June 26, 2023 - An international team of scientists utilizing data from the NASA/ESA/CSA James Webb Space Telescope has achieved a groundbreaking milestone by detecting a molecule known as the methyl cation (CH3+) for the first time. This significant discovery was made in the protoplanetary disc surrounding a young star, demonstrating the cross-disciplinary expertise of the researchers involved.
The methyl cation is a simple molecule that possesses a remarkable characteristic: it reacts with other molecules readily, except for hydrogen, which is the most abundant element in the universe. This unique property initiates the growth of more complex carbon-based molecules, making it an essential component of carbon chemistry. Carbon compounds are of immense interest to astronomers because all known life is carbon-based. The detection of CH3+ in a region of space where potentially life-sustaining planets could form is a testament to the James Webb Space Telescope's unparalleled capabilities.
Carbon compounds serve as the building blocks of life as we know it and are crucial to understanding the development of life on Earth and its potential existence elsewhere in the universe. Scientists are particularly fascinated by interstellar organic chemistry, which explores the chemistry occurring in the environments where new stars and planets take shape. Molecular ions containing carbon play a vital role in this field, as they react with other small molecules, even at low interstellar temperatures, to form complex organic compounds. Among these carbon-based ions, the methyl cation (CH3+) has been theorized to hold significant importance since the 1970s and 1980s. However, its detection has remained elusive until now. The James Webb Space Telescope's unique capabilities have finally allowed a group of international scientists to observe CH3+ for the first time, confirming its central role in interstellar chemistry.
The CH3+ signal was detected in the d203-506 star-protoplanetary disc system located approximately 1350 light years away in the Orion Nebula. Although the star in d203-506 is a small red dwarf, with only a tenth of the Sun's mass, the system experiences intense ultraviolet radiation from nearby hot, young, massive stars. Scientists believe that most planet-forming protoplanetary discs undergo a phase of such ultraviolet radiation, as stars often form in groups that include massive ultraviolet-producing stars. Intriguingly, evidence from meteorites suggests that the protoplanetary disc that gave rise to our Solar System was also exposed to significant ultraviolet radiation emitted by a now-extinct stellar companion to our Sun. This poses a puzzle, as ultraviolet radiation has long been regarded as destructive to the formation of complex organic molecules. Nevertheless, the detection of CH3+ in d203-506 may hold the key to unraveling this conundrum. The researchers propose that ultraviolet radiation serves as the energy source for the formation of CH3+ and that the period of intense ultraviolet radiation experienced by certain discs profoundly affects their chemistry. For instance, observations of protoplanetary discs not subjected to intense ultraviolet radiation revealed a high abundance of water, whereas water was not detected in d203-506. Olivier Berné, the lead author of the study from the University of Toulouse, France, suggests that ultraviolet radiation may play a critical role in the early chemical stages of life's origins by aiding in the production of CH3+, a factor that has perhaps been underestimated until now.
The detection of CH3+ has been a long-standing challenge due to its symmetrical nature, which prevents its observation using radio telescopes that rely on the presence of a permanent dipole moment in molecules. While spectroscopic lines emitted by CH3+ could theoretically be observed in the infrared, the Earth's atmosphere makes it virtually impossible to observe them from the ground. Therefore, the researchers turned to the James Webb Space Telescope's MIRI and NIRSpec instruments, which are capable of sensitive infrared observations. Remarkably, even when the team first spotted the CH3+ signal in their data, they were unsure how to identify it. However, within four weeks, the international team's collective expertise allowed them to interpret the results accurately.
The discovery of CH3+ would not have been possible without the collaboration of observational astronomers, astrochemical modelers, theoreticians, and experimental spectroscopists. By combining the unique capabilities of the James Webb Space Telescope with the resources of Earth-based laboratories, this multidisciplinary team successfully investigated and interpreted the composition and evolution of our local universe. Marie-Aline Martin of Paris-Saclay University, France, and a member of the science team, emphasizes the significance of this collaboration, stating, "Our discovery was only made possible because astronomers, modelers, and laboratory spectroscopists joined forces to understand the unique features observed by James Webb."
As the James Webb Space Telescope continues to explore the cosmos with its extraordinary capabilities, scientists are hopeful that more groundbreaking discoveries await, furthering our understanding of the origins of life and the potential for habitable worlds beyond Earth.