Astrophile is Joshua Sokol’s monthly column on curious cosmic objects, from the solar system to the far reaches of the multiverse
Regular readers may have the same expectations of this column as they would a safari: something huge has to show up.
Greedy black holes. Giant lava lakes. Stars too big to exist. Even the comparatively small stuff in outer space, like asteroids or geologic features on a world’s surface, would effortlessly dwarf you if stood in front of them in a space suit.
But on scale far below the cosmic megafauna is a different world, one of tiny carbon molecules mixing and changing in the void. Its poster child is the charming buckyball, a curious round agglomeration of carbon atoms.
This chemical ecosystem can be a nuisance for astronomers, because the little molecules block out parts of the light we see from stars and galaxies. But it’s also important on its own.
Recent discoveries have shown that the chemical reactions between stars can build the constituents of biological molecules like amino acids and sugars. These substances, raining from space, may have contributed to the origin of life on Earth.
But these reactions are intricate and hard to track, leaving us searching for beacons – a molecule we understand that could help us navigate through the fog. This is where the small stuff becomes a big deal. Hang on as we zoom down.
To envision a buckyball bouncing around in outer space, picture it like a little football: 60 atoms of carbon arranged in a rough sphere.
In the mid 20th century, architect Buckminster Fuller (also known as “Bucky”) and others had figured out that a network of pentagons and hexagons would fold into a stable geodesic structure. As it turned out, nature had already come to the same realisation. In 1985, earthbound researchers cooked a disc of graphite, a carbon mineral, in a plasma chamber to recreate the conditions around a red giant star. To their surprise, they discovered they had made weird new forms of carbon – buckyballs and other examples of even larger molecules that looked like carbon cages.
They chose to nod to Fuller by calling them fullerenes – thankfully – after first considering names like ballene, spherene, soccerene, and carbosoccer.
But, even after astronomers began to look for fullerenes in space, they took two and a half decades to find. It wasn’t until 2010 that a team led by Jan Cami at the University of Western Ontario in Canada found their spectral signatures in the colorful gas around a dying star.
Since then, traces of fullerenes have popped up again and again in many different environments. A 2015 paper argued that their presence in the Milky Way may even explain weird spectral features of interstellar space – certain wavelengths of light from distant stars that are being mysteriously absorbed on the way to us. These features have been unexplained for over a century.
Chemistry in the void
That’s not to say we understand where the fullerenes are coming from.
There is plenty of carbon in space, and a heated carbon-rich gas will produce buckyballs and similar molecules because their closed cages are incredibly stable and resilient. But colder regions of space should instead make flat, soda-ring structures of carbon, with hydrogen atoms around the outside. To get those structures to fold into a cage, you would need to get rid of the hydrogen. This could happen either because there were no hydrogens around to begin with, or if the molecules were exposed to ultraviolet light that can bake the hydrogens away.
How these processes interact to explain the full spread of interstellar fullerenes is unclear, Cami said at a recent lecture. “I’ve been scratching my head about this for a long time.”
Solving the mystery of this little molecule could have a big payoff. Most of our spectral measurements of carbon molecules floating around in space are a garbled mess. Too many different kinds of other molecules are overlapping, making it hard to understand what’s going on.
Enter fullerenes, with their clear and unique signals, showing us at least one part of the rhythms and reactions of interstellar carbon. Eventually, perhaps, we can use them as tracers to understand how prebiotic molecules form in space, giving us hints about our own existence.
Like soil bacteria in the savannah, buckyballs might not be as eye catching as the astronomical titans that tower over them. But try taking them and their relatives away and we might not be here to appreciate the cosmos in the first place.
Source: New Scientist