Stars are the engines of creation in many ways. Your energy drives a whole series of processes that are necessary for life. Scientists believed that stellar radiation was needed to make compounds like the amino acid glycine, one of the building blocks of life.
However, a new study found that glycine was detected in comets that formed in deep interstellar space when there was no star energy.
What natural processes created the building blocks from which life emerged? This question drives a lot of research. We know that amino acids like glycine are vital, but scientists lack a full understanding of how these building blocks are formed.
Of the roughly 500 known amino acids, glycine is the simplest and one of the 20 amino acids in the genetic code. It is not one of the essential amino acids as it can be synthesized in the human body.
For example, scientists have found glycine in the comet of comet 67P / Churyumov-Gerasimenko and in comet Wild-2. In recent years, scientists have discovered other complex organic molecules (COMs) in meteorites. However, our understanding of how complex molecular building blocks form is far from complete. And without this understanding, we will never find out how life began here on earth.
Scientists discovered glycine in the coma of comet 67P / Churyumov-Gerasimenko. In this picture, Rosetta's scientific camera OSIRIS shows the sudden onset of a well-defined beam-like feature that occurs on the side of the comet's neck in the Anuket region. Photo credit: ESA / Rosetta / OSIRIS
Comets are considered ancient archetypes. They formed directly from the solar nebula when the planets and the sun wanted to form. Finding glycine in comets means that it can be made without direct input of star energy. This has an impact on how widespread this simplest building block can be and how likely it is that life will arise.
The production of glycine with no energy from a star is called "dark chemistry". Now a team of researchers has carried out laboratory simulations of the interior of dark interstellar clouds. These simulations generated methylamine, a precursor to glycine, and then showed that glycine can form itself.
"Dark chemistry means chemistry without energetic radiation," says Sergio Ioppolo from Queen Mary University in London. Ioppolo is the lead author of a new article published this week in Nature Astronomy. The article is entitled "A non-energetic mechanism for glycine formation in the interstellar medium".
“In the laboratory we simulated the conditions in dark interstellar clouds: 10-20 K (-263 C to -253 C) cold dust particles are covered by thin layers of copious ice – frozen CO, NH3, CH4 and H2O – and then processed by Atoms are hit, thereby fragmenting precursor species and recombining reactive intermediates, ”lead author Ioppolo said in a press release.
Artist's impression of the molecule glycine together with dark interstellar clouds in the laboratory. (c) Harold Linnartz
The glycine precursor methylamine was detected in the coma of comet 67P together with glycine itself. Another glycine precursor, ethylamine, has also been detected. In a 2019 paper titled "Dispersed Glycine in Comet 67P / Churyumov-Gerasimenko," the researchers concluded that the glycine observed likely originated from "glycine molecules embedded in water ice that sublimated from the dust particles that are expelled from the ice core. "In the laboratory process of this new study, water ice was essential for the eventual formation of glycine.
The most important finding from this study is that glycine, a basic building block of life and the simplest amino acid, is in the form of a planet, embedded in the original ice of the comet.
“The important conclusion from this work is that molecules, which are considered to be the building blocks of life, are already formed at a stage well before the start of star and planet formation,” says study co-author Harold Linnartz, director of the laboratory for Astrophysics at Leiden Observatory. “Such an early formation of glycine in the development of star-forming regions implies that this amino acid can be formed more ubiquitously in space and is retained in the bulk of the ice before it is taken up in comets and planetesimals, which make up the material that ultimately becomes Planets are made. "
This figure from the study contrasts its findings with previous research. The new results show that glycine can form on water-rich, imaginary ice grains and requires neither heat nor UV energy. Photo credit: Ioppolo et al., 2020.
This is a very different result from some previous studies. Previous work indicated that UV radiation was required for the formation of glycine.
One of the strengths of these lab simulations is that they can compress time. A day of lab work can be a surrogate for millions of years in a cold, dark interstellar cloud. "The result is that small but significant amounts of glycine can be formed in space over time," said co-author Herma Cuppen (Radboud University, Nijmegen), who was responsible for some of the modeling studies featured in Nature Astronomy .
Glycine is a real building block. This can lead to the formation of more complex molecules, which means that these too can form via the dark chemistry.
“Once formed, glycine can also become a precursor for other complex organic molecules,” concludes Sergio Ioppolo. "Using the same mechanism, in principle, other functional groups can be added to the glycine backbone, resulting in the formation of other amino acids such as alanine and serine in dark clouds in space."
The Murchison meteorite fell to Earth in Australia in 1969. It contained 15 amino acids, including glycine. Photo credit: According to user: Basilicofresco – derivative work of image: Murchison meteorite.jpg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4301968
In their work, the research team summarizes their work: “An early formation of glycine in the evolution of star-forming regions implies that glycine can be formed more ubiquitously in space and conserved in the bulk of polar ice types before it is trapped in meteorites and comets during the Planetary formation in protoplanetary disks surrounding newborn stars. Once formed, prestellar glycine can also become a precursor species for more complex molecules through “energetic” and “non-energetic” surface reaction pathways. "
The fact that glycine can form in the cold darkness of interstellar space, prior to any interaction between a planet and a star, could significantly change our understanding of the origins of life. This study shows how primary building blocks can be easily created in unlikely locations. After they were created in primordial bodies like comets, they were eventually given over to planets like Earth.
"The bottom line is that glycine and possibly other building blocks of life are expected to be present, at least in the solid phase, in many star-forming environments, including the coldest and earliest stages of solar-type systems formation," the authors write.