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this presentation has been prepared for

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the standards of evidence for life

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detection community workshop

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i'm richard quinn and i'll be talking

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about the viking biology experiments

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in this presentation i'll provide some

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background on the viking biology

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experiments i'll talk about the life

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detection knowledge base which is a

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community tool designed to support

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discussion about the detection of signs

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of life

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talk about some of the viking biology

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results and interpretations in the

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context of the kv structure

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and then finally conclude with some

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thoughts for our upcoming workshop

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to begin i'd like to point out that

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during the time of the viking mission

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the way science and technology was

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developed for flight was in many ways

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the same as it's done today

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including performing analog field

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studies and the development of

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instrument concepts

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in the case of viking this included the

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biological capacity to generate

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metabolic

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carbon dioxide from labeled organics and

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the ability of soils to fixate labeled

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carbon dioxide

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these instrument concepts were then

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further developed for flight as part of

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the

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viking biology experiment payload under

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a demanding delivery schedule that

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included a preliminary design review in

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october of 1971

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a critical design review in may of 73

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and then in march to 75 the simultaneous

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delivery of the qualification unit

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the biological payload for viking 1

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and the biological payload for the

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viking 2 lander

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shown in parentheses is the number of

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months the delivery was behind the

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originally scheduled delivery date

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the viking life detection payload

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ultimately developed into three biology

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experiments

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designed to identify the presence of

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microbial metabolism in martian surface

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samples

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each experiment used different induced

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test environments

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which included dry to wet light and dark

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no additional nutrients the addition of

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simple nutrients

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or the addition of complex nutrients

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for each experiment a heat sterilized

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sample served as the control

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the viking gas exchange experiment was

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based on the hypothesis

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that soil gas exchange kinetics could be

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used to determine the absence or

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presence of biology

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and correspondingly was designed to

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measure changes in gas composition that

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headspace above

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martian samples it was based on the

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assumption that gas compensational

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changes in soils are mainly the result

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of biology

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second that metabolism and populations

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of soil organisms change when

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environmental conditions are perturbed

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and finally a complex nutrient medium

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can be used to alter the conditions and

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induce or inhibit metabolism

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the design of the experiment was quite

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simple a surface sample was placed in a

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test cell

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the cell was sealed and gas

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chromatography was used to monitor the

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headspace as a function of time

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under different conditions which

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included dry incubation

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a human mode and the addition of a

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complex

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aqueous nutrient medium

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the carbon assimilation experiment also

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known as the pyrolytic release

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experiment

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is based on the hypothesis that martian

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life would be carbonaceous and exchange

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carbon with the atmosphere corresponding

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was designed to measure the

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incorporation of radioactively labeled

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carbon monoxide and carbon dioxide into

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organic matter

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the experiment could measure either

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photosynthetic or chemosynthetic

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fixation

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[Music]

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and it approximated martian surface

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conditions of pressure

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atmospheric composition solar radiation

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and water abundance

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in a pyrolytic release experiment a

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surface sample is placed in the test

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cell

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and after sealing a small amount of

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radioactively labeled carbon dioxide and

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carbon monoxide

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was injected after incubation

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the sample was heated to 600 degrees c

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driving fragments of any organics that

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had formed

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onto a sample trap excess labeled co2

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and co was then purged from the system

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and following that the trap was heated

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to 700 degrees to decompose any labeled

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organics that had formed

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for detection as co2 or co

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the labeled release experiment assumed

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that martian organisms if present could

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assimilate carbon compounds and produce

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carbon dioxide

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or carbon monoxide as an end product

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correspondingly was designed to measure

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radioactively

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labeled carbon dioxide or carbon

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monoxide

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evolved from the assimilation of

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radioactively labeled organics that were

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added to the soil

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metabolism and growth could be detected

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and rates could be determined by

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measuring

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radioactivity over time and a positive

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result

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could be confirmed using a heat

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sterilized control

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very simply in a labeled release

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experiment a surface sample is sealed in

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a test cell

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and a dilute aqueous mixture of simple

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labeled organics was added

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following that the sample is allowed to

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incubate and the production of labeled

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carbon containing gas was monitored as a

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function of time

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with that brief introduction to the

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viking biology experiments

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i'd like to introduce the life detection

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knowledge base

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which is an online community-owned

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resource to provide knowledge and

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support discourse about the detection of

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signs of life

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these signs known as biosignatures

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consist of substances structures

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patterns or processes

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that indicate the current or form or

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presence of life

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in the life detection knowledge base

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information is presented according to

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arguments that support or contradict

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the value of a given bio signature is a

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sign of life

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all organized according to criteria and

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supported by evidence drawn from the

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scientific literature

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currently the astrobiology community is

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engaged in populating the knowledge base

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if you'd like to become involved you can

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find more information at the link shown

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at the bottom of this slide

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when you enter the life detection

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knowledge base you'll be asked to select

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a biosignature category

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in the case of the viking biology

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experiments we'd select activity

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the knowledge base is structured using

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criteria where criteria

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are a set of standards against which to

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evaluate the utility

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of specific life detection measurements

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two of the criteria in the knowledge

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base are feature strength which is the

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prominence of a feature that provides

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evidence regarding the past or extant

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presence of life

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or a non-biological process and feature

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prevalence

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which expresses the likelihood that the

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feature is produced by a particular

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source

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such as life or non-biological process

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and on the lower left hand side of the

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slide you can see that strength and

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prevalence criteria

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are categorized by biological feature

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strength

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biological prevalence as well as abiotic

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feature strength

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and abiotic prevalence each along with

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corresponding pros and cons for a given

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argument

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now i'd like to briefly walk through the

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results of the viking biology

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experiments

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and loosely place them in the

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knowledge-based structure

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there are precise ways in which

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arguments and their corresponding pros

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and cons should be crafted in the

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knowledge base

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which i'm not doing here nor am i

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including all the possible arguments and

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evidence related to the biology

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experiments that could be included

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in the knowledge base instead i'm

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demonstrating the basic structure of the

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knowledge base that can be used to

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evaluate biosignatures

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in the gas exchange experiment when a

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sample was humidified or wetted

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there was a rapid release of oxygen

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which was disproportionately large

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relative to other gases released

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including nitrogen and argon a slow

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linear release of carbon dioxide was

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also observed which persisted

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after a second injection of aqueous

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nutrients

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additionally no significant changes were

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observed during prolonged incubation

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this gas release pattern was observed

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for all samples tested

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including stored samples samples

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preheated to 145 c before testing

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and a sample that was collected from

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if we consider the hypothesis that the

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signal is biological

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we can examine both pro and con

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arguments and the evidence that supports

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or refutes this assertion

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characteristics of the gas exchange

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response included that the reaction

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survives heating to 145 degrees c

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the release of oxygen is extremely rapid

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and the second injection of nutrient did

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not result in additional gas production

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which indicates that biological growth

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for the hypothesis that the signal is

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abiotic we can again examine the results

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in the context of pros and cons

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post viking it was shown that multiple

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plausible inorganic

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oxidants can explain the gas exchange

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experiment oxygen release

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also post post-viking experiments showed

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that iron oxide can reproduce the carbon

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in the pyrolytic release experiment all

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tested samples were statistically

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positive

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which is indicative of the incorporation

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of radioactively labeled carbon dioxide

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or carbon monoxide into organic carbon

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nine samples were tested under different

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conditions that included

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dry and wet light and dark a sample that

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was heated to 175 degrees c

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prior to testing a sample that was

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heated to 90 degrees c

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and a sample that was stored for 139

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soles before testing

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additionally sample splits from the same

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sample collection

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but tested under different conditions

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shown in yellow

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produce nearly identical results

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if we consider whether the signal may be

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biological

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the results show that heat treatment to

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90 degrees c did not reduce the reaction

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and heat treatment to 175 degrees c did

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not eliminate the reaction

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if we consider whether the signal may be

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abiotic

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the results show again that heat

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treatment at 90 degrees c

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did not reduce the reaction and heat

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treatment at 175 degrees c

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did not eliminate the reaction

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additionally post viking experiments

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demonstrated positive results using iron

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oxides

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clays and mars analog mixtures

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indicating that the viking pyrolytic

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release results were false positives

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in the labeled release experiment when a

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dilute solution of simple organics was

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added to the sample

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shown at zero hours in the plot on the

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right there was a rapid release of

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radioactively labeled gas

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presumably carbon dioxide a second slow

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log linear release of carbon dioxide was

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also observed

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significant gas release was not observed

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after the injection of additional

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organics

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additionally the gas release was

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observed in the sample excavated from

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under a rock

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the initial release was reduced by

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preheating the sample to 50 degrees c

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for 3 hours it was eliminated by heating

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to 160 c

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for 3 hours also the slow release was

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not

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eliminated by heating to 160 degrees

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and finally the initial release was

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observed from a sample

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stored for three souls but not from the

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sample stored for 80 souls

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for the hypothesis that the labeled

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release signal is biological

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the results indicate that the initial

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release of gas resembled biological

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responses observed with the flight test

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module

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also the initial release was not

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observed in samples preheated to 160

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degrees prior to testing

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on the other hand as chuck klein has

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pointed out the initial response would

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require a large biological load

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a lag phase was not observed the

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reaction lasts only about 24 hours

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only approximately 10 percent of the

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available carbon substrate is utilized

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an injection of additional organics did

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not result in additional gas release

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for the hypothesis that the signal is

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abiotic the post viking literature shows

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that there are multiple plausible

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inorganic

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oxidants that can explain the labeled

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release results

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the gex results also provide evidence

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for the presence of oxidants at the

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viking sites

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which is also supported by the findings

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of the phoenix

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and out missions

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to conclude i hope that this

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presentation can serve as a starting

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point for discussion at the upcoming

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workshop

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in particular how the life detection

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knowledge base can be used as a tool

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to achieve both short-term and long-term

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workshop goals

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also going back to the third slide in

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this presentation

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a discussion on the risk associated with

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the application of standards to

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instrument verification and validation

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this is a quote from levin and strat

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about the labeled release experiment

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a science testing program was evolved to

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obtain data relevant to the

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interpretation of a flight experiment

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however because a program demands on the

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test standards module for engineering

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purposes

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not as much science data has been

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collected as had been planned

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i think that every scientist who has

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been involved with the

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delivery of a flight instrument has said

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these very words

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and finally a discussion on the risk of

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false positives

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there was a tremendous amount of testing

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for biology and analog samples in

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preparation for viking

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but for the most part consideration of

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abiotic feature strength and prevalence

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is absent

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in the pre-viking literature i'm looking

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forward to seeing everyone at the

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upcoming workshop and beginning a

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discussion on these aspects of