Viking Lander Labeled Release Dataset Description Extracted from the PDS dataset catalog file. Additional information about the Labeled Release dataset can be found in the lr_archive.txt file in document collection. Dataset Overview ================= The Labeled Release (LR) instrument on each Viking Lander operated throughout the Primary Mission and continued into the Extended Mission. The experiment conducted several analyses on each lander, each of which is referred to as a cycle. The basic analysis cycle for the LR experiment was to deliver a sample of martian soil to one of four test cells, seal the cell and moisten the soil with an aqueous solution of carbon-14 labeled organic media. A second nutrient injection was typically done about 7-8 Mars days after the first injection. The test cell was continuously monitored for the release of radioactive labeled gas as an indicator of heterotrophic metabolism. Viking Lander 1 (VL1) conducted four analysis cycles with two nutrient injections for cycles 1, 2, and 4 and three injections for cycle 3. Viking Lander 2 (VL2) conducted five analysis cycles. The first four cycles had two nutrient injections each, and the fifth cycle had one injection [Levin and Straat, 1976B; 1977A; 1979A]. Data collected by the LR instruments included radioactivity counts from evolved carbon-14 labeled gas and temperatures of the detectors and the head-end assembly. Radioactivity was counted for 16-minute intervals during an analysis cycle, except for several hours around the time of nutrient injection where intervals of 2- to 4-minutes were used. Detector and head-end temperatures were measured at 16-minute intervals throughout the cycle. The LR data were originally archived on microfilm housed at NSSDC. LR data were also available from a set of computer listings in the personal archives of Co- Investigator Dr. Patricia Ann Straat. The data in the Planetary Data System (PDS) archive were transcribed into digital files from these two sources. The Straat listings were the primary source used. The original archive of this dataset used PDS3 standards. This version of the dataset contains the original PDS3 data updated to PDS4 standards. The LR experiment included an extensive test program that not only tested the operating characteristics of the LR instrument, but also analyzed many terrestrial samples for comparison with the Mars results. These test data are not currently part of the PDS Labeled Release archive, but much of it has been published in the scientific literature [e.g., Levin and Straat,1981A; 1981B; 1979B; 1977B; 1976B]. Parameters ========== The LR dataset contains three basic data measurements: radioactivity counts, detector temperature, and head-end temperature. Measurements are tagged with the time they were made and are stored in a time-ordered format. RADIOACTIVITY COUNTS: Radioactivity in the LR dataset are given as counts/minute. Counting was generally done over a 16-minute period and then normalized by the length of the counting interval to determine the average number of counts/minute within that interval. Each LR instrument had two solid- state beta detectors and could be commanded to use either one or both detectors. In cases where only one detector was used, radioactivity values were corrected to values equivalent to counting with both detectors. The radioactivity recorded by the LR detectors included a background signal from the Mars environment and from the Radioisotope Thermoelectric Generators (RTGs) that powered the Viking Landers. Background levels were determined from radioactivity measurements made prior to the start of an analysis cycle. Radioactivity values with and without background correction are provided for measurements made during the incubation period of an analysis cycle. TEMPERATURES: Both detector and head-end temperatures in the LR dataset are given in degrees Celsius. Temperatures were measured every 16 minutes throughout an analysis cycle. Sample temperatures are less than those recorded by the head- end temperature sensor because the test cell heaters and temperature sensors are located at the top of the test cell above the sample. See Levin and Straat [1977A] for information on correlating head-end and sample temperatures. TIME: The primary time tag for the LR dataset is known as Mars Mission Time (MMT). It is defined as the number of Earth seconds past midnight of Sol 0, where Sol 0 is the day of landing (P. A. Straat, personal communication, 2000). Mars mission time values in this archive have been transcribed from the computer listings or microfilm. The LR data files include several other time-related fields that were computed from the transcribed MMT values during archive production (see Processing Section below). The LR data files include time fields for elapsed time from nutrient injection and elapsed time from a specific Sol number. These fields are included to allow display of the data in forms similar to previously published graphs [e.g., Levin and Straat [1979A; 1977A; 1976B]. Other computed time fields are UTC and local lander time. The Viking project used the format of sol number, hour, minute, and second for local lander time with times in a sol extending beyond 24 hours. This usage is different from the PDS standard for local time that is used on later Mars rover missions. As a result, local lander time is called native time in the LR data files. Processing ========== All radioactivity, temperature and MMT data in this LR dataset were transcribed by hand into data files. The primary data source was computer listings supplied by P. A. Straat. The NSSDC microfilm was used to recover data for gaps in the computer listings. Personnel at the PDS Geosciences Node transcribed the computer listings, whereas personnel at NSSDC transcribed some of the microfilm. All data entered by hand was checked for accuracy. However, typographical errors may still exist in the dataset. See the CONFIDENCE_LEVEL_NOTE for estimates of the data entry accuracy. All ancillary time fields in the LR dataset were computed from the MMT parameter. The computation of UTC and local lander time from MMT require the UTC of midnight at Sol 0 and the number of seconds in a martian day. The intent of including these time fields in the LR dataset was to provide a means of comparison with times in other Viking datasets. As such, the methods used here to compute UTC and local lander time attempted to reproduce, as closely as possible, values consistent with values from the Viking project. A value of 88775.241 seconds/Sol was derived from analyzing a series of local lander time and UTC values published in Clark et al. [1977}. The UTC value for midnight of Sol 0 was estimated from times in Clark et al. [1977} and from acquisition times of Viking Lander images taken on Sol 0 for each lander [Tucker, 1978]. The estimated UTC values were 1976-07-19T19:39:54 and 1976-09-03T12:48:45 for VL1 and VL2, respectively. These estimates were reviewed by NAIF personnel. These values are slightly different from those published in Allison [1997] and Allison and McEwen [2000]. Data ==== The LR data consists of three files for each analysis cycle. Each table has an associated detached PDS4 label. The tables are: (1) Detector temperatures (2) Head-end temperatures (3) Radioactivity counts (1) Detector temperatures This table includes fields of detector temperature, MMT, and several derived time fields (see the PDS4 label). Data are sorted in increasing MMT order. (2) Head-end temperatures This table includes fields of head-end temperature, MMT, and several derived time fields (see the PDS4 label). Data are sorted in increasing MMT order. (3) Radioactivity counts This table includes fields of raw and background-corrected radioactivity counts, channel number, MMT, and several derived time fields (see the PDS4 label). The background-corrected field was derived from the raw radioactivity field by subtracting a constant background value determined from data collected prior to nutrient injection. Data collected in single channel mode were corrected to dual channel mode (using a constant multiplier) before background correction. Data are sorted in increasing MMT order. Analysis Cycles =============== A number of published papers describe the soil sampling and analysis rationale for the LR experiment, along with the scientific results [e.g., Levin Straat, 1979A; 1977A; 1976B]. A summary of the sampling and analysis strategy information from these papers is given here. Viking Lander 1 Cycle 1 ----------------------- The sample for VL1 cycle 1 was acquired from a smooth patch of fine-grained material named Sandy Flats. The sample came from within 4 cm of the surface. VL1 cycle 1 was performed autonomously according to preflight instructions. Sample Site : Sandy Flats Collection Temperature : -83 deg C Collection Sol : 8 (fresh) Experiment Type : Active First Injection Sol : 10 Second Injection Sol : 17 Purge Sol : 23 Viking Lander 1 Cycle 2 ----------------------- This sample was acquired on Sol 8 (see VL1 cycle 1) from Sandy Flats and stored in the biology hopper for about 20 sols. Before nutrient incubation, this sample was heated to 160 deg C for about 3 hours to sterilize the sample as a control for comparison to VL1 cycle 1 results. Sample Site : Sandy Flats Collection Temperature : -83 deg C Collection Sol : 8 (stored in hopper for 20 sols) Experiment Type : 160 deg C control First Injection Sol : 29 Second Injection Sol : 35 Purge Sol : 37 Viking Lander 1 Cycle 3 ----------------------- The VL1 cycle 3 sample was also acquired from Sandy Flats close to the site of the first VL1 sample (cycles 1 and 2). The sample came from within 4-5 cm of the surface. This analysis was a long active incubation (about 50 sols), where the sample received three nutrient injections. Sample Site : Sandy Flats Collection Temperature : -21 deg C Collection Sol : 36 (fresh) Experiment Type : Active, long incubation First Injection Sol : 39 Second Injection Sol : 55 Third Injection Sol : 80 Purge Sol : 89 Viking Lander 1 Cycle 4 ----------------------- This sample was collected during the Extended Mission from the same Sandy Flats area as the previous VL1 samples. It was collected on Sol 91 and stored in the Biology hopper in the dark, open to the Mars atmosphere, and at temperatures between 10 and 26 deg C until analysis started on Sol 230. The original intent for this cycle was to collect a fresh sample, but concerns by the surface sampler team about possible damage to the sampler arm changed the scenario. The two nutrient injections for this sample occurred about 3 hours apart. It was calculated that enough nutrient remained in the reservoir for the two injections [Levin and Straat, 1979A]. Sample Site : Sandy Flats Collection Temperature : -71 deg C Collection Sol : 91 (stored) Experiment Type : Active First Injection Sol : 232 Second Injection Sol : 232 Purge Sol : N/A Viking Lander 2 Cycle 1 ----------------------- This sample was collected from a crusty to cloddy material in an area known as Beta. The material came from within 3.5 cm of the surface. VL2 cycle 1 was performed autonomously according to preflight instructions. Sample Site : Beta Collection Temperature : -23 +/- 5 deg C Collection Sol : 8 (fresh) Experiment Type : Active First Injection Sol : 11 Second Injection Sol : 18 Purge Sol : 24 Viking Lander 2 Cycle 2 ----------------------- The VL2 cycle 2 sample was collected from the same area of Beta as for VL2 cycle 1 sample. It was a fresh sample collected on Sol 28. The sample was heated in the test cell at about 50 deg C for 3 hours before the nutrient was injected. The sterilization process was intended as a control for comparison to cycle 1 results. Sample Site : Beta Collection Temperature : -23 +/- 5 deg C Collection Sol : 28 (fresh) Experiment Type : 51 deg C control First Injection Sol : 34 Second Injection Sol : 38 Purge Sol : 47 Viking Lander 2 Cycle 3 ----------------------- This sample was acquired from under a rock called Notch Rock. The rock was pushed aside to expose the soil. The pushing occurred about 1 hour after sunrise and the soil was exposed to low angle sunlight for approximately 37 minutes before delivery to the biology sample processor. The intent of this sample was to analyze soil that was protected from ultraviolet radiation for a long period of time. This analysis performed a long incubation of nearly 90 sols with two nutrient injections. Radioactivity data was collected in single channel mode for part of the beginning of this cycle. Data were corrected to dual channel mode by multiplying by a factor of 1.95 prior to nutrient injection and a factor of 2.06 after the first injection. Sample Site : Beneath Notch Rock Collection Temperature : -66 deg C Collection Sol : 51 (fresh) Experiment Type : Active, long incubation First Injection Sol : 53 Second Injection Sol : 60 Purge Sol : 140 Viking Lander 2 Cycle 4 ----------------------- This sample was collected from the same general area as the samples for VL2 cycles 1 and 2 in the Beta location. The material for this sample mostly came from the top 5 cm of the surface. The sample may also contain material disturbed during the cycle 2 sample acquisition. The sample was heated to 46 deg C for about 3 hours before nutrient was injected. Sample Site : Beta Collection Temperature : -84 deg C Collection Sol : 145 (fresh) Experiment Type : 46 deg C, control First Injection Sol : 147 Second Injection Sol : 161 Purge Sol : 171 Viking Lander 2 Cycle 5 ----------------------- The original intent for VL2 cycle 5 was to incubate a fresh sample at sub- freezing temperatures to more closely simulate the actual Mars surface conditions. A previously used test cell was required for this cycle because all four test cells had been used. A surface sampler anomaly during the sample acquisition attempt on Sol 195 prevented the collection of a fresh sample. Thus, a sample collected on Sol 145 was used for VL2 cycle 5. The sample was stored for 84 sols prior to nutrient injection. The 0.5 cc sample was placed on top of about 1.2 cc of unused sample dumped into the cell from previous acquisitions plus about 0.5 cc of material from VL2 cycle 1. The LR instrument froze prior to nutrient injection during a power shutdown. It is possible that nutrient delivery lines or valves may have ruptured due to freezing. In addition, only a small amount of nutrient (0.64 cc) was calculated to remain in the reservoir. Thus, it is not clear whether a complete nutrient injection was delivered, although as least a partial delivery is likely [Levin and Straat, 1979A]. Sample Site : Beta Collection Temperature : -84 deg C Collection Sol : 145 (stored) Experiment Type : Soil-on-soil in used cell First Injection Sol : 229 Purge Sol : N/A Confidence Level Overview ========================= The sources for the LR data were microfilm stored at NSSDC and photocopies of Co-Investigator P.A. Straat's original computer listings. The P.A. Straat computer listings were used as the primary data source with the microfilm data used to fill in gaps. The microfilm contained images of computer pages with variable quality. The data transcribed from the P.A. Straat source were entered twice. The two versions were compared and corrected to ensure that the two versions exactly matched. For the microfilm data source, information was manually entered by one person and then checked by a different individual. For VL2 Cycle 3, there was some data that were available in both sources. A comparison of about 2000 radioactivity readings revealed a 0.25% error rate (5 values total) in NSSDC's transcribing and quality control process. The errors found included a single digit miskeyed, two digits reversed, or fractional digits replaced with zeroes. It is possible that the error rate is similar for data values where the microfilm is the only source. The NSSDC microfilm remains available from NSSDC for access by future users. Data Coverage and Quality ========================= Steps were taken to insure that this dataset is complete and contains as few errors as possible. However, there are several data gaps. Most data gaps are on the order of one or two sampling intervals, but some are on the order of sols. It would appear that these data were never taken or lost in transmission. The dataset contains a few spikes of spurious readings. These are usually obvious as a single data point that is very much larger than the values prior to and after the spike. References Cited ================ Allison, M., Accurate analytic representations of solar time and seasons on Mars with applications to the Pathfinder/Surveyor missions, Geophys. Res. Lett., 24, 1967-1970, 1997, doi: 10.1029/97GL01950. Allison, M. and M. McEwen, A post-Pathfinder evaluation of areocentric solar coordinates with improved timing recipes for Mars seasonal/diurnal climate studies, Planet. Space Sci., 48, 215-235, 2000, doi: 10.1016/S0032-0633(99)00092-6. Clark, L. V., D. S. Crouch, and R. D. Grossart, Summary of Primary Mission surface sampler operations, Viking '75 Project Document, VFT-019, 224 pp., 1977. Levin, G. V. and P. A. Straat, Viking Labeled Release biology experiment: Interim results, Science, 194, 1322-1329, 1976b, doi: 10.1126/science.194.4271.1322. Levin, G. V. and P. A. Straat, Recent results from the Viking Labeled Release experiment on Mars, J. Geophys. Res., 82, 4663-4667, 1977a, doi: 10.1029/JS082i028p04663. Levin, G. V. and P. A. Straat, Life on Mars? The Viking Labeled Release experiment, BioSystems, 9, 165-174, 1977b. Levin, G. V. and P. A. Straat, Viking Mars Labeled Release results, Nature, 277, 326, 1979a, doi: 10.1038/277326a0. Levin, G. V. and P. A. Straat, Completion of the Viking Labeled Release experiment on Mars, J. Mol. Evol., 14, 167-183, 1979b, doi: 10.1007/BF01732376. Levin, G. V. and P. A. Straat, A search for a nonbiological explanation of the Viking Labeled Release life detection experiment, Icarus, 45, 494- 516, 1981a, doi: 10.1016/0019-1035(81)90048-8. Levin, G. V. and P. A. Straat, Antarctic soil no. 726 and implications for the Viking Labeled Release experiment, J. Theor. Biol., 9, 41-45, 1981b. Tucker, R. B., Viking Lander imaging investigation: Picture catalog of Primary Mission Experiment Data Record, NASA Ref. Pub. 1007, 558 pp., 1978.