Chemists uncover how unthinkable reactions occur in unimaginable conditions

Before there was Earth, there was chemistry.

In the unimaginable cold, dark clouds where stars and planets are born, carbon molecules assemble into more complex forms — starting a chemical journey that could eventually deliver some of life’s basic ingredients to young planets. There’s only one problem — these molecules need heat to form. At least that’s what scientists have long believed. But new research from FIU chemist Alexander Mebel reveals such chemistry can actually happen at temperatures nearing absolute zero, which is -460 degrees Fahrenheit.

On Earth, these complex carbon molecules are usually associated with extremely hot temperatures, like those associated with combustion. It has long been presumed that heat is necessary for these molecules to assemble in space. But when astronomers detected one of these molecules last year, it was found in the cold, dark region known as Taurus Molecular Cloud-1. This region, where solar systems begin, is anything but hot. Temperatures there hover around -443 degrees. Mebel’s research, published in the Journal of Physical Chemistry A, offers a possible answer as to how these molecules formed there and could improve understanding of how worlds like Earth can form.

Mebel and collaborator Ralf Kaiser of the University of Hawaiʻi at Mānoa studied phenalene, the complex carbon molecule recently discovered in Taurus Molecular Cloud-1. They explored new possibilities to find some way phenalene could form that did not require heat. Using computer modeling, they discovered a series of chemical reactions that can actually happen without heat to form phenalene.

Phenalene belongs to a large family of carbon molecules called polycyclic aromatic hydrocarbons, or PAHs. Scientists believe these molecules hold a significant amount of the carbon found in space, but detecting individual PAHs has been difficult. The discovery of phenalene gives scientists another piece of evidence that these complex molecules can exist — and form — in extremely cold regions of space.

Gravity pulls together gas and dust within these clouds to form stars. Material left around a young star can eventually come together to form planets. Molecules already present in the cloud can become part of those new worlds. Mebel’s findings suggest some of that complex carbon chemistry can get its start even earlier, in the extreme cold before planets exist.

Scientists have found more evidence of that connection much closer to home. PAHs have been discovered in samples collected from asteroids and returned to Earth. Some appear to have formed in very cold environments.

And the story may not end with planets.

Scientists are investigating whether PAHs and other carbon molecules may have helped create the conditions that allowed more complicated organic molecules to form before life began.

One place that chemistry can happen is on tiny pieces of cosmic dust.

“The surface of cosmic dust particles are believed to serve as ‘molecular factories’” that help form more complex organic molecules,” Mebel said.

Some of those molecules are considered building blocks of life. They can become trapped in asteroids and other objects and later be carried to young planets through impacts.

That doesn’t mean phenalene created life. Far from it. But learning how molecules like phenalene can form in the freezing darkness of space helps scientists trace a much bigger chemical journey — from simple molecules, to stars and planets, and to the increasingly complex chemistry that can make worlds like Earth possible.