1st How many of these objects actually even worked when sent there?
2nd The surface of Mars is also a sterile enviroment.
CLEANING AND STERILIZATION STANDARDS
NASA's current planetary protection requirements for Mars missions are derived from the procedures applied to the Viking landers. Missions not carrying life-detection experiments must be cleaned to ensure that the spacecraft's total bioload does not exceed 300,000 spores and that the density of spores on the spacecraft's surfaces does not exceed 300 m-2.
Missions with life-detection experiments must undergo additional procedures to ensure that the total bioload does not exceed 30 spores.
The effectiveness of the various procedures currently used by NASA and its contractors to meet these bioload standards is determined by the use of reference organisms, including Bacillus subtilis (var. niger), Bacillus pumilis, and Bacillus stearothermophilus. Bacillus spp. (endospore formers) were originally selected as a microbiological indicator of sterilization success on the basis of their enhanced resistance to heat, desiccation, and radiation.
http://www7.nationalacademies.org/ssb/europach4.html
300,000 spores is not 100% sterile! 8)