Surprising reservoir full of molecules found in space

March 18, 2021

Space might hold a wealth of molecules. (Center for Astrophysics | Harvard & Smithsonian, M. Weiss)

Scientists have located tons of essential aromatic compounds in a special yet unexpected laboratory that's naturally conducive to examining the highly reactive and typically transient molecules: outer space.

Researchers from NASA, Massachusetts Institute of Technology and other prominent institutions around the world have added two aromatic compounds to a staggering amount of new molecules recently found to exist within a cold, dark, space-borne cloud. Their findings, published Thursday in Science, could broaden the of field of chemistry as it's known.

Aromatic compounds are essential for life, but they're very difficult to study because most can't be isolated or manipulated in a standard laboratory setting without quickly reacting away.

"Observing molecules in space does provide a unique laboratory that we don't have access to here on Earth," said Brett McGuire, lead author of the study and an assistant professor of chemistry at MIT. "It allows us to study more complex molecules than we have, basically, ever been able to study before."

McGuire is the principal investigator of the large-scale project that headed the discovery, called GOTHAM, or Green Bank Telescope, GBT, Observations of TMC-1: Hunting Aromatic Molecules. TMC-1 is the cloud where the molecules were found. Over the course of nine papers published in the last seven months, GOTHAM has found many there. 

"What these studies allow us to do are simply learn more about fundamental chemical reactions and principles," he said. "Every time you learn one of those, it affects the overall theory of chemistry."

Not only is the sheer magnitude of the vast collection of molecules exciting — they have never before been seen in space — but their being aromatic compounds supplies a huge element to the discovery, McGuire told The Academic Times. 

The discovery of the new molecules, technically called polycyclic aromatic hydrocarbons, or PAH, means scientists can use this "space laboratory" to thoroughly study the large, complex compounds vital for life on Earth.

Aromatic compounds are classic organic chemistry molecules characterized by their carbon rings. Every single living thing on Earth is made up of carbon; 18% of the human body consists of carbon alone. Carbon is most stable and reactive when in the form of a ring, because of the way that the atom's electrons are structured. 

"If you look in databases of all the known molecules to mankind, something like 80% of them have a five- or six-membered ring," McGuire said. "A huge number of those rings will be aromatic."

The downside of the structure's reactivity is that it raises the likelihood of the ring bumping into something in the air, particularly because Earth has very high air pressure. 

As it turns out, this isn't an issue in space, where, "Molecules can go minutes or hours or days without bumping into something else and reacting away," McGuire explained.

The theory of PAHs subsisting in space traces back to the 1980s, said McGuire, but he and his team are the first to actually prove it. 

"This provides us the first definitive proof that these hypotheses that we've been tossing around for the last three decades is actually correct," he said. "These molecules are out there." 

Another striking factor is where the PAH compounds were found. These molecules were previously suspected to only reside in the atmospheres of dying stars. That's because on Earth, the compounds come about when things are burned with very high energy; a common example is charring vegetables. 

"We found them in this cold, dark cloud, as far away from a dying star that you can get," he said. "That means that either they were made in an old star and survived the masses of space … or they were built from the ground up using some type of chemical process we haven't heard about before." 

McGuire and his team aren't the only ones working on locating and studying these space-borne molecules. If the scientists have slowly been shopping for them, then this milestone was like opening a back door to the warehouse, the researchers said.

"It's not just us; this source has been known to be rich in molecules for some time," McGuire said. "There's an entire other team based out of Spain right now that's looking with a different telescope at slightly different frequencies of light and discovering additional molecules."

The findings even show promise to help physicists understand how carbon is moving and evolving as stars and planets form. 

McGuire says the next step for his team is to map out every molecule and understand how they react alone and with each other, as well as how they die. 

"When you're looking at molecules in space, you need to see not how much of one molecule is there, but you need to see how much a whole bunch of molecules that are chemically related to it are there," he said. "Then, you can start asking questions. Which ones are being formed, which are being destroyed and how are they reacting together?"

The researchers are also looking into other similar locations in the universe, in hopes of detecting even more molecules. McGuire urges scientists to test the boundaries of the crossover between chemistry and radio astronomy.

"I certainly didn't think three years ago that pointing a radio telescope at this source, we would detect PAHs. It was such a radical idea to me. But, here we are," he said. "Now, we have to plow ahead and see what else is hiding there." 

The paper, "Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering," published March 18 in Science, was authored by Brett A. McGuire and Kin Long Kelvin Lee, Massachusetts Institute of Technology; Ryan A. Loomis and Anthony J. Remijan, National Radio Astronomy Observatory; Andrew M. Burkhardt and Michael C. McCarthy, Center for Astrophysics | Harvard & Smithsonian; Christopher N. Shingledecker, Benedictine College; Steven B. Charnley and Martin A. Cordiner, NASA Goddard Space Flight Center; Ilsa R. Cooke, Institut de Physique de Rennes; Eric Herbst, Eric R. Willis, Ci Xue and Mark A. Siebert, University of Virginia; and Sergei Kalenskii, Russian Academy of Sciences. 

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