Suzy B Software 2/Suzy B Software CD-ROM 2 (1994).iso/adult_ed/lectures/lect15.txt

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 ----- The following copyright 1991 by Dirk Terrell
 ----- This article may be reproduced or retransmitted
 ----- only if the entire document remains intact
 ----- including this header

 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.