Kenneth H. Nealson
Center for Life Detection
Jet Propulsion Laboratory
The Mars sample-return (MSR) missions are presently in a state of reorganization as a result of the recent reports by the committees that examined the failed missions (Mars Climate Orbiter [MCO] and Mars Polar Lander [MPL]). There is little doubt that MSR is still an important and viable component of the Mars Exploration Program, and remains a central goal of the program, but the exact nature of the mission (e.g., the time of launch, the architecture of the mission, the international partners) cannot be specified. However, the basic components of sample return will remain the same: spacecraft assembly, launch, transit to Mars, landing on Mars, sample retrieval, launch of the sample to Mars orbit, sample retrieval in Mars orbit, return to Earth, Earth entry, sample retrieval and containment, and sample analysis. Life detection will play a prominent role throughout the mission, from the point of view of planetary protection, science protection, and life detection of terrestrial life forms, either extant or extinct.
The MSR missions have been dominated by a desire for rapid sample return for several years, with a program for sample return aimed at the year 2008. This mission design included two separate launches (2003 and 2005) of lander-rover combinations that would retrieve samples (soil samples, drilled rock cores, and unconsolidated martian surface materials), place the samples into a sample container called an OS (orbiting sample), and launch the OS into low Mars orbit using the Mars Ascent Vehicle (MAV). After the second sample was placed in orbit, an orbiter was to be sent to fetch both samples and place them into the Earth Entry Vehicle (EEV), which would deliver them to the surface of the Earth via a hard landing at a site to be determined. Some variation on this was expected to occur with a sample returned to Earth at the target date of 2008.
With the unfortunate loss of two Mars missions (MCO and MPL), both the architecture and the timing of the MSR program are being reexamined. At this point in time it is difficult to present any details of the missions. What can be said with some authority is that MSR is still a major component of the Mars program, and the return of a pristine sample from the surface of Mars remains a major goal.
While neither the exact nature of the mission nor the timing of the MSR effort can be specified, it is possible to identify many parts of the mission and of the total program that will occur, and to discuss the role that life detection will play, in fact must play, in the various stages.
The components of the mission that will almost certainly occur in any future mission are shown in Table 1, although the details surrounding them may vary considerably.
For the purpose of the discussion, we divide the issue of life detection into two parts: earthly life, and extraterrestrial life. For the former, standard methods and logic can be used, while for the latter, other methods (so-called non-Earthcentric methods) must be employed.
The need for these analyses has been clearly noted by previous task groups of the NRC in reports presented in 1992 and 1997.1,2 In these reports it was noted that while earthly life is not likely to prosper on Mars, in the interest of protecting the science of the mission, it is necessary to fastidiously clean any spacecraft that will land on the surface of Mars. This so-called science protection is of great importance to avoid false positives during in situ life detection experiments, as well as those that might occur in returned samples as the result of “roundtrippers”— earthly contaminants that survive the transit in both directions.