It’s a relatively little-known fact outside of astrophysics that the key to the first stars in the universe, and the earliest structures condensing out of the primordial murk, was chemistry.
Specifically, the key was the formation of molecular hydrogen or H2. A pair of atoms bonded together and capable of rotating and vibrating. A few years ago I wrote about some of the details in this column. In brief, without the formation of molecular hydrogen it’s very hard for cosmic gas to cool off. If it can’t cool off it can’t condense to make stars, and for those stars to forge the first heavier elements that act as much more efficient coolants for subsequent generations of forming objects. (It could be argued that helium hydride, forming before molecular hydrogen, was also key, but more so for enabling the formation of molecular hydrogen in the first place).
Closely related to molecular hydrogen is the ‘mother molecule’ of protonated molecular hydrogen, H3+. Once this forms it unlocks an astonishing network of chemistry that includes (after such elements form) carbon, nitrogen and oxygen.
We’ve also long known that molecules form in the chill of interstellar space, especially in the great nebula or molecular clouds that dot our galaxy and others. We've furthermore seen that a majority of these molecules involve carbon. And over the years there’s been slow but steady progress in decoding the details of the chemical mix, including recent work that hints at the likelihood of biologically important nucleobases like cytosine and adenine forming in space.
It’s awfully tough to detect specific molecules in nebula though. The spectra of light we can measure from these clouds tend to be complex and a bit confounding.
Somewhat easier is the detection of molecules in meteorites and in comets and asteroids in our own solar system. From these we know that there is a wealth of organic chemistry that not only takes place in the swirl of material as a star and its planets form, but is also preserved through time and dumped onto planetary surfaces across the history of a system.
One of the biggest questions is whether any of this chemistry matters for the initiation of life in a suitable environment. Was it, for instance, the infall of locally-formed organic chemistry onto a young Earth 4 billion years ago that helped kick start life? Or, further up the chain, was the formation of organic molecules in interstellar space, long before our sun came along, a critical factor in setting up the conditions that would make ours a living solar system?
The truth is that we don’t know. Even if there were juicy amino acids floating around before the sun formed, it’s far from clear that these molecules ended up intact on planetary surfaces, or that being without them would’ve posed a problem. Tracing those pathways is very difficult, and arguably we’ve only just started to make any real progress.
But it might also be that we’re simply looking at this all wrong. We’re so predisposed to be awed by all the pretty sparkly things in the universe that perhaps we’re missing an alternatively informative picture.
Imagine that we could strip away all those pesky galaxies, stars, black holes, and planets. Remove their distracting structures and non-chemical properties and just see the molecules that make the cosmos. There would likely be vast regions of intergalactic space with very different chemical makeup and some with a paucity of molecular diversity. There would be vibrant incubators: zones of molecular formation and chemical evolution. There would be steady fortresses of minerals. There would also be places where molecules undergo astonishing complexification, including into the form of microscopic machines propagating and parsing information and processing chemical energy – that phenomenon we call life.
There would also be a timeline, a history of the molecules of the observable universe. It would start with molecular hydrogen and then eventually kick into higher gear, with compounds like water and the simplest organics. But there is noise, stochasticity to this history. Chemistry can be wiped out by supernova, kilonova, hypernova, and even hot proto-stars. Molecules can be dissociated by shockwaves and surges of particle radiation. And in amongst this noise may be the spikes of unparalleled chemical richness that signal the rise of living systems.
If we could develop the population statistics of this timeline and of the spatial distribution of molecules across the cosmos, we would have a powerful new lens to examine ourselves through. It would be enormously difficult, and it is of course to a large extent a rephrasing of what astrochemists and astronomers are already doing, but it would be fascinating to try to pull all of that work together in a new way to see the universe. Not just as a realm of gravity and physics, but as a vast and ancient system of connected and disconnected chemistry.