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Researchers have cracked how polycyclic aromatic hydrocarbons (PAHs) survive in space, this unlock clues to prebiotic chemistry and the origin of life.

What Are Polycyclic Aromatic Hydrocarbons (PAHs)?

They are a special type of organic molecule, consisting of carbon and hydrogen atoms. These atoms arrange themselves into flat, ring-shaped structures, much like tiny, intricate molecular building blocks.

Formation on Earth => PAHs also form on Earth. They are created when organic materials, like fossil fuels (coal, oil, gas) or biomass (wood, plants), burn without enough oxygen (incomplete combustion) or break down at high temperatures without oxygen (pyrolysis). For example, the soot from a smoky campfire, car exhaust, or industrial smoke all contain PAHs.

Properties => On Earth, PAHs do not dissolve easily in water but readily dissolve in most organic liquids, such as oils and solvents.

Vulnerability in Space => In space, PAHs face a constant threat. When they collide with other tiny particles or absorb high-energy radiation, such as harsh starlight, they gain a lot of internal energy. If a PAH molecule takes in more internal energy than its weakest chemical bond can hold, it will break apart, or "disintegrate."

Why Are PAHs Important in Astrobiology?

Abundance in Space =>: Astronomers estimate that PAHs make up —about one-fifth of all the carbon found in the vast, empty regions between stars, known as interstellar space.  

"Building Blocks of Life" Hypothesis => Scientists hypothesize that meteors traveling from space brought these PAHs to a young Earth billions of years ago.

• Once they arrived on Earth, these simple molecules could have combined and transformed, eventually leading to the complex chemical processes that initiated life.
• This idea, sometimes linked to panspermia (the theory that life or its building blocks can spread through space from one celestial body to another), highlights how critical their ability to survive the harsh conditions of space is for understanding our own origins.
• If they broke apart easily, they would never have made it to Earth intact.

What is Taurus Molecular Cloud 1 (TMC1)?

It is a giant cosmic nursery located in the constellation Taurus, about 430 light-years away from Earth. It is a vast collection of gas, dust, and plasma (an ionized gas).

Ideal Conditions for Molecules => It is well-known for its extremely cold and dense conditions. These specific conditions are perfect for the formation of complex molecules.

Primary Composition => The cloud mainly consists of molecular hydrogen (H2), which is the most abundant molecule in the universe. It also contains other important molecules like carbon monoxide (CO), ammonia (NH3), and various other organic compounds.

In TMC1, scientists observed that small "closed-shell PAHs" (molecules whose electrons are in stable pairs) appeared in much greater quantities than expected. This was a mystery because, despite the cold, these molecules were still frequently exposed to starlight, which should have destroyed them.

The DESIREE Experiment Shows How PAHs Survive in Space

Focusing on a Specific Molecule => They focused their studies on the indenyl cation (C9H7+), which is a small, charged fragment that comes from a slightly larger PAH called indene.

The DESIREE Facility =>The team used an advanced facility at Stockholm University in Sweden called DESIREE. This facility features special "ion-storage rings" kept at incredibly cold temperatures—below –260°C. These extreme conditions create a near-perfect vacuum, allowing charged molecules (ions) to float around for many minutes without colliding with anything.

The Discovery => The key discovery was that the C9H7+ ions cooled down much faster than other similar molecules previously studied. It provides a clear explanation for why many PAHs, especially the smaller ones, can cool down and remain stable for long periods in the harsh conditions of space. 

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Source: 

THE HINDU