Carl Sagan, he has written so many popular science books
and brought us the original Cosmos series which has inspired so many people to dream about space.
The surface of the earth is the shore of the cosmic ocean.
On this shore we've learned most of what we know.
Recently we've waded a little way out, maybe ankle deep, and the water seems inviting.
Some part of our being knows this is where we came from. We long to return and we can because
the cosmos is also within us, we're made of star stuff. We are a way for the cosmos to know itself.
Sagan was also an accomplished researcher and is one of the most highly cited planetary scientists
so I wanted to take a look today at where that all started by taking a look at his PhD thesis.
Now Sagan went to the University of Chicago and he completed his PhD in 1960
when he was age 25. The title is 'Physical studies of planets' and his supervisor
was Gerard Kuiper of whom the Kuiper belt is named after.
On the cover page here we can see the name Carl Sagan
and his signature. The thesis is in four parts.
Part one: Indigenous organic matter on the moon.
Part two: biological contamination of the moon.
Part three: the radiation balance of Venus.
Part 4: production of organic molecules and planetary atmospheres.
These topics reflect his interest in astrobiology, he was known for thinking a lot about life in
the cosmos and he was a big promoter of SETI - the search for extraterrestrial intelligence.
There is some chance that in the next few decades we will get a signal from some spectacularly
distant spectacularly exotic civilization and everything on earth will as a consequence change.
If there's a plausible argument that there isn't anybody out there
bearing in mind that we can be wrong we ought to keep looking because the question is of the
most supreme importance. It calibrates our place in the universe, it tells us who we are and so
it is worthwhile trying to find other civilizations I would say no matter what.
Part one starts off by saying that for some time after its formation
the moon possessed an atmosphere composed of methane, ammonia, water vapor and hydrogen, and
says the effect of solar UV light on an atmosphere is that organic molecules of fair complexity are
produced and the purpose of this present paper is to estimate the quantity of organic matter which
formed in the primitive lunar atmosphere, diffused to the surface and survived to the present day.
This was written 10 years before the Apollo astronauts would land on the moon
and Sagan is pretty interested in the idea of finding organic molecules there. Organic molecules
I guess are of special interest since they are precursors to life or are used a lot in biology.
You may have heard that the moon has such a weak atmosphere now that it could be considered to have
no atmosphere or actually be considered a pretty good vacuum but Sagan is referencing material
that says that that wasn't always the case. The moon's atmosphere requires replenishment from the
interior of the moon and gradually escapes so the moon's atmosphere might once have been very thick
before most of it has been lost to space. Sagan first works out a surface density of synthesized
material so this would be a covering of these organic molecules and it's more common to hear of
uv light breaking down molecules than helping to build them but remember that sunlight is thought
to be an essential part of the equation for how we got life in the first place. That the effect of
UV radiation on bonds and molecules helps them break down but also builds into longer chains.
The effect of heat and UV light on the molecules
is remarkable, he says. A large fraction of the molecules partake in organic synthesis
of a higher order of complexity. Polypeptides arise from amino acids, hydrocarbon dimers
form long chain polymers and in general very complex organic molecules are constructed.
This continued radiation and high temperatures would eventually destroy these molecules but
during this time there were a lot of meteors hitting the moon and a lot of this meteorite
material falling into the lunar atmosphere so Sagan says the moon's surface must have received
a dust cover probably composed primarily of silicates and ices. The organic molecules
would then be covered by a protective layer insulating them from the extremes of temperature
and absorbing the radiation so he says that provided no large-scale destructive events we may
anticipate the presence of complex organic matter beneath the moon's dust layer. This would only
apply to regions that have had no extensive lava flows, the southern highland appears to be such
a region as does much of the far side of the moon and he finishes this first section of the thesis
by saying that to figure out much more what we'll need is a sample of lunar material from below the
surface. Scientists have since found some of these molecules in samples that we took from the moon
and although we haven't found any life there we have found some of the essential ingredients.
Part two is about the biological contamination of the moon. Sagan is expecting that soon humans will
start landing on the moon and he expresses concern that terrestrial microorganisms
meaning from earth and organic matter deposited with the packages may obscure detection of
or interact with possible organisms or organic matter indigenous to the moon.
Such biological contamination of the moon would represent an unparalleled scientific disaster
and because of it, scientific opportunities lost on the moon may not be recoupable elsewhere.
He lists four classes of possible lunar biological contamination and I haven't found reference to
these words anywhere outside this thesis so maybe they are words of his own invention
but the first one is biomixy which is that the moon may contain no indigenous living organisms
and may be incapable of supporting terrestrial organisms. However there may be relics of
primitive indigenous organisms deposited on or beneath the surface and a vehicle impacting the
moon may distribute its contents over the surface such that further investigations might be unable
to distinguish between the primitive indigenous organisms and ones that came along from earth.
This is pretty similar to the second type listed as sapromixy and then we have the third type
phagomixy which is that the moon may contain no indigenous living organisms but may be capable
of supporting some terrestrial organisms. This would require subsurface organic matter
moisture and heat sources. The possibility then exists that deposited microorganisms from earth
in the absence of any competitors or predators will multiply at a geometric rate limited only by
the availability of water and metabolites. This would give a biological explosion and you can
probably see that this wouldn't be very helpful for trying to study the history of the moon.
And the fourth type of contamination is ecomixy, that the moon itself may contain
indigenous living organisms, that is that there may be life on the moon. There is then the
possibility that deposited microorganisms from earth by competition with or parasitism upon
even one species of lunar organism will disrupt the ecology completely. So these are kind of all
the ways we could screw things up on the moon by accidentally depositing some of our own biology,
and doing a bit of math and looking at a few of the numbers including the survival law which would
tell how long the organisms from earth could even survive if they were accidentally left on
the moon, Sagan comes up with a few conclusions about how likely each of these possibilities are.
He finds that most microorganisms would be killed by the UV radiation within a few hours
but if any make their way into a lunar crevasse or are otherwise shielded from the radiation
then they might survive for quite some time and while the possibilities may be low of
life spreading or surviving or even getting there in the first place, Sagan finds that all
of those types of contamination cannot be excluded and are not negligible,
and I suppose the whole paper is a little bit of a warning to make sure that when spacecraft
leave earth on their way to the moon that we sterilize them really thoroughly.
The third part of the thesis the radiation balance of Venus. It is the longest section and probably
contains the most notable work. Sagan was trying to explain a recent microwave observation of Venus
that gave its surface temperature as being near 600 kelvin. Previously scientists had taken what
they thought they knew about the surface of Venus and used that to try and work out a projected
temperature but Sagan worked backwards, he took this temperature measurement and tried to figure
out how it came about. It was certainly higher than the expected temperature of such a planet
which is quoted here as being no more than 350 degrees kelvin
and what Sagan says here is that it is clear that a surface temperature of 600 kelvin demands a very
efficient greenhouse effect. So his calculations found that essentially a runaway greenhouse effect
was able to explain this very high temperature. This effect would occur when there are a lot
of greenhouse gases in the atmosphere trapping radiation from the sun and heating up the planet.
Carbon dioxide and water vapor are both greenhouse gases and Sagan proposes that
it is water, excess water, in the atmosphere that could explain the greenhouse effect on Venus but
later missions to Venus actually found that there was very little water in the atmosphere
and instead it was almost entirely carbon dioxide. The radiation balance of a planet is a very
delicate thing and it seems likely that Venus wasn't always so hot and unwelcoming it might
have been much more liveable like Earth but it is closer to the sun and hotter and drier than Earth
and the carbon compounds might have evaporated rather than remaining in the rocks leading to its
greenhouse effect to essentially run away leading to a vicious cycle where the planet just gets
hotter and hotter. Sagan discusses what might have happened if the Earth had been placed in the orbit
of Venus in its primitive times and essentially its fate is much the same the oceans would boil,
the carbon dioxide abundance would go up and Earth wouldn't be the home that we know it to
be. All of this research into what caused the fate of Venus and thinking about what might
happen to Earth in different circumstances probably led Carl Sagan to be quite worried
about things like global warming and passionate about trying to communicate what was going on.
Now no one has proposed that the trouble with Venus is that there once was
venusians who drove fuel inefficient cars but our nearest neighbor nevertheless is a stark warning
on the possible fate of an earth-like world.
The last section of the thesis is this one here which is actually an experimental project. Sagan
is again talking about how organic molecules are produced when energy is supplied to an atmosphere
of methane, ammonia ,water and hydrogen. He uses spectroscopy to find the spectra of
some of these known end products and lists the features that he finds in this table.
What he then does is compares this laboratory spectra to spectra taken with a telescope looking
at some of the jovian planets including Jupiter and Saturn. From his observations he thinks that
it's possible that there is hydrogen cyanide present in the atmosphere of Jupiter however
this was only a preliminary report and so he's not able to really conclusively say these things
but has set up this field of science for some further investigation.
And that is a look at Carl Sagan's thesis which would set him up for
a very successful career further tackling all of these questions
thinking about the atmospheres of planets and the likelihood of finding life there.
Thanks for watching and thanks as always to my Patreon supporters who make these videos
possible. A special shout out to today's Patron cats of the day, Minerva and Isis.
I hope to see you next time :)