02 April 2004

Calling All Martians! The Viking Mission Labeled Release Experiment and the Search for Martian Life: Part II

Reginald Smith

Hello fellow amateur scientists. Welcome to the second installment of the analysis of the data from the Viking Lander Labeled Release Experiment. For those who are new, I would recommend you read the first installment of this article here .

In this edition, we will finally take a look at the data from both Viking Landers and the total of nine separate cycles in which the Labeled Release Experiment was conducted. In my opinion, this is the most exciting part. We are analyzing data that originated on another planet!

At this time I hope you have downloaded the necessary data. I would encourage you also to look at the *.lbl files for each of the radiation count, head-end temperature, and detector temperature files, respectively. If you know the format of the data, it will be easier to follow along and understand what we are doing.

Setting up the data for graphing

I imported the data into Excel using a different workbook for each cycle and placing radiation count, detector temperature, and head end temperature on different tabs. Let's look at the contents of each type of data.

Radiation count files ("rc")

These files contain the radiation counts by the beta detector. The two leftmost columns are the radiation levels in counts per minute. The first column has the total radiation count from the detector. This includes background radiation that is attributed to the thermoelectric power source on the lander. In most data sets, this averages around 500 counts per minute. Only radiation detected above this level of background noise can be considered real data.

The second leftmost column was prepared by NASA. It is the radiation count with the average background radiation subtracted. This column should show a significant positive change only if there is real activity. However, since it is the result of a subtraction operation, some of the values are negative.

The next three columns count MMT (Mars mission time) in both seconds and sols (1 Martian day) and show the Universal Standard Time (Greenwich mean time) back on Earth when the data were collected. Those with a serious knowledge of physics may object that the "time" at a distant astronomical object is not simultaneous due to the theory of relativity, but Mars is close enough so that the designation is not too inaccurate.

There are also columns that count the time until or since each injection of nutrients. There are usually two injections per cycle, with only two exceptions where Viking Lander 1 Cycle 3 had three injections and Viking Lander 2 Cycle 5 only had one injection.

Finally there is a count in sols from a set point, the time interval in seconds between each reading, and a column where an "A" indicates data values NASA thinks are anomalous. Usually you can tell since they are very large.

Head end temperature and detector temperature ("ht" & "dt")

The format for these data sets is nearly identical to the radiation count file, except that the leftmost column is the measurement in degrees Celsius of either the head end temperature or the detector temperature. The Viking Lander incubation chamber insulated the samples from the Martian environment. The head end temperature fluctuated between 9-13 C on average and the detector temperature usually fluctuated between 14-26 C (1). The temperature cycles sometimes affect the radiation count but only slightly.

Displaying the data

In each data set, I created a new column, called sols at 0. I made this column by subtracting the time elapsed in sols at each data row and subtracting from it the original elapsed time in sols (the column after the columns showing the time from the injections).

I just did this so we could start at 0 and count elapsed time in sols. I created one graph for each cycle. On the graph I placed all three data sets. I used a double axis so the left y-axis measured radiation in counts per minute and the right y-axis measured the temperature of the head end and detector in degrees Celsius. For the x-axis I used the time elapsed in sols we calculated above.

Note that when you first graph this data in Excel (I used the scatter graph mode), there may be issues with extremely large anomalous data values. I just changed the y-axis maximum so that the data we wanted to see was clearly and easily visible.

Below are the graphs I obtained from the data.

					Charts of data from the Viking Labeled Release experiment. In Figures 10 & 11 I started 0 at the time of the first injection for each cycle. Click images to enlarge

Explanation of cycles and examination of data sets

The cycles conducted by the landers are divided into two categories: active and control. The active category is another name for experimental. Since the experiment is testing for the presence of life, the purpose of the control cycles was to first expose the samples to preheating of 160 C in Viking Lander 1 and 50 C in Viking Lander 2 to attempt to sterilize any biological agents. It was assumed that Martian biological agents would not be able to stand such uncharacteristically high temperatures and you could then disambiguate a response of a chemical reaction from a reaction due to biological metabolism. The control cycles are Viking Lander 1 Cycle 2 and Viking Lander 2 Cycles 2 & 4.

You will notice at the end of several charts a spike in the temperature reading. This spike is not an anomaly. At the end of each cycle, the sample was "cleaned up" by exposing it to a high temperature.

After perusing each of the data sets, you will notice some similarities. In the active samples, and even in the controls to a much lesser extent, there is an immediate evolution of CO₂ which is shown by the spike in the radiation count. This evolution of gas eventually plateaus. One would hypothesize that a second or third injection of nutrients would cause even more gas to evolve, but this is not the case. Interestingly enough, the gas evolution actually decreases when a second or third injection of nutrients is made into the sample.

The immediate discovery, however, is that there is a process that is converting an aqueous nutrient mix to CO₂ gas. This factor, be it biological or non-biological in origin, is present at both of the remotely separated landing sites. It seems from the control samples that this process is inhibited by high temperatures prior to nutrient injections.

Finally, it also seems that the agent is inhibited by long storage times outside of the Martian environment. Long time lags are attributed to the lower level responses in Viking Lander 1 Cycle 4 and Viking Lander 2 Cycle 5 which were stored for 136 and 84 sols respectively before nutrient injection. The undeniable result of these experiments is a positive reading, in contrast to the other biological payloads, which failed to give a positive reading. However, does a positive reading necessitate a biological explanation? Is this proof of microbial life on Mars or is it as the old saying goes "the devil is in the details?"

Next time I will explain to those who are certain this shows either life or non-life the scientific debate and explanations that are attached to the data. Who thinks life is on Mars? Why? Why is the current scientific consensus neutral or negative? I hope you will find the final installment of this series to be the most interesting and thought provoking.

Until then, I propose an exercise. Look at the data for yourself. Then get a piece of paper and write down two columns: "Life" and "Not Life". Under each column write down everything about the data that suggests either a life or a non-life explanation.

Next time, check your thoughts against those from the scientists of the Viking mission. Also, ask yourself how the discoveries of the last thirty years, including those by the rovers on Mars, might have affected the conclusions of the data if they had been known at the time of the Viking Landers. Once again, I urge ambitious readers to refer to some of the literature in Part I.

Though I have tried to give an adequate explanation of the experiment in these articles, it is by no means comprehensive. The level of technical knowledge required to read these papers for the most part is not beyond someone who has had high school biology and chemistry. I look forward to revealing all (and no I don't mean an evil NASA conspiracy) in the final installment!

References

1. Klein, Harold et. al. "The Viking Biological Investigation: Preliminary Results." Science, 194 October 1, 1976 99-105.