The Measure of Life: The Scientific Search for Alien Life  

by Maurice Pinzon

In 1665, Isaac Newton was studying at Trinity College in Cambridge when the bubonic plague spread to the college town. The school closed, forcing him to go home, where he had his miracle year, formulating laws of gravity, optics, and calculus. However, according to scholars and Thomas Levenson at The New Yorker, Newton’s memory may be faulty, the truth less legendary, putting the miracle year in question. Newton may have spent his time consolidating knowledge in the fields that would later serve his remarkable scientific breakthroughs.

But I still wondered if, in our time of pandemic, there’d come a day when this year would be remembered, not just for COVID-19 but also for significant scientific breakthroughs. There’s one area where it could happen, and it’s not Navy pilots observing extraterrestrial spacecraft off the U.S. coast. Until there’s concrete data, that’s not science. It’s optics and recollection.

Nonetheless, there may be a scientific story about alien life this year, but on a very different border.

At the University of Glasgow in Scotland, scientists recently announced a new theory to detect alien life. The laboratory team claims they have a scientifically rigorous universal method that can detect life anywhere people can send probes into space. The driving force behind this scientific exploration is Professor Lee Cronin, Regius Chair of Chemistry at the University of Glasgow. Professor Sara Walker, an astrobiologist and theoretical physicist at Arizona State University, has assisted Professor Cronin with theoretical insights.  

Cronin said the other day, “I’m a chemist. The only thing I know how to do is do stuff with chemicals.” His comment was clearly modest as he leads a chemistry laboratory, where he runs daring experiments using chemicals and machines to test theories of life that he’s thought about for a long time. He has successfully compiled some of his ideas into scientific theories.

Cronin’s collaboration with Walker, who is also interested in the origin of life, has been invaluable. In their discussions, her insights about physics, life, and information, convinced him they were on a promising path. Their intellectual collaboration and his experiments have been presented in a paper published in May in the prestigious peer-reviewed science journal Nature, titled, “Identifying molecules as bio-signatures with assembly theory and mass spectrometry“.

That paper may have significant, even revolutionary implications, for how we think about the biochemistry of life.

“People will propose biosignatures based on features of life as we know it on earth, and then we go look for those elsewhere. But they’re not really telling us anything about the nature of life, or what it is that we’re actually discovering,” Walker said.  

The Nature paper, Walker added, is “the first approach where you have this really deep connection between these theoretical ideas about the nature of what life is and what it might be doing, and the experiments that allow us to start actually scaffolding toward a deeper understanding of what’s the phenomena that we’re talking about.”  

“This idea that living systems are the only systems that can actually use information to produce specific complex objects in the universe. It ties to a lot of features that we might more typically associate to life and our definitions for it. But it has this sort of deeper set of principles that are more like how we talk about universal laws and physics,” said Walker.  

Walker concluded, “I’m very excited about this idea that we might actually be able to get at ways of merging some very powerful, predictive theories about the nature of life with these experimental systems that are able to fly, and actually go look for it.”

Cronin and Walker have theorized a fundamentally new way to see life, not only as it is on Earth, but also anywhere in the world. It’s as if they repurposed Chomsky’s theory of universal grammar, applied it to life, and figured out a way to measure it. A deep structure of life’s biosignature.  

Cronin doesn’t mind being challenged about all this. He seems to thrive on the vigorous back and forth discussions. However, he also wants a fair hearing by the orthodox thinkers in physics and biochemistry. He’s not shy about cutting you off mid-sentence to tell someone that they’re wrong when he vehemently disagrees. The next minute if he finds someone’s question or argument insightful, he will respond with “brilliant”. Cronin can also be disarmingly modest, charming, and generous. He’ll often end an exchange with, “does that answer your question?” He’s also quick to give credit to the Glasgow laboratory team for developing procedures and running experiments to test the theories that have been percolating in his mind.  

One place outside the laboratory where detecting life is vital is NASA’s search for alien life beyond Earth because NASA’s probes to other planets might not detect life if the biochemistry there is different from Earth’s.

Cole Mathis, a co-author of the Nature paper and a member of the lab team, explained why another way of looking for life was needed when he stated, “What we really needed was a way to think about” whether there are “organisms out there that are using – not DNA, not RNA, not ATP.” This is why what was needed was a more fundamental theory of life, accompanied by a scientific technique to measure it anywhere in the universe. Mathis said, “Lee and Stuart [Marshall], the first author on the paper, came up with this way to quantify the complexity of a molecule in terms of the number of steps you need to make that molecule. The team named it molecular assembly (MA) defined as the minimum number of steps it takes to make the molecule.”  

Molecular assembly (MA), complexity, information? What does all that have to do with the living organisms?  

Mathis said MA was a new theory where, “you realize that the only way you know very specific things are able to be made, is because of that information.” Mathis explained it means “this hypothesis that only living systems, because they are able to process information, would be able to make really complex molecules, really high [levels of molecular assembly] MA molecules.” Mathis added, “the more complex a molecule is the more pieces it breaks into. If you can count up the number of pieces you can say how complex is this molecule even if you don’t know exactly what the identity of the molecule is.”

The idea originated with Professor Cronin, Mathis said. “He realized that he could – we can – use mass spectrometry to break a molecule up and count the number of pieces that it breaks into. That the number of pieces that it breaks into should roughly give you an idea of the complexity, that’s the MA.”

In the Nature paper, the authors wrote, “We show why complex molecules found in high abundance are universal biosignatures and demonstrate the first intrinsic experimentally tractable measure of molecular complexity, called the molecular assembly index (MA).”

To do this, the Glasgow lab team used mass spectrometry to measure lots of different stuff. Rocks, a meteorite, ancient Antarctica biology, yeast, E. coli, homemade beer, and Scotch whiskey – the lab is in Scotland after all. These samples were analyzed with a mass spectrometer to test whether only complex molecules uniquely resulted in living samples precisely because of their MA index number. Mathis said, “living systems are as far as we can tell, uniquely able to make these very complex molecules. When we see those complex molecules, we know that they were made by life. The chance that they were made by any non-living process is exceedingly small to the point where you shouldn’t even consider it as possible.”

Cronin added, “We don’t need to know anything about the molecules. We’re able to basically tell if there’s intrinsic information in the object. But it’s not just one object. When you detect these molecules in the mass spectrometer you have to detect many identical copies. And that’s when you kind of go. Oh! Holy smokes! There’s something going on here.”  

The AMU [atomic mass units] is important, Cronin clarified, because “what we found is that right around about 600 [AMU] in our mass spec, although you should have a combinatorial explosion, if everything was possible, what you see physically is a drop off. That means you can tell the difference between the noise and interesting things that were happening.” Interesting things because it’s not simply about molecular weight, but the numerous differing fragments. If Cronin’s theory is correct, this complex information pattern is the signature of life.    

As the authors wrote in the Nature paper: “By mapping the complexity of molecular space it is possible to place molecules on a scale of complexity from those able to form abiotically to those so complex they require a vast amount of encoded information to produce their structures, which means that their abiotic formation is very unlikely.”

Jim Green, NASA’s Chief Scientist, was ecstatic about the paper’s results. Green said, “This, to me, is an absolute game changer!”  

Cronin had presented his idea to Green a few years back before these most recent results were published. Green was intrigued. He said Cronin’s MA theory “had a number of profound effects to the NASA program.” Professor Cronin had told Green the mass spectrometer had to read beyond a particular threshold, above 150 AMU in size. In that range, Green said, “you’re now getting into the regime where they can’t be randomly put together, particularly if you find a whole lot of them.”

There have been NASA missions with mass spectrometers. The Cassini spacecraft visited Saturn and its moons. It ended after Cassini dived into Saturn’s atmosphere in September of 2017. On NASA’s website, Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, said one of those moons, Enceladus, should be considered “as a possible habitat for life.”

But according to Green, the mass spectrometer on Cassini’s instruments weren’t sensitive enough to reach the Cronin threshold. Green said, “The end story of that is how disappointed I was to learn that the ability of the mass spectrometer could only go up to 150 AMU. So even though we might have wonderful indications of life that go into the instrument, it couldn’t measure it. That changed my thinking from then on that we were never going to fly mass spectrometers out into the solar system with such a low range in atomic mass units.”  

According to Green the Curiosity Mars rover, “has a mass spectrometer on it that goes well above 600, atomic mass units.” Curiosity landed on Mars in August 2012. Green said he was very excited about the paper’s results. “And what it’s done to our program is really changed it.”

About Maurice Pinzon

Maurice Pinzon writes an opinion column.
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