Webb detects a crucial carbon molecule in a planet-forming disk for the first time

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An international team of scientists, using data from the NASA/ESA/Canadian Space Agency’s James Webb Space Telescope, has detected for the first time a molecule known as a methyl cation (CH3+) present in the protoplanetary disk around a young star. They accomplished this feat with multidisciplinary analysis by experts, including key input from spectroscopy experts in the lab. This simple molecule has a unique property: it interacts relatively inefficiently with the most abundant element in our universe (hydrogen), but readily interacts with other molecules to start the growth of more complex carbon molecules.

The chemistry of carbon is of particular interest to astronomers because all known forms of life depend on carbon. CH3’s vital role in interstellar carbon chemistry was first predicted in the 1970s, but Webb’s unique abilities finally made it possible to notice it — in a region of space where planets that could eventually support life could form.

Carbon compounds are the basis of all known forms of life and are therefore of particular interest to scientists trying to understand how life evolved on Earth and how it might have evolved elsewhere in the universe. Therefore, interstellar organic chemistry is a fascinating topic for astronomers who study the places where new stars and planets form. Carbon-containing molecular ions are particularly important, because they react with other small molecules to form more complex organic compounds, even at low interstellar temperatures.

A methyl cation (CH3+) is such a carbon ion. Since the 1970s and 1980s, scientists have considered CH3+ to be of particular interest. This is due to a remarkable property of CH3+, which is that it interacts with a large number of other molecules. This tiny cation is important enough to be a cornerstone of interstellar organic chemistry, but it has yet to be discovered. The James Webb Space Telescope’s unique features have made it the ideal tool to search for this crucial cation – and a group of international scientists have already spotted it for the first time using Webb. “This detection of CH3+ not only proves James Webb’s amazing sensitivity, but also confirms the putative centrality of CH3+ in interstellar chemistry,” explains Marie-Alain Martin of Paris-Saclay University in France, spectroscopist and member of the science team.

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Image: ESA/Webb, NASA, CSA, M. Zamani (ESA/Webb) and the PDRs4All ERS Team

The CH3+ signal was detected in the star-protoplanetary disk system known as d203-506, which lies about 1,350 light-years away in the Orion Nebula. Although the star in d203-506 is a small red dwarf star, about a tenth the mass of the Sun, the system is heavily bombarded by ultraviolet radiation from nearby, massive, hot young stars. Scientists believe that most planet-forming protoplanetary disks experience such a period of intense ultraviolet radiation, because stars usually form in clusters that often contain massive ultraviolet-producing stars. Amazingly, meteorites show that the protoplanetary disk from which our solar system formed was also exposed to a huge amount of ultraviolet radiation – from a stellar companion to our long-dead Sun (massive stars burn brightly and die much faster than less massive stars). The confounding factor in all this is that ultraviolet radiation has long been considered quite destructive to the formation of complex organic molecules – yet there is clear evidence that the only life-supporting planet we know of evolved from a disk so exposed to it.

The team that conducted this research may have found the solution to this puzzle. Their work predicts that the presence of CH3+ is in fact related to ultraviolet radiation, which provides the energy source necessary for CH3+ formation. In addition, the period of ultraviolet radiation to which some tablets are exposed appears to have a significant effect on their chemical composition. For example, Webb’s observations of protoplanetary disks that are not subject to intense ultraviolet radiation from a nearby source show a large abundance of water – in contrast to d203-506, where the team was unable to detect any water at all. Lead author, Olivier Bernier from the University of Toulouse, France, explains: “This clearly shows that UV radiation can completely alter the chemistry of a protoplanetary disk. It can even play a crucial role in the early chemical stages of life by helping to produce CH3 + – Something that may have been underestimated in the past.”

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Although research published since the 1970s has predicted the importance of CH3+, it was previously almost impossible to detect. Many particles are observed in protoplanetary disks using radio telescopes. For this to be possible, the molecules involved must have what’s called a ‘permanent dipole moment’, which means that the geometry of the molecule is permanently unbalanced, giving the molecule a positive and negative ‘end’ has. CH3+ is symmetrical and therefore has a balanced charge, so It does not have the permanent dipole moment needed for radio telescope observations.It would theoretically be possible to observe the spectral lines of CH3 + in the infrared, but the Earth’s atmosphere makes it impossible to observe these lines from Earth.So it was necessary to use a sufficiently sensitive space telescope It can monitor signals in infrared.The NIRSpec instruments, part of the European contribution to Webb, and MIRI, of which Europe contributes half, were ideal for the task.In fact, the detection of CH3+ had previously been so elusive that when the team first saw it The signal in their data, they weren’t sure how to identify it.Remarkably, the team was able to interpret its results within four short weeks, drawing on the expertise of an international team with diverse expertise.

The discovery of CH3 was made possible only by a collaboration between observational astronomers, astrochemical modellers, theorists and experimental spectroscopy scientists, who combined the unique capabilities of JWST in space with those of terrestrial laboratories to successfully study the formation and evolution of our local universe. explains. Mary Ellen Martin adds, “Our discovery was only possible because astronomers, modellers, and laboratory spectroscopists joined forces to understand the unique features observed by James Webb.”

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