal communication, John Rummel, May 6, 1998). Categories I through IV apply to missions or targets where "forward contamination" is a concern. Category I applies to all missions to targets thought to be of no biological interest. These missions have no associated planetary protection requirements. Category II applies to all missions to targets in which there

is a minimal biological interest, but which may be of intrinsic interest for the study of chemical evolution and for which documentation is required to ensure that planetary protection goals are being met. Categories III and IV apply to targets with significant biological interest, or with a potential to be contaminated. Category III applies to missions intended to make direct contact with these targets. Category IV applies to missions intended to make direct contact.

Category V applies to all missions that make contact with another solar system body and then return to Earth and is given in addition to the category assigned for the outbound phase. Category V missions can be designated either as "unrestricted Earth return," in which case they would warrant no further planetary protection requirements, or as "restricted Earth return," which might involve requirements for extensive constraints on the mission to guarantee the safety of Earth's biosphere.

NASA's program in planetary protection is represented on the international stage largely through the mediation of the International Council of Scientific Unions' Committee on Space Research (COSPAR), a nongovernmental organization that consults with the United Nations on planetary protection issues, particularly with respect

to the provisions of the 1967 Space Treaty. COSPAR comprises several scientific commissions, and planetary protection is the province of Scientific Commission F, which is concerned with "life sciences as related to space." COSPAR policy is proposed by Scientific Commission F and adopted by the COSPAR Council, which is made up of commission representatives and the representatives of national members and international scientific unions. In the past, U.S. representatives have taken a leading role in the formulation of COSPAR planetary protection policy, and COSPAR policy has roughly mirrored NASA policy. NASA document NPG 8020.12 stipulates that NASA will not participate in international missions unless each international partner agrees to follow COSPAR planetary protection policy.

DeVincenzi, D.L., and P.D. Stabekis. 1984. Revised planetary protection policy for solar system exploration. Adv. Space Res. 4:291-295.

DeVincenzi, D.L., P. Stabekis, and J. Barengoltz. 1996. Refinement of planetary protection policy for Mars missions. Adv. Space Res. 18:311-316.