By Joseph King
NASA placed two Viking Landers (VL) on the surface of Mars in 1976 to study the physical environment there and to look for evidence of life. Three distinct biology experiments were carried on each Viking Lander. According to Viking Project Scientist Dr. Gerald Soffen the post-mission consensus was that life on Mars was not found. However, Dr. Gilbert Levin, principal investigator of the Labelled Release (LR) experiment (one of the three biology experiments), has maintained over the years that the results of his experiment were consistent with and suggestive of the presence of microbial life on Mars.
In April 2000 NASA Headquarters (HQ) received a query on the availability of data from the LR experiment and a request to mount an effort to recover the data and to make them computer-usable if needed. HQ turned to NSSDC and to the Geosciences node of the Planetary Data System (PDS) at Washington University (PDS/WU) for help in finding, and upgrading as needed, these LR data. The recovery and upgrade effort make an interesting story, related herein, but first a brief introduction to the Labelled Release experiment is useful.
In the LR experiment Martian soil samples were brought into a test cell to which was also added a radioactive nutrient containing seven C14-labelled substrates. Any soil-resident living organisms were expected to ingest these nutrients and via some "heterotrophic metabolism" process (e.g., respiration) to excrete radioactive material into the gas of the test cell. Measuring radioactive decay rates in the gas could then give evidence of the buildup of the C14 atoms in the gas with implications for the occurrence of metabolic processes. Further details of the experiment and its results are given in a paper by Dr. Levin and Co-Investigator Dr. Patricia Straat published in the Journal of Geophysical Research in 1977 (p. 4663).
Nine distinct soil samples were analyzed over the course of the two Viking Lander missions. Each analysis involved the collection of data over many days or weeks. The data were radioactivity count rates mostly taken at 16-min intervals, accompanied by similarly resolved temperature values obtained in the test cell and at the radioactivity detector to help with the interpretation of the count rates. Thus, the basic data are time-tagged sets of three numbers mostly every 16 minutes for each of nine multiday periods.
LR data were available at NSSDC in two forms. First, NSSDC held 24 reels of microfilm whose frames contained images of pages of computer printout generated by the Viking Project for archiving. While each reel was specific to either Viking Lander 1 or 2, the data from the three biology experiments were highly intermixed. Further, while the focus of the 24 reels was the VL biology data, the reels contained engineering and other data vastly more than needed for the use of the LR count rate and temperature data. Attempting to scan these reels of microfilm would have been expensive and owing to the poor quality of many frames would likely have produced very unreliable ASCII files. Even if done reliably, the further effort to develop software to recognize, extract, and organize the desired LR data would also have been expensive.
NSSDC as well had some CDs of Viking Lander data generated by the Jet Propulsion Laboratory as part of its institutional data restoration effort. A sample of these with the limited available documentation was sent by NSSDC to PDS/WU where Dr. Ed Guinness and his colleagues determined that the VL data could not be used to identify and retrieve the desired LR data. Further, PDS/WU identified, requested, and through JPLs Michael Martin received copies of another set of VL CDs; again, insufficient documentation prevented their use in retrieving the desired data.
Thus, at this point the best option for recovering the desired LR data was a very tedious and labor-intensive reading of many microfilm reels to find all the desired LR reading of data and to key these data as encountered into a computer. Fortunately, an attractive alternative materialized.
Labelled Release Principal Investigator Dr. Levin operates a company, Biospherics, Inc., located in Beltsville, Maryland, less than ten miles from Goddard. NSSDC contacted Dr. Levin, who was very enthusiastic about the possibility of the recovery and new analyses of his data. NSSDC Planetary Acquisition Scientist Dr. David Williams and this author met twice at Biospherics with Dr. Levin and his colleague, Dr. Pat Straat, who is now working in an unrelated field in nearby Bethesda, Maryland. Dr. Straat was able to produce from her personal archives computer listings generated during the Viking missions that were LR-specific and were greatly more convenient to use than the NSSDC microfilm frames.
She initially provided a copy of the listings for cycle 3 of the Viking Lander 2 mission. A "cycle" was everything connected with a specific soil sample. This cycle, of about 12 weeks duration, was the cycle of most interest to the researcher whose request stimulated this recovery effort. A copy of the copy was created at NSSDC and sent to PDS/WU, where it was keyed by Phil Valko, a WU student, under Dr. Ed Guinnesss watchful eye.
This material contained much but not all of the count rate and temperature data for this cycle. The additional data were on the NSSDC microfilm and were keyed by NSSDC staff, mainly Allison Lopez and Lois Hughes, then quality-checked and sent as a file to PDS/WU for the preparation of the complete VL 2, Cycle 3 data set.
PDS/WU has prepared an LR Experimenters Notebook, an LR Web page (whose URL will be given in the Web-version of this article once the page is publicly available), and the new data set, which integrates the PDS/WU and NSSDC data recovery efforts. They have also made arrangements for PDS peer review of the VL 2, Cycle 3 data as per standard PDS practice. The data will be publicly accessible via network from PDS/WU shortly after the peer review slated for September 2000.
As of early September 2000 NSSDC was acquiring from Dr. Straat copies of her voluminous printouts for the other LR cycles. These printouts will be student-keyed at PDS/WU. In the coming months well-organized LR data for all cycles will be network-accessible from PDS/WU and will also reside on PDS/WU-created CDs at the NSSDC archive. [Data are now available at http://pds-geosciences.wustl.edu/missions/vlander/lr.html]
PDS hopes to mount an equivalent effort for the other two Viking Lander biology experiments. Whether data as conveniently organized as the LR data provided by Dr. Straat are needed and available outside NSSDC/PDS remains to be seen.
Fortunately for posterity, data prepared for archiving by current and recent NASA space science missions are done digitally and in adherence to standards that did not exist in the 1970s.
Link to September 2001 Article on Results from the Viking Labelled Release Data Restoration
[Article internal links modified 9 March 2006]
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Author: Miranda Beall