What is so special about carbon is that it’s doubtful (although possible) that life could have used something other than carbon. Each carbon atom can form four strong bonds that allow for an extraordinary variety of long-chain molecules, notably proteins, lipids, sugars and DNA, according to evolutionary biologist, Anthony Lane in The Vital Question: Energy, Evolution, and the Origin of Complex Life. Silicon, for example, can’t manage anything close to this complexity.
Carbon Equals “Complexity”
A new discovery shows complex carbon molecules can form and survive in the harsh environment of interstellar space. “In some ways, life can be thought of as the ultimate in chemical complexity,” said Martin Cordiner of the Catholic University of America about NASA’s Hubble Space Telescope confirmation of the presence of electrically-charged molecules in space, pointing toward a strong likelihood for other extremely complex, carbon-bearing molecules arising spontaneously in space.
“The presence of 60 carbon atoms (C60) unequivocally demonstrates a high level of chemical complexity intrinsic to space environments,” adds Cordiner.
Scientists using NASA’s Hubble Space Telescope have confirmed the presence of electrically-charged molecules shaped like soccer balls, shedding light on the mysterious contents of the interstellar medium (ISM) – the gas and dust that fills interstellar space.
Since stars and planets form from collapsing clouds of gas and dust in space, “The diffuse ISM can be considered as the starting point for the chemical processes that ultimately give rise to planets and life,” said Cordiner. “So fully identifying its contents provides information on the ingredients available to create stars and planets.”
Cordiner, who is stationed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, is lead author of a paper on this research published in the Astrophysical Journal Letters.
A Form of Carbon Called “Buckminsterfullerene”
The molecules identified by Cordiner and his team are a form of carbon called “Buckminsterfullerene,” carbon cages also known as “Buckyballs,” which consists of 60 carbon atoms (C60) arranged in a hollow sphere. C60 has been found in some rare cases on Earth in rocks and minerals, and can also turn up in high-temperature combustion soot.
C60 has been seen in space before. However, this is the first time an electrically charged (ionized) version has been confirmed to be present in the diffuse ISM. The C60 gets ionized when ultraviolet light from stars tears off an electron from the molecule, giving the C60 a positive charge (C60+).
Everything you need for life is out there in certain space environments. But where do these molecules come from?”
The Diffuse ISM
Interstellar space is bombarded with cosmic rays and ultraviolet radiation that typically dissociates (breaks up) molecules before they have a chance to form long chains or structures. “The diffuse ISM was historically considered too harsh and tenuous an environment for appreciable abundances of large molecules to occur,” said Cordiner. “Prior to the detection of C60, the largest known molecules in space were only 12 atoms in size. Our confirmation of C60+ shows just how complex astrochemistry can get, even in the lowest density, most strongly ultraviolet-irradiated environments in the Galaxy.”
“The diffuse interstellar medium is a very harsh environment, so tenuous that chemical encounter reactions are very slow and where UV can destroy molecules,” explains astrobiologist Bernard Foing, at Leiden University and advisor to the ESA in an email to The Daily Galaxy. “However C60+ is a strong survivor to these conditions without breaking its beautiful and magical cage. What other complex molecules could be synthetized in the outflow of dying stars or in interstellar clouds, and survive these UV conditions ? Our search is still open.”
Most of the ISM is hydrogen and helium, but it’s spiked with many compounds that haven’t been identified. Since interstellar space is so remote, scientists study how it affects the light from distant stars to identify its contents. As starlight passes through space, elements and compounds in the ISM absorb and block certain colors (wavelengths) of the light. When scientists analyze starlight by separating it into its component colors (spectrum), the colors that have been absorbed appear dim or are absent. Each element or compound has a unique absorption pattern that acts as a fingerprint allowing it to be identified.
Diffuse Interstellar Bands (DIBs) –Different from any known atom or molecule on Earth
However, some absorption patterns from the ISM cover a broader range of colors, which appear different from any known atom or molecule on Earth. These absorption patterns are called Diffuse Interstellar Bands (DIBs). Their identity has remained a mystery ever since they were discovered by Mary Lea Heger, who published observations of the first two DIBs. In 1922 Heger saw that there were absorption features in the spectra of starlight, with different intensities, widths and shapes called diffuse interstellar bands and are caused when starlight passes through interstellar clouds that contain a higher density of hydrogen atoms, grains of material.
A DIB can be assigned by finding a precise match with the absorption fingerprint of a substance in the laboratory. However, there are millions of different molecular structures to try, so it would take many lifetimes to test them all.
DIBs indicate the presence of a large amount of carbon-rich molecules in space”
None has been conclusively identified
“About 500 diffuse Interstellar Bands have been observed in spectra towards distant stars, they are suspected to be large organics, but their identification is an unsolved mystery for more than 110 years,” wrote Foing in his email to The Daily Galaxy. “As of today C60+ is the only molecule identified as a DIB carrier. We could expect it to host and catalyze reactions on its surface leading to other intriguing compounds still to be detected.”
“Together, the appearance of the DIBs indicate the presence of a large amount of carbon-rich molecules in space, some of which may eventually participate in the chemistry that gives rise to life,” notes Cordiner. “However, the composition and characteristics of this material will remain unknown until the remaining DIBs are assigned.”
Decades of laboratory studies have failed to find a precise match with any DIBs until the work on C60+. In the new work, the team was able to match the absorption pattern seen from C60+ in the laboratory to that from Hubble observations of the ISM, confirming the recently claimed assignment by a team from University of Basel, Switzerland, whose laboratory studies provided the required C60+ comparison data.
.Hubble Detects Faint Fingerprints of C60+
The big problem for detecting C60+ using conventional, ground-based telescopes, is that atmospheric water vapor blocks the view of the C60+ absorption pattern. However, orbiting above most of the atmosphere in space, the Hubble Space Telescope has a clear, unobstructed view. Nevertheless, they still had to push Hubble far beyond its usual sensitivity limits to stand a chance of detecting the faint fingerprints of C60+.
Observed Stars were Blue Supergiants
The observed stars were all blue supergiants, located in the plane of our Galaxy, the Milky Way. The Milky Way’s interstellar material is primarily located in a relatively flat disk, so lines of sight to stars in the Galactic plane traverse the greatest quantities of interstellar matter, and therefore show the strongest absorption features due to interstellar molecules.
The detection of C60+ in the diffuse ISM supports the team’s expectations that very large, carbon-bearing molecules are likely candidates to explain many of the remaining, unidentified DIBs. This suggests that future laboratory efforts measure the absorption patterns of compounds related to C60+, to help identify some of the remaining DIBs.
The team is seeking to detect C60+ in more environments to see just how widespread buckyballs are in the Universe. According to Cordiner, based on their observations so far, it seems that C60+ is very widespread in the Galaxy.
The Last Word
Chemist John P. Maier, a Fellow of the Royal Society and currently Chair of Physical Chemistry at the University of Basel, where he leads the Maier Group who strive to determine the properties of important carbon-containing compounds, wrote in an email to The Daily Galaxy:
“First of all the 2018 Hubble detection is not of C60 but just a confirmation of the first reported identification of C60+ in 2015. This was followed by several papers supporting this as well as identification of two to three further DIBs due to C60+. C60 was actually identified in space in 2010 by its infrared bands- J. Cami et al, Science 329, 1180, 2010. The Hubble 2018 article has nothing to do with this.”
After two decades of research, Maier, confirmed in 2015 the hypothesis that deep space is littered with buckyballs, the molecules responsible for unusual features in the spectra of starlight, known as diffuse interstellar bands (DIBs).
“Microwave spectroscopists have identified the simplest molecules required for building up DNA in places like interstellar clouds,” Maier said in a 2015 interview. “Everything you need for life,” he observed, “is out there in certain space environments. But where do these molecules come from?
“Back in 2010, astronomers found C60 in planetary nebulae [clouds of material ejected from aging stars], and now you see C60+ in the interstellar clouds, so maybe this is the source of carbon. After all,” Maier concluded, “there are cosmic rays and all sorts zapping it, so maybe this breaks up C60 to provide the simplest carbon molecules. I think people trying to explain the formation of these molecules will have a heyday now with C60+.”
The false color image at the top of the page shows a diffraction pattern from the first interstellar dust candidate Orion, collected by NASA’s Stardust spacecraft in 2004 (Zack Gainsforth).