From Nature.com

(excerpt)

Mark Sims, Beagle 2's project manager at the University of Leicester, says his team will definitely be using plasma sterilization on some of Beagle's metal parts, but other areas will have to be treated in different ways. Parts of the craft that come into direct contact with samples may also be heat-treated, he says.

The teams are also testing alternative ways of cleaning the probes before sterilization. The traditional technique - wiping with alcohol - can compound the problem. On aluminium, for example, this bursts cells and glues their innards to the surface.

NASA is currently experimenting with alternatives, including ultrapure water and the water-based cleaning fluids that the semiconductor industry is developing to replace the chlorofluorocarbons used to clean circuit boards. So far, no single method has proved adequate for aluminium - a potential problem as the metal is a common component of spacecraft.

The nylon brushes used to scrub surfaces before wiping with alcohol can also cause difficulties. To a mass spectrometer - standard equipment for detecting the molecular signatures of life - the bonds between nitrogen atoms in nylon could easily be confused with those in amines, the building blocks of proteins. NASA has now taken the advice of David White, an environmental microbiologist at Oak Ridge National Laboratory in Tennessee, who suggested using polypropylene instead, which should not confuse the analysis.

The teams are also working on techniques to determine how well their attempts at cleaning and sterilization have worked. Because removing all traces of contaminating microorganisms is impossible, it is important to estimate the number of microbes that remain. Upper limits agreed before Viking reflect the level of cleanliness that was achievable at the time - in this case, a maximum of 300 bacterial spores per square metre on any one part of the probe's surface, together with an upper limit of 300,000 spores for the whole craft.

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Thanks.

Marcia