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Student questions: George Cody colloquium on “Shining Light on the Dark History of the
Early Solar System”
October 7, 2015
Question 1: If the habitable zone refers to the radial distance required between a planet and a star
for liquid water to exist, have you found any relation between distance of a planet from a star and
geologic activity? Is it possible that geologic activity is dependant on radial distance, and could
that be relevant in the search for habitable planets?
That is a great question. No I have not searched for, nor found, any such relationship, but I would not be surprised that there might be one. We do not yet know enough about our own Solar System that we can make such predictions. We have a lot of work to do! Question 2: There is often excitement in the media over the prospect of finding habitable planets,
sometimes to the point of a terrestrial planet alone being considered a viable prospect for further
study. Does this excitement in society affect your projects at all? And if so, are the effects
beneficial or harmful to your efficiency?
In my view anything that gets society interested in science is a great thing-­‐ for society. We enjoy an amazing quality of life because scientists have persued fundamental science questions-­‐ practical applications spin off… GPS is now considered a given! 35 years ago when I was a college student the concept of GPS would have been considered science fiction. I personally feel that attempting to understand the origin of life is more important now as we know that exosolar planets appear to be the norm. Question 1: What does “comet organic carbon more complicated” mean in the talk? Is it more
complicated molecules or different reactivity compared to organic carbon on Earth?
What I mean is that carbon atoms in organic solids in comets exist in many different electronic environments (bonding) as opposed to just a few. Question 2: How to collect the material to characterize organic carbon with XANES from space
and how to preseve it?
One thought is to keep the samples as cold as possible and return to Earth frozen, then keep them frozen. Sample prep for XANES can be done in cold rooms. Cody_Answers to student questions O15.pdf
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Question 1: What is the general size of any solar system's habitable zone relative to the size of its
star?
This is great question. The term “habitable zone” means that liquid water could exist on the surface of a planet, i.e., surface temps greater than 0 and less than 100 °C. So subject to varying atmospheres green house capability provides the range. As I understand it under the right atmospheric conditions Venus, Earth and Mars are all in the sun’s potential habitable zone. Question 2: Is there an estimate for the amount of habitable zone planets containing liquid water
within the Milky Way?
Not yet, at least robustly. I am sure that some are already using statistics derived from Kepler data to say some thing about this-­‐ we will know better as time moves on. Question 1: What measures have to be taken to satisfy planetary protection for a mission like
stardust?
Great question. Of course comet 81p/Wild 2 was safe from us, but were we safe from it? Hope so! Seriously, this is a very difficult question and we hope to get it right. Question 2: Do you think a non-negligible amount of earth's organics may have been deposited
on the surface after it has cooled a bit?
There have been estimates that there should be considerable input of organics to Earth from comets, meteorites, and IDP’s. For my part, I am not sure that this organic matter was directly useful to jump start the origin of life, but as no one knows how life emerged on Earth-­‐ all bets are on the table. Question 1: I'm not sure I understood the primitive meteorites. How are they distinguished?
I whizzed past this, blinked and you missed it. Bottom line is technically “primitive” means the meteorite came from planetesimal that had not undergone differentiation (formation of a mantle and core). However, you still can get very hot and stay solid and undifferentiated. I personally think that even the most “primitive” meteorites have been processed quite a bit. Question 2: You stated that the primitive meteorites were substantially heated. When did this
occur and what was the process?
There are two ways to heat up a body: 1) is through the kinetic energy of accretion, that is kinetic energy is converted to thermal energy during accretion . 2) radiogenic heating, if a planetesimal is big enough, then heat generated by radioactive decay will increase faster than it can conductively discipate. This can lead to long term heating. Cody_Answers to student questions O15.pdf
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Question 1: Are there current searches for regions where formeldehyde and C12/C13 can be
measured simultaneously?
Not that I am aware of. While I am interested in this question -­‐ in the scheme of things this question is not a “big question” in astronomy, so would not be on a lot of people’s radar screens. It was brought to my attention that one might search available data and derive a potentially robust statistical argument. This might be a great undergraduate or Masters thesis. Question 2: Why are changes to organic matter fundamentally irreversible?
I am glad you asked this. For sure organic reactions can be and are often reversible. What makes thermal metamorphism of organic matter in planetesimals irreversible is that the volatile products of such reactions are, more likely than not, lost from the system. So, even if there existed a pathway of reversal-­‐ there no longer remains the component (e.g. H2) to drive the reversal. Question 1: How large were the aerogel sections in the spacecraft? It seems like they would have
to be quite large to be able to stop a grain traveling so fast.
I think that they were a couple inches deep, but I believe that particles stopped within a couple of millimeters. It is interesting that the particles (at ~ 6 km/sec) were stopped so quickly with out obvious damage-­‐ this is something that we do not understand very well. Question 2: How much material was collected by the spacecraft in total?
My guess is possibly less than a couple milligrams. But this to plenty for us to analyze. The challenge was as follows: try to get a lot and you risk destroying the space craft (a marble going 6 km/sec [a bullet flys at ~ 0.5 km/sec] could destroy the space craft); be too cautious and you get nothing! My understanding is that they exceeded what they wanted. I got what I needed! Cody_Answers to student questions O15.pdf
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Question 1: How do we know that the main source of carbon comes from the interplanetary dust
particles?
The only thing we know for sure is that carbon is made in stars. Carbon was not made in the “big bang”. So we understand that carbon, and every other element that can only be made through nuclear fusion, was made in stars and when stars end their “lives” they expel these elements into the galactic space to be used by other star/planet systems. We owe our existence to Stars!!! Question 2: During the aerogel capture process, did the device attach to the meteorite while it
took samples or how did that process go?
It was kind of crazy-­‐ the idea was that the flight engineers (navigators!) at the Jet Propulsion Laboratory would steer the space craft through the tail of a comet. Imagine that! Go too close and you destroy a 330 million dollar mission, be too cautious and your 330 million dollar mission is a fail. I am happy I did not have to make such decisions! Question 1: Just how dense was the aerogel used in particle capture?
Really really low density: I really don’t know how low – but this is knowable-­‐ google-­‐able. Question 2: How do we know the composite particle captured by the aerogel was formed in the
inner solar system?
We think this is so. This is because the particle has minerals that we understand can only form at high temperatures, whereas we think (for a pretty good reason!) that primitive silicates from stars don’t look like these minerals. Astronomers look at such stars and early disks to understand this. So… we only find such minerals at high temperatures… so there you go! Maybe you will find an alternative explanation: just because we think so does not make it so! Cody_Answers to student questions O15.pdf
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Question 1: How do the thermal effects of the particle impact on the aerogel affect the chemistry
of the sample that you are examining?
That is exactly the question I asked that led me to study just this. I both learned that thermal effects were minimal (not sure why!) and that the kinetics of graphene formation with thermal metamorphisms could be used as thermometer for primitive bodies. So I solved one problem but raised another problem not yet solved… Question 2: What is the standard carbon cycle?
I am not sure that we understand our carbon cycle, let alone a carbon cycle on any other body that we could define a “standard”. Lots of work needs to be done! Question 1: What would be the effect that carbon exists in different form as searching target
habitable zone?
Carbon chemistry is based on quantum mechanics and in a universe where quantum mechanics is valid-­‐ like ours-­‐ we can be sure that this is not something we need to worry about. In parallel universes this is not necessarrily true. Question 2: Does the abundance of carbon affect the temperature of the surface of the planet?
Great question: I am a chemist-­‐ I have no idea what the correct answer is to this question-­‐ but I know there is likely an answer. The simple and correct view is that green house gasses are principally carbon bearing, CO2 and CH4, this is because the mass of carbon is such that bonded to either O or H leads to a window of energy absorption that is very effective for trapping (IR) radiation-­‐ hence heat-­‐ carbon species warm our planet. Swap Si for C and you get all sorts of variations, SiO2 is a solid, but SiH4 is a gas, but does SiH4 provide as powerful green house effect? Hmmmm lots to think about!!!!! That is nature of the game-­‐ have at it! Cody_Answers to student questions O15.pdf
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Question 1: Is it possible that carbon monoxide could play a similar role to other planets as CO2
does for Earth since most of the carbon in space comes from carbon monoxide?
So you have tapped into my bias-­‐BTW bias does not equal reality. What I mean is that to do chemistry you need reactive molecules. CO2 is really boring, CO is really interesting. You can do a lot with CO, if all you have is CO2 well then you have to first convert CO2 to CO to get the interesing chemistry going. Bottom line, IMHO, is that CO had to be in play-­‐ however it occurred. Please be aware in Chem/Geochem/Cosmochem there are “CO” equivalents-­‐ CO generators. I think you know what I mean. Question 2: Will the definition of habitable zone one day include something about the abundance
of carbon needed to warm the planet?
That was my primary point in this talk and that you are asking this question means that I succeeded in putting this question on your radar screen! Yes! Go study this! Thank you! Question 1: How is it determined where the particle being analyzed started from?
Well for the “STARDUST” samples, this was easy-­‐ the particles had to clearly show that they were captured hyper-­‐velocity into the capture medium-­‐ aerogel. For sure we really appreciated not having to worry about contaminants-­‐ your question is excellent in this regard. This not to say that there were not contaminants, even as JPL did their very best regarding cleanliness. Question 2: What is the leading hypothesis on where the organics originate from?
Hah! Well for sure I attempted to guide you towards my thinking, but I am completely frank when I say that there are many people that have different ideas. So I would ask you to study the evidence. I believe in data. You will have to figure this out for your self-­‐ maybe you agree with me, but may be you agree with others that disagree with me. Either way I hope that the only thing that guides you is the 1) quality of data and 2) the logic of interpretation. Study the evidence and come up with your own opinion. Question 1: Do we know, or have an idea on where the origin of Carbon came from in the
universe?
Yes see above-­‐ STARS Question 2: Because of the elements found in terminal particles (Mg, Fe, Ca), does it support the
theory of life in other universes/planets?
We are working hard on constraining this problem. This is not a simple question, were it were so it would have been solved a long time ago. Cody_Answers to student questions O15.pdf
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Question 1: Chondrites are rich in chondrules. Many believe chondrules are building blocks of
planetary system bodies. Can the lack of carbon planets in a system indicate that the senerio is
incorrect?
Chondrule’s origins are complex. Yes they are likely very important in planet chemistry. This is an old question and remains unanswered. Question 2: Carbon cycle only happens on Earth (not Venus and Mars). If plate tectonics drive
the cycle, is it possible that the occur of plate tectonics is connected to habitable zone itself?
(only HZ planets are possible to develop plate tectonics)
We do not know enough about how Earth is Earth-­‐like, Mars is Mars-­‐like, and Venus is Venus-­‐
like. It is amazing that we do not yet know these things, but we do not! Question 1: You mentioned that interplanetary spaces are low-temperature areas, but I wonder
about the ubiquity of high-energy cosmic rays and particles. Could there be enough radiation to
modify the chemistry of organics in comets and minerals on a general scale?
There is a lot of energy around-­‐ how energy couples to material requires more study. Question 2: Thanks for telling us about Rosalind Franklin's discovery: I didn't know about nongraphetizable carbon! It seems that this polymerization effect occurs in a narrow range of
temperatures, similar to the habitable zone we talk about. How do you characterize the locations
in the solar system (and its history) where this polymerization could occur?
There is no simple answer to your question. At the end of the day polymerization is all about thermodynamics. Dr. Franklin’s discovery is also something that I am happy to report! Dr. Frankin is also a role model to me! Cody_Answers to student questions O15.pdf
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Question 1: I am very intrigued by the aerogel used to capture these materials, can you explain
how they are deployed, i.e. how are they integrated into a system so that they can be exposed to
the particles of interest at one time and then stowed for their return to Earth without significant
loss of materials or damage to samples?
Aerogel is really interesting and there is lots of room for development here. So at the start you need some silica system that “wants” to polymerize with it self-­‐ ideally so fast that things like density don’t matter-­‐ this is where some careful chemistry-­‐ largely-­‐ phase chemistry (physical chemistry) plays a critical role. (I did dabble a bit on phase chemistry in my talk!) My understanding is that the reactant molecule is tetraethyl-­‐orthosilicate. A reactive compound, but less so than tetrachlorosilane (way reactive!-­‐ watch out if you find yourself with this one-­‐ it is really reactive!!!! TEOS (tetraethyl orthosilicate-­‐ TEOS) does do the trick). There is plenty of literature here and I encourage you to study it-­‐ make it better!!! BTW, tetrachlorosilane is very very reactive-­‐ beware!!!! Question 2: When you reduce the meteorite to dust one might think that any process to break
down the object would leave some trace of the tools used behind. You seem very confident that
you have not added anything foreign to the sample. What steps to you take to measure any level
of contamination in the sample?
Yes, you have the right idea here. So the bottom line is that we worry a lot about this. We hope and do experiments to confirm that we are not perturbing things. If we do perturb things then we study the signature of that or those… We study and study and study and worry, worry, worry. This is what we do. What we don’t do is assume that what ever we detect is a “primary signal”. We worry about artifacts all the time! You would-­‐ and you should, do as well! Cody_Answers to student questions O15.pdf
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Question 1: It was difficult to follow, but is Fermaldehyde sort of like the catalyst for creation of
carbon?
Yes, I pushed you all a lot further than you have a basis of knowledge yet! You will have this basis coming soon-­‐ that is why you are here learning. I also did not know any of these things originally. It is so cool to see how little we know and yet we have so many tools to learn-­‐ so we learn the tools and then go to ask the questions and answer them. So… as I noted above-­‐ carbon becomes from a process called “stellar nucleosynthesis”. This is really cool and you should study it! Formaldehyde is made through low T reactions of CO with H2 yielding H2CO… Question 2: What are the carbon levels on other planets in the solar system? Are they also low
like on Earth because everthing was generally really hot during that accreting phase? Do we
know of any carbon-rich planets, or is that sort of impossible?
This is exactly the question that we all need to ask. The cool thing is that we actually don’t know! This is why we study this. Question 1: Do you think it's a possibility that life could exist on planets that don't have plate
tectonics?
I am really interested in this question. I don’t know. This seems like a really fundamental question. Question 2: If you do think that life could exist on planets without plate tectonics, what would
plate tectonics provide for life to begin?
Above! Big question-­‐ no answer-­‐ just saying-­‐ a great question! Cody_Answers to student questions O15.pdf
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Question 1: Are there combinations of carbon and other elements that can be classified as
refractory elements instead of volatile elements?
That was the direction I was going with “non graphitizable carbon” – yes some carbon is very stable to very high T; provided that O2 is not lurking around, or for that matter H2. Question 2: I understand that modeling early solar systems can be quite difficult especially when
looking at the formation of planets from accretion disks. Inner planetary accretion is more
difficult to model because in order for protoplanetary objects to start forming, accretion must
come in the form of collisions of bodies with high eccentricty. My question is, given that comets'
orbits are highly eccentric- and volatile carbon would be able to form far away from a star, is it
possible the main form of carbon deposition on Earth-like planets originated purely from
comets?
So my personal view (and published view) is that carbon solids in our solar system (as we find them so far) share a common origin. I would be very surprised if we had two (or more) different reservours and that I would not detect such-­‐ I know this sounds arrogant but I do not mean to be so. What I mean is that I study this material quite extensively and find no evidence for anything other than one source. So in all honesty I can only support a single source of such organic solids-­‐ of course I might be wrong, but based on my observations and my understandings of others-­‐ this is my understanding. Question 1: Is there any difference (i.e. compositional) between the “Trojan” and “Greek”
asteroids besides their location relative to Jupiter?
I and no one knows, I can’t wait to find out! I have no idea-­‐ lets Go!!!! I am totally pro-­‐ missions! Question 2: How specific can we get when detecting “organic molecules” remotely? In other
words, do we just know the elemental composition or can we also know conformations of larger
molecules?
The reality is that there is really no substitute for “sample return”. Our Earth based analytical facilities are way beyond what we might imagine sending to space. Cody_Answers to student questions O15.pdf
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Question 1: How high was the chance that the Stardust probe was going to get destroyed by Wild
2?
I don’t know-­‐ but what I was told was that the final choice of where to be was extremely scary-­‐ the possibility of destruction was very high. Question 2: How complicated was the path of the Stardust probe? Was it launched at other
planets and slung around their orbits to match the path of Wild 2, or were you able to launch it
directly towards the comet?
Again, I was not there…but what I heard was that piloting the stardust space craft towards the target was really really difficult-­‐ basically comets look like “fuzz balls” and this does not improve as you get closer to them. I am told that navagating around 81P was really scary and unknown territory! I am told that it is amazing that “Stardust” succeeded. But it did!!! Question 1: If organics were delivered to Earth by a comet or meteorite, what type of Earth
environment would be needed at the time of impact in order for the organics to “take hold” and
lead to future life?
We do not know! Question 2: Is delivery of organics to Earth by comets or meteorites a more likely scenario in
your opinion?
I am more interested in what organic molecules do once on Earth-­‐ where they come from is less interesting (to me!). But for sure I believe that we needed to get some sort of carbon cycle going (I could be completely wrong-­‐ just what I think); so how ever you find this happening-­‐ I am interested in entertaining the possibility. Cody_Answers to student questions O15.pdf
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Question 1: Formaldehyde usually breaks down in sunlight. Does solar raditation help put it past
the glass transition or was there some other process that helped this along?
The interesting thing about formaldehyde is that it is completely reactive and will not hang around. That is why I think it is potentially interesting. I am not interested in molecules that are stable (“dead”); they do nothing. Question 2: Are there other examples of glasses that help corraborate the formaldehyde theory?
On what time scale did this cooling take place?
My point about glass transition has nothing to do with the reactivity of formaldehyde. This is my fail of communication to you. Sorry!!!! So what I meant was that I think that formaldehyde chemistry is a source of carbon chemical complexity and I think that this chemistry had to occur at liquid water temperatures. I argued that the shape of organic solids in comets and meteorites show that whatever happened did so in liquid water. Not at very low temperatures. Question 1: The Earth has a sustained carbon cycle, but apparently has very little carbon. How
little carbon do you think is necessary to develop a cycle?
We do not know!!!-­‐ this should be determined! Question 2: Are there future missions in the works to collect samples from comets and return
them to Earth?
We are planning such-­‐ I think that we should! Question 1: Is areogel expensive to use in quantities large enough for sample collection? is it
viable for repeat use, or suitable for other forms of sample return?
NO! Yes, and other Question 2: You mentioned that earth's hydrosphere has been stable for a very long time. Was
organic material brought here before the hydrosphere was stable lying dormant until suitable
conditions were present for it to flourish? Would it have been neutralized or could it have been
preserved?
We do not know-­‐ this is something that we need to determine. Cody_Answers to student questions O15.pdf
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Question 1: Could the higher temperature carbon chemistry that you are seeing in primitive dust
grains be explained as condensing in the outflows of AGB stars?
The mystery to me is that we do not see any evidence of carbon directly from AGB stars in comets or meteorites. Note: that there are some that claim to do so-­‐ I am simply saying that I do not. Maybe I am wrong, but maybe I am right-­‐ I aim to get things right! Question 2: Suppose I build spectrometers to look at rotational lines of molecules in giant
molecular clouds, are there any new allotropes of carbon that I should be looking for?
I am a molecular spectroscopist, so I would simply say the following-­‐ Look for everything thing that you can see and see every thing that you can look for!!!! Question 1: How is the early carbon record preserved in comets?
That was the point of my talk-­‐ so it is preserved in complex organic solids… Question 2: Would a much lower abundance of carbon behave differently in the evolution of a
molecular cloud?
A molecular cloud is going to evolve how ever it does-­‐ whether a star system evolves out of it and what it looks like is not yet known-­‐I agree that this is something we should know better! Question 1: With the recent large jump in the number of exoplanets identified, does the
probability of finding of finding life on any one of these “habitable zone” planets equally
increase?
We really don’t know-­‐ that is why I think we have a lot more work to do-­‐ we really don’t have a clear definition as to what means what! Question 2: You ended your talk by previously touching on connecting plate tectonics and life,
could this potential connection have any implications for either plate tectonic theory or the
search for life on Mars?
This is something that I think might be important. I obviously have no answers here-­‐ I only have my ideas. You all need to jump in and solve this problem… Thanks for you questions! Cody_Answers to student questions O15.pdf