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Astrochemist Christopher Arumainayagam and his students create super cold conditions in his laboratory at Wellesley College to imitate temperatures in the ISM (Inter Stellar Medium), where stars form.
What’s the coldest you have ever been? Where were you when this happened?
Is there life anywhere in outer space — living organisms that exist outside of our planet? What does a physical chemist who studies atoms and molecules that may have helped create the first life here on Earth have to say about the answer to that question? Read on to find out.
Physical Chemist Christopher Arumainayagam, an astrochemist, praises the education he received as a child in Sri Lanka, off the coast of India. His parents were both doctors, “so I had a lot of mentoring.” He remembers his mother reading chemistry and biology textbooks to him when he was ill, “trying to explain … the biology that is still a mystery to me.”
Allen Abraham, Christopher’s great-grandfather, “was I believe one of the first people in Asia to be given the fellowship of the Royal Astronomical Society: he was my hero and he is still my hero.” He studied Halley’s Comet, which comes close enough to be seen from Earth every 75-79 years and was nearby in 1910. Many decades later, Christopher himself would do work related to comets.
Harvard College brought Arumainayagam (pronounced “Ah-roo-my-NY-ah-gahm”) to the United States on what he calls “essentially a full scholarship.” He majored in chemistry and physics and then went to Stanford to do his PhD in chemical physics. At the time, he was not aware of astrochemistry, but “one of my colleagues in astronomy told me decades later that my research seemed relevant for understanding what’s going on in interstellar ices.”
Arumainayagam wrote his doctoral thesis on adsorption — the process by which atoms or molecules stick to a surface. (Absorption involves particles sinking below the surface.) Adsorption is an important part of catalysis — speeding up chemical reactions. And catalysis is enormously important. In Arumainayagam’s words, “One third of the U.S. economy involves a catalytic step.” When we make semiconductors, which are used in computers and other electronics, or the ammonia that’s used in fertilizer, for instance, we rely on chemical reactions sped up by catalysts.
Chemical reactions happen very quickly. When he teaches reaction dynamics, Arumainayagam tells students about processes understood only now that it is possible to take photographs of those reactions every femto-second. Just a few decades ago, scientists had to hypothesize about how those reactions work and the most important steps could not be pieced together.
Then, femtosecond spectroscopy was developed and the transitions between different chemical states could be captured “in exquisite detail.” (A femtosecond is 10^-15 of a second. That’s .000000000000001 seconds … a quadrillionth of a second. When Math4Science spoke with Arumainayagam, scientists working at the speed of 10^-18 of a second — an attosecond — had recently received the Nobel prize in physics. How much faster are the events they are analyzing? What is a “zeptosecond?” Arumainayagam tells us that scientists working towards analyzing time down to zeptoseconds are creating what is “going to be a very exciting field, mostly in physics but it has applications for chemistry” as well.)
The experiments Arumainayagam and his students at Wellesley College do help them explore how matter behaves in outer space. Recently, they showed that “electrons produced by cosmic rays interacting with interstellar ices” may have helped create the molecules necessary to generate life. “That was all pure math,” he told Math4Science. “It was a Fermi problem,” involving evidence-based estimation.
Mentally head for a space ship and travel into outer space. At first, you’ll be traveling through the Milky Way galaxy, where Earth is located. If you move beyond the Milky Way, you will enter the intergalactic medium (IGM): the space between galaxies, where scientists believe there may only be, on average, one atom per cubic meter.
Head back into the Milky Way (or another galaxy, if you’re feeling adventuresome) and you will be in the space between stars: the ISM or interstellar medium. Here, you’ll encounter, on average, one atom per cubic centimeter: lots more stuff than in the IGM…but much less of it than we have here on Earth.
The conditions between the stars (in the ISM) are very different from conditions here on our planet. Temperatures get very, very low out there: on average, the ISM is 2.7 Kelvin. All motion stops at 0 Kelvin, which is known as “absolute zero.” Think about how cold you feel at 0 degrees Fahrenheit (32 degrees below the temperature at which water freezes)… or even at 0 degrees Celsius (that’s freezing temperature, for water, or 32 degrees F). Cold, right? 2.7 Kelvin is -454.81 degrees Fahrenheit: more than 454 degrees below zero! -270.45 degrees Celsius is the average temperature in outer space, 2.7 Kelvin.
To learn more about Kelvin, Celsius, and Fahrenheit and how to go from one way of measuring temperature to another, check out this Math4Science worksheet.
In laboratories on our planet, it was not possible to cool things down below 95 Kelvin until about thirty years ago, according to Arumainayagam. (There was a way, but it was very costly and complicated.) That temperature was achieved using liquid nitrogen. It was quite cold … but a fair amount warmer than the average temperature in the ISM.
Now, in an ultra-high vacuum (10^(-10) Torr) chamber in Arumainayagam’s lab, he and his students can get the temperature down to 10 Kelvin, using helium. Arumainayagam explains that their ultra-high vacuum chamber contains “basically a helium refrigerator.” 10 Kelvin is the temperature of the ice that surrounds dust in star-forming regions of the ISM…before the new star warms them up.
Remember how few atoms there are in the ISM — about one per cubic centimeter? Dark, dense molecular clouds where stars form contain about one million molecules per cubic centimeter. That means that the pressure in the star-forming regions can also get very low — even below 10^-10 Torr, more than a trillion times lower than atmospheric pressure here on Earth, which is 760 Torr. (Torr, atmospheres, bars, and pascals are different units for measuring pressure. What is pressure itself? Mechanical Engineer Alex Fowler describes it as “the force exerted by a fluid (gas or liquid) against whatever is seeking to constrain its volume.” So it’s the force of the air you blow into a balloon against the balloon’s membrane or the force of atoms and molecules against “whatever surrounds them.”)
Arumainayagam and his students use four different kinds of pumps to reduce the pressure in the ultra-high vacuum chamber to 5×10^(-10) Torr.
One of Arumainayagam’s goals in his lab is to compare the effects of photons (tiny particles of light) to electrons (negatively-charged particles). When they collide with atoms or molecules in the ices in the ISM, what happens?
Arumainayagam and his students cooled a film of water to 10 K and exposed it to high-energy electrons whose energy was as high as 1,000 electron volts…enough to break a chemical bond. Having done that (exposed water to conditions similar to those in the ISM, in the dust where a star is forming), they were able to identify hydrogen peroxide H2O2 desorbing from the film during electron irradiation.
Until the early twentieth century, scientists were not even aware that there were molecules beyond planet Earth. “I think they thought that what existed in outer space were just atoms.” Arumainayagam believes his predecessors assumed that the cold temperatures, low pressure, and high ionizing radiation of outer space were too “hostile to the synthesis of molecules.”
A century ago, Annie Jump Canon studied astronomy and physics at Wellesley College, where Arumainayagam and his students explore the ways molecules are created in outer space. She later “catalogued hundreds of thousands of stars” at Harvard University.
“Her method of categorizing stars is still used today” and Arumainayagam calls her accomplishments “stunning. I think she was the first person to discover what is called diffuse interstellar bands” — bands that come from outer space molecules. In other words, Canon’s research in the 1920s helped scientists figure out that yes, molecules exist in the interstellar medium. Since then, over 250 molecules have been found in outer space in the ISM.
Does Arumainayagam believe there’s life outside Earth? “There might be,” he told Math4Science, “but I don’t think we’re going to find evidence, certainly not in my lifetime and maybe never.” Why not? Because planets that might be able to support life are at such great distances from us. “What is possible, perhaps, is life in the oceans below ices in some of the moons surrounding Jupiter and Saturn: these are called ocean worlds.”
More interesting to Arumainayagam is the question “‘Where did we come from?’” He believes the answer “lies among the stars. The very act of forming a new star provides the ingredients necessary” to create molecules that make life possible. When those molecules end up in asteroids and on meteorites, they “could rain upon a newly formed planet and provide the ingredients for life to begin.” Look up “molecular panspermia” to learn more about this theory of the origins of life.
Are you curious about exactly what’s out there in the interstellar medium? Professor Arumainayagam suggests that you check out Jacob Berkowitz‘s book Stardust Revolution, in which he claims that “the stardust revolution is the third scientific revolution, after Copernicus and Darwin.” Arumainayagam explains that “we can trace every atom in our body to the stars — the atoms in your left hand might have come from one star and the atoms in your right hand might have come from another.”
And he also recommends that you watch videos about astrochemistry, like this one, starring Neil DeGrasse Tyson. “The way he starts from stars and then ends up with humanity and talks about how everyone is interconnected is just done so beautifully.” In DeGrasse Tyson’s words, “we are stardust” — “the universe is in us.”
