PURPOSE OF STRATEGY DOCUMENT

Exobiological exploration encompasses many different lines of scientific inquiry, but one of the most prominent of these is the search for evidence of life elsewhere in the universe and specifically within our own solar system. It follows that there is an abiding exobiological interest in the planet Mars, which of all the planets most closely matches the conditions within which terrestrial biota are known to exist. A major goal of the highly successful Viking mission, described further below, was the search for evidence of life on the surface of Mars. Since that mission, whose results are generally interpreted as inconsistent with extant life at the two sites visited by the Viking landers, the scientific focus of planning for future Mars missions has tended towards geological, geophysical and meteorological issues, largely bypassing those of exobiology. The purpose of this document is to attempt to ensure balance in Mars mission planning by showing that (a) exobiology is an integral part of the scientific history of Mars, and (b) pursuit of exobiological goals is generally compatible with the broader-based scientific exploration of Mars.

Establishment of an exobiological strategy for Mars exploration is particularly timely in light of recent developments in several different scientific areas, such as theories of the origin and early evolution of life, Precambrian paleontology, fossil-ization processes, biochemistry of primitive terrestrial organisms, biology of hydrothermal systems on Earth, geomorphology of Mars, and analysis of SNC meteorites and recognition of their martian origin. These diverse lines of inquiry all combine to generate a powerful scientific justification for an exobiological exploration of Mars that goes beyond the pioneering efforts of the Viking missions.

In addition to a positive scientific context, there are good programmatic reasons for a resumption of the exobiological exploration of Mars. Those reasons may be characterized as follows.

First, the tragic loss of Mars Observer has resulted in a delay of at least four years for the global reconnaissance data needed for detailed planning of later landed missions. Following the recommend-ations of the Elachi Committee for recovery of Mars Observer data, those global data will now be acquired using two Mars Surveyor spacecraft scheduled for launch in 1996 and 1998, respectively.

Second, as a result of the problems plaguing the Russian economy, the Mars '94 and '96 missions have been delayed until 1996 and 1998 (or later), respectively. The Chief Scientist for these missions has indicated an interest in establishing an interdisciplinary science team which will "create recommendations...for small modification of the [spacecraft] instruments (if...possible) and recommendations for program of operation of the instruments expedient from the exobiology point of view." The earlier mission already carries a U.S. experiment designed to study the oxidant(s) believed to be responsible for elimination of organic molecules from martian soil at the two Viking landing sites.

Third, Mars Pathfinder, NASA's technical trial of a direct- landing approach, is scheduled for launch in 1996, with deployment of a mini-rover on the martian surface in 1997.

Fourth, NASA's plan to establish a geophysical/meteorological network on the martian surface, MESUR Network, has been postponed indefinitely because the estimated cost of the mission is considered prohibitive under present funding constraints. It seems likely that deployment of such a network would be feasible only within the context of a joint international project that is unlikely to occur before the 2003 launch opportunity.

Fifth, with the shelving of MESUR Network, the focus of NASA's near-term Mars strategy has shifted towards a combination of surface geology, geochemistry and climatology. Within this context, the Mars Science Working Group has recommended that the study of volatiles and climate history should constitute the near-term goal for Mars exploration.

Finally, NASA's Mission From Planet Earth Study Office (Code SX) has formally decided to make the search for life on Mars one of the overarching goals of long-term solar-system exploration.

From these considerations, it is clear that, not only is planning for Mars exploration in a very active phase at this time, but exobiology is well placed to make a major contribution to that exploration. The aim of this document is therefore to define the exobiological issues which will serve as the scientific foundation to that contribution, and to provide a scientifically sound exobiological context within which scientists, engineers and managers will be able to optimize science return from future missions. Such optimization could involve design and development of instrumentation, instrument selection or modification, definition of spacecraft operations, and/or selection of landing sites or targets for remote sensing.

OUTLINE OF APPROACH

The approach adopted in this document largely follows that employed by Klein and DeVincenzi in their report on a NASA Ames workshop on exobiological exploration of Mars held in 1992. After a brief summary of the present state of knowledge about Mars, its geology and atmosphere, and the results from the Viking biology experiments, the strategy for further exobiological exploration of Mars is discussed from the perspective of three distinct scientific aspects: The search for evidence of prebiotic chemical evolution; the search for evidence of an ancient biota that is now extinct; and the search for life extant on Mars today. Then, the extent to which missions that are currently either proposed or planned will fulfill those strategic elements is discussed. Finally, a brief discussion of planetary protection issues, more completely covered in the recent Space Studies Board report [see Additional Reading], will be followed by a set of recommendations in the areas of basic research support, development of instruments and spacecraft, and mission planning.

BACK TO THE TABLE OF CONTENTS!