Archive of Viking Lander 1 and 2 Labeled Release Biology Experiment Data 1. Introduction The Labeled Release (LR) instruments [Levin et al., 1962; Levin and Carriker, 1962; Levin et al., 1964; Levin and Heim, 1965; Levin, 1972; Levin and Straat, 1976a] were part of the biology experiment flown to Mars on the Viking Lander spacecraft [Klein, 1974]. The two Viking Lander spacecraft were the first spacecraft to operate successfully for an extended period of time on the surface of Mars [Soffen, 1977]. Both spacecraft operated from 1976 through April 1980 and Viking Lander 1 (VL1) continued to operate until November 1982. The primary scientific objective of the lander mission was to test for the presence of life on Mars. Secondary objectives were embodied in the seismology, meteorology, inorganic chemical analysis, imaging, magnetic, and physical properties investigations. This archive includes data collected by the LR instruments on Mars. It was produced by the Geosciences Node of NASA's Planetary Data System (PDS) in cooperation with the National Space Science Data Center (NSSDC) and the principal LR investigators Gilbert V. Levin and Patricia Ann Straat. The intent was to produce a digital version of the dataset in order to provide electronic distribution to interested scientific research organizations and universities. The dataset was original archived using the PDS3 standards. This current version has been updated to conform 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 LR archive. However, many of the terrestrial sample analyses have been published in the scientific literature [Levin and Straat, 1976a; 1977b; 1979a; 1979c; 1981a; 1981b]. The material in this document, largely based on the equivalent document in the PDS3 dataset, provides the primary documentation for the LR PDS4 archive. Included in this document are sections on: A) the Viking Mission; B) the Viking Lander spacecraft; C) the LR instrument; D) processes used in generating the archive; and E) the PDS file structure. There is other documentation files are included in the document collection. The release_notes.txt file contains notes and comments about the about the PDS4 archive and includes information from the PDS3 errata.txt file. 2. Viking Mission The Viking Mission consisted of four spacecraft: two identical orbiters and two identical landers [Soffen, 1977]. The landers were attached to the orbiters during cruise to Mars. After orbit insertion around Mars and landing site selection, the landers separated from the orbiters for descent to the surface and a soft landing. The primary scientific objective of the mission was to search for life on Mars. Other science questions addressed by the mission were the composition and physical properties of the atmosphere, the distribution of atmospheric water vapor, global and local meteorology, the composition and physical properties of the surface, nature of Mars seismicity, and gravity field of Mars. The combined orbiter and lander spacecraft supported thirteen science investigations. The orbiters had three mapping experiments (imaging, infrared thermal mapper, and water vapor mapper). Atmospheric properties were also measured during lander descent to the surface. The landers had eight scientific experiments (see section 3) [Snyder, 1977; Snyder and Moroz, 1992]. In addition, several radio science investigations were conducted using both the lander and orbiter radio systems [Yoder and Standish, 1997]. The Viking 1 and 2 spacecraft were launched on August 20 and September 9, 1975, respectively. Below is a table showing major events of the mission. Orbiter 1 Lander 1 Orbiter 2 Lander 2 Launch 8/20/75 8/20/75 9/09/75 9/09/75 Orbit Insertion 6/19/76 6/19/76 8/07/76 8/07/76 Landing 7/20/76 9/03/76 Transmissions End 8/07/80 11/13/82 7/25/78 4/11/80 Viking Lander 1 (VL1) landed at 22.533 deg N latitude and 48.264 deg W longitude planetographic [Yoder and Standish, 1997] in the western portion of Chryse Planitia, which is a region of smooth plains and impact craters. Viking Lander 2 (VL2) landed at 48.039 deg N latitude and 226.032 deg W longitude planetographic [Yoder and Standish, 1997] about 200 km west of the Crater Mie in Utopia Planitia, which consists of plains with broad swales and bulges [Moore et al., 1987]. The four spacecraft operated independently after lander separation. The orbiters served as communication relay stations to transfer data from lander to orbiter, and then on to Earth. The orbiters would also transmit data to Earth from its three mapping instruments. The landers could also transfer data directly to Earth, but at a lower transfer rate. The initial orbit periapses were placed over the candidate landing sites to allow for maximum viewing resolution and relay of the lander data. After the primary lander missions were completed, the orbiters' orbits were allowed to drift so that the entire planetary surface could be systematically mapped by the three remote sensing experiments. Each spacecraft operated for a number of years and long after their primary missions were completed. Viking Orbiter 2 (VO2) was the first of the four spacecraft to terminate its mission. It developed a leak in its propulsion system and lost its attitude control gas. VO2 was turned off after 706 orbits around Mars. Viking Orbiter 1 (VO1) consumed the last of its attitude control gas and was turned off after 1485 orbits around Mars. VL2 operated on the surface for 1281 Mars days and was turned off when its batteries failed. VL1 operated the longest of the four Viking spacecraft. It returned data for nearly 6.5 Earth years (2252 Mars days or over 3 Mars years). Its mission ended when communications with the spacecraft were lost in November 1982 [Arvidson et al., 1983]. 3. Viking Lander Spacecraft The two Viking Landers were identical and each contained the same instrument payload. The main lander structure was a hexagonal prism body that housed the spacecraft computers, tape recorder, batteries, several science instruments, and controls for the surface sampler, thermal system, and data handling system. The spacecraft body was supported above the surface by three legs, each with a saucer-shaped footpad. The legs were arranged in a triangle pattern with two at the front of the lander and one at the rear. Mounted to the sides of the spacecraft were three terminal descent engines, two propellant tanks, and the extendible surface sampler arm with a collector head and backhoe [Moore et al., 1987]. Also mounted on the spacecraft body were two cameras, two radioisotope thermoelectric generators (RTG) with covers, sample entry ports for the biology, organic chemistry and inorganic chemistry instruments, the seismometer, the meteorology boom, a magnifying mirror, a magnet, and three imaging reference test charts. The spacecraft had three antennas for communications; a high-gain S-band antenna (large dish antenna), a low-gain S-band antenna, and a UHF antenna. The two S-band antennas were used to communicate with Earth, whereas the UHF antenna communicated with the orbiters. Each lander body was about 1.5 m across. Nominal clearance between the surface and the spacecraft body was about 22 cm. After landing the spacecraft mass was about 610 kg. Power for the spacecraft was supplied by rechargeable batteries; the batteries were recharged by the two RTGs. Excess heat from the RTGs was used to heat the instruments and control systems in the spacecraft body [Soffen, 1977]. Lander science investigations employed eight instruments. The imaging system included two identical facsimile cameras that imaged the surface and atmosphere with high resolution broad band channels and low resolution color and infrared channels. The meteorology instrument was mounted on a mast and was capable of measuring atmospheric temperature, pressure, wind speed, and wind direction. Each lander had a three-axis, short-period seismometer to measure Mars seismic activity. The seismometer on VL1 failed to deploy and no data were returned, while the one on VL2 operated as planned. An X-ray fluorescence spectrometer (XRFS) measured the inorganic elemental composition of soils at the landing sites. A gas chromatograph mass spectrometer (GCMS) measured the composition of the atmosphere and searched for organic compounds in the soils. The biology investigation consisted of three experiments (and instruments) to search for biological metabolism, growth, or photosynthesis: Labeled Release (LR) of metabolized carbon-14, and Gas Exchange (GEx) in a chamber caused by growing organisms, and Pyrolytic Release (PR) of photosynthetically fixed carbon-14. The physical properties investigation used information from several lander operations, such as sampling activities, digging trenches, pushing rocks, forming soil piles, and footpad penetration during landing to characterize the properties of rocks and soils at the landing sites. The magnetic properties investigation employed two magnets on the backhoe of the surface sampler collector head and a magnet array on the center reference test chart mounted on the lander body [Hargraves et al., 1979]. The three reference test charts also contained two patches coated with paint that degraded when exposed to ultraviolet radiation. Finally, lander communication systems were used for radio science experiments [Snyder and Moroz, 1992]. The lander mission can be divided into a number of periods (mission phases) in terms of activity level and the types of observations. The table below lists lander mission phases and their dates. Snyder [1979] provides a narrative of the activities for most of these mission phases. The time ranges listed below apply to both Viking Landers. Mission Phase Start End Primary Mission 7/20/76 11/15/76 Extended Mission 11/15/76 5/31/78 Continuation Mission 5/25/78 2/26/79 Interim Period 2/26/79 7/19/79 Survey Mission 7/19/79 8/07/80 Completion Mission 8/07/80 11/19/82 The landed Primary Mission began with VL1 landing and continued until the solar conjunction in November 1976. The Primary Mission was highlighted by the collection and analysis of soil samples and characterization of the landing site and atmosphere. The Extended Mission began after the solar conjunction with a smaller ground operations staff. However, the Extended Mission provided an opportunity to monitor the surface of Mars through a complete Mars year and to perform a variety of experiments that were not possible during the Primary Mission. During the Extended Mission, additional soil samples were collected for biological and chemical analyses. Three deep holes (ranging from 8 to 23 cm in depth) were dug at both landing sites. The physical properties investigation executed many experiments with the surface sampler system [Moore et al., 1987]. The imaging experiment studied the surface and atmosphere through the cycle of Mars seasons. During the first Mars winter of the Extended Mission, VL2 was programmed to operate in an automatic manner designed to allow the spacecraft to survive the cold winter temperatures and still return data (mainly imaging, meteorology, and seismology data). VL1 continued to operate normally during the winter because of its more equatorial location. VL2 returned to full operation after the winter passed. A major limitation was placed on VL2 when a portion of its communication system failed in the Extended Mission, leaving VL2 with no direct downlink to Earth. At the end of the Extended Mission, all lander instruments were turned off except for imaging, meteorology, and XRFS. These three instruments continued to operate during the Continuation Mission in a fully automated manner. Observation sequences collected data on a 37 sol (Mars day) cycle that repeated throughout the Continuation Mission. There was an Interim Period after the Continuation Mission ended where communications with the Viking spacecraft were severely limited because of Voyager encounters with Jupiter. During the Interim Period, imaging and meteorology data were collected and returned when possible. A final VL2 surface sampler sequence was conducted during this period as an engineering test in the cold temperatures of mid winter. The final phases of the lander mission were the Survey and Completion Missions, where image and meteorology data were collected for as long as possible. For VL2 this meant for as long as VO1 provided a relay link because VL2 no longer had a direct downlink capability. Relay opportunities with VO1 occurred every seven weeks during the Survey Mission. VL2 was finally turned off after its batteries could no longer hold a charge. VL1 operated in a cyclic and automatic mode by returning data about once a week with the image sequences repeating every 37 Mars days. The VL1 high-gain antenna was programmed to track the Earth until December 1994. However, communications with the Mutch Memorial Station (VL1) were lost in November 1982 after a command sequence uplink, and thus, ended the Viking Lander mission [Arvidson et al., 1983]. 4. Labeled Release Instrument The LR instrument was part of a package of three biology experiments on the Viking Landers. All were assembled in clean rooms and heat-sterilized with the entire spacecraft to prevent the transport of terrestrial organisms to Mars. The major scientific objective of the Viking Lander biology investigation was to detect the plausibility and/or presence of life on Mars [Klein, 1974; Klein et al., 1976]. In particular, the LR experiment was designed to detect microbial life in the martian soil. The LR experiment tested for heterotrophic metabolism by monitoring the release of radioactive gases from a soil sample inoculated with carbon-14 labeled organic substrates. The experiment also was designed to analyze heat sterilized control samples for comparison to the unheated samples [Levin and Straat, 1976a]. Several assumptions were used in the design and operation of the LR experiment. These assumptions included: A) life on Mars was carbon based; B) one or more of the nutrient compounds would be metabolized by possible microbial life; and C) one end product of metabolism would be a carbon based gas [Levin and Straat, 1976a]. The period during which each sample was analyzed is referred to as a cycle. The two Viking Landers had identical LR instruments that used two solid-state beta detectors to measure the release of radioactive gas from samples of martian soil that had been inoculated with an aqueous nutrient solution. The instrument contained temperature sensors to measure head-end assembly and detector temperatures. There also were heaters in the detectors and head-end assembly of the instrument. The LR instrument contained four incubation test cells mounted on a carousel. Each test cell could be rotated and sealed beneath a head-end assembly that contained a heater, plumbing terminals for nutrient delivery and gas removal, and a tube leading to the beta detectors. Gas and nutrient moving through the plumbing system were controlled by eight miniaturized solenoid valves. The head-space (i.e., the space in the test chamber above the sample) was connected to the two solid-state beta detectors through a tube bent at several spots. A connecting tube was bent to prevent the detectors from seeing radioactivity of the liquid nutrient, and to prevent radioactive particles from reaching the detectors from the test cell [Levin and Straat, 1976a], permitting only gas to pass from the test cell to the detector. The LR nutrient was stored in a sealed glass ampoule within a reservoir. The reservoir, in turn, was connected to the test cells by the instrument plumbing system. The ampoule containing the nutrient was broken by a mechanical striker driven by high pressure helium shortly after the spacecraft landed on the surface of Mars. Low pressure helium was then bubbled through the nutrient in the reservoir for several hours in order to degas the nutrient. At the start of an analysis cycle high pressure helium was used to route a portion of the nutrient into a sealed test cell. Testing prior to launch indicated that 0.115 cc +/- 8% of nutrient was delivered to the 0.5 cc soil sample by each injection. The pressure in the test cell head-space was kept above Mars ambient atmospheric pressure with helium from the plumbing system to prevent boiling of the nutrient. The total pressure at the start of an analysis cycle was about 9200 Pa (92 millibar). At the end of an analysis cycle, radioactive gas was purged from the test cell through the plumbing system and exhausted to the martian atmosphere. The LR instrument's two identical solid-state beta detectors monitored for any radioactive gas evolved from the soil sample. There were two detectors as a contingency against failure of one detector. The detectors continuously counted gaseous radioactivity as it evolved from the test cell. The instrument could be commanded to count with either one or both detectors. Detectors were referred to as the right and left channels. The Viking Landers were powered by radioisotope thermoelectric generators (RTGs), which produced minor background radiation to the detectors. This background signal was determined by monitoring the detectors for a period after the sample was delivered to the test cell, but before nutrient injection. The background was then subtracted from any signal measured. Test cell heaters were used in a number of ways. Samples could be heated in the test cell prior to nutrient injections to provide sterilized control samples. During an analysis cycle the test cell was heated to maintain the temperature at about 9-10 degrees C during the martian night to prevent freezing. The heater was also used at the end of an analysis cycle to dry the sample. The LR instrument shared common support services with the other biology instruments. This included the sample delivery system [Klein, 1974]. Martian soil samples were collected by the Viking Lander surface sampler arm [Crouch, 1977; Moore et al., 1987]. Soil from the sampler arm was dumped into a hopper located on top of the lander. The hopper, which was open to the atmosphere, but shielded from sunlight, contained a sieve that only allowed particles less than 2 mm in size to enter the instrument test cells. The sieved samples entered a distribution assembly that automatically delivered measured volumes of soil to each biology experiment [Klein, 1974]. The LR instrument typically received 0.5 cc of soil. The biology common support services and the LR instrument held enough nutrient and helium to conduct two injections on each of four soil samples. Testing prior to launch showed that, after proper drying of a soil sample and purging of gases from a test cell, the cell could be used a second time by adding more soil and nutrient. One of the test cells on Viking Lander 2 was used a second time [Levin and Straat, 1976a; Levin and Straat, 1979b]. An integral part of the LR experiment was the nutrient used in sample incubation. Considerable effort went into selecting, preparing, and testing the nutrients for the LR experiment [Levin and Straat, 1976a]. Selection criteria were partially based on the assumption that life evolved similarly on Mars as on Earth. There were several criteria used in selecting compounds for the nutrient that included: A) Compounds that were likely to have been produced on Mars from its primordial atmosphere by Miller-Urey type reactions; B) Compounds that a wide variety of terrestrial microorganisms used in metabolism based on an extensive test program; and C) Compounds that were unlikely to have nonbiological reactions with martian soil. In the test program, each compound in the nutrient was tested to show that it produced a rapid response in a variety of terrestrial soils and in pure and mixed cultures of hundreds of types of organisms. The stability of the materials was also considered given that the nutrient was stored for about 2 years from the time it was prepared until it was used on Mars. The storage period included the nearly one-year cruise phase of the spacecraft on its journey to Mars. Although filter-sterilized prior to being sealed in its ampoule, nutrient material also had to undergo sterilization of the biology module (54 hr at 120 degree C) and the entire spacecraft (20 hr at 100 degree C). It was expected that some decomposition (<1%) of the nutrient would occur because of the long storage time and sterilization. Any radioactive carbon dioxide produced by the nutrient decomposition was removed by flushing the nutrient reservoir with helium before the first injection. A complete list of nutrient compounds is given in Levin and Straat [1976a]. The nutrient included sodium formate, calcium glycolate, glycine, D- and L-alanine, sodium D- lactate and sodium L-lactate. The concentrations of each nutrient component were dilute in case any particular compound might be toxic to possible martian organisms. Each compound in the nutrient was labeled with a precise amount of radioactive carbon-14 [Levin and Straat, 1976a]. The nutrient solution was unbuffered so that it would not alter the natural pH in the martian soil. 5. Instrument Operating Modes As mentioned, each soil analysis was referred to by the LR team as a cycle. The basic analysis cycle began with the delivery of a martian soil sample to a test cell and moistening of the sample with an aqueous solution of carbon-14 labeled organic media. A second nutrient injection was typically done about 7-8 sols (Mars days) after the first injection. The head-space above the sample was monitored continuously for evolved radioactive gas as evidence for metabolism. Viking Lander 1 completed four cycles, whereas Viking Lander 2 completed five cycles for a total of nine cycles between the two landers. VL2 cycle 5 was performed with a previously used test cell and a stored portion of the cycle 4 soil sample. Seven of the cycles received two nutrient injections. VL1 cycle 3 received three nutrient injections, whereas VL2 cycle 5 received only one nutrient injection [Levin and Straat, 1979b]. Three of the analysis cycles were control cycles (VL1 cycle 2, and VL2 cycles 2 and 4) where the soil sample was heated for several hours before nutrient injection. The control cycle for Viking Lander 1 was heated to 160 degree C. After receiving highly attenuated results from the Viking Lander 1 control cycle, the two Viking Lander 2 control cycles were modified to heat the sample to 50 degree C in order to improve the discrimination between biological and chemical responses. Radioactivity was accumulated in 16-minute (960 seconds) bins during most of an analysis cycle, except for several hours around the time of nutrient injection when bin intervals of 2- to 4-minutes were used. Background levels were determined by measuring radiation penetrating the detector cell prior to nutrient injection. The head-end and detector temperatures were measured every 16 minutes throughout an analysis cycle. At the end of the cycle, the radioactive gas was removed by purging and the soil was dried by brief heating to prevent evaporation upon opening the cell. Gases and water vapor were vented to the martian atmosphere. A fresh test cell was then rotated beneath the head-end assembly and a three-hour cleanup was accomplished by heating both the test cells and the detectors during continuous helium purging. After cooling, trapped nutrient was vented from the system. The LR instrument was fairly automated with preprogrammed sequences. However, commands could be sent from the ground to change the preprogrammed sequences to perform nutrient injections, to select active or control sequences, to change the temperature of the control sample, to select a fresh soil sample, and to initiate or terminate an analysis cycle. Commands also could be sent to conduct single or double channel counting. 6. Sample Description The LR investigators have published several papers that describe their soil sampling and analysis rationale, along with the scientific results [e.g., Levin and Straat, 1976b; Levin and Straat, 1977a; Levin and Straat, 1979a]. Results from recent analysis of the LR data have also been published [Levin and Straat, 1977c; Levin and Straat, 1977d; Levin and Straat, 1978; Levin, 1998; Levin and Levin, 1998]. A summary of the sampling and analysis strategy is given here as a high-level description of the LR experiment. There were a total of nine analysis cycles conducted by the two Viking Lander LR instruments, four on VL1 and five on VL2. In addition, there were several periods of data collection known as initiation or set-up sequences done on both landers. These sequences were conducted with empty test cells and sometimes tested the single counting modes. Data from these set-up sequences are included in the dataset. 6.1. Viking Lander 1 The Viking Lander 1 LR experiment completed four analysis cycles during the Primary and Extended Missions. Each of the samples came from a smooth patch of fine-grained material named Sandy Flats [Moore et al., 1987]. The samples used by the LR experiment were collected during three separate surface sampler arm sampling sequences. The soil collections occurred on sols 8 (LR cycles 1 and 2), 36 (LR cycle 3), and 91 (LR cycle 4). Each VL1 LR sample was collected from a depth of less than 4 cm below the surface. VL1 cycle 1 was an active analysis (i.e., a test for life) performed autonomously according to programmed preflight instructions. Upon obtaining a positive response from cycle 1, a duplicate sample from soil collected on Sol 8 and used in cycle 1 was heat sterilized and then tested as a control in cycle 2. Logistics required that the cycle 2 sample be stored in the biology hopper for about 20 sols before the second cycle began. Before nutrient injection, the control sample was heated to 160 deg C for about 3 hours as a sterilization procedure. VL1 cycle 3 used a fresh soil sample and performed a long active incubation (lasting about 50 sols) with three nutrient injections. VL1 cycle 4 used a sample that was collected during the Extended Mission on Sol 91. The sample had been 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 because of the seasonal decrease in surface temperature changed the scenario. Two nutrient injections for VL1 cycle 4 occurred about 4 hours apart. It was calculated that enough nutrient remained in the reservoir for these two injections [Levin and Straat, 1979a]. Below is a table that summarizes some of the important parameters related to the Viking Lander 1 analysis cycles. Analysis Cycle 1 2 3 4 Sample Site Sandy Flats Sandy Flats Sandy Flats Sandy Flats Collection Temperature (C) -83 -83 -21 -71 Collection Sol 8 8 36 91 Experiment Type Active Control Active Active First Inject Sol 10 29 39 232 Second Inject Sol 17 35 55 232 Third Inject Sol 80 Purge Sol 23 37 89 N/A 6.2. Viking Lander 2 Viking Lander 2 completed five LR analysis cycles during the Primary and Extended Missions. Four samples came from crusty to cloddy material in an area known as Beta. The other sample was acquired from under a rock called Notch Rock after it was pushed aside to expose the soil [Moore et al., 1987]. The VL2 samples were collected from within several cm of the surface. VL2 cycle 1 was an active analysis performed autonomously according to preflight instructions. The VL2 cycle 2 sample was a fresh sample collected from the Beta area that was heated in the test cell 51 deg C for 3 hours before the nutrient was injected. The sterilization process was intended to serve as a control for comparison to cycle 1 results. The lower control temperature, commanded from Earth, was intended to discriminate between a biological and chemical reaction more precisely than the 160 deg C sterilization. The sample for VL2 cycle 3 was collected from under Notch Rock. The intent of this sample was to analyze soil protected from ultraviolet radiation for a long period of time as a check of the hypothesis that UV radiation of the soil was responsible for the LR positive response. The rock pushing occurred about 1 hour after sunrise and the soil was exposed to low angle sunlight for only about 37 minutes before delivery to the biology sample processor [Levin and Straat, 1977a]. VL2 cycle 3 also performed a long incubation of nearly 90 sols with two nutrient injections. VL2 cycle 4 was another control analysis where the sample was heated to 46 deg C for about 3 hours and then allowed to cool before nutrient was injected. It was done because of the seemingly erratic response of the cycle 2 control sample [Levin and Straat, 1977b]. 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 already been used. A surface sampler anomaly during the sample acquisition attempt on Sol 195 prevented the collection of a fresh sample. Thus, a part of the sample collected on Sol 145, a portion of which had been used as a control in cycle 4, was used for VL2 cycle 5. The sample had been stored for 84 sols in the biology hopper and the LR test cell prior to the cycle 5 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 also possible that nutrient delivery lines or valves may have ruptured because of freezing. In addition, only a small amount of nutrient (0.64 cc) was calculated to remain in the reservoir. These two facts suggest that the complete nutrient delivery may not have occurred, although as least a partial delivery was likely [Levin and Straat, 1979a]. Below is a table that summarizes some of the important parameters related to the Viking Lander 2 analysis cycles. Analysis Cycle 1 2 3 4 5 Sample Site Beta Beta Notch Beta Beta Collection Temperature (deg C) -23 -23 -66 -84 -84 Collection Sol 8 8 51 145 145 Experiment Type Active Control Active Control Active First Inject Sol 11 34 53 147 229 Second Inject Sol 18 38 60 161 Purge Sol 24 47 140 171 N/A 7. Data Archive Parameters and Preparation The LR data were originally archived on microfilm and housed at NSSDC. A second copy of the LR data consisted of computer listings from the personal files of Co-Investigator Dr. Patricia Ann Straat. The data in the original PDS3 archive were keypunched into digital files from these two sources with the Straat computer listings being the primary source used. The data were entered twice by two different people, The two copies were compared to detect any data entry errors. Differences in the two copies were then compared to the microfilm or computer listings to make corrections. The PDS4 version used the data files from the PDS3 volume. The LR dataset consists of three measurements: radioactivity counts, detector temperature, and head-end temperature. Measurements are tagged with the acquisition time. Data are stored in a time-ordered format in ASCII tables with fixed-width columns. 7.1. Radioactivity Counts Radioactivity values 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 particle detectors and the instrument could be commanded to use either one or two detectors. Only one detector was used for a portion of VL2 cycle 3. These single detector measurements from VL2 cycle 3 were corrected to equivalent dual detector counting values. Single detector values were multiplied by 1.95 for data collected prior to the first injection, and by 2.06 after the first injection. The LR detectors recorded low background signal compared to the positive test results. The background came from the two Radioisotope Thermoelectric Generators (RTGs) that powered the Viking Landers and from the martian background. Background levels were determined from radioactivity measurements made at the start of an analysis cycle. In addition, radioactivity values with and without background correction are provided for measurements made during the incubation period of an analysis cycle. Background Levels (Counts/Minute) Lander Cycle Background 1 1 490.75 1 2 507.90 1 3 518.94 1 4 730.00 2 1 540.66 2 2 590.00 2 3 658.46 2 4 754.45 2 5 948.00 7.2. 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 probably less than those recorded by the head-end temperature sensor because the test cell heaters and temperature sensors are located above the sample. See Levin and Straat [1977a] for information on correlating head-end and sample temperatures. 7.3. 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). MMT 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 Mars mission time values during archive production. 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, 1976b; Levin and Straat, 1977a; Levin and Straat, 1979a]. 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 usage by recent Mars rover missions and PDS standard for local time. As a result, local lander time is called native time in the LR data files. The computation of UTC and native time (local lander time) from MMT require the value of 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 native 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 native 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 for midnight on Sol 0 were 1976-07-19T19:39:54 and 1976-09- 03T12:48:45 for VL1 and VL2, respectively. These values are slightly different from those published in Allison [1997] and Allison and McEwen [2000]. 7.4. Data File Preparation The radioactivity, temperature and Mars Mission Time data for this LR dataset were keypunched by hand into data files. The primary data source was the copies of computer listings supplied by P. A. Straat. The NSSDC microfilm was used to recover data for gaps in the computer listings. The computer listing copy quality was good, yet there still existed a few values that were difficult to decipher. The microfilm contained images of computer pages with variable quality. Again, some values were difficult to decipher. Personnel at the PDS Geosciences Node did the keypunching of the computer listings, whereas personnel at NSSDC transcribed the microfilm. All data entered by hand was checked for accuracy by an independent person. Typographical errors may still exist in the dataset. For example, some data for VL2 Cycle 3 were available in both sources. A comparison of about 2000 radioactivity readings revealed a 0.25% error rate (5 values total) in NSSDC's keypunch 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. The data keypunched from the P. A. Straat source were entered twice into spread sheet files. The two versions were compared and corrected to ensure that the two versions exactly matched. 8. File Types The LR dataset consists of three data files for each analysis cycle. There is a separate file for radioactivity counts, beta particle detector temperatures, and head-end assembly temperatures. There are separate files becauase measurements were made at slightly different times during a cycle and the number of measurements can be different. All three data file types use the PDS4 Table_Character object. The Table_Character object consists of a series of Field_Character objects, each has a fixed data type and width in terms of the number of characters. Each table is associated with a detached PDS4 XML label. Thus the full PDS4 product consists of the data file and its label. The file naming scheme for LR data files has the format: VLnCmxx.TAB where n is the Lander number, m is the cycle number for that lander, and xx is the data type code. Values for data type are DT for detector temperatures, HT for head- end temperatures, and RC for radioactivity count measurements. Note that data collected during "set-up" periods prior to an analysis cycle are stored in separate files and are named as: VLnSmxx.TAB, where S is for set-up and m is the cycle number. Detached PDS4 labels have similar file names, but with XML as the file extension. The original PDS3 label are included in the PDS4 archive and have file extensions of LBL. The file naming scheme maintains the file names from the original PDS3 dataset. These short names were required by PDS3 standards and CD-ROM constraints in use at the time that the PDS3 dataset was created. The data tables are: 8.1. Detector temperatures This table includes fields of beta particle detector temperature, Mars Mission Time, and several derived time fields (see the PDS4 label). The table also has a field to indicate possible anomalous values. This field contains a tag if a temperature value was more than four standard deviations from the surrounding mean value. Data are sorted in increasing Mars Mission Time order. 8.2. Head-end temperatures This table includes fields of head-end temperature, Mars Mission Time, and several derived time fields (see the PDS4 label). The table also has a field to indicate possible anomalous values. This field contains a tag if a temperature value was more than four standard deviations from the surrounding mean value. Data are sorted in increasing Mars Mission Time order. 8.3. Radioactivity counts during incubation This table includes fields of raw and background-corrected radioactivity counts, channel number, Mars Mission Time, counting period, and several derived time fields (see the PDS4 label). Data usually start shortly before the first injection of an analysis cycle and continue until the purge sequence occurs. 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. The table also has a field to indicate possible anomalous values. This field contains a tag if a radioactivity value was more than four standard deviations from the surrounding mean value. Data are sorted in increasing Mars Mission Time order. 9. References 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. Arvidson, R. E., E. A. Guinness, H. J. Moore, J. Tillman, and S. D. Wall, Three Mars years: Viking Lander 1 imaging observations, Science, 222, 463-468, 1983, doi: 10.1126/science.222.4623.463. 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. Crouch, D. S., Mars Viking surface sampler subsystem, Proc. 25th Conf. Remote Sens. Tech., The American Nuclear Society, Anniversary issue, 141-152, 1977. Hargraves, R. B., D. W. Collinson, R. E. Arvidson, and P. M. Cates, Viking magnetic experiment: Extended Mission results, J. Geophys. Res., 84, 8379-8384, 1979, doi: 10.1029/JB084iB14p08379. Klein, H. P., Automated life-detection experiments for the Viking Mission to Mars, Origins of Life, 5, 431-441, 1974, doi: 10.1007/BF01207642. Klein, H. P., J. Lederberg, A. Rich, N. H. Horowitz, V. I. Oyama, and G. V. Levin, The Viking Mission search for life on Mars, Nature, 262, 24-27, 1976, doi: 10.1038/262024a0. Levin, G. V., Detection of metabolically produced labeled gas: The Viking Mars Lander, Icarus, 16,153-166, 1972, doi: 10.1016/0019-1035(72)90143-1. Levin, G. V., An unambiguous martian life detection experiment (abstract), in The Future Search for Life on Mars, Lunar and Planet. Inst., Houston, 1998. Levin, G. V. and R. L. Levin, Liquid water and life on Mars, Instruments, methods, and missions for astrobiology, SPIE Procedings, 3441, 30-41, 1998, doi: 10.1117/12.319849. Levin, G. V. and A. W. Carriker, Life on Mars?, Nucleonics, 20, 71-72, 1962. Levin, G. V., A. H. Heim, J. R. Clendenning, and M. F. Thompson, 'Gulliver' - A quest for life on Mars, Science, 138, 114-121, 1962, doi: 10.1126/science.138.3537.114. Levin, G. V., A. H. Heim, M. F. Thompson, D. R. Beem, and N. H. Horowitz, 'Gulliver' - An experiment for extraterrestrial life detection and analysis, Life Sciences and Space Research II, 6, 124-132, North- Holland Publishing, Amsterdam, 1964. Levin, G. V. and A. H. Heim, Gulliver and Diogenes - Exobiological antithesis (COSPAR), Life Sciences and Space Research III, 7, 105-119, North- Holland Publishing, Amsterdam, 1965. Levin, G. V. and P. A. Straat, Labeled Release - An experiment in radiorespirometry, Origins of Life, 7, 293-311, 1976a, doi: 10.1007/BF00926948. 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, The Viking Labeled Release experiment: Current status of flight data and laboratory simulations (abstract), Annual Meeting, American Society for Microbiology, 95, 1977c. Levin, G. V. and P. A. Straat, Biology or chemistry? The Viking Labeled Release experiment on Mars (abstract), XXth Plenary Meeting of COSPAR, Tel Aviv, 1977d. Levin, G. V. and P. A. Straat, The Labeled Release experiment - New laboratory and Mars data (abstract), XXIth Plenary Meeting of COSPAR, Innsburch, 1978. 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, Laboratory simulations of the Viking Labeled Release Experiment: Kinetics following second nutrient injection and the nature of the gaseous end product, J. Mol. Evol., 14, 185-197, 1979c, doi: 10.1007/BF01732377. 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. Moore, H. J., R. E. Hutton, G. D. Clow, and C. R. Spitzer, Physical properties of the surface materials at the Viking landings sites on Mars, USGS Professional Paper 1389, 1987. Snyder, C. W., The missions of the Viking Orbiters, J. Geophys. Res., 82, 3971-3983, 1977, doi: 10.1029/JS082i028p03971. Snyder, C. W., The extended mission of Viking, J. Geophys. Res., 84, 7911- 7933, 1979; doi: 10.1029/JB084iB14p07917. Snyder, C. W. and I. V. Moroz, Spacecraft Exploration of Mars, in Mars, Kieffer et al., eds., Univ. of Arizona Press, Tucson, 1992. Soffen, G. A., The Viking Project, J. Geophys. Res., 82, 3959-3970, 1977, doi: 10.1029/JS082i028p03959. Tucker, R. B., Viking Lander imaging investigation: Picture catalog of Primary Mission Experiment Data Record, NASA Ref. Pub. 1007, 558 pp., 1978. Yoder, C. F. and E. M. Standish, Martian precession and rotation from Viking Lander range data, J. Geophys. Res., 102, 4065-4080, 1997, doi: 10.1029/96JE03642.