Astronomers just discovered a complex carbon molecule in space—one step closer to deciphering the origin of life

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A research team led by researchers at the Massachusetts Institute of Technology in the United States has discovered large molecules containing carbon in distant interstellar gas and dust clouds. |Image credit: Space Telescope Science Institute Office of Public Outreach

A research team led by researchers at the Massachusetts Institute of Technology in the United States has discovered large molecules containing carbon in distant interstellar gas and dust clouds.

This is exciting for those of us who keep inventories of known interstellar molecules in the hope of figuring out how life arose in the universe.

But it’s not just another molecule in the series. The results are reported today in the magazine scienceshowing that complex organic molecules (containing carbon and hydrogen) may have existed in the cold, dark gas clouds that formed our solar system.

Furthermore, these molecules remained together until after the Earth was formed. This is important for our understanding of the early origins of life on Earth.

Difficult to destroy and difficult to detect

This molecule is called pyrene, a polycyclic aromatic hydrocarbon, or PAH. The complex-sounding name tells us that these molecules are made of rings of carbon atoms.

Carbon chemistry is the backbone of life on Earth. The interstellar medium has long been known to be rich in polycyclic aromatic hydrocarbons, so they figure prominently in theories of how carbon-based life formed on Earth.

We know there are many large PAHs in space because astrophysicists have detected signs of them in visible and infrared light. But we don’t know exactly which PAHs they are.

Pyrene is the largest PAH currently detected in space, although it is known as a “small” or simple PAH, with 26 atoms. It has long been thought that these molecules cannot survive the harsh environment of star formation, because the complex molecules are destroyed when everything is bathed in radiation from the newborn sun.

In fact, for this reason, it was once thought that molecules with more than two atoms could not exist in space until they were actually discovered. Furthermore, chemical modeling shows that pyrene is difficult to destroy once formed.

Last year, scientists reported that they had found large amounts of pyrene in samples from the solar system asteroid Ryugu. They believe that at least some of it must have come from cold interstellar clouds that preceded our solar system.

So why not take a look at another cold interstellar cloud to find some? The problem for astrophysicists is that we don’t have the tools to detect pyrene directly—it can’t be seen with radio telescopes.

Use a tracker

The molecule the team detected is called 1-cyanopyrene, which we call a “tracer” of pyrene. It is formed by the interaction of pyrene with cyanide, which is common in interstellar space.

Researchers used the Green Bank Telescope in West Virginia to observe the Taurus Molecular Cloud, or TMC-1, in the constellation Taurus. Unlike pyrene itself, 1-cyanopyrene can be detected through radio telescopes. This is because the 1-cyanopyrene molecule acts as a small radio wave transmitter – a miniature version of an Earth radio station.

When scientists know the ratio of 1-cyanopyrene to pyrene, they can estimate the pyrene content in interstellar clouds.

The amount of pyrene they found was significant. Importantly, this discovery in the Taurus Molecular Cloud demonstrates the presence of large amounts of pyrene in the cold, dark molecular clouds that ultimately formed stars and solar systems.

The complex birth of life

We are gradually building a picture of how life on Earth evolved. This picture tells us that life came from space—well, at least the complex organic, pre-biological molecules needed to form life came from space.

As Ryugu’s findings show, pyrene’s survival of the harsh conditions associated with star birth is an important part of the story.

Simple life composed of single cells appears (geologically and astronomically) in Earth’s fossil record almost immediately after the Earth’s surface cooled enough not to evaporate complex molecules. This happened 3.7 billion years ago in Earth’s roughly 4.5 billion year history.

For simple organisms to appear so quickly in the fossil record, there wasn’t enough time for chemical reactions to start with simple molecules of two or three atoms.

The new discovery of 1-cyanopyrene in the Taurus Molecular Cloud shows that complex molecules can indeed survive the harsh conditions in which the solar system formed. So when pyrene emerged on the early Earth about 3.7 billion years ago, it could have been the backbone of carbon-based life.

This discovery is also related to another important discovery of the past decade – propylene oxide, the first chiral molecule in the interstellar medium. We needed chiral molecules for the evolution of simple life forms to work on the surface of the early Earth.

So far, our theory that the molecules of early life on Earth came from space looks good.

This article is republished from The Conversation under a Creative Commons license. Read the original article here.

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