Mission Outcome

 

Mission

Type

Country

Launch Date

Success

Failure

Comments

Mars Odyssey

Orbiter

USA

04-07-01

X

 

 

Mars Express

Orbiter

ESA

06-02-03

X

 

 

Beagle 2

Lander

UK

06-02-03

 

X

Unknown EDL failure; excessive impact velocity suspected

MER (Spirit)

Lander/Rover

USA

06-10-03

X

 

 

MER (Opportunity)

Lander/Rover

USA

07-07-03

X

 

 

 

Total Successes/Failures

15

21

 

 

Overall Success Rate

42%

 

 

NASA Successes/Failures

13

7

 

 

NASA Success Rate

65%

 

 

NASA Lander Successes/Failures

5

3

 

 

NASA Lander Success Rate

63%

 

 

SOURCES: Data for missions launched before 1992 were taken from NASA (1991), Siddiqi (2002), and <http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1971-049A>, accessed on November 15, 2005. Data for all subsequent missions were obtained from NASA Web sites.

and growth) are inherently probabilistic. Even if each previous mission did have some probability of having contaminated Mars, those probabilities were likely small (see Chapters 4 and 5), so that care with subsequent missions is still important for keeping at a low level the probability of contaminating Mars summed over all missions. The committee illustrates this concept with an analogy: even if the campfires of a dozen campers have previously posed the risk of a forest fire, it is still important that subsequent campers extinguish their campfires properly.13

Unless a previous mission has delivered microbes to an environment in which they can reproduce and geographically expand via the martian subsurface, existing experimental evidence for the survival of microorganisms at the surface of Mars suggests that the contamination resulting from these missions is likely to be at most local. More than 30 research papers have been published reporting experimental results for microbial survival under simulated martian conditions, with inconsistent results. Only recently have such experiments been conducted in a Mars simulation chamber that permitted good simulation of the pressure, temperature, atmospheric composition, and ultraviolet (UV)-visible-infrared light environment at Mars (Schuerger et al., 2003). These experiments showed that B. subtilis spores were rapidly (timescales of hours at most) killed even when partly shielded against UV light by being covered with simulated martian dust particles up to 50 microns in diameter. Viable spores were significantly reduced after an 8-h period even when covered by a 0.5-mm contiguous dust layer. Experiments with the dessication-tolerant, endolithic cyanobacterium Chroococcidiopsis sp. 029 (Cockell et al., 2005) showed survival for this organism, when exposed to martian-simulated UV, about 10 times higher than that previously reported for B. subtilis, but there was still a 99 percent loss of cell viability after 5 minutes. However, if protected by 1 mm of rock, Chroococcidiopsis sp. could survive and potentially grow, if water and nutrient requirements for growth were met.

It appears likely that most microorganisms exposed to the martian UV environment and unable to gain access to the martian subsurface will rapidly die. Moreover, because windblown dust particles on Mars have diameters in the range of 1 to 2 microns, transport via dust particles is also likely to lead to rapid death, and so windblown transport of microorganisms on Mars seems unlikely to contaminate distant parts of Mars.

13  

The committee called this the “Smokey the Bear” argument for ongoing planetary protection.



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