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Planning for the Scientific Exploration of Mars by Humans By the mepag human Exploration of Mars Science Analysis Group (hem-sag)


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Biology/Life: Human Exploration Goals and Objectives

What are the key scientific goals and objectives of human exploration of Mars in biology/life and what are sample Human Science Reference Missions (HSRM) in biology/life?

Human enabled biological investigations on Mars would focus on taking samples and making measurements to Determine if Life Ever Arose on Mars. This goal is consistent with the 2006 Mars Exploration Program Analysis Group (MEPAG) goals and priorities, and we do not see this goal changing in the next 30 year period.

The search for life on Mars can be generally broken into two broad categories: 1) the search for past (extinct) life on Mars and 2) the search for present (extant) life. Both have been, and will continue to be based on a search for water, since all life on Earth requires water for survival. Abundant evidence on the Martian surface of past water activity (e.g. rivers, lakes, groundwater discharge) has lead to Mars becoming a strong candidate as a second planet in our solar system with a history of life. With increasing knowledge of the extremes under which organisms can survive on Earth, especially in the deep subsurface, whether Martian life is still present today has become a compelling and legitimate scientific question.

The National Research Council (NRC) was recently commissioned to do a study to develop “an up-to-date integrated astrobiology strategy for Mars exploration that brings together all the threads of this diverse topic into a single source for science mission planning” (Jakosky et al 2007). This report did not consider how to do science with humans, but we rely heavily on it and earlier MEPAG documents here as snapshots of the current community thinking on astrobiological investigations on Mars.

As pointed out by Jakosky et al (2007), the search for life on Mars requires a very broad understanding of Mars as an integrated planetary system. Such an integrated understanding requires investigation of the following:


Many of these investigations are well underway robotically and would be much further advanced through further robotic missions and sample return. However, a human presence would…

The Search for Extant Life


Jakosky et al (2007) suggested a number of high priority targets based on evidence for present-day or geologically recent water near the surface:


  • The surface, interior, and margins of the polar caps;

  • Cold, warm, or hot springs or underground hydrothermal systems; and

  • Source or outflow regions associated with near-surface aquifers that might be responsible for the “gullies” that have been observed.

SR-SAG noted that sites where recent water may have occurred would also include mid-latitude deposits indicative of shallow ground ice.

Conditions in the top 5 m of the Martian surface are considered extremely limiting for life. Limiting conditions include high levels of ultraviolet radiation and purported oxidants as well as most of the surface being below the limits of water activity and temperature for life on Earth For these reasons, finding evidence of extant life near the surface would likely be difficult and the search would almost certainly require subsurface access. This was also a key recommendation of Jakosky et al (2007).


The Search for Extinct Life


Jakosky et al (2007) list sites pertinent to geologically ancient water (and by association past life) include the following:


  • Source or outflow regions for the catastrophic flood channels;

  • Ancient highlands that formed at a time when surface water might have been widespread (e.g., in the Noachian); and

  • Deposits of minerals that are associated with surface or subsurface water or with ancient

  • hydrothermal systems or cold, warm, or hot springs.

Human Science Reference Mission to Address Biological Goals


As a demonstration of how HEM-SAG envisions carrying out the biological goals, a human science reference mission was designed to the Centauri Montes region. This region has drawn attention from astrobiologists as a result of the discovery by Malin et al (2006) that a flow feature (gully) inside a crater wall has apparently been active in the last decade, thereby providing the intriguing prospect of liquid water at or near the surface (Figure 20). This region has also been well documented for its concentration of young, volatile-rich deposits and figures prominently in recent GCM simulations at different obliquities, which indicate that the eastern-Hellas region should be receiving significant amounts of water-ice from the south pole (Forget et al, 2006). Centauri Montes is also at the head of major Amazonian/Hesperian outflow channels.



Figure 20. Southeast wall of an unnamed crater in the Centauri Montes region, as it appeared in August 1999, and later in September 2005 (MGS MOC Release No. MOC2-1619, 6 December 2006).
The indicators of ice deposits and liquid water today, as well as the region being associated with outflow channels, provide ample local targets for the search for extant and extinct life. For geological investigations, this region has the attraction of all three epochs being represented in close proximity. We understand that the connection between the active gully features and liquid water is controversial (e.g. McEwen et al. 2007). This site was chosen because at the time of writing, it was one of the two most promising sites on the planet for finding liquid water near the surface. If other more promising sites are discovered, site selection for addressing biological goals should follow these new discoveries.
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