The latest requirements and guidelines - Planetary Protection Provisions for Robotic Extraterrestrial Missions - define a series of categories designed to ensure that there is no forward contamination of a "habitable zone" by terrestrial organisms. The Mars Express Orbiter is classified as a Class III mission as it will not encounter the planet's surface, whilst the lander is clearly designed to do just that.
To meet the International Treaty on Planetary Protection, Beagle 2 can only be given the go-ahead to be launched if it has no more than 300 spores per square metre and a total number of less than 3 x 105 spores, defined in Planetary Protection terms as a Category IVA mission.
Some scientists believe that forward contamination of Mars by landing spacecraft is so unlikely it does not warrant the additional costs imposed on a mission by stringent sterilisation. But any experiments designed to detect minute traces of the chemistry of life, such as those of Beagle 2, clearly could be compromised by the presence of terrestrial organisms. In our case, even dead spores, or other carbon-containing debris, are unwelcome in the vicinity of Beagle 2's sampling and analysis facility which will be stringently chemically cleaned, amounting to an additional level on Category IVA which we have designated Category IVA+.
Sophisticated space instrumentation, electronic and communication
systems do not lend themselves to standard methods of sterilisation.
When the favoured method of prolonged dry heat (111-125ºC
for 35-50 hours) is not acceptable, alternative sterilisation
methods such as gamma radiation have been used. The efficacy
of each method to reduce the microbial burden has been verified,
protocols approved and integrity of materials following treatment
confirmed. Matted surfaces and thick layers of composites
and foams presented additional challenges.
Beagle 2 passed its Planetary Protection requirements review,
carried out by a committee established by the Royal Society
and chaired by Prof. G. Eglinton.
