There has been much disagreement in the scientific literature about how long and under what conditions terrestrial life could survive exposure to vacuum. Recently, there was a unique opportunity to obtain factual data on the subject, with the return of Apollo 12, bearing pieces of the Surveyor 3 spacecraft. On 20 November 1969, the entire TV camera and other selected components were removed from Surveyor on the Moon, where they had been since 20 April 1967. They were sealed and returned to Earth, stored in the Lunar Receiving Laboratory for the quarantine period, and then disassembled and examined.
Pre-launch sterilization of spacecraft is only a partial affair, since sterilization conditions are chosen to give an acceptable trade-off between micro-organism killing and the chance of disabling components by the heat and chemicals used. Consequently, all spacecraft contain a small number of viable micro-organisms at launch.
It was not anticipated that any part of Surveyor 3 would be returned to Earth, and so there was no before launch examination of back-up components to determine their degree and nature of contamination by micro-organisms. This is unfortunate, since there could be no examination of a 'before-and-after' nature. However, backup cameras were available, having been stored since 1967. One was used for testing the techniques, and another was used in parallel with the one returned from the Moon.
The cameras were placed within an iso-propanol washed sterile cabinet, fitted with a laminar-flow sterile air supply. This ensured that no contamination was possible from organisms drifting into the cabinet. The operators wore sterile caps, face-masks and gloves, and all other possible precautions were taken against accidental contamination.
The camera itself contained no lunar material, showing it to have remained leakproof.
A number of cotton swabs were taken from inside the cameras, and inoculated into trypticase soy broth (TSB, for growth of aerobic organisms), into thioglycollate broth (THIO, for anaerobic organisms), and into yeast malt broth containing streptomycin and penicillin (YMB, for growth of fungi) [ 1 ]. The sites tested are listed in the Table 1.
Table 1. Microbial sampling sites of the Surveyor 3 and TAT-1 TV cameras. Sampling sites 1 and 2 are camera samples pertaining to the Surveyor 3 TV camera only. The TAT-1 camera had no collar cables; consequently, no sample of site 1 was taken. Site 2 included all 3 exterior metal cable connector surfaces.
| Sampling site | Tube number | ||
| TSB | THIO | YMB | |
1. Metal surface under front half of collar
2. Nylon ties, Teflon wrapping, cable connector surface
3. Surface area on support studs
4. Surface area on electronic conversion unit
5. Circuit board support-plate edges and screw studs
6. Surface area of all 3 cable connectors inside camera
7. Nylon ties and cable wrappings
8, Debris in bottom of shroud
9. Large area on inside of shroud
10. Top surface of exposed circuit boards
11. Foam samples from between circuit boards | 1 2 3 4 5 6 7 8 9 10 31 | 11 12 13 14 15 16 17 18 19 20 32 | 21 22 23 24 25 26 27 28 29 30 33 |
Standard precautions were taken against contamination of the culture tubes. The original culture was diluted by 10 and 100 with fresh broth, and samples of each dilution were plated on to 3 agar-nutrient plates to permit colony development. This is so that the number of micro-organisms present in the original sample could be determined. Failure to show consistent results, such as, for example, growth in a ten-fold dilution tube without growth in the undiluted sample, or differing number of colonies on the 3 plates inoculated from the same sample tube, was taken as evidence of contamination, and the result was ignored.
The only positive result obtained was from 32, which showed growth in 3-4 days incubation in undiluted THIO medium, from a 1 mm3 piece of foam from the Surveyor 3 camera. The organism was identified as Streptococcus mitis.
The backup camera contained more organisms, identified as a Bacillus species, an Aureobasidium species, and Aspergillus pulvinis.
Since only 1 tube showed growth, from a single sample, possibly from only a single microbial cell, the result is in question. No growth was obtained from other parts of the lunar-retrieved camera, or from electrical cabling similarly examined [2]. The bodies of the astronauts were host to S. mitis, together with a number of other organisms. Despite the careful approach, contamination by the investigators is a possibility, which is why the result has been met with scepticism.
If we believe it, a terrestrial organism remained viable after 2½ years on the Moon, in vacuum, alternately heated and frozen, and subjected to solar radiation. Perhaps future missions to the Moon will be able to confirm or deny this report.
1. F. J. Mitchell and W. L. Ellis, 'Surveyor III: Bacterium isolated from lunar-retrieved TV camera', Proc. 2nd Lunar Sci. Conf., Vol. 3, 2721-2733 (1971), M.I.T.Press.
2. M. D. Knittel, M. S. Favero and R. H. Green, 'Microbiological sampling of returned Surveyor III electrical cabling', Proc. 2nd Lunar Sci. Conf., Vol. 3, 2715-2719 (1971), M.I.T.Press.
| *Laboratory of Chemical Evolution, Department of Chemistry, University of Maryland, College Park, Md.20742, USA. |