----- The following copyright 1991 by Dirk Terrell
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 Lecture #15     "Is anyone home?"

   In the last lecture we talked about the planet Mars, and of human 
fascination with it. This time I want to talk about the most comprehensive 
search yet for the existence of life on Mars -- the Viking landers. Viking 1 
landed in a young basin called Chryse Planitia and Viking 2 landed in the 
plains region Utopia Planitia. These sites were chosen because they were 
fairly flat, safe places to land, although when you see pictures from Viking 
2, the horizon is tilted because one of the footpads came to rest on a large 
rock.

   One of the major missions of the Viking landers was to determine if there 
was life on Mars. How do you do that? Perhaps the simplest way is to 
photograph some little creature scurrying around on the surface, and the 
landers' cameras were listed as part of the biology experiment. But I doubt 
that anyone really expected to find such a beast. A much more likely 
possibility was that there might be microbes in the soil. To test this 
possibilty, scientists constructed the biology package, a remarkable piece 
of equipment. The package performed three experiments. One was called the 
Gas Exchange Experiment and this one was perhaps the simplest. A sample of 
soil was scooped up and sealed away with a sample of Martian atmosphere. The 
sample was allowed to sit for several days, and then it was determined if 
metabolic waste gases (carbon dioxide and monoxide, methane, etc.) had 
increased in proportion to other gases. Imagine sealing a group of people in 
an airtight chamber. The carbon dioxide level would go up, while oxygen 
would go down. That's the idea behind the Gas Exchange Experiment. This 
experiment gave a negative result -- no life on Mars.

   Another experiment was called the Pyrolitic Release Experiment. Here, the 
soil sample was given a simulated Martian atmosphere, except that the carbon 
dioxide had radioactive carbon 14 atoms as opposed to the more common carbon 
12 atom. The sample was incubated for several days, and then heated up to 
see if any carbon 14 had been absorbed. This experiment also gave a null 
result.

   The last experiment was the Labeled Release Experiment, in which the soil 
sample was immersed in a broth (organic liquid) that microbes would devour 
readily. The broth had carbon 14 in it (we say it was "labeled" with carbon 
14), which could be detected if the broth were ingested and used by the 
microbes (i.e., the would eat this stuff, and then give off metabolic waste 
gases such as carbon dioxide, which would have carbon 14). This experiment 
turned out positive -- an indication of life on Mars?

   Before we answer that question, let's look at the biology package itself. 
This device had a volume of about 1 cubic foot -- several shoeboxes. Keep 
that in mind as I tell you a few more things about it. There were 
approximately 40,000 parts in the thing -- about 3-4 times as many as in the 
average car. It had its own computer, separate from the main computer on the 
lander. Nowadays that doesn't mean much, since the kitchen sink has its own 
computer. But remember, this box was built in the early 1970's, with 1960's 
technology. Remember how big hand calculators used to be back then?

   It also had: 43 heaters, 19 coolers, and 39 miniature latching valves to 
control the flow of fluids. It also had around 2000 electronic parts, 
equivalent to 20,000 transistors. This one always gets me -- several MILES 
of wire (in 1 cubic foot!!). It also had several tens of feet of plumbing 
for liquids and gases. Now, this wasn't your basic PVC pipe either. The pipe 
had an inside diameter of 0.003 inches. That's about the thickness of hair. 
In fact, they had trouble making bends in the pipe -- the pipe would close up.

   There were eight separate cells for the experiments, and containers for 
the following materials: 2 organic lquids (one radioactively labeled), 
water, carbon dioxide (both carbon 12 and carbon 14), carbon monoxide, 
helium, krypton, neon, and oxygen.

   Of course, it would be necessary to move test samples around during the 
experiments, so the unit had miniature carousels and elevators. Instead of 
using motors to drive these devices, they used helium at a pressure of 4500 
psi to push them along. This method did have some problems. At those 
pressures, the helium would leak through the walls of the tank, through the 
impurities in the stainless steel. Therefore the tank had to be made out of 
absolutely pure stainles steel. To my knowledge, this is the purest 
stainlest ever produced.

   The radiation detectors were the most sensitive ever made, and the seals 
were the most leakproof ever made. Remember, all of this stuff was contained 
in 1 cubic foot. If you were going to do these experiments in a laboratory, 
you would use about 3 large rooms full of equipment.

   Sounds like a pretty compact and sensitive device, doesn't it? But this 
thing had to survive a launch, which is not exactly a gentle process, a 1 
year flight in space, and a landing. You also don't want to go all the way 
to Mars to discover microbes that you brought along with you. To sterilize 
the biology package, it was heated to 254F for 54 hours. Then, when it was 
integrated with the spacecraft, the whole spacecraft was heated to 232F for 
30 hours. (I don't think this could have been a manned mission. Something in 
government regulations about heating humans to 232F.) Once it went through 
sterilization, launch, flight, and landing, what happened? We threw a 
shovelful of dirt in it!

   The package took 550 full-time people and 450 part-time people six years 
to build. In all, it would have taken one person 1000 years to do all of the 
work. It cost 50 million (1976) dollars to build, which was 20 times as much 
as the equivalent volume of gold. I was amused to find out that the US spent 
as much money to find out whether there was life on Mars as we did to find 
out if Evel Kneivel could jump the Snake River Canyon. It's probably no 
secret which one I consider to be the better deal.

   So what did we find out? Is there life on Mars? We did get a positive 
result from the labeled release experiment, although most people were 
skeptical of the result. That's why several different experiments were done. 
Remember the gas exchange experiment we talked about (putting people in a 
room)? What if we had no people in the sealed room, but instead had a fire 
raging in the middle? The carbon dioxide level would go up, oxygen down, but 
I don't think many people consider a fire to be a living organism. It turns 
out that the positive result of the labeled release experiment was due to 
peroxides in the Martian soil. The only thing we can really conclude is that 
there doesn't not appear to be life at the landing sites. But these sites 
were probably not the best places to look for life. A better place would be 
one of the dry riverbeds, where we know there once was water. But in 1976, 
those sites were considered too risky for a landing. Perhaps the upcoming US 
and Soviet missions will give us a more conclusive answer.