“Now it appears the opposite is true,” MPIA researcher Kamber Schwarz comments, of long-standing debate about the cosmic origin of life. Discovery of complex organic molecules potential precursors to life within the protoplanetary disk around V883 Orionis has reopened debate over whether the raw materials of Earth are local or cosmic.
The Atacama Large Millimeter/submillimeter Array high in the Chilean Atacama Desert recently allowed astronomers to identify17 complex organic molecules in the disk around outbursting protostar V883 Ori, including the first preliminary detections of ethylene glycol and glycolonitrile. The molecules, each containing more than five atoms and at least one carbon, are regarded by astrochemists to be prebiotic building blocks for sugars, amino acids, and even nucleic acids the principal building blocks of life. Glycolonitrile, for instance, is a direct precursor to both glycine and alanine, and the nucleobase adenine, the basis of DNA and RNA.
What is so astonishing about this discovery is not only the presence of these molecules, but that they had survived the catastrophic transition of protostar to star. When a protostar explodes, it emits enormous radiation and high-energy outflows which, according to previous theories, could “reset” the chemical budget, wiping off any advanced chemistry accumulated in earlier stages. This so-called reset hypothesis had suggested that each planetary system would have to synthesize its own prebiotic molecules de novo, setting a constraint on the universality of the chemical origin of life.
But the latest results from V883 Ori tell a different story. “Our results suggest that protoplanetary disks inherit complex molecules from earlier stages, and the formation of complex molecules can continue during the protoplanetary disk stage,” Schwarz describes. The timescale between the energetic protostellar stage and the establishment of a protoplanetary disk is, in itself, too brief for COMs to be formed in detectable quantities. Their survival through this turbulent stage implies that the ingredients for life are not only being built in space but that they are widespread throughout the galaxy Complex organic molecules in disk of young star suggest cosmic origin of life.
ALMA’s detection capabilities lie at the core of this discovery. “Complex molecules, including ethylene glycol and glycolonitrile, radiate at radio frequencies. ALMA is perfectly suited to detect those signals,” Schwarz explains. The radio interferometer’s high sensitivity allowed astronomers to detect weak spectral signatures, the telltale signs of the molecules being expelled from icy grains by the protostar’s outbursts. This process mimics what occurs in our solar system, where sunlight’s heat on comets expels gases and allows spectroscopy to determine their chemical makeup.
Laboratory simulations have further illuminated how these molecules arise. Research shows that UV irradiation of ethanolamine can yield ethylene glycol, which is evidence for the potential formation of such molecules under early interstellar conditions and subsequent UV-rich periods of molecular evolution COMs are found in interstellar ices, and thus are additional proof of a solid-state origin of these species in star-forming regions. Similarity in the ice composition in comet 67P to protostars like IRAS 2A is proof of direct inheritance from the protostellar stage to planetary bodies.
Survival of such molecules in the energetic turmoil of star formation is no simple feat. Radiative transfer modeling, including Monte Carlo calculations using the radmc-3d code, has demonstrated that the destiny of astrophysical ices and the embedded COMs hangs by a thin thread of temperature, density, and radiation. Where external ultraviolet fields are intense, as in the protostar Elias 29, photodissociation jeopardizes survival of these molecules. Heating events in V883 Ori, on the other hand, seem to liberate and isolate COMs, instead of annihilating them survival of astrophysical ices in star formation regions hinges on the appropriateness of temperature, density and radiation conditions.
The implications extend far beyond a single star system. “Our finding points to a straight line of chemical enrichment and increasing complexity between interstellar clouds and fully evolved planetary systems,” says Abubakar Fadul, lead author of the study. If COMs are indeed inherited and preserved across the star and planet formation process, then the chemical prerequisites for life may be common throughout the cosmos.
As the cosmos continue to be probed by astronomers with ALMA, the James Webb Space Telescope, and sophisticated lab models, the inventory of prebiotic molecules found grows. With every discovery, we draw closer to understanding whether the birthplace of life is an odd phenomenon of Earth or a cosmic outcome of chemistry everywhere.
