The joint committee was asked to review the current planetary protection requirements for Mars Special Regions and their proposed revision as outlined in the SR-SAG2 report and to suggest updates to the planetary protection requirements for Special Regions. Based on its discussions and deliberations, the review committee organized its conclusions under the following five headings:
- Overall Assessment of the SR-SAG2 Report;
- Environmental Parameters Defining a Special Region;
- Identification of Special Regions;
- Specific Terrains Identified as Special Regions; and
- Updated Definition of a Special Region
The authors of the SR-SAG2 report are to be commended for their comprehensive review of the issues associated with Special Regions and the factors used to define them. The SR-SAG2 report contained 45 findings and the review committee supports 29 of them. The committee’s assessments of the remaining 16 are detailed below:
- Finding not supported—The committee does not support Finding 3-14 of the SR-SAG2 report. The committee does not agree with the idea that that the atmospheric pressure on Mars is generally high enough “to allow any unfrozen (pure) water to exist as a liquid for short periods of time before it either evaporates or boils away” as suggested by Finding 3-14.
- Finding supported in modified form—The committee proposed revisions to several findings in order to eliminate ambiguities or incorporate some recent findings that were made after the SR-SAG2 report was written. In particular, the committee supports 13 in revised form (2-1, 2-4, 3-1, 4-1, 4-2, 4-8, 4-9, 4-14, 4-16, 5-3, 5-4, 5-7, and 5-9). In addition, the committee suggests that two findings (4-6 and 47) be combined. The committee notes that the proposed revisions to two of these findings (2-4 and 4-1) have a direct impact to the definition of a Special Regions.
- New finding—The committee proposes a new finding, with regard to human spaceflight, which will
- strengthen future efforts to update planetary policy findings (i.e., the need to be explicit with regard to the limits of human exploration (6-1) and the need to update policy based upon the proposed revision to Finding 5-9.
The specific wording of all of the findings in the SR-SAG2 report and the review committee’s revised and new findings can be found in Appendix B.
The review committee concluded that environmental parameters used to define Special Regions (currently in the COSPAR policy and agreed upon in the SR-SAG2 report) of temperature and water activity are still appropriate. However, the review committee believes that if the detection of methane in the martian atmosphere—which is almost certainly indicative of the presence of water and may indicate biogenic activity—is confirmed, that may demand that the source region—that is, the zone where methane is being produced—be designated as a Special Region.
The review committee concluded that the identification of Mars Special Regions is problematic for several reasons. First, detailed knowledge of the physical and chemical conditions of the surface and sub-surface of Mars at various scales is lacking, particularly the microscale. Second, current understanding of the ability of life to propagate is limited. It is not known if one, ten, or a million cells from a single species are required for propagation in an extraterrestrial environment. Alternatively, propagation may only be possible for microbial communities (i.e., collections of many different species). In view of the rapid development of powerful new techniques in biology and the increase in knowledge of the martian environment by ongoing and future space missions, the current practice of reassessing the concept of a Special Region and its definition every 2 years is both appropriate and essential.
The specific terrains identified as Special Regions in both the COSPAR policy and in the SR-SAG2 report (i.e., “gullies, and bright streaks associated with gullies, pasted-on terrains, subsurface below 5 meters, others, to be determined, including dark streaks, possible geothermal sites, fresh craters with hydrothermal activity, modern outflow channels, or sites of recent seismic activity” and “spacecraft-induced Special Regions”) are best regarded as “Uncertain Regions.” The final determination of a Special Region would depend on the review of the latest scientific knowledge about a specific site in order to verify if it is within the environmental parameters defining Special Regions, taking into consideration the potential existence of microscale habitats.
Based on its discussions and deliberations, the review committee proposes an update to the definition of a Special Region (COSPAR 2015). The proposed changes are based on the critical new findings the committee identified that have a direct bearing on the designation of Special Regions. Two of the critical new findings came to the fore because of reconsideration of the relevance of methane to planetary protection (see Revised Finding 2-4) and the realization that recurring slope lineae are best treated as Uncertain Regions (see Revised Finding 4-1).
Given current understanding of terrestrial organisms, Special Regions are defined as areas or volumes within which sufficient water activity AND sufficiently warm temperatures to permit replication of Earth organisms may exist. The physical parameters delineating applicable water activity and temperature thresholds are given below:
- Water activity: lower limit, 0.5; upper limit, 1.0;
- Temperature: lower limit, –25°C; no upper limit defined; and
- Timescale within which limits can be identified: 500 years.
Observed features for which there is a significant (but still unknown) probability of association with liquid water, and which should be considered as Uncertain Regions and treated as Special Regions until proven otherwise
- Sources of methane (if identified);
- Recurring slope lineae;
- Gullies and bright streaks associated with gullies;
- Pasted-on terrains;
- Caves, subsurface cavities, and subsurface below 5 meters; and
- Others, to be determined, including dark slope streaks, possible geothermal sites, fresh craters with hydrothermal activity, modern outflow channels, or sites of recent seismic activity.
Spacecraft-induced special regions are to be evaluated, consistent with these limits and features, on a case-by-case basis.
Organizations proposing to investigate any region that may meet the criteria above, have the responsibility to demonstrate, based on the latest scientific evidence and mission approach, whether or not their proposed landing sites are or are not Special Regions.
In the absence of specific information, no Special Regions are currently identified on the basis of possible martian life forms. If and when information becomes available on this subject, Special Regions will be further defined on that basis.