Our Astrochemical Heritage

Astrochemical Complexity

This paper is based in part on “Our astrochemical heritage”, by Paola Caselli and Cecilia Ceccarelli (C&C)

Term Paper for the Introduction to Astronomy course Fall 2012

Waubonsee Community College

Eduardo Cantoral

Plano, IL
USA

Wikipedia

“Our Sun and planetary system were born about 4.5 billion years ago. How did this happen and what is our heritage from these early times? This review tries to address these questions from an astrochemical point of view. On the one hand, we have some crucial information from meteorites, comets and other small bodies of the Solar System. On the other hand, we have the results of studies on the formation process of Sun-like stars in our Galaxy. These results tell us that Sun-like stars form in dense regions of molecular clouds and that three major steps are involved before the planet formation period. 

They are represented by the pre-stellar core, protostellar envelope and protoplanetary disk phases. Simultaneously with the evolution from one phase to the other, the chemical composition gains increasing complexity.

In this review, we first present the information on the chemical composition of meteorites, comets and other small bodies of the Solar System, which is potentially linked to the first phases of the Solar System's formation. Then we describe the observed chemical composition in the pre-stellar core, protostellar envelope and protoplanetary disk phases, including the processes that lead to them. Finally, we draw together pieces from the different objects and phases to understand whether and how much we inherited chemically from the time of the Sun's birth.”

1 Introduction

When I was a student at UCSB in the early 70s, my English proficiency was insufficient for College level work. They advised me to take a class. During the first quarter my language skills improved enough, so I only took the class once. I remember one assignment. Go to a lecture and report the content to the class. Professor Herbert Broida was a distinguished scientist at the Physics Department, he organized lectures on Molecular and Atomic Physics. During the time of the assignment, I had the good fortune of reporting on a lecture on Organic Molecules in the Universe. It was fascinating to know how complex molecules were located all over space.

The Mexican astronomer Guillermo Haro, in collaboration with the Armenian scientist Victor Ambartsumian, pioneered the study, together with George Herbig, of planetary producing regions, the so-called, Herbig-Haro objects. These three scientists contributed to the understanding of “Our astrochemical heritage”.


One can read in Wikipedia:

“The existence of 'protostars' was first proposed and postulated by Soviet-Armenian scientist, Viktor Ambartsumian.[1]”

I write this term paper on a recent Review Article by Caselli & Ceccarelli (C&C), accepted for publication in “The Astronomy and Astrophysics Review”.

This is a recopilation of work done by these two Italian women to understand the origin of life in the Universe. In an unexpected way, the solar system seems to be a big living organism. There is differentiation, like in the formation of planets we talked about in class. The mechanism discovered by these scientists has to do with surface chemistry, i.e., atoms get adsorbed on the surface, and at the right temperature and pressure, organic molecules are formed. These phenomena are previous to the formation of the central star. There seems to be a two-dimensional architecture for life. In a seemingly unrelated manner, a Black Hole contains all the Information of what went inside it, stored on the surface, this is the so-called Holographic Principle.

From the mathematical point of view, two-dimensional phenomena are less complex than three-dimensional ones. It could be that from the physical and chemical point of view, Nature organizes itself this way. From one, to two, to three, and then to four dimensions. There are indications nowadays of more dimensions. Right now the LHC accelerator at CERN is looking for signals of more dimensions. In any case, the purpose of this “Term Paper” is to explain the Review by C&C.

More important, from the astrophysical point of view, is the work of Arcadio Poveda and Luis F. Rodriguez. These Mexican astrophysicists have continued the work of Guillermo Haro. In particular professor Poveda has studied groups of stars formed in clusters. There is the Trapezium Cluster in the Orion Nebula , which Poveda has studied for many years. Using classical mechanics, he has been able recently, with Rodriguez and other collaborators, to determine that an event occurred  there, around five hundred years ago. This event is recent from a cosmological point of view, which has the potential to take our understanding, to the beginning of our own Solar System. In particular the so-called BN/KL region is the site of this recent event. These stars are bigger than our Sun, but nevertheless they teach us about the beginning of complexity, which is the main thrust of this paper.

It is unclear where the Sun comes from. Stars are not formed alone, we do not know which cluster gave origin to our Sun, since it is formed with its planetary disk, it could have come out with a slow velocity, maybe like the stars observed in the Orion Trapezium Cluster.

Recently professor David Deutsch published a new scientific paradigm: “Constructor Theory”. Here I use this paradigm to present my ideas on “Our astrochemical heritage”. Professor Deutsch writes about rules, which rules are valid in Nature, and which ones are not. Humans can make any number of rules, nonetheless not all of them describe actual observed processes. These rules apply to objects, which if they obey the rules, are instances of the rules. The set of valid rules form what we call Natural Laws. The new element in Deutsch’s paradigm is “The Constructor”. This object can be a human, or a human society, but it does not have to be. He defines it as one element which does not change when the process happens: Like a catalyst. 

                                       constructor
input state of substrate(s)         output state of substrate(s)

For solar system formation we need a substratum. C&C tell us that dust and gas are the substratum. Cavities are formed with these elements and light does not get in, making it a cold region inside a Molecular Gas Cloud. These nurseries of new stars can be 10 . This protection is necessary - space around is hotter - for formation of the complex molecules, which in some sense are our ancestors. Water and sugar have been found floating in space. The ingredients for life are there. To find these complex molecules in space nowadays, we need the Atacama Large Millimeter Array (ALMA) in Chile. Rodriguez and other radio astronomers, have used this array of radio antennas to study the Herbig-Haro objects. Atacama was chosen because it is one of the driest places on Earth’s surface. Water is welcome to make planetesimals, asteroids, comets, and so on, but it is not welcome to observe these nurseries, it obscures the view. The constructor is not a chemist, or a physicist, we only understand, it is a catalyst. The catalyst remains, as the inputs are converted into products. Deutsch has codified time as permanence. The formation of stars and planets needs permanence. In the quiet and cold cavities, on the surface of dust, molecules are formed. Remember that gravity makes bodies approach each other, but there are also electrostatic forces involved in keeping the atoms on the surface of dust particles, so chemical reactions can occur. For gravity to keep an atmosphere, say, the body has to grow much more, than these tiny dust particles, just a few sub-microns across. These particles serve as laboratory tables, steady surfaces, keeping the reactants in place through electric forces, called Van der Waal forces.

Life is one of the process allowed in Deutsch’s paradigm. How do we know?

Because we are here.

The problem of three-dimensions vs. other dimensions, is not closed. Mathematics is easier in zero, one, and two dimensions, but the Universe has three spatial dimensions. Recently Mukhopadhyay et al. have discussed rotation of hydrodynamic disks. It is known though, that stars are born in clouds under rotation, with inflows, and outflows. One can see jets coming out of Herbig-Haro objects, even the ultra massive black hole in the center of the galaxy shows angular motion, with stars going almost at the speed of light around it. Next year a big gas cloud is going to the hole, we expect to see radiation coming our way.

A new book just came out, “The Stardust Revolution”, by Jacob Berkowitz. This book is written in the way I try to follow in this paper. It is about new discoveries made in the submillimeter part of electromagnetic radiation, both by radio telescopes on Earth, like ALMA, and in space, like HERSCHEL. C&C derive part of their insights from these observations also.

In conclusion I report here on the C&C review. Next section: “Solar-type star formation and chemical complexity,” describes the initial stages of the origin of complexity,  3 : “Pieces of the puzzle from the Solar System”, uses our knowledge of the immediate neighborhood, to test the theory,  4: “The calm before the storm: pre-stellar cores”, continues with the formation of more complex molecules like water and sugar, 5 :“The cocoon phase: protostars”, concerns itself with even more complicated molecules and their production processes, 6: “Toward planet formation: protoplanetary disks”, introduces proplyds, and their formation,,  7: “Putting together some pieces of the puzzle”, considers the evidence from meteorites and comets, together with theory to test our current understanding of our heritage, 8: “Concluding remarks”, a summary of the deciphering of the given information is presented .

2 Solar-type star formation and chemical complexity

C&C study our Sun, as an example of a more general process of complexity generation. The Sun is here, the solar system also, we can use this framework, for a general theory of complexity generation. There are three main phases in this process. Pre-stellar cores, protostellar envelopes, .and protoplanetary disks, or proplyds

Each phase needs telescope observations, spectral analyses, both emission, and absorption, and model building. There are data bases for spectral properties, and collision probabilities. Professor Eric Herbst from The Ohio State University, calculates and predicts chemical species abundances. The presence of water, and carbon based molecules, is proven beyond reasonable doubt, in these regions. Also the increasing complexity of molecular chemistry is well established. The Universe is a factory of organic complexity. The constructor is the catalyst, i.e., that object which does not change. Thus, there is heritage. This complexity is not lost as the different stages continue their course, on the contrary, it increase even more. Dust particles, are like laboratory surfaces, where these organic molecules are formed.

“The sub-micron dust grains coagulate into larger rocks, called planetesimals, the seeds of the future planets, comets and asteroids. Some of the icy grain mantles are likely preserved while the grains glue together. At least part of the previous chemical history may be conserved in the building blocks of the Solar System rocky bodies.”

3 Pieces of the puzzle from the Solar System

Given what we know we can construct a story for the origin of complexity.

3.1 Where does the terrestrial water come from?

Among the many uses I know of water, one that surprises me is as lubricant for tectonic plates. The carbon cycle on Earth, depends on continental plates bringing up sedimented carbon, in the form of mountains, and continents. Water is a polar molecule, both hydrogen atoms attach to oxygen at an angle, moving the geometric center of negative charge to a different position than the positive. This separation of charges, turns the molecule into a tiny battery. This electric force dissolves other substances, and now I know, facilitates tectonic plate motion.

The fractionalization of deuterium and hydrogen, in Earth’s water, gives us a clue, of where is the water coming. Meteorites, and comets give us now, a consistent picture on the deuterium to hydrogen ratio. Our water came down through meteoritic activity. The ratio is now consistent with measurements on these objects. Nature. 478, 218-220

3.2 Molecular species in comets and KBOs

i)have been detected in more than 10 comets;
ii) HCOOH, HNCO,, OCS and have been detected in more than 1 comet;

iii) have been observed in one comet, Hale-Bopp.

There are plenty of organics in the Solar System, the original cloud, left us a rich heritage.

NASA has a spacecraft, Stardust, which has added even glycin, the simplest of amino acids, to the list of “Our astrochemical heritage”.

Ethane, , has been detected in Makemake.

3.3 Organics in meteorites and IDPs (Interplanetary Dust Particles)

There are more amino acids in space than those used in life on Earth. The Murchison meteorite, is carbonaceous chondrite, like the Allende. They are rich in organics, even some different chirality than on Earth, i.e., we know they were not produced by the type of life we have here.

3.4 The hydrogen and nitrogen isotopic anomalies

“A common origin for the D- and -enrichment in comets and the organic material in carbonaceous chondrites and IDPs? Since comets and the organic material in chondrites and IDPs are enriched in both D and , the question whether the enrichment has a common origin is a natural one (e.g. [8]). Against this hypothesis is that D-enriched spots in chondrites and IDPs do not coincide spatially with -enriched ones ([8]; [376]). Similarly, while the D-enrichment differs by a factor two in 103P/Hartley2 and the other six comets, the - enrichment is practically the same in all comets (Fig. 4). Therefore, very likely D- and - enrichments do not have a common origin (see also [466]).”

There is a rich source of information in the isotopic anomalies, these are clues waiting to be deciphered. Like  forensic scientists, astrochemists are looking for our extreme genealogy. One thing is clear though, when our origins are found, I believe we will feel more like a part of the Universe. Paraphrasing Woody Guthrie, “This Universe is my Universe, this Universe is your Universe”.

3.5 A violent start in a crowded violent environment

There are reasons to believe a supernova exploded nearby, giving us a violent past. It is like if you find out that you are a descendant of Jesse James, or Genghis Khan. You can read Alan Boss’s article here.

The Dawn spacecraft purpose is to study two asteroids, Vesta and Ceres. Their structure has been discovered, they are rocky planets, in the resonance region of Jupiter, which could not grow as much as the other rocky planets, due to this resonance. Based on these observations Boss et al. were able to know of the presence of  , an isotope with a half life of .  This is a Short-Lived Radioisotope (SLRI). On the basis of this, and other observations, they proposed a model for Solar System formation, the Supernovae as  trigger model.

“A supernova is a likely source of short-lived radioisotopes (SLRIs) that were present during the formation of the earliest solar system solids. A suitably thin and dense supernova shock wave may be capable of triggering the self-gravitational collapse of a molecular cloud core while simultaneously injecting SLRIs. Axisymmetric hydrodynamics models have shown that this injection occurs through a number of Rayleigh-Taylor (RT) rings. Here we use the FLASH adaptive mesh refinement (AMR) hydrodynamics code to calculate the first fully three dimensional (3D) models of the triggering and injection process. The axisymmetric RT rings become RT fingers in 3D. While ~ 100 RT fingers appear early in the 3D models, only a few RT fingers are likely to impact the densest portion of the collapsing cloud core. These few RT fingers must then be the source of any SLRI spatial heterogeneity in the solar nebula inferred from isotopic analyses of chondritic meteorites. The models show that SLRI injection efficiencies from a supernova several pc away fall at the lower end of the range estimated for matching SLRI abundances, perhaps putting them more into agreement with recent reassessments of the level of  present in the solar nebula.”

4 The calm before the storm: pre-stellar cores

Before the Sun lights up, the cloud is calm. It has conditions like L1527 IRS as you can read published  in Nature. This protostar is less than 300,000 years old, and has a mass like one fifth that of the Sun. It was observed in Chile.


4.1 Freeze-out, deuterium fractionation and the ionization fraction

The first miracle is the separation of hydrogen and deuterium. This is achieved with a combination of temperature, density, and surface catalysis. This marks the future differences. Fractionation is born.

4.2 Ice formation and evolution

Cold water on grain surfaces becomes ice, chemical evolution begins.

4.2.1 The origin of water

It is not understood yet, how water appeared on Earth, but a lot of it came in meteorites. The initial place where the Earth is now was dry. The Earth could have been formed in another place and then moved nearer the Sun.

4.3 Complex organic molecules

These are the origins of life, now it is well established that organics are being formed everywhere as I write this. The Universe is busy making the stuff of life.

5 The cocoon phase: protostars

5.1 The chemical composition of protostellar envelopes: a powerful tool to understand the present and the past

In the Orion Nebula and other places there are cradles of structure and complex chemistry. They are studied with radio telescopes like those in Atacama, Chile. These are powerful tools.

5.2 The chemical complexity in hot corinos

If the cloud is big, they are called hot cores, if small, hot corinos. More than a physical process, the Universe enters into a chemical process, maybe we do not know how the chemicals are physically located, but we do know, the story and conditions of the chemical reactions. There are catalysts, pressures, temperatures, and densities, writing the book of the Universe. The information is right there, we just have to decipher it. Hot corinos are defined chemically.

5.3 The chemical complexity in molecular outflows

It is difficult to study the turbulent jets that take chemicals out, but we know material is going in and out, like in any construction project. Inputs and outputs.

5.4 Water and deuterated water

The difference is big, one deuterium has twice the mass of hydrogen, it is relatively easy to separate water from heavy water, this is done on the surface of the Earth, and in the rocks coming from the sky.

5.5 Deuteration of other species

Besides deuterium, other chemical have important isotopes, like nitrogen, which eventually will give what we do recognize as our heritage, genetics through aminoacids. Heavy hydrogen also attaches itself to other atoms, beside oxygen, and the presence of deuterium is an important tool to understand our origin.

Caves form serving as nurseries to stars, complex molecules are formed in the cocoon which stay in regions outside the star, this phase produces complexity that persists. This is our astrochemical heritage, the marks are stored like in a computer hard drive.

6 Toward planet formation: protoplanetary disks

Observed proplyds are like polyps for life forms. Astronomers have seen them, and can be considered the mother of all life forms. They have stored information which can be used to produce future life.

6.1 Embedded disks: chemistry at the dawn of planet formation

Many new stars have disks like our Sun, so we believe they have planets. Over six hundred stars have been found to have planets. Kepler has a big sample of possible planets.

6.2 "Naked" protoplanetary disks

When the fog goes away, we can see what is inside, a disk similar to our old disk, where our planet was formed.

6.3 From debris to icy worlds

The rocks coming to Earth, bring messages from the past, they allow us to understand the icy worlds away from the neighborhood of the Sun. We have Pluto and other dwarf planets, to bear witness to ice worlds.

7 Putting together some pieces of the puzzle

Not completely understood, but recent progress is unprecedented in the Universe, the image is slowly coming through, and it is pretty.

7.1 Molecules in comets and solar-type protostars

Herschel has solved some old problems, like the apparent difference in the deuterium composition between Earth’s water, and the one in meteorites.

7.2 Origin of deuterated molecules in comets and chondrites

With new equipment astrochemists have been able to understand more and more, how deuterium appears in the rocks we can study, like Carbonaceous chondrites.

7.3 The -enrichment in comets and chondrites

This isotope of nitrogen, is crucial to understand aminoacids, which form the basis of our astrochemical heritage. It is studied with new instruments.

The origin of life is a hard scientific problem. C&C do not solve it, they concern themselves with the origin of molecular complexity in dust and gas clouds in the Universe. They have produced the correct platform for this future work.

8 Concluding remarks

• Water on Earth.
• Complex organic molecules
• D-fractionation in water
• D-fractionation in other molecules
• -fractionation

Professor Townes started the astrochemical revolution, now we know of chemical processes which only happen in space, and which  have not been possible to repeat in our laboratories. They can be modeled with computers though, so we know we are not so off the mark. The Universe appears under this paradigm shift, as a nursery for chemical complexity, we are its more complex manifestation: Intelligent Life is the end of the line. It seems then, that it is not so crucial to put all the pieces of the puzzle for our planet, as C&C try to do in this review. The whole Universe, from the Big Bang to us, seems to be an experiment in producing Intelligence in the Universe.

If this is not so, it certainly looks like that!  

There is no apparent chemical engineer, but we end up with water, sugar, and alcohol. The genesis is written in rocks coming from space, better known as meteorites. With telescopes we see the cradle, not only of civilization but of the Solar System itself, our house and mother. We come from the womb of our mothers, repeating for the time the cocoon process which made us. We can see in the crucible of the Orion Nebula, our siblings being formed. Herbig-Haro objects, with their jets and disks, are preludes to our mother Tonantzin, which will be remembered by all Mexicans this December 12, 2012, in Mexico City, Monterrey, New York, and many other centers of city life. It is interesting that Guillermo Haro looked through his Schmidt camera in Tonantzintla, to discover these cradles of stars and planets. We witness the sacred and the material, in a coherent picture of our remote, very remote origins.

Everything is written out there, every single rock going around the Sun, has clues of our origins. We are slowly learning how to decipher the message left by “The Constructor”, for us to understand. The Universe is not hostile to life, the Universe made us. As I write this, more sugar is being created, more alcohol, more water. This Universe is made for you and me. This is the biggest puzzle ever made. Come join us!

A “New Era of Astronomy” is upon us. For the first time in Human History, we know about the existence of planets outside of our Solar System. There are new reports of non-equilibrium atmospheric compositions in HD 209458b. We are a few baby steps away from discovering, how life friendly the Universe is. For the observation of this hot-Jupiter, astronomers had to consider leap seconds, to correlate with other measurements by other astronomers. These ongoing observations of another world, are done with the utmost precision, with the hope to learn more on our own origins on Earth, up to a second.

“For late M stars, the location of the habitable zone is within the region in which we would expect tidal locking to occur (Kasting et al. 1993); it is therefore likely that the first atmosphere studies of potentially habitable worlds with the James Webb Space Telescope will focus on these tidally locked systems.”

Taken from arXiv

This is the end of the story, we have come a long way to understand the physical and chemical processes that produced us. We are the children of the Universe. We are home!